A plasma display panel (PDP) is an emissive flat panel display where light is created by phosphors excited by a plasma discharge between two flat panels of glass. The gas discharge contains no mercury (contrary to the backlights of an AMLCD). An inert mixture of noble gases (neon and xenon) is used instead.
General characteristics
Plasma displays are bright (1000 lx or higher for the module), have a wide color
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Pros and cons
(comparison with LCD and Plasma)
Pros
* Slim design (Wall mountable)
* Larger than LCD screens
Cons
* Expensive, although cheaper than LCDs at larger sizes.
* Is subject to screen burn-in, but modern panels have a manufacturer rated lifespan of 50,000 or more hours.
* First 2000 hours is its brightest point. Every hour there after, the display gradually dims.
* At higher elevations, usually 6000 ft or higher, they exhibit noticeable humming.
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Functional details
The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two plates of glass. Long electrodes are also sandwiched between the glass plates, on both sides of the cells. The address electrodes sit behind the cells, along the rear glass plate. The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted above the cell, along the front glass plate.
In a monochrome plasma panel, control circuitry charges the electrodes that cross paths at a cell, causing the plasma to ionize and emit photons between the electrodes. The ionizing state can be maintained by applying a low-level voltage between all the horizontal and vertical electrodes - even after the ionizing voltage is removed. To erase a cell all voltage is removed from a pair of electrodes. This type of panel has inherent memory and does not use phosphors. A small amount of nitrogen is added to the neon to increase hysteresis.
To ionize the gas in a color panel, the plasma display's computer charges the electrodes that intersect at that cell thousands of times in a small fraction of a second, charging each cell in turn. When the intersecting electrodes are charged (with a voltage difference between them), an electric current flows through the gas in the cell. The current creates a rapid flow of charged particles, which stimulates the gas atoms to release ultraviolet photons.
The phosphors in a plasma display give off colored light when they are excited. Every pixel is made up of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color of the pixel. By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each subpixel color to create billions of different combinations of red, green and blue. In this way, the control system can produce colors across the entire visible spectrum. Plasma displays use the same phosphors as CRTs, accounting for the extremely accurate color reproduction.
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Contrast ratio claims
Contrast ratio indicates the difference between the brightest part of a picture and the darkest part of a picture, measured in discrete steps, at any given moment. The implication is that a higher contrast ratio means more picture detail. Contrast ratios for plasma displays are often advertised as high as 10000:1. On the surface, this is a great thing. In reality, there are no standardized tests for contrast ratio, meaning each manufacturer can publish virtually any number that they like. To illustrate, some manufacturers will measure contrast with the front glass removed, which accounts for some of the wild claims regarding their advertised ratios. For reference, the page you're reading now (on a computer monitor) is actually about 50:1. A printed page is about 80:1. A really good print at a movie theater will be about 500:1
Cannons
A cannon is any large tubular firearm designed to fire a heavy projectile over a considerable distance. The term can apply to a modern day rifled machine gun with a calibre of 20 mm or more (see autocannon).
Cannon also refers to a large, smooth-bored, muzzle-loading gun used before the advent of breech-loading, rifled guns firing explosive shells. Although a variety of such guns are commonly referred to as "cannon", the term specifically refers to a gun designed to fire a 42 lb shot as opposed to a "Demi-cannon" (32 lb), Culverin (18 lb) or Demi-culverin (9 lb).
"Cannon" derives from the Latin canna—a tube. Bombard was earlier used for "cannon", but from the early 15th century came to refer only to the largest weapons. "Cannon" can serve both as the singular and plural of the noun.
Modern cannon
A modern artillery piece is generally referred to either as a "gun", or by the name of its specific type, such as a Howitzer.
Since World War II the term cannon is used to refer to a gun of around 20 mm to 125 mm calibre, sometimes with an automatic loading action capable of firing explosive ammunition, an auto-cannon.
The minimum calibre of a cannon, 20 mm, has been a de facto standard since WWII, when heavy machine guns of 12.7 mm (0.5 inches) and 13.2 mm calibre were used side by side with 20 mm and larger guns, the latter using explosive ammunition, e.g., RAF fighters with 20 mm Hispano cannon and Luftwaffe with 20 mm and 30 mm cannon. The Bofors 40 mm gun and Oerlikon 20 mm cannon are two examples largely used during the Second World War, and still in usage today.
Most nations use these modern (auto-) cannon on their lighter vehicles. Typical of the type is the 25 mm 'Bushmaster' cannon mounted on the LAV and Bradley armoured vehicles.
A cannon generally refers to a high velocity, low trajectory, direct fire weapon such as the main gun on most modern main battle tanks.
A howitzer generally refers to a weapon using a lower velocity than a cannon, which fires on a higher trajectory, and provides indirect fire.
These are both differentiated from a mortar, which fires a low velocity (by comparison) round at very high trajectory at much more limited range.
Projectiles fired from cannon
Round shot
A solid projectile made, in early times, from dressed stone but, by the 17th century, from iron. The most accurate projectile that could be fired by a smooth-bore cannon, used to batter the wooden hulls of opposing ships, forts, or fixed emplacements, and as a long-range anti-personnel weapon.
Chain shot or bar shot
Two sub-calibre round shot (a good deal smaller than the bore of the barrel) linked by a length of chain or a solid bar, and used to slash through the rigging and sails of an enemy ship so that it could no longer manoeuvre. It was inaccurate and only used at close range.
Canister shot (or case shot)
An anti-personnel weapon which included many small round shot or lead musket balls in a metal can, which broke up when fired, scattering the shot throughout the enemy personnel, like a large shotgun.
Shell
An anti-personnel weapon, similar to canister shot, but with a can that was much more robust and which also contained a fused explosive charge, trimmed to explode above the heads of the enemy, spreading shot and can fragments in the form of shrapnel over the enemy. First used in the 16th century as a siege weapon fired from mortars, and later as a battlefield weapon.
Grapeshot
An anti-personnel weapon, similar to canister shot, but with the shot being contained in a canvas bag, and generally of a larger calibre. So called because of the resemblance of the clustered shot in the bag to a cluster of grapes on the vine.
Carcass
An incendiary/antipersonnel projectile designed to burn fiercely and produce poisonous fumes. It was constructed of an iron frame bound with sack cloth and filled with various ingredients such as pitch, antimony, sulphur, saltpeter, tallow and venetian turpentine. It was ignited by the cannon's propellant charge, bursting on impact with the target and releasing noxious fumes while setting fire to its surroundings. It was effectively an early chemical weapon as well as an incendiary and area denial weapon.
Heated (or hot) shot
A process where the cannonball is heated red hot and shot at flammable targets with the intent of starting a fire.
Cannon also refers to a large, smooth-bored, muzzle-loading gun used before the advent of breech-loading, rifled guns firing explosive shells. Although a variety of such guns are commonly referred to as "cannon", the term specifically refers to a gun designed to fire a 42 lb shot as opposed to a "Demi-cannon" (32 lb), Culverin (18 lb) or Demi-culverin (9 lb).
"Cannon" derives from the Latin canna—a tube. Bombard was earlier used for "cannon", but from the early 15th century came to refer only to the largest weapons. "Cannon" can serve both as the singular and plural of the noun.
Modern cannon
A modern artillery piece is generally referred to either as a "gun", or by the name of its specific type, such as a Howitzer.
Since World War II the term cannon is used to refer to a gun of around 20 mm to 125 mm calibre, sometimes with an automatic loading action capable of firing explosive ammunition, an auto-cannon.
The minimum calibre of a cannon, 20 mm, has been a de facto standard since WWII, when heavy machine guns of 12.7 mm (0.5 inches) and 13.2 mm calibre were used side by side with 20 mm and larger guns, the latter using explosive ammunition, e.g., RAF fighters with 20 mm Hispano cannon and Luftwaffe with 20 mm and 30 mm cannon. The Bofors 40 mm gun and Oerlikon 20 mm cannon are two examples largely used during the Second World War, and still in usage today.
Most nations use these modern (auto-) cannon on their lighter vehicles. Typical of the type is the 25 mm 'Bushmaster' cannon mounted on the LAV and Bradley armoured vehicles.
A cannon generally refers to a high velocity, low trajectory, direct fire weapon such as the main gun on most modern main battle tanks.
A howitzer generally refers to a weapon using a lower velocity than a cannon, which fires on a higher trajectory, and provides indirect fire.
These are both differentiated from a mortar, which fires a low velocity (by comparison) round at very high trajectory at much more limited range.
Projectiles fired from cannon
Round shot
A solid projectile made, in early times, from dressed stone but, by the 17th century, from iron. The most accurate projectile that could be fired by a smooth-bore cannon, used to batter the wooden hulls of opposing ships, forts, or fixed emplacements, and as a long-range anti-personnel weapon.
Chain shot or bar shot
Two sub-calibre round shot (a good deal smaller than the bore of the barrel) linked by a length of chain or a solid bar, and used to slash through the rigging and sails of an enemy ship so that it could no longer manoeuvre. It was inaccurate and only used at close range.
Canister shot (or case shot)
An anti-personnel weapon which included many small round shot or lead musket balls in a metal can, which broke up when fired, scattering the shot throughout the enemy personnel, like a large shotgun.
Shell
An anti-personnel weapon, similar to canister shot, but with a can that was much more robust and which also contained a fused explosive charge, trimmed to explode above the heads of the enemy, spreading shot and can fragments in the form of shrapnel over the enemy. First used in the 16th century as a siege weapon fired from mortars, and later as a battlefield weapon.
Grapeshot
An anti-personnel weapon, similar to canister shot, but with the shot being contained in a canvas bag, and generally of a larger calibre. So called because of the resemblance of the clustered shot in the bag to a cluster of grapes on the vine.
Carcass
An incendiary/antipersonnel projectile designed to burn fiercely and produce poisonous fumes. It was constructed of an iron frame bound with sack cloth and filled with various ingredients such as pitch, antimony, sulphur, saltpeter, tallow and venetian turpentine. It was ignited by the cannon's propellant charge, bursting on impact with the target and releasing noxious fumes while setting fire to its surroundings. It was effectively an early chemical weapon as well as an incendiary and area denial weapon.
Heated (or hot) shot
A process where the cannonball is heated red hot and shot at flammable targets with the intent of starting a fire.
Bombs
A bomb is an explosive device that, although not containing more energy than ordinary fuel, except in the case of a nuclear weapon, generates and releases its energy very rapidly, as an explosion, a violent, destructive shock wave. It is usually some kind of container filled with explosive material, designed to cause random destruction when set off. The word comes from the Greek word βόμβος (bombos), an onomatopoetic term with approximately the same meaning as "boom" in English.
These are first and foremost weapons; the term "bomb" is not usually applied to explosive devices used for civilian purposes, such as construction or mining, although the people using the devices may or may not sometimes refer to them as bombs. Many military explosive devices are not called "bombs". The military mostly calls airdropped, unpowered explosive weapons "bombs," and such bombs are normally used by air forces and naval aviation. Other military explosive devices are called grenades, such as hand grenades), shells, depth charges, warheads when in missiles, or land mines.
They have been used for centuries in warfare and are a central part of a terrorist's arsenal. They fall into three distinct categories: conventional if filled with chemical explosives, dispersive if filled with submunitions, chemicals or other disruptive agents which are spread on or shortly before impact, or nuclear if relying on nuclear fission or nuclear fusion for their effect.
Experts commonly distinguish between civilian and military bombs. The latter are almost always mass-produced weapons, developed and constructed to a standard design out of standard components and intended to be deployed in a standard way each time. By contrast, terrorist bombs are usually custom-made, developed to any number of designs, use a wide range of explosives of varying levels of power and chemical stability, and are used in many different ways. For this reason, they are generally referred to as improvised explosive devices (IEDs).
The most powerful bomb in existence is the hydrogen bomb, a nuclear weapon. The most powerful bombs ever used in combat were the two nuclear bombs dropped by the United States to attack Hiroshima and Nagasaki. The most powerful non-nuclear bomb is the United States Air Force's MOAB (Massive Ordnance Air Blast).
The most powerful bomb ever was Tsar Bomba: ca. 50 Mt; it had a mass of 27 tons; it was dropped from a bomber for a test, but was for various reasons not very suitable for combat.
The first hydrogen "bomb" Ivy Mike (10.4 Mt) was even heavier in mass, 82 tons. It was too heavy to be deliverable by a plane or rocket, and therefore not very suitable for an attack.
Another type of bomb is called an EMP (Electro-Magnetic Pulse) and its primary function is to terminate all working electrical equipment in the vicinity. Its power can range from one machine to an entire state.
Delivery
The usual method of delivering military bombs to their target is by bombing, i.e. dropping them from a bomber airplane. Modern bombs, precision-guided munitions, may be guided after they leave an airplane by remote control, by autonomous guidance or (in the case of nuclear weapons) mounted on a guided missile.
Some bombs are equipped with a parachute, such as the World War Two "parafrag", which was an 11kg fragmentation bomb, the Vietnam-era daisy cutters, and the bomblets of some modern cluster bombs. Parachutes slow the bomb's descent, giving the dropping aircraft time to get to a safe distance from the explosion. This is especially important with airburst nuclear weapons, and in the case that the aircraft releases the bomb at low altitude.
A hand grenade is delivered by being thrown. Grenades can also be projected by other means using a grenade launcher, such as being launched from the muzzle of a rifle using the M203 or the GP-30 or by attaching a rocket to the explosive grenade as in a rocket propelled grenade (RPG).
A bomb may also be positioned in advance and concealed, for example in a garbage container, car or truck as a car bomb, or by the roadside in a roadside bomb, in a building as a booby trap, or in lugguage and in a vehicle.
A bomb destroying a rail track just before a train arrives causes a train to derail. Apart from the damage to vehicles and people, a bomb exploding in a transport network often also damages, and is sometimes mainly intended to damage, that network. This applies for railways, bridges, runways, and ports, and to a lesser extent, depending on circumstances, to roads.
In the case of suicide bombing the bomb is often carried by the attacker on his or her body, or a in a vehicle driven to the target.
The Blue Peacock nuclear mines, which were also termed "bombs", were planned to be positioned during wartime and be constructed such that, if they were disturbed, they would explode within ten seconds.
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Detonation
The explosion of the bomb has to be triggered by a detonator or a fuse. Detonators are triggered by clocks, remote controls like cell phones or some kind of sensor, such as pressure (altitude), radar, vibration or contact. Detonators vary in ways they work, they can be electrical, fire fuze or blast initiated detonators and others.
[edit]
Bombing
Bombing may be directed at military targets; such as ships, logistic and transportation centres, warehouses or weapons industries such as armament factories. They may be detonated also at civilian targets, such as office buildings, commercial areas or whole cities. Bombing of particular targets such as ships, railroad trains or military vehicles such as tanks is called tactical bombing; bombing of areas such as military bases or infrastructure, such as bridges, industrial centres, transport facilities) is called strategic bombing. Strategic bombing of civilian targets is controversial and considered a war crime by most and a defining characteristic of terrorism by others, and may be considered terror bombing. Area or carpet bombing of cities using incendiary bombs may result in a firestorm and extensive casualties especially when the city is fire-prone, largely constructed of timber buildings or used to store flammable materials, and it is windy.
These are first and foremost weapons; the term "bomb" is not usually applied to explosive devices used for civilian purposes, such as construction or mining, although the people using the devices may or may not sometimes refer to them as bombs. Many military explosive devices are not called "bombs". The military mostly calls airdropped, unpowered explosive weapons "bombs," and such bombs are normally used by air forces and naval aviation. Other military explosive devices are called grenades, such as hand grenades), shells, depth charges, warheads when in missiles, or land mines.
They have been used for centuries in warfare and are a central part of a terrorist's arsenal. They fall into three distinct categories: conventional if filled with chemical explosives, dispersive if filled with submunitions, chemicals or other disruptive agents which are spread on or shortly before impact, or nuclear if relying on nuclear fission or nuclear fusion for their effect.
Experts commonly distinguish between civilian and military bombs. The latter are almost always mass-produced weapons, developed and constructed to a standard design out of standard components and intended to be deployed in a standard way each time. By contrast, terrorist bombs are usually custom-made, developed to any number of designs, use a wide range of explosives of varying levels of power and chemical stability, and are used in many different ways. For this reason, they are generally referred to as improvised explosive devices (IEDs).
The most powerful bomb in existence is the hydrogen bomb, a nuclear weapon. The most powerful bombs ever used in combat were the two nuclear bombs dropped by the United States to attack Hiroshima and Nagasaki. The most powerful non-nuclear bomb is the United States Air Force's MOAB (Massive Ordnance Air Blast).
The most powerful bomb ever was Tsar Bomba: ca. 50 Mt; it had a mass of 27 tons; it was dropped from a bomber for a test, but was for various reasons not very suitable for combat.
The first hydrogen "bomb" Ivy Mike (10.4 Mt) was even heavier in mass, 82 tons. It was too heavy to be deliverable by a plane or rocket, and therefore not very suitable for an attack.
Another type of bomb is called an EMP (Electro-Magnetic Pulse) and its primary function is to terminate all working electrical equipment in the vicinity. Its power can range from one machine to an entire state.
Delivery
The usual method of delivering military bombs to their target is by bombing, i.e. dropping them from a bomber airplane. Modern bombs, precision-guided munitions, may be guided after they leave an airplane by remote control, by autonomous guidance or (in the case of nuclear weapons) mounted on a guided missile.
Some bombs are equipped with a parachute, such as the World War Two "parafrag", which was an 11kg fragmentation bomb, the Vietnam-era daisy cutters, and the bomblets of some modern cluster bombs. Parachutes slow the bomb's descent, giving the dropping aircraft time to get to a safe distance from the explosion. This is especially important with airburst nuclear weapons, and in the case that the aircraft releases the bomb at low altitude.
A hand grenade is delivered by being thrown. Grenades can also be projected by other means using a grenade launcher, such as being launched from the muzzle of a rifle using the M203 or the GP-30 or by attaching a rocket to the explosive grenade as in a rocket propelled grenade (RPG).
A bomb may also be positioned in advance and concealed, for example in a garbage container, car or truck as a car bomb, or by the roadside in a roadside bomb, in a building as a booby trap, or in lugguage and in a vehicle.
A bomb destroying a rail track just before a train arrives causes a train to derail. Apart from the damage to vehicles and people, a bomb exploding in a transport network often also damages, and is sometimes mainly intended to damage, that network. This applies for railways, bridges, runways, and ports, and to a lesser extent, depending on circumstances, to roads.
In the case of suicide bombing the bomb is often carried by the attacker on his or her body, or a in a vehicle driven to the target.
The Blue Peacock nuclear mines, which were also termed "bombs", were planned to be positioned during wartime and be constructed such that, if they were disturbed, they would explode within ten seconds.
[edit]
Detonation
The explosion of the bomb has to be triggered by a detonator or a fuse. Detonators are triggered by clocks, remote controls like cell phones or some kind of sensor, such as pressure (altitude), radar, vibration or contact. Detonators vary in ways they work, they can be electrical, fire fuze or blast initiated detonators and others.
[edit]
Bombing
Bombing may be directed at military targets; such as ships, logistic and transportation centres, warehouses or weapons industries such as armament factories. They may be detonated also at civilian targets, such as office buildings, commercial areas or whole cities. Bombing of particular targets such as ships, railroad trains or military vehicles such as tanks is called tactical bombing; bombing of areas such as military bases or infrastructure, such as bridges, industrial centres, transport facilities) is called strategic bombing. Strategic bombing of civilian targets is controversial and considered a war crime by most and a defining characteristic of terrorism by others, and may be considered terror bombing. Area or carpet bombing of cities using incendiary bombs may result in a firestorm and extensive casualties especially when the city is fire-prone, largely constructed of timber buildings or used to store flammable materials, and it is windy.
Gas turbine in vehicles
Gas turbines are used on ships, locomotives, helicopters, and in tanks. A number of experiments have been conducted with gas turbine powered automobiles.
In 1950, designer F. R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum. Rover and the BRM Formula One team joined forces to produce a gas turbine powered coupe, which entered the 1963 24 hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km) and had a top speed of 142 mph (229 km/h). In 1971 Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney gas turbine. Colin Chapman had a reputation of building radical championship-winning cars, but had to abandon the project because there were too many problems with turbo lag. The fictional Batmobile is often said to be powered by a gas turbine or a jet engine.
American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. Chrysler built fifty Chrysler Turbine Cars in 1963 and conducted the only consumer trial of gas turbine-powered cars.
In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator.
Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. Also, turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small turbines are rarities. It is also worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Their use in hybrids reduces the second problem. Capstone currently lists on their website a version of their turbines designed for installation in hybrid vehicles.
The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a jet engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283kW (380shp). Speed-tested to 365km/h or 227mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000.
Use of gas turbines in military tanks has been more successful. In the 1950s, a Conqueror heavy tank was experimentally fitted with a Parsons 650-hp gas turbine, and they have been used as auxiliary power units in several other production models. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See tank for more details.
Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See Gas turbine-electric locomotive for more information.
[edit]
Naval use
Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961.
The next series of major naval vessels were the four Canadian Iroquois class helicopter carrying destroyers first commissioned in 1972. They used 2 FT-4 main propulsion engines, 2 FT-12 cruise engines and 3 Solar Saturn 750 KW generators.
The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines.
An example of commercial usage of a gas turbine in a ship is the Stena Discovery, using the GE LM2500.
Amateur gas turbines
A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies manufacture small turbines and parts for the amateur. See external links for resources.
[edit]
Advances in technology
Gas turbine technology has steadily advanced since its inception and continues to evolve; research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher compression ratios and temperatures, more efficient combustion, better cooling of engine parts and reduced emissions. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system.
On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power. An excellent example is the Capstone line of micro turbines, which do not require an oil system and can run unattended for months on end.
In 1950, designer F. R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum. Rover and the BRM Formula One team joined forces to produce a gas turbine powered coupe, which entered the 1963 24 hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km) and had a top speed of 142 mph (229 km/h). In 1971 Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney gas turbine. Colin Chapman had a reputation of building radical championship-winning cars, but had to abandon the project because there were too many problems with turbo lag. The fictional Batmobile is often said to be powered by a gas turbine or a jet engine.
American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. Chrysler built fifty Chrysler Turbine Cars in 1963 and conducted the only consumer trial of gas turbine-powered cars.
In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator.
Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. Also, turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small turbines are rarities. It is also worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Their use in hybrids reduces the second problem. Capstone currently lists on their website a version of their turbines designed for installation in hybrid vehicles.
The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a jet engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283kW (380shp). Speed-tested to 365km/h or 227mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000.
Use of gas turbines in military tanks has been more successful. In the 1950s, a Conqueror heavy tank was experimentally fitted with a Parsons 650-hp gas turbine, and they have been used as auxiliary power units in several other production models. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See tank for more details.
Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See Gas turbine-electric locomotive for more information.
[edit]
Naval use
Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961.
The next series of major naval vessels were the four Canadian Iroquois class helicopter carrying destroyers first commissioned in 1972. They used 2 FT-4 main propulsion engines, 2 FT-12 cruise engines and 3 Solar Saturn 750 KW generators.
The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines.
An example of commercial usage of a gas turbine in a ship is the Stena Discovery, using the GE LM2500.
Amateur gas turbines
A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies manufacture small turbines and parts for the amateur. See external links for resources.
[edit]
Advances in technology
Gas turbine technology has steadily advanced since its inception and continues to evolve; research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher compression ratios and temperatures, more efficient combustion, better cooling of engine parts and reduced emissions. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system.
On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power. An excellent example is the Capstone line of micro turbines, which do not require an oil system and can run unattended for months on end.
Space Shuttle
NASA's Space Shuttle, officially called Space Transportation System (STS), is the United States government's current manned launch vehicle. The winged shuttle orbiter is launched vertically, usually carrying five to seven astronauts (although eight have been carried) and up to 22,700 kg (50,000 lb) of payload into low earth orbit. When its mission is complete, it re-enters the earth's atmosphere and makes an unpowered horizontal landing.
The Shuttle is the first orbital spacecraft designed for partial reusability. It is also so far the only winged manned spacecraft to achieve orbit and land. It carries large payloads to various orbits, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can recover satellites and other payloads from orbit and return them to Earth, but this capacity has not been used often. However, it has been used to return large payloads from the International Space Station to earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a projected lifespan of 100 launches or 10 years' operational life.
The program started in the late 1960s and has dominated NASA's manned operations since the mid-1970s. According to the Vision for Space Exploration, use of the Space Shuttle will be focused on completing assembly of the ISS in 2010, after which it will be replaced by the Crew Exploration Vehicle (CEV).
Description
The Shuttle is a partially reusuable launch system composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable External Tank (ET), and the two reusable Solid Rocket Boosters (SRBs). The tank and boosters are jettisoned during ascent; only the orbiter goes into orbit. The vehicle is launched vertically like a conventional rocket, and the orbiter glides to a horizontal landing, after which it is refurbished for reuse.
The Orbiter resembles an airplane with double-delta wings, swept 81° at the inner leading edge and 45° at the outer leading edge. Its vertical stabilizer's leading edge is swept back at a 45° angle. The four elevons, mounted at the trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabilizer, with the body flap, control the Orbiter during descent and landing.
The Orbiter's crew cabin consists of three levels: the flight deck, the mid-deck, and the utility area. The highest flight deck seats the commander and pilot, with two mission specialists behind them. The mid-deck has three more seats for the rest of the crew members. The galley, toilet, sleep locations, storage lockers, and the side hatch for entering/exiting the vehicle are also located there, as is the airlock hatch. The airlock has another hatch into the payload bay. It allows two astronauts, wearing their Extravehicular Mobility Unit (EMU) space suits, to depressurize before a space walk.
The Orbiter has a large 60 by 15 ft (18 m by 4.6 m) payload bay, filling most of the fuselage. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while the Shuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm used to retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missions where it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for Shuttle flights, it will probably be included on all future flights.
Three Space Shuttle Main Engines (SSMEs) are mounted on the Orbiter's aft fuselage in a triangular pattern. The three engines can swivel 10.5 degrees up and down and 8.5 degrees from side to side during ascent to change the direction of their thrust and steer the Shuttle as well as push.
The Orbital Maneuvering System (OMS) provides orbital maneuvers, including insertion, circularization, transfer, rendezvous, abort to orbit, and abort once around.
The Reaction Control System (RCS) provides attitude control and translation along the pitch, roll, and yaw axes during the flight phases of orbit insertion, orbit, and re-entry.
The Thermal Protection System (TPS) covers the outside of the Orbiter, protecting it from the cold soak of -121 °C (-250 °F) in space to the 1649 °C (3000 °F) heat of reentry
The orbiter structure is made primarily from aluminium alloy, although the engine thrust structure is made from titanium.
The External Tank (ET) provides 2.025 million liters (535,000 gallons) of liquid hydrogen and liquid oxygen propellant to the SSMEs. It is discarded 8.5 minutes after launch at an altitude of 60 nautical miles (111 km) then breaks up on reentry. The ET is constructed mostly of aluminium-lithium alloy about 1/8 inch thick. Many people think that the ET is painted orange. In reality, the orange color is the true color of the tank's insulation. If it were painted, it would add another 1,000 lbs. of unnecessary payload.
Two Solid Rocket Boosters (SRBs) provide about 83% of the vehicle's thrust at liftoff and during the first stage ascent. They are jettisoned two minutes after launch at a height of about 150,000 feet (45.7 km), then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1/2 inch (1.27 cm) thick.
Computerized fly-by-wire digital flight control
The shuttle was one of the earliest craft to use a computerized fly-by-wire digital flight control system. This means no mechanical or hydraulic linkages connect the pilot's control stick to the control surfaces or reaction control system thrusters.
A primary concern with digital fly-by-wire systems is reliability. Much research went into the shuttle computer system. The shuttle uses five identical redundant IBM 32-bit general purpose computers (GPCs), model AP-101, constituting a type of embedded system. Four computers run specialized software called the Primary Avionics Software System (PASS). A fifth backup computer runs separate software called the Backup Flight System (BFS). Collectively they are called the shuttle Data Processing System (DPS).
The design goal of the shuttle DPS is fail operational/fail safe reliability. After a single failure the shuttle can continue the mission. After two failures it can land safely.
The four general-purpose computers operate essentially in lockstep, checking each other. If one computer fails, the three functioning computers "vote" it out of the system. This isolates it from vehicle control. If a second computer of the three remaining fails, the two functioning computers vote it out. In the rare case of two out of four computers simultaneously failing (a two-two split), one group is picked at random.
The Backup Flight System (BFS) is separately developed software running on the fifth computer, used only if the entire four-computer primary system fails. The BFS was created because although the four primary computers are hardware redundant, they all run the same software, so a generic software problem could crash all of them. This should never happen, as embedded system avionic software is developed under totally different conditions from commercial software. For example, the number of code lines is tiny compared to a commercial operating system, changes are only made infrequently and with extensive testing, and many programming and test personnel work on the small amount of computer code. However in theory it can fail, and the BFS exists for that contingency.
The software for the shuttle computers is written in a high-level language called HAL/S, somewhat similar to PL/I. It is specifically designed for a real time embedded system environment.
The IBM AP-101 computers originally had about 424 kilobytes of magnetic core memory each. The CPU could process about 400,000 instructions per second. They have no hard disk drive, but load software from tape cartridges.
In 1990 the original computers were replaced with an upgraded model AP-101S, which has about 2.5 times the memory capacity (about 1 megabyte) and three times the processor speed (about 1.2 million instructions per second). The memory was changed from magnetic core to semiconductor with battery backup.
[edit]
Other improvements
Internally the Shuttle remains largely similar to the original design, with the exception of the improved avionics computers. In addition to the computer upgrades, the original vector graphics monochrome cockpit displays were replaced with modern full-color, flat-panel display screens, similar to contemporary airliners like the Airbus A320. This is called a "glass cockpit". In the Apollo-Soyuz Test Project tradition, programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the Orbiter's internal airlocks are being replaced with external docking systems to allow for a greater amount of cargo to be stored on the Shuttle's mid-deck during Station resupply missions.
The Space Shuttle Main Engines have had several improvements to enhance reliability and power. This explains phrases such as "Main engines throttling up to 104%." This does not mean the engines are being run over a safe limit. The 100% figure is the original specified power level. During the lengthy development program, Rocketdyne determined the engine was capable of safe reliable operation at 104% of the originally specified thrust. They could have rescaled the output number, saying in essence 104% is now 100%. However this would have required revising much previous documentation and software, so the 104% number was retained. SSME upgrades are denoted as "block numbers", such as block I, block II, and block IIA. The upgrades have improved engine reliability, maintainability and performance. The 109% thrust level was finally reached in flight hardware with the Block II engines in 2001. The normal maximum throttle is 104%, with 106% and 109% available for abort emergencies.
For STS-1 and STS-2 the external tank was painted white to protect the insulation that covers much of the tank, but improvements and testing showed that it was not required. The weight saved by not painting the tank results in an increase in payload capability to orbit. Additional weight was saved by removing some of the internal "stringers" in the hydrogen tank that proved unnecessary. The resulting "light-weight external tank" has been used on the vast majority of Shuttle missions. STS-91 saw the first flight of the "super light-weight external tank". This version of the tank is made of the 2195 aluminium-lithium alloy. It weighs 7,500 lb (3.4 t) less than the last run of lightweight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been "tested" on operational flights.
The SRBs (Solid Rocket Boosters) have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident.
Several other SRB improvements were planned in order to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost, probably safer and better performing Advanced Solid Rocket Booster which was to have entered production in the early to mid-1990s to support the Space Station, but was later cancelled to save money after the expenditure of $2.2 billion. The loss of the ASRB program forced the development of the Super LightWeight external Tank (SLWT), which provides some of the increased payload capability, while not providing any of the safety improvements. In addition the Air Force developed their own much lighter single-piece SRB design using a filament-wound system, but this too was cancelled.
A cargo-only, unmanned variant of the Shuttle has been variously proposed and rejected since the 1980s. It is called the Shuttle-C and would trade re-usability for cargo capability with large potential savings from reusing technology developed for the Space Shuttle.
On the first four Shuttle missions, astronauts wore full-pressure Launch Entry Suit (LES) during ascent and descent. The pressured helmet was used from STS-5 until the loss of Challenger. The LES was reinstated when Shuttle flights resumed in 1988. The LES ended its service life in late 1995, replaced by the Advanced Crew Escape Suit (ACES).
[edit]
Technical data
Orbiter Specifications (for Endeavour, OV-105)
* Length: 122.17 ft (37.24 m)
* Wingspan: 78.06 ft (23.79 m)
* Height: 58.58 ft (17.25 m)
* Empty Weight: 151,205 lb (68,586.6 kg)
* Gross Liftoff Weight: 240,000 lb (109,000 kg)
* Maximum Landing Weight: 230,000 lb (104,000 kg)
* Main Engines: Three Rocketdyne Block 2 A SSMEs, each with a sea level thrust of 393,800 lbf (178,624 kgf / 1.75MN)
* Maximum Payload: 55,250 lb (25,061.4 kg)
* Payload Bay dimensions: 15 ft by 60 ft (4.6 m by 18.3 m)
* Operational Altitude: 100 to 520 nmi (185 to 1,000 km)
* Speed: 25,404 ft/s (7,743 m/s, 27,875 km/h, 17,321 mi/h)
* Crossrange: 1,085 nautical miles (2,009.4 km)
* Crew: Seven (Commander, Pilot, two Mission Specialists, and three Payload Specialists), two for minimum.
External Tank Specifications (for SLWT)
* Length: 153.8 ft (46.9 m)
* Diameter: 27.6 ft (8.4 m)
* Propellent Volume: 535,000 gallon
* Empty Weight: 58,500 lb (26,559 kg)
* Gross Liftoff Weight: 1.667 million lb (757,000 kg)
Solid Rocket Booster Specifications
* Length: 149.6 ft (45.6 m)
* Diameter: 12.17 ft (3.71 m)
* Empty Weight: 139,490 lb (63,272.7 kg)
* Gross Liftoff Weight: 1.3 million lb (590,000 kg)
* Thrust (sea level, liftoff): 2.8 million lbf (1,270,058 kgf / 12.46MN)
System Stack Specifications
* Height: 184.2 ft (56.14 m)
* Gross Liftoff Weight: 4.5 million lb (2.04 million kg)
* Total Liftoff Thrust: 6.781 million lbf (3.076 million kgf / 30.18MN)
The Shuttle is the first orbital spacecraft designed for partial reusability. It is also so far the only winged manned spacecraft to achieve orbit and land. It carries large payloads to various orbits, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can recover satellites and other payloads from orbit and return them to Earth, but this capacity has not been used often. However, it has been used to return large payloads from the International Space Station to earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a projected lifespan of 100 launches or 10 years' operational life.
The program started in the late 1960s and has dominated NASA's manned operations since the mid-1970s. According to the Vision for Space Exploration, use of the Space Shuttle will be focused on completing assembly of the ISS in 2010, after which it will be replaced by the Crew Exploration Vehicle (CEV).
Description
The Shuttle is a partially reusuable launch system composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable External Tank (ET), and the two reusable Solid Rocket Boosters (SRBs). The tank and boosters are jettisoned during ascent; only the orbiter goes into orbit. The vehicle is launched vertically like a conventional rocket, and the orbiter glides to a horizontal landing, after which it is refurbished for reuse.
The Orbiter resembles an airplane with double-delta wings, swept 81° at the inner leading edge and 45° at the outer leading edge. Its vertical stabilizer's leading edge is swept back at a 45° angle. The four elevons, mounted at the trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabilizer, with the body flap, control the Orbiter during descent and landing.
The Orbiter's crew cabin consists of three levels: the flight deck, the mid-deck, and the utility area. The highest flight deck seats the commander and pilot, with two mission specialists behind them. The mid-deck has three more seats for the rest of the crew members. The galley, toilet, sleep locations, storage lockers, and the side hatch for entering/exiting the vehicle are also located there, as is the airlock hatch. The airlock has another hatch into the payload bay. It allows two astronauts, wearing their Extravehicular Mobility Unit (EMU) space suits, to depressurize before a space walk.
The Orbiter has a large 60 by 15 ft (18 m by 4.6 m) payload bay, filling most of the fuselage. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while the Shuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm used to retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missions where it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for Shuttle flights, it will probably be included on all future flights.
Three Space Shuttle Main Engines (SSMEs) are mounted on the Orbiter's aft fuselage in a triangular pattern. The three engines can swivel 10.5 degrees up and down and 8.5 degrees from side to side during ascent to change the direction of their thrust and steer the Shuttle as well as push.
The Orbital Maneuvering System (OMS) provides orbital maneuvers, including insertion, circularization, transfer, rendezvous, abort to orbit, and abort once around.
The Reaction Control System (RCS) provides attitude control and translation along the pitch, roll, and yaw axes during the flight phases of orbit insertion, orbit, and re-entry.
The Thermal Protection System (TPS) covers the outside of the Orbiter, protecting it from the cold soak of -121 °C (-250 °F) in space to the 1649 °C (3000 °F) heat of reentry
The orbiter structure is made primarily from aluminium alloy, although the engine thrust structure is made from titanium.
The External Tank (ET) provides 2.025 million liters (535,000 gallons) of liquid hydrogen and liquid oxygen propellant to the SSMEs. It is discarded 8.5 minutes after launch at an altitude of 60 nautical miles (111 km) then breaks up on reentry. The ET is constructed mostly of aluminium-lithium alloy about 1/8 inch thick. Many people think that the ET is painted orange. In reality, the orange color is the true color of the tank's insulation. If it were painted, it would add another 1,000 lbs. of unnecessary payload.
Two Solid Rocket Boosters (SRBs) provide about 83% of the vehicle's thrust at liftoff and during the first stage ascent. They are jettisoned two minutes after launch at a height of about 150,000 feet (45.7 km), then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1/2 inch (1.27 cm) thick.
Computerized fly-by-wire digital flight control
The shuttle was one of the earliest craft to use a computerized fly-by-wire digital flight control system. This means no mechanical or hydraulic linkages connect the pilot's control stick to the control surfaces or reaction control system thrusters.
A primary concern with digital fly-by-wire systems is reliability. Much research went into the shuttle computer system. The shuttle uses five identical redundant IBM 32-bit general purpose computers (GPCs), model AP-101, constituting a type of embedded system. Four computers run specialized software called the Primary Avionics Software System (PASS). A fifth backup computer runs separate software called the Backup Flight System (BFS). Collectively they are called the shuttle Data Processing System (DPS).
The design goal of the shuttle DPS is fail operational/fail safe reliability. After a single failure the shuttle can continue the mission. After two failures it can land safely.
The four general-purpose computers operate essentially in lockstep, checking each other. If one computer fails, the three functioning computers "vote" it out of the system. This isolates it from vehicle control. If a second computer of the three remaining fails, the two functioning computers vote it out. In the rare case of two out of four computers simultaneously failing (a two-two split), one group is picked at random.
The Backup Flight System (BFS) is separately developed software running on the fifth computer, used only if the entire four-computer primary system fails. The BFS was created because although the four primary computers are hardware redundant, they all run the same software, so a generic software problem could crash all of them. This should never happen, as embedded system avionic software is developed under totally different conditions from commercial software. For example, the number of code lines is tiny compared to a commercial operating system, changes are only made infrequently and with extensive testing, and many programming and test personnel work on the small amount of computer code. However in theory it can fail, and the BFS exists for that contingency.
The software for the shuttle computers is written in a high-level language called HAL/S, somewhat similar to PL/I. It is specifically designed for a real time embedded system environment.
The IBM AP-101 computers originally had about 424 kilobytes of magnetic core memory each. The CPU could process about 400,000 instructions per second. They have no hard disk drive, but load software from tape cartridges.
In 1990 the original computers were replaced with an upgraded model AP-101S, which has about 2.5 times the memory capacity (about 1 megabyte) and three times the processor speed (about 1.2 million instructions per second). The memory was changed from magnetic core to semiconductor with battery backup.
[edit]
Other improvements
Internally the Shuttle remains largely similar to the original design, with the exception of the improved avionics computers. In addition to the computer upgrades, the original vector graphics monochrome cockpit displays were replaced with modern full-color, flat-panel display screens, similar to contemporary airliners like the Airbus A320. This is called a "glass cockpit". In the Apollo-Soyuz Test Project tradition, programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the Orbiter's internal airlocks are being replaced with external docking systems to allow for a greater amount of cargo to be stored on the Shuttle's mid-deck during Station resupply missions.
The Space Shuttle Main Engines have had several improvements to enhance reliability and power. This explains phrases such as "Main engines throttling up to 104%." This does not mean the engines are being run over a safe limit. The 100% figure is the original specified power level. During the lengthy development program, Rocketdyne determined the engine was capable of safe reliable operation at 104% of the originally specified thrust. They could have rescaled the output number, saying in essence 104% is now 100%. However this would have required revising much previous documentation and software, so the 104% number was retained. SSME upgrades are denoted as "block numbers", such as block I, block II, and block IIA. The upgrades have improved engine reliability, maintainability and performance. The 109% thrust level was finally reached in flight hardware with the Block II engines in 2001. The normal maximum throttle is 104%, with 106% and 109% available for abort emergencies.
For STS-1 and STS-2 the external tank was painted white to protect the insulation that covers much of the tank, but improvements and testing showed that it was not required. The weight saved by not painting the tank results in an increase in payload capability to orbit. Additional weight was saved by removing some of the internal "stringers" in the hydrogen tank that proved unnecessary. The resulting "light-weight external tank" has been used on the vast majority of Shuttle missions. STS-91 saw the first flight of the "super light-weight external tank". This version of the tank is made of the 2195 aluminium-lithium alloy. It weighs 7,500 lb (3.4 t) less than the last run of lightweight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been "tested" on operational flights.
The SRBs (Solid Rocket Boosters) have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident.
Several other SRB improvements were planned in order to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost, probably safer and better performing Advanced Solid Rocket Booster which was to have entered production in the early to mid-1990s to support the Space Station, but was later cancelled to save money after the expenditure of $2.2 billion. The loss of the ASRB program forced the development of the Super LightWeight external Tank (SLWT), which provides some of the increased payload capability, while not providing any of the safety improvements. In addition the Air Force developed their own much lighter single-piece SRB design using a filament-wound system, but this too was cancelled.
A cargo-only, unmanned variant of the Shuttle has been variously proposed and rejected since the 1980s. It is called the Shuttle-C and would trade re-usability for cargo capability with large potential savings from reusing technology developed for the Space Shuttle.
On the first four Shuttle missions, astronauts wore full-pressure Launch Entry Suit (LES) during ascent and descent. The pressured helmet was used from STS-5 until the loss of Challenger. The LES was reinstated when Shuttle flights resumed in 1988. The LES ended its service life in late 1995, replaced by the Advanced Crew Escape Suit (ACES).
[edit]
Technical data
Orbiter Specifications (for Endeavour, OV-105)
* Length: 122.17 ft (37.24 m)
* Wingspan: 78.06 ft (23.79 m)
* Height: 58.58 ft (17.25 m)
* Empty Weight: 151,205 lb (68,586.6 kg)
* Gross Liftoff Weight: 240,000 lb (109,000 kg)
* Maximum Landing Weight: 230,000 lb (104,000 kg)
* Main Engines: Three Rocketdyne Block 2 A SSMEs, each with a sea level thrust of 393,800 lbf (178,624 kgf / 1.75MN)
* Maximum Payload: 55,250 lb (25,061.4 kg)
* Payload Bay dimensions: 15 ft by 60 ft (4.6 m by 18.3 m)
* Operational Altitude: 100 to 520 nmi (185 to 1,000 km)
* Speed: 25,404 ft/s (7,743 m/s, 27,875 km/h, 17,321 mi/h)
* Crossrange: 1,085 nautical miles (2,009.4 km)
* Crew: Seven (Commander, Pilot, two Mission Specialists, and three Payload Specialists), two for minimum.
External Tank Specifications (for SLWT)
* Length: 153.8 ft (46.9 m)
* Diameter: 27.6 ft (8.4 m)
* Propellent Volume: 535,000 gallon
* Empty Weight: 58,500 lb (26,559 kg)
* Gross Liftoff Weight: 1.667 million lb (757,000 kg)
Solid Rocket Booster Specifications
* Length: 149.6 ft (45.6 m)
* Diameter: 12.17 ft (3.71 m)
* Empty Weight: 139,490 lb (63,272.7 kg)
* Gross Liftoff Weight: 1.3 million lb (590,000 kg)
* Thrust (sea level, liftoff): 2.8 million lbf (1,270,058 kgf / 12.46MN)
System Stack Specifications
* Height: 184.2 ft (56.14 m)
* Gross Liftoff Weight: 4.5 million lb (2.04 million kg)
* Total Liftoff Thrust: 6.781 million lbf (3.076 million kgf / 30.18MN)
Gas Turbines
A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.)
Energy is released when air is mixed with fuel and ignited in the combustor. Combustion increases the temperature, which in turn increases the pressure (due to ideal gas law) resulting in an increase in the velocity and volume of the gas flow (see gas laws). This is directed through a nozzle over the turbine's blades, spinning the turbine and powering the compressor.
Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks.
Gas turbines for electrical power production
Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems.
The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated building.
They can be particularly efficient — up to 60% — when waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle configuration. They can also be run in a cogeneration configuration, where the exhaust is captured to heat steam which is then used to heat buildings or to run airconditioners through a steam turbine.
Simple cycle gas turbines in the power industry require smaller capital investment than combined cycle gas, coal or nuclear plants and can be designed to generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for baseload plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Large simple cycle gas turbines may produce several hundred megawatts of power and approach 40 % thermal efficiency.
Scale jet engines (micro turbines)
Also known as:
* Minature Gas Turbines
* Micro-jets
Many model engineers relish the challenge of re-creating the grand engineering feats of today as tiny working models. Naturally, the idea of re-creating a powerful engine such as the jet, fascinated hobbyists since the very first full size engines were powered up by Hans von Ohain and Frank Whittle back in the 1930s.
Re-creating machines such as engines to a different scale is not easy. The laws of physics governing the behaviour of many machines do not always scale up or down at the same rate as the machine's size (and often not even in a linear way), usually at best causing a dramatic loss of power or efficiency, and at worst causing them not to work at all. An automobile engine, for example, will not work if re-produced in the same shape at the size of a human hand.
With this in mind the pioneer of modern Micro-Jets Kurt Schreckling, produced one of the world's first Micro-Turbines, the FD3/67. This amazing little engine can give out 22 newtons of thrust, and can be built by most mechanically minded people with basic engineering tools, such as a metal lathe.
[edit]
Micro turbines
Also known as:
* Turbo alternators
* Gensets
* MicroTurbine® (registered trademark of Capstone Turbine Corporation)
* Turbogenerator® (registered tradename of Honeywell Power Systems, Inc.)
Micro turbines are becoming wide spread for distributed power and combined heat and power applications. They range from handheld units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts.
Part of their success is due to advances in electronics, which allow unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows, for example, the generator to be integrated with the turbine shaft, and to double as the starter motor.
Micro turbine systems have many advantages over piston engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. However, piston engine generators are quicker to respond to changes in output power requirement.
They accept most commercial fuels, such as natural gas, propane, diesel and kerosene. The are also able to produce renewable energy when fueled with biogas from landfills and sewage treatment plants.
Micro turbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy.
Typical micro turbine efficiencies are 25 to 35 %. When in a combined heat and power cogeneration system, efficiencies of greater than 80 % are commonly achieved.
[edit]
Auxiliary power units
Auxiliary power units (APUs) are small gas turbines designed for auxiliary power of larger machines, usually aircraft. They are well suited for supplying compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, and electrical and hydraulic power. (These are not to be confused with the auxiliary propulsion units, also abbreviated APUs, aboard the gas-turbine-powered Oliver Hazard Perry-class guided-missile frigates. The Perrys' APUs are large electric motors that provide maneuvering help in close waters, or emergency backup if the gas turbines are not working.)
Energy is released when air is mixed with fuel and ignited in the combustor. Combustion increases the temperature, which in turn increases the pressure (due to ideal gas law) resulting in an increase in the velocity and volume of the gas flow (see gas laws). This is directed through a nozzle over the turbine's blades, spinning the turbine and powering the compressor.
Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks.
Gas turbines for electrical power production
Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems.
The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated building.
They can be particularly efficient — up to 60% — when waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle configuration. They can also be run in a cogeneration configuration, where the exhaust is captured to heat steam which is then used to heat buildings or to run airconditioners through a steam turbine.
Simple cycle gas turbines in the power industry require smaller capital investment than combined cycle gas, coal or nuclear plants and can be designed to generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for baseload plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Large simple cycle gas turbines may produce several hundred megawatts of power and approach 40 % thermal efficiency.
Scale jet engines (micro turbines)
Also known as:
* Minature Gas Turbines
* Micro-jets
Many model engineers relish the challenge of re-creating the grand engineering feats of today as tiny working models. Naturally, the idea of re-creating a powerful engine such as the jet, fascinated hobbyists since the very first full size engines were powered up by Hans von Ohain and Frank Whittle back in the 1930s.
Re-creating machines such as engines to a different scale is not easy. The laws of physics governing the behaviour of many machines do not always scale up or down at the same rate as the machine's size (and often not even in a linear way), usually at best causing a dramatic loss of power or efficiency, and at worst causing them not to work at all. An automobile engine, for example, will not work if re-produced in the same shape at the size of a human hand.
With this in mind the pioneer of modern Micro-Jets Kurt Schreckling, produced one of the world's first Micro-Turbines, the FD3/67. This amazing little engine can give out 22 newtons of thrust, and can be built by most mechanically minded people with basic engineering tools, such as a metal lathe.
[edit]
Micro turbines
Also known as:
* Turbo alternators
* Gensets
* MicroTurbine® (registered trademark of Capstone Turbine Corporation)
* Turbogenerator® (registered tradename of Honeywell Power Systems, Inc.)
Micro turbines are becoming wide spread for distributed power and combined heat and power applications. They range from handheld units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts.
Part of their success is due to advances in electronics, which allow unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows, for example, the generator to be integrated with the turbine shaft, and to double as the starter motor.
Micro turbine systems have many advantages over piston engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. However, piston engine generators are quicker to respond to changes in output power requirement.
They accept most commercial fuels, such as natural gas, propane, diesel and kerosene. The are also able to produce renewable energy when fueled with biogas from landfills and sewage treatment plants.
Micro turbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy.
Typical micro turbine efficiencies are 25 to 35 %. When in a combined heat and power cogeneration system, efficiencies of greater than 80 % are commonly achieved.
[edit]
Auxiliary power units
Auxiliary power units (APUs) are small gas turbines designed for auxiliary power of larger machines, usually aircraft. They are well suited for supplying compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, and electrical and hydraulic power. (These are not to be confused with the auxiliary propulsion units, also abbreviated APUs, aboard the gas-turbine-powered Oliver Hazard Perry-class guided-missile frigates. The Perrys' APUs are large electric motors that provide maneuvering help in close waters, or emergency backup if the gas turbines are not working.)
Space Shuttle
NASA's Space Shuttle, officially called Space Transportation System (STS), is the United States government's current manned launch vehicle. The winged shuttle orbiter is launched vertically, usually carrying five to seven astronauts (although eight have been carried) and up to 22,700 kg (50,000 lb) of payload into low earth orbit. When its mission is complete, it re-enters the earth's atmosphere and makes an unpowered horizontal landing.
The Shuttle is the first orbital spacecraft designed for partial reusability. It is also so far the only winged manned spacecraft to achieve orbit and land. It carries large payloads to various orbits, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can recover satellites and other payloads from orbit and return them to Earth, but this capacity has not been used often. However, it has been used to return large payloads from the International Space Station to earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a projected lifespan of 100 launches or 10 years' operational life.
The program started in the late 1960s and has dominated NASA's manned operations since the mid-1970s. According to the Vision for Space Exploration, use of the Space Shuttle will be focused on completing assembly of the ISS in 2010, after which it will be replaced by the Crew Exploration Vehicle (CEV).
Description
The Shuttle is a partially reusuable launch system composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable External Tank (ET), and the two reusable Solid Rocket Boosters (SRBs). The tank and boosters are jettisoned during ascent; only the orbiter goes into orbit. The vehicle is launched vertically like a conventional rocket, and the orbiter glides to a horizontal landing, after which it is refurbished for reuse.
The Orbiter resembles an airplane with double-delta wings, swept 81° at the inner leading edge and 45° at the outer leading edge. Its vertical stabilizer's leading edge is swept back at a 45° angle. The four elevons, mounted at the trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabilizer, with the body flap, control the Orbiter during descent and landing.
The Orbiter's crew cabin consists of three levels: the flight deck, the mid-deck, and the utility area. The highest flight deck seats the commander and pilot, with two mission specialists behind them. The mid-deck has three more seats for the rest of the crew members. The galley, toilet, sleep locations, storage lockers, and the side hatch for entering/exiting the vehicle are also located there, as is the airlock hatch. The airlock has another hatch into the payload bay. It allows two astronauts, wearing their Extravehicular Mobility Unit (EMU) space suits, to depressurize before a space walk.
The Orbiter has a large 60 by 15 ft (18 m by 4.6 m) payload bay, filling most of the fuselage. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while the Shuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm used to retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missions where it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for Shuttle flights, it will probably be included on all future flights.
Three Space Shuttle Main Engines (SSMEs) are mounted on the Orbiter's aft fuselage in a triangular pattern. The three engines can swivel 10.5 degrees up and down and 8.5 degrees from side to side during ascent to change the direction of their thrust and steer the Shuttle as well as push.
The Orbital Maneuvering System (OMS) provides orbital maneuvers, including insertion, circularization, transfer, rendezvous, abort to orbit, and abort once around.
The Reaction Control System (RCS) provides attitude control and translation along the pitch, roll, and yaw axes during the flight phases of orbit insertion, orbit, and re-entry.
The Thermal Protection System (TPS) covers the outside of the Orbiter, protecting it from the cold soak of -121 °C (-250 °F) in space to the 1649 °C (3000 °F) heat of reentry
The orbiter structure is made primarily from aluminium alloy, although the engine thrust structure is made from titanium.
The External Tank (ET) provides 2.025 million liters (535,000 gallons) of liquid hydrogen and liquid oxygen propellant to the SSMEs. It is discarded 8.5 minutes after launch at an altitude of 60 nautical miles (111 km) then breaks up on reentry. The ET is constructed mostly of aluminium-lithium alloy about 1/8 inch thick. Many people think that the ET is painted orange. In reality, the orange color is the true color of the tank's insulation. If it were painted, it would add another 1,000 lbs. of unnecessary payload.
Two Solid Rocket Boosters (SRBs) provide about 83% of the vehicle's thrust at liftoff and during the first stage ascent. They are jettisoned two minutes after launch at a height of about 150,000 feet (45.7 km), then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1/2 inch (1.27 cm) thick.
[edit]
Computerized fly-by-wire digital flight control
The shuttle was one of the earliest craft to use a computerized fly-by-wire digital flight control system. This means no mechanical or hydraulic linkages connect the pilot's control stick to the control surfaces or reaction control system thrusters.
A primary concern with digital fly-by-wire systems is reliability. Much research went into the shuttle computer system. The shuttle uses five identical redundant IBM 32-bit general purpose computers (GPCs), model AP-101, constituting a type of embedded system. Four computers run specialized software called the Primary Avionics Software System (PASS). A fifth backup computer runs separate software called the Backup Flight System (BFS). Collectively they are called the shuttle Data Processing System (DPS).
The design goal of the shuttle DPS is fail operational/fail safe reliability. After a single failure the shuttle can continue the mission. After two failures it can land safely.
The four general-purpose computers operate essentially in lockstep, checking each other. If one computer fails, the three functioning computers "vote" it out of the system. This isolates it from vehicle control. If a second computer of the three remaining fails, the two functioning computers vote it out. In the rare case of two out of four computers simultaneously failing (a two-two split), one group is picked at random.
The Backup Flight System (BFS) is separately developed software running on the fifth computer, used only if the entire four-computer primary system fails. The BFS was created because although the four primary computers are hardware redundant, they all run the same software, so a generic software problem could crash all of them. This should never happen, as embedded system avionic software is developed under totally different conditions from commercial software. For example, the number of code lines is tiny compared to a commercial operating system, changes are only made infrequently and with extensive testing, and many programming and test personnel work on the small amount of computer code. However in theory it can fail, and the BFS exists for that contingency.
The software for the shuttle computers is written in a high-level language called HAL/S, somewhat similar to PL/I. It is specifically designed for a real time embedded system environment.
The IBM AP-101 computers originally had about 424 kilobytes of magnetic core memory each. The CPU could process about 400,000 instructions per second. They have no hard disk drive, but load software from tape cartridges.
In 1990 the original computers were replaced with an upgraded model AP-101S, which has about 2.5 times the memory capacity (about 1 megabyte) and three times the processor speed (about 1.2 million instructions per second). The memory was changed from magnetic core to semiconductor with battery backup.
[edit]
Other improvements
Internally the Shuttle remains largely similar to the original design, with the exception of the improved avionics computers. In addition to the computer upgrades, the original vector graphics monochrome cockpit displays were replaced with modern full-color, flat-panel display screens, similar to contemporary airliners like the Airbus A320. This is called a "glass cockpit". In the Apollo-Soyuz Test Project tradition, programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the Orbiter's internal airlocks are being replaced with external docking systems to allow for a greater amount of cargo to be stored on the Shuttle's mid-deck during Station resupply missions.
The Space Shuttle Main Engines have had several improvements to enhance reliability and power. This explains phrases such as "Main engines throttling up to 104%." This does not mean the engines are being run over a safe limit. The 100% figure is the original specified power level. During the lengthy development program, Rocketdyne determined the engine was capable of safe reliable operation at 104% of the originally specified thrust. They could have rescaled the output number, saying in essence 104% is now 100%. However this would have required revising much previous documentation and software, so the 104% number was retained. SSME upgrades are denoted as "block numbers", such as block I, block II, and block IIA. The upgrades have improved engine reliability, maintainability and performance. The 109% thrust level was finally reached in flight hardware with the Block II engines in 2001. The normal maximum throttle is 104%, with 106% and 109% available for abort emergencies.
For STS-1 and STS-2 the external tank was painted white to protect the insulation that covers much of the tank, but improvements and testing showed that it was not required. The weight saved by not painting the tank results in an increase in payload capability to orbit. Additional weight was saved by removing some of the internal "stringers" in the hydrogen tank that proved unnecessary. The resulting "light-weight external tank" has been used on the vast majority of Shuttle missions. STS-91 saw the first flight of the "super light-weight external tank". This version of the tank is made of the 2195 aluminium-lithium alloy. It weighs 7,500 lb (3.4 t) less than the last run of lightweight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been "tested" on operational flights.
The SRBs (Solid Rocket Boosters) have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident.
Several other SRB improvements were planned in order to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost, probably safer and better performing Advanced Solid Rocket Booster which was to have entered production in the early to mid-1990s to support the Space Station, but was later cancelled to save money after the expenditure of $2.2 billion. The loss of the ASRB program forced the development of the Super LightWeight external Tank (SLWT), which provides some of the increased payload capability, while not providing any of the safety improvements. In addition the Air Force developed their own much lighter single-piece SRB design using a filament-wound system, but this too was cancelled.
A cargo-only, unmanned variant of the Shuttle has been variously proposed and rejected since the 1980s. It is called the Shuttle-C and would trade re-usability for cargo capability with large potential savings from reusing technology developed for the Space Shuttle.
On the first four Shuttle missions, astronauts wore full-pressure Launch Entry Suit (LES) during ascent and descent. The pressured helmet was used from STS-5 until the loss of Challenger. The LES was reinstated when Shuttle flights resumed in 1988. The LES ended its service life in late 1995, replaced by the Advanced Crew Escape Suit (ACES).
[edit]
Technical data
Orbiter Specifications (for Endeavour, OV-105)
* Length: 122.17 ft (37.24 m)
* Wingspan: 78.06 ft (23.79 m)
* Height: 58.58 ft (17.25 m)
* Empty Weight: 151,205 lb (68,586.6 kg)
* Gross Liftoff Weight: 240,000 lb (109,000 kg)
* Maximum Landing Weight: 230,000 lb (104,000 kg)
* Main Engines: Three Rocketdyne Block 2 A SSMEs, each with a sea level thrust of 393,800 lbf (178,624 kgf / 1.75MN)
* Maximum Payload: 55,250 lb (25,061.4 kg)
* Payload Bay dimensions: 15 ft by 60 ft (4.6 m by 18.3 m)
* Operational Altitude: 100 to 520 nmi (185 to 1,000 km)
* Speed: 25,404 ft/s (7,743 m/s, 27,875 km/h, 17,321 mi/h)
* Crossrange: 1,085 nautical miles (2,009.4 km)
* Crew: Seven (Commander, Pilot, two Mission Specialists, and three Payload Specialists), two for minimum.
External Tank Specifications (for SLWT)
* Length: 153.8 ft (46.9 m)
* Diameter: 27.6 ft (8.4 m)
* Propellent Volume: 535,000 gallon
* Empty Weight: 58,500 lb (26,559 kg)
* Gross Liftoff Weight: 1.667 million lb (757,000 kg)
Solid Rocket Booster Specifications
* Length: 149.6 ft (45.6 m)
* Diameter: 12.17 ft (3.71 m)
* Empty Weight: 139,490 lb (63,272.7 kg)
* Gross Liftoff Weight: 1.3 million lb (590,000 kg)
* Thrust (sea level, liftoff): 2.8 million lbf (1,270,058 kgf / 12.46MN)
System Stack Specifications
* Height: 184.2 ft (56.14 m)
* Gross Liftoff Weight: 4.5 million lb (2.04 million kg)
* Total Liftoff Thrust: 6.781 million lbf (3.076 million kgf / 30.18MN)
The Shuttle is the first orbital spacecraft designed for partial reusability. It is also so far the only winged manned spacecraft to achieve orbit and land. It carries large payloads to various orbits, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can recover satellites and other payloads from orbit and return them to Earth, but this capacity has not been used often. However, it has been used to return large payloads from the International Space Station to earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a projected lifespan of 100 launches or 10 years' operational life.
The program started in the late 1960s and has dominated NASA's manned operations since the mid-1970s. According to the Vision for Space Exploration, use of the Space Shuttle will be focused on completing assembly of the ISS in 2010, after which it will be replaced by the Crew Exploration Vehicle (CEV).
Description
The Shuttle is a partially reusuable launch system composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable External Tank (ET), and the two reusable Solid Rocket Boosters (SRBs). The tank and boosters are jettisoned during ascent; only the orbiter goes into orbit. The vehicle is launched vertically like a conventional rocket, and the orbiter glides to a horizontal landing, after which it is refurbished for reuse.
The Orbiter resembles an airplane with double-delta wings, swept 81° at the inner leading edge and 45° at the outer leading edge. Its vertical stabilizer's leading edge is swept back at a 45° angle. The four elevons, mounted at the trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabilizer, with the body flap, control the Orbiter during descent and landing.
The Orbiter's crew cabin consists of three levels: the flight deck, the mid-deck, and the utility area. The highest flight deck seats the commander and pilot, with two mission specialists behind them. The mid-deck has three more seats for the rest of the crew members. The galley, toilet, sleep locations, storage lockers, and the side hatch for entering/exiting the vehicle are also located there, as is the airlock hatch. The airlock has another hatch into the payload bay. It allows two astronauts, wearing their Extravehicular Mobility Unit (EMU) space suits, to depressurize before a space walk.
The Orbiter has a large 60 by 15 ft (18 m by 4.6 m) payload bay, filling most of the fuselage. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while the Shuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm used to retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missions where it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for Shuttle flights, it will probably be included on all future flights.
Three Space Shuttle Main Engines (SSMEs) are mounted on the Orbiter's aft fuselage in a triangular pattern. The three engines can swivel 10.5 degrees up and down and 8.5 degrees from side to side during ascent to change the direction of their thrust and steer the Shuttle as well as push.
The Orbital Maneuvering System (OMS) provides orbital maneuvers, including insertion, circularization, transfer, rendezvous, abort to orbit, and abort once around.
The Reaction Control System (RCS) provides attitude control and translation along the pitch, roll, and yaw axes during the flight phases of orbit insertion, orbit, and re-entry.
The Thermal Protection System (TPS) covers the outside of the Orbiter, protecting it from the cold soak of -121 °C (-250 °F) in space to the 1649 °C (3000 °F) heat of reentry
The orbiter structure is made primarily from aluminium alloy, although the engine thrust structure is made from titanium.
The External Tank (ET) provides 2.025 million liters (535,000 gallons) of liquid hydrogen and liquid oxygen propellant to the SSMEs. It is discarded 8.5 minutes after launch at an altitude of 60 nautical miles (111 km) then breaks up on reentry. The ET is constructed mostly of aluminium-lithium alloy about 1/8 inch thick. Many people think that the ET is painted orange. In reality, the orange color is the true color of the tank's insulation. If it were painted, it would add another 1,000 lbs. of unnecessary payload.
Two Solid Rocket Boosters (SRBs) provide about 83% of the vehicle's thrust at liftoff and during the first stage ascent. They are jettisoned two minutes after launch at a height of about 150,000 feet (45.7 km), then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1/2 inch (1.27 cm) thick.
[edit]
Computerized fly-by-wire digital flight control
The shuttle was one of the earliest craft to use a computerized fly-by-wire digital flight control system. This means no mechanical or hydraulic linkages connect the pilot's control stick to the control surfaces or reaction control system thrusters.
A primary concern with digital fly-by-wire systems is reliability. Much research went into the shuttle computer system. The shuttle uses five identical redundant IBM 32-bit general purpose computers (GPCs), model AP-101, constituting a type of embedded system. Four computers run specialized software called the Primary Avionics Software System (PASS). A fifth backup computer runs separate software called the Backup Flight System (BFS). Collectively they are called the shuttle Data Processing System (DPS).
The design goal of the shuttle DPS is fail operational/fail safe reliability. After a single failure the shuttle can continue the mission. After two failures it can land safely.
The four general-purpose computers operate essentially in lockstep, checking each other. If one computer fails, the three functioning computers "vote" it out of the system. This isolates it from vehicle control. If a second computer of the three remaining fails, the two functioning computers vote it out. In the rare case of two out of four computers simultaneously failing (a two-two split), one group is picked at random.
The Backup Flight System (BFS) is separately developed software running on the fifth computer, used only if the entire four-computer primary system fails. The BFS was created because although the four primary computers are hardware redundant, they all run the same software, so a generic software problem could crash all of them. This should never happen, as embedded system avionic software is developed under totally different conditions from commercial software. For example, the number of code lines is tiny compared to a commercial operating system, changes are only made infrequently and with extensive testing, and many programming and test personnel work on the small amount of computer code. However in theory it can fail, and the BFS exists for that contingency.
The software for the shuttle computers is written in a high-level language called HAL/S, somewhat similar to PL/I. It is specifically designed for a real time embedded system environment.
The IBM AP-101 computers originally had about 424 kilobytes of magnetic core memory each. The CPU could process about 400,000 instructions per second. They have no hard disk drive, but load software from tape cartridges.
In 1990 the original computers were replaced with an upgraded model AP-101S, which has about 2.5 times the memory capacity (about 1 megabyte) and three times the processor speed (about 1.2 million instructions per second). The memory was changed from magnetic core to semiconductor with battery backup.
[edit]
Other improvements
Internally the Shuttle remains largely similar to the original design, with the exception of the improved avionics computers. In addition to the computer upgrades, the original vector graphics monochrome cockpit displays were replaced with modern full-color, flat-panel display screens, similar to contemporary airliners like the Airbus A320. This is called a "glass cockpit". In the Apollo-Soyuz Test Project tradition, programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the Orbiter's internal airlocks are being replaced with external docking systems to allow for a greater amount of cargo to be stored on the Shuttle's mid-deck during Station resupply missions.
The Space Shuttle Main Engines have had several improvements to enhance reliability and power. This explains phrases such as "Main engines throttling up to 104%." This does not mean the engines are being run over a safe limit. The 100% figure is the original specified power level. During the lengthy development program, Rocketdyne determined the engine was capable of safe reliable operation at 104% of the originally specified thrust. They could have rescaled the output number, saying in essence 104% is now 100%. However this would have required revising much previous documentation and software, so the 104% number was retained. SSME upgrades are denoted as "block numbers", such as block I, block II, and block IIA. The upgrades have improved engine reliability, maintainability and performance. The 109% thrust level was finally reached in flight hardware with the Block II engines in 2001. The normal maximum throttle is 104%, with 106% and 109% available for abort emergencies.
For STS-1 and STS-2 the external tank was painted white to protect the insulation that covers much of the tank, but improvements and testing showed that it was not required. The weight saved by not painting the tank results in an increase in payload capability to orbit. Additional weight was saved by removing some of the internal "stringers" in the hydrogen tank that proved unnecessary. The resulting "light-weight external tank" has been used on the vast majority of Shuttle missions. STS-91 saw the first flight of the "super light-weight external tank". This version of the tank is made of the 2195 aluminium-lithium alloy. It weighs 7,500 lb (3.4 t) less than the last run of lightweight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been "tested" on operational flights.
The SRBs (Solid Rocket Boosters) have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident.
Several other SRB improvements were planned in order to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost, probably safer and better performing Advanced Solid Rocket Booster which was to have entered production in the early to mid-1990s to support the Space Station, but was later cancelled to save money after the expenditure of $2.2 billion. The loss of the ASRB program forced the development of the Super LightWeight external Tank (SLWT), which provides some of the increased payload capability, while not providing any of the safety improvements. In addition the Air Force developed their own much lighter single-piece SRB design using a filament-wound system, but this too was cancelled.
A cargo-only, unmanned variant of the Shuttle has been variously proposed and rejected since the 1980s. It is called the Shuttle-C and would trade re-usability for cargo capability with large potential savings from reusing technology developed for the Space Shuttle.
On the first four Shuttle missions, astronauts wore full-pressure Launch Entry Suit (LES) during ascent and descent. The pressured helmet was used from STS-5 until the loss of Challenger. The LES was reinstated when Shuttle flights resumed in 1988. The LES ended its service life in late 1995, replaced by the Advanced Crew Escape Suit (ACES).
[edit]
Technical data
Orbiter Specifications (for Endeavour, OV-105)
* Length: 122.17 ft (37.24 m)
* Wingspan: 78.06 ft (23.79 m)
* Height: 58.58 ft (17.25 m)
* Empty Weight: 151,205 lb (68,586.6 kg)
* Gross Liftoff Weight: 240,000 lb (109,000 kg)
* Maximum Landing Weight: 230,000 lb (104,000 kg)
* Main Engines: Three Rocketdyne Block 2 A SSMEs, each with a sea level thrust of 393,800 lbf (178,624 kgf / 1.75MN)
* Maximum Payload: 55,250 lb (25,061.4 kg)
* Payload Bay dimensions: 15 ft by 60 ft (4.6 m by 18.3 m)
* Operational Altitude: 100 to 520 nmi (185 to 1,000 km)
* Speed: 25,404 ft/s (7,743 m/s, 27,875 km/h, 17,321 mi/h)
* Crossrange: 1,085 nautical miles (2,009.4 km)
* Crew: Seven (Commander, Pilot, two Mission Specialists, and three Payload Specialists), two for minimum.
External Tank Specifications (for SLWT)
* Length: 153.8 ft (46.9 m)
* Diameter: 27.6 ft (8.4 m)
* Propellent Volume: 535,000 gallon
* Empty Weight: 58,500 lb (26,559 kg)
* Gross Liftoff Weight: 1.667 million lb (757,000 kg)
Solid Rocket Booster Specifications
* Length: 149.6 ft (45.6 m)
* Diameter: 12.17 ft (3.71 m)
* Empty Weight: 139,490 lb (63,272.7 kg)
* Gross Liftoff Weight: 1.3 million lb (590,000 kg)
* Thrust (sea level, liftoff): 2.8 million lbf (1,270,058 kgf / 12.46MN)
System Stack Specifications
* Height: 184.2 ft (56.14 m)
* Gross Liftoff Weight: 4.5 million lb (2.04 million kg)
* Total Liftoff Thrust: 6.781 million lbf (3.076 million kgf / 30.18MN)
Multiple rocket launcher
A multiple rocket launcher is a type of unguided rocket artillery system. Like other rocket artillery, MRLs are less accurate and have a much lower rate of fire than batteries of traditional artillery guns. However, they have the capability of simultaneously dropping many hundreds of kilograms of explosive, with devastating effect.
The earliest model is probably the Hwacha used by Koreans, first deployed in 1451. It consists of small rockets attached to arrows which flung spikes upon detonation. Hwachas fire multiple anti-personnel firearms at once in battle and its fire model of was kept until today.
The most famous system is the Katyusha rocket launcher used by the Soviet Union during World War II and by its allies during the Cold War. This was a simple system in which a rack of launch rails were mounted on the back of a truck. In the same conflict Germany and Britain produced towed rocket systems known as the Nebelwerfer and Land Mattress respectively. Modern systems are often mounted on armoured, tracked vehicles, have a range of tens of kilometers, and may be guided for accuracy.
The U.S. Army's M270 MLRS (Multiple Launch Rocket System) is an example of a modern system, also in service with several other nations
The earliest model is probably the Hwacha used by Koreans, first deployed in 1451. It consists of small rockets attached to arrows which flung spikes upon detonation. Hwachas fire multiple anti-personnel firearms at once in battle and its fire model of was kept until today.
The most famous system is the Katyusha rocket launcher used by the Soviet Union during World War II and by its allies during the Cold War. This was a simple system in which a rack of launch rails were mounted on the back of a truck. In the same conflict Germany and Britain produced towed rocket systems known as the Nebelwerfer and Land Mattress respectively. Modern systems are often mounted on armoured, tracked vehicles, have a range of tens of kilometers, and may be guided for accuracy.
The U.S. Army's M270 MLRS (Multiple Launch Rocket System) is an example of a modern system, also in service with several other nations
Tanks
A tank is a tracked armored fighting vehicle, designed primarily to engage enemy forces by
the use of direct fire. A tank is characterised by heavy weapons and armor, as well as by a
high degree of mobility that allows it to cross rough terrain at relatively high speeds.
While tanks are expensive to operate and logistically demanding, they are among the most
formidable and versatile weapons of the modern battlefield, both for their ability to engage
other ground targets and their shock value against infantry.
While tanks are powerful fighting machines, they seldom operate alone, being organised into
armoured units in combined arms forces. Without such support, tanks, despite their armour
and mobility, are vulnerable to infantry, mines, artillery, and air power. Tanks are also at
a disadvantage in wooded terrain and urban environments, which cancel the advantages of the
tank's long-range firepower, limit the crew's ability to detect potential threats, and can
even limit the turret's ability to traverse.
Tanks were first used in the First World War to break the deadlock of the trenches, and they
evolved gradually to assume the role of cavalry on the battlefield. The name tank first
arose in British factories making the hulls of the first battle tanks: the workmen were
given the impression they were constructing tracked water containers for the British Army,
hence keeping the production of a fighting vehicle secret.
Tanks and armour tactics have undergone many generations of evolution over nearly a century.
Although weapons systems and armour continue to be developed, many nations have reconsidered
the need for such heavy weaponry in a period characterised by unconventional warfare.
Design
The three traditional factors determining a tank's effectiveness are its firepower, mobility
and protection. The psychological effect on enemy soldiers of a tank's imposing battlefield
presence is called shock action.
Firepower is the ability of a tank to defeat a target. This takes into account the maximum
distance at which targets can be engaged, the ability to engage moving targets, the speed
with which multiple targets can be attacked, and the capability to defeat armoured vehicles
or entrenched infantry.
Mobility includes the speed and agility of driving cross-country, the types of terrain that
can be covered, the dimensions of obstacles, trenches, and water that can be crossed, the
ability to cross small bridges, and the distance that can be covered before refuelling is
required. "Strategic mobility" also includes the ability to travel at high speed on roads,
and the ability to be carried on rail or truck transport. Traditionally AFV mobility is
measured by the following metrics:
* engine power
* engine torque
* power-to-weight ratio
* road speed
* off-road speed (a somewhat nebulous figure given the possible variation)
* road range
* off-road range
* weight (bridge classification)
* ground pressure
* width of trench crossed
* vertical step climbed
* angle of slope that can be climbed
* angle of side slope that can be negotiated
* ground clearance
* unprepared fording depth
* prepared fording depth (if different)
Protection is the amount of armour, the type(s), how it is arranged (i.e., sloped or not),
and which areas are given more protection (e.g., the turret and tracks) and which receive
less (e.g., the rear of the chassis). It also includes low profile, low noise and thermal
signature, active countermeasures and other methods of avoiding enemy fire, and the ability
to continue fighting after damage has been sustained.
Tank design is traditionally held to be a compromise between these three factors—it is not
considered possible to maximise all three. For example, increasing protection by adding
armour will increase weight and therefore decrease manoeuvrability; increasing firepower by
using a larger gun will decrease both manoeuvrability and protection (due to decreased
armour at the front of the turret).
How the compromise is achieved is influenced by a combination of factors, including military
strategies, budget, geography, political will, and the requirement to sell the tank to other
countries.
Examples of how different countries are influenced in their decisions are as follows:
* Britain has historically opted for better firepower and increased protection at the
expense of some manoeuvrability. Britain maintains a small, highly-trained professional
army, and so tank crew survivability is important. As limited resources may be available,
the crew needs to be able to maintain their tanks in the field.
* The USA has a large army with sophisticated weaponry and a complex array of mobile
support services. As their tanks are expected to rarely be away from support and repair
units, less emphasis is placed on the crew's ability to maintain the tank themselves or to
continue fighting with it once damage has been sustained.
* Soviet tanks are traditionally rugged, simple for production and maintenance
(characteristic of the Soviet-era idiom that "quantity has a quality of its own"), as
exemplified by the T-34. State-controlled design development proceeds in incremental
changes. Extensive maintenance is expected to be done in specialised depots. Tanks of this
class are opted to have the best combination of firepower, mobility, and protection.
* Israel is a small, but relatively rich, nation, with limited manpower in a hostile
political environment. Its primary concern is therefore crew survivability. To this end it
is the only nation to have produced a main battle tank with the engine placed at the front
and fuel surrounding the crew, to increase protection.
Weapons
Main article: tank gun
The main weapon of any modern tank is a single large gun. Tank guns are among the
largest-calibre weapons in use on land, with only a few artillery pieces being larger.
Although the calibre has not changed substantially since the end of the Second World War,
modern guns are technologically superior. The current common sizes are 120mm calibre for
Western tanks and 125mm for Eastern (Soviet and Chinese legacy) tanks. Tank guns have been
able to fire many types of rounds, but their current use is commonly limited to kinetic
energy (KE) penetrators and high explosive (HE) rounds. Some tanks can fire missiles through
the gun. Smoothbore (rather than rifled) guns are the dominant type of gun today. The
British Army and the Indian Army are now the only ones to field main battle tanks carrying
rifled guns.
Modern tank guns are generally fitted with thermal jackets which reduce the effect of uneven
temperature on the barrel. For instance, if it were to rain on a tank barrel the top would
cool faster than the bottom, or a breeze on the left might cause the left side to cool
faster then the right. This uneven cooling will cause the barrel to bend slightly and will
affect long range accuracy.
Usually, tanks carry other armament for short range defence against infantry or targets
where the use of the main weapon would be ineffective or wasteful. Typically, this is a
small calibre (7.62 to 12.7 mm) machine gun mounted coaxially with the main gun. However, a
couple of French tanks such as the AMX-30 and AMX-40 carry a coaxial 20mm cannon that has a
high rate of fire and can destroy lightly armoured vehicles. Additionally, many tanks carry
a roof-mounted or commander's cupola machine gun for close-in ground or limited air defence.
The 12.7-mm and 14.5-mm machine guns commonly carried on U.S. and Russian tanks and the
French Leclerc are also capable of destroying lightly-armoured vehicles at close range.
Some tanks have been adapted to specialised roles and have had unusual main armament such as
flame-throwers. These specialised weapons are now usually mounted on the chassis of an
armoured personnel carrier.
Fire control
Historically, tank weapons were aimed through simple optical sights and laid onto target by
hand, with windage estimated or assisted with a reticule. Range to the target was estimated
with the aid of a reticule (markings in the gun sight which are aligned to frame an object
of known size, in this case a tank). Consequently, accuracy was limited at long range and
concurrent movement and accurate shooting were largely impossible. Over time these sights
were replaced with stereoscopic range-finders. These were eventually replaced by Laser
range-finders.
Most modern main battle tanks in the armies of industrialised countries use laser
range-finders but optical and reticule range-finders are still in use in older and less
sophisticated vehicles. Modern tanks have a variety of sophisticated systems to make them
more accurate. Gyroscopes are used to stabilise the main weapon; computers calculate the
appropriate elevation and aim-point, taking input from sensors for wind speed, air
temperature, humidity, the gun-barrel temperature, warping and wear, the speed of the target
(calculated by taking at least two sightings of the target with the range-finder), and the
movement of the tank. Infrared, light-amplification, or thermal night vision equipment is
also commonly incorporated. Laser target designators may also be used to illuminate targets
for guided munitions. As a result modern tanks can fire reasonably accurately while moving.
[edit]
Ammunition
There are several types of ammunition designed to defeat armour, including High explosive
squash head (HESH, also called high explosive plastic, HEP), High explosive antitank (HEAT),
and kinetic energy penetrators (KEP, or armour-piercing discarding sabot APDS). For
accuracy, shells are spun by gun-barrel rifling, or fin-stabilized (APFSDS, HEAT-FS, etc.).
Some tanks, including the M551 Sheridan, T-72, T-64, T-80, T-90, T-84, and PT-91 can fire
ATGMs (anti-tank guided missile) through their gun barrel or from externally mounted
launchers. This functionality can extend the effective combat range of the tank beyond the
range afforded by conventional shells, depending on the capabilities of the ATGM system. It
also provides the tank with a useful weapon against slow, low-flying airborne targets like
helicopters. The United States has abandoned this concept, phasing the M551 and M60A2 out of
their forces in favour of helicopters and aircraft for long range anti-tank roles, but CIS
countries continue to employ gun-missile systems in their main battle tanks.
Protection
The main battle tank is the most heavily armoured vehicle in modern armies. Its armour is
designed to protect the vehicle and crew against a wide variety of threats. Commonly,
protection against kinetic energy penetrators fired by other tanks is considered the most
important. Tanks are also vulnerable to antitank guided missiles; antitank mines, larger
bombs, and direct artillery hits, which can disable or destroy them. Tanks are especially
vulnerable to airborne threats. Most modern MBTs do offer near complete protection from
artillery fragmentation and lighter antitank weapons such as rocket propelled grenades. The
amount of armour needed to protect against all conceivable threats from all angles would be
far too heavy to be practical, so when designing an MBT much effort goes into finding the
right balance between protection and weight.
Armour
Main article: vehicle armour
Most armoured fighting vehicles are manufactured of hardened steel plate, or in some cases
aluminium. The relative effectiveness of armour is expressed by comparison to rolled
homogeneous armour.
Most armoured vehicles are best-protected at the front, and their crews always try to keep
them pointed toward the likeliest direction of the enemy. The thickest and best-sloped
armour is on the glacis plate and the turret front. The sides have less armour and the rear,
belly and roof are least protected. World War II American M4 Medium tank crews found the
German Tigers to be practically invulnerable from the front, and were forced to employ flank
attacks. Today, tanks are vulnerable to specialised top-attack missile weapons and air
attack. During WW2, aircraft rockets earned a formidable reputation, especially in France
after the Normandy landings (Operation Neptune); post-war analysis revealed many reported
kills were near-misses. Aircraft cannon firing armour-piercing ammunition, such as the
Hurribomber's 40mm or Stuka's 37mm, could be effective, also. Even a simple Molotov cocktail
on the engine deck, however, may disable most tanks.
Before the Second World War, several tank designers tried sloping the armour on experimental
tanks. The most famous and successful example of this approach at the time was the T-34.
Angling armour plates greatly increases their effectiveness against projectiles, by
increasing the effective perpendicular thickness of the armour, and by increasing the chance
of deflection. German tank crews were said to be horrified to find that shots fired at the
angled plates of T-34s would sometimes simply ricochet.
Even light infantry antitank weapons can immobilise a tank by damaging its suspension or
track. Many tracked military vehicles have side skirts, protecting the suspension.
High explosive antitank weapons (HEAT), such as the bazooka, were a new threat in the Second
World War. These weapons carry a warhead with a shaped charge, which focuses the force of an
explosion into a narrow penetrating stream. Thin plates of spaced armour, steel mesh "RPG
screens", or rubber skirts, were found to cause HEAT rounds to detonate too far from the
main armour, greatly reducing their penetrating power.
Some antitank ammunition (HESH or HEP) uses flexible explosive material, which squashes
against a vehicle's armour, and causes dangerous spalling of material inside the tank when
the charge explodes. This may kill the crew without penetrating the armour, still
neutralizing the tank. As a defence, some vehicles have a layer of anti-spall material
lining their insides.
Since the 1970s, some tanks have been protected by more complex composite armour, a sandwich
of various alloys and ceramics. One of the best types of passive armour is the
British-developed Chobham armour, which is comprised of spaced ceramic blocks contained by a
resin-fabric matrix between layers of conventional armour. A form of Chobham armour is
encased in depleted uranium on the very well-protected M1A1 Abrams MBT.
The Israeli Merkava tank takes the design of protection systems to an extreme, using the
engine and fuel tanks as secondary armour.
[edit]
Grenade launchers, smoke and passive defences
Most armoured vehicles carry smoke grenade launchers which can rapidly deploy a smoke screen
to visually shield a withdrawal from an enemy ambush or attack. The smoke screen is very
rarely used offensively, since attacking through it blocks the attacker's vision and gives
the enemy an early indication of impending attack. Modern smoke grenades work in the
infrared as well as visible spectrum of light.
Some smoke grenades are designed to make a very dense cloud capable of blocking the laser
beams of enemy target designators or range finders and of course obscuring vision, reducing
probability of a hit from visually aimed weapons, especially low speed weapons, such as
antitank missiles which require the operator to keep the tank in sight for a relatively long
period of time. In many MBTs, such as the French-built Leclerc, the smoke grenade launchers
are also meant to launch tear gas grenades and anti-personnel fragmentation grenades. Many
Israeli tanks contain small vertical mortar tubes which can be operated from within the
tank, enhancing the anti-personnel capabilities and allowing it to engage targets which are
behind obstacles. There have been proposals to equip other tanks with dual-purpose
smoke/fragmentation grenade launchers that can be reloaded from the interior.
Prior to the widespread introduction of thermal imaging the most common smoke grenade in AFV
launchers was white phosphorus which created a very rapid smoke screen as well as having a
very useful incendiary effect against any infantry in the burst area (e.g., infantry
attempting to close with hand placed charges or mines).
Since the advent of thermal imagers most tanks carry a smoke grenade that contains a plastic
or rubber compound whose tiny burning fragments provide better obscurant qualities against
thermal imagers.
Some tanks also have smoke generators which can generate smoke continuously, rather than the
instantaneous, but short duration of smoke grenades. Generally smoke generators work by
injecting fuel into the exhaust, which partially burns the fuel, but leaves sufficient
unburned or partially burned particles to create a dense smoke screen.
Modern tanks are increasingly being fitted with passive defensive systems such as laser
warning devices, which activate an alarm if the tank is "painted" by a laser range-finder or
designator.
Other passive defences include radio warning devices, which provide warning if the tank is
targeted by radar systems that are commonly used to guide antitank weapons such as
millimetre and other very short wave radar.
[edit]
Countermeasures
Passive countermeasures, like the Russian Shtora system, attempt to jam the guidance systems
of incoming guided missiles.
Explosive reactive armour, or ERA, is another major type of protection against high
explosive antitank weapons, in which sections of armour explode to dissipate the focussed
explosive force of a shaped charge warhead. Reactive armour is attached to the outside of an
MBT in small, replaceable bricks.
Active protection systems go one step further than reactive armour. An APS uses radar or
other sensing technology to automatically react to incoming projectiles. When the system
detects hostile fire, it calculates a firing resolution and directs an explosive-launched
counter-projectile to intercept or disrupt the incoming fire a few metres from the target.
the use of direct fire. A tank is characterised by heavy weapons and armor, as well as by a
high degree of mobility that allows it to cross rough terrain at relatively high speeds.
While tanks are expensive to operate and logistically demanding, they are among the most
formidable and versatile weapons of the modern battlefield, both for their ability to engage
other ground targets and their shock value against infantry.
While tanks are powerful fighting machines, they seldom operate alone, being organised into
armoured units in combined arms forces. Without such support, tanks, despite their armour
and mobility, are vulnerable to infantry, mines, artillery, and air power. Tanks are also at
a disadvantage in wooded terrain and urban environments, which cancel the advantages of the
tank's long-range firepower, limit the crew's ability to detect potential threats, and can
even limit the turret's ability to traverse.
Tanks were first used in the First World War to break the deadlock of the trenches, and they
evolved gradually to assume the role of cavalry on the battlefield. The name tank first
arose in British factories making the hulls of the first battle tanks: the workmen were
given the impression they were constructing tracked water containers for the British Army,
hence keeping the production of a fighting vehicle secret.
Tanks and armour tactics have undergone many generations of evolution over nearly a century.
Although weapons systems and armour continue to be developed, many nations have reconsidered
the need for such heavy weaponry in a period characterised by unconventional warfare.
Design
The three traditional factors determining a tank's effectiveness are its firepower, mobility
and protection. The psychological effect on enemy soldiers of a tank's imposing battlefield
presence is called shock action.
Firepower is the ability of a tank to defeat a target. This takes into account the maximum
distance at which targets can be engaged, the ability to engage moving targets, the speed
with which multiple targets can be attacked, and the capability to defeat armoured vehicles
or entrenched infantry.
Mobility includes the speed and agility of driving cross-country, the types of terrain that
can be covered, the dimensions of obstacles, trenches, and water that can be crossed, the
ability to cross small bridges, and the distance that can be covered before refuelling is
required. "Strategic mobility" also includes the ability to travel at high speed on roads,
and the ability to be carried on rail or truck transport. Traditionally AFV mobility is
measured by the following metrics:
* engine power
* engine torque
* power-to-weight ratio
* road speed
* off-road speed (a somewhat nebulous figure given the possible variation)
* road range
* off-road range
* weight (bridge classification)
* ground pressure
* width of trench crossed
* vertical step climbed
* angle of slope that can be climbed
* angle of side slope that can be negotiated
* ground clearance
* unprepared fording depth
* prepared fording depth (if different)
Protection is the amount of armour, the type(s), how it is arranged (i.e., sloped or not),
and which areas are given more protection (e.g., the turret and tracks) and which receive
less (e.g., the rear of the chassis). It also includes low profile, low noise and thermal
signature, active countermeasures and other methods of avoiding enemy fire, and the ability
to continue fighting after damage has been sustained.
Tank design is traditionally held to be a compromise between these three factors—it is not
considered possible to maximise all three. For example, increasing protection by adding
armour will increase weight and therefore decrease manoeuvrability; increasing firepower by
using a larger gun will decrease both manoeuvrability and protection (due to decreased
armour at the front of the turret).
How the compromise is achieved is influenced by a combination of factors, including military
strategies, budget, geography, political will, and the requirement to sell the tank to other
countries.
Examples of how different countries are influenced in their decisions are as follows:
* Britain has historically opted for better firepower and increased protection at the
expense of some manoeuvrability. Britain maintains a small, highly-trained professional
army, and so tank crew survivability is important. As limited resources may be available,
the crew needs to be able to maintain their tanks in the field.
* The USA has a large army with sophisticated weaponry and a complex array of mobile
support services. As their tanks are expected to rarely be away from support and repair
units, less emphasis is placed on the crew's ability to maintain the tank themselves or to
continue fighting with it once damage has been sustained.
* Soviet tanks are traditionally rugged, simple for production and maintenance
(characteristic of the Soviet-era idiom that "quantity has a quality of its own"), as
exemplified by the T-34. State-controlled design development proceeds in incremental
changes. Extensive maintenance is expected to be done in specialised depots. Tanks of this
class are opted to have the best combination of firepower, mobility, and protection.
* Israel is a small, but relatively rich, nation, with limited manpower in a hostile
political environment. Its primary concern is therefore crew survivability. To this end it
is the only nation to have produced a main battle tank with the engine placed at the front
and fuel surrounding the crew, to increase protection.
Weapons
Main article: tank gun
The main weapon of any modern tank is a single large gun. Tank guns are among the
largest-calibre weapons in use on land, with only a few artillery pieces being larger.
Although the calibre has not changed substantially since the end of the Second World War,
modern guns are technologically superior. The current common sizes are 120mm calibre for
Western tanks and 125mm for Eastern (Soviet and Chinese legacy) tanks. Tank guns have been
able to fire many types of rounds, but their current use is commonly limited to kinetic
energy (KE) penetrators and high explosive (HE) rounds. Some tanks can fire missiles through
the gun. Smoothbore (rather than rifled) guns are the dominant type of gun today. The
British Army and the Indian Army are now the only ones to field main battle tanks carrying
rifled guns.
Modern tank guns are generally fitted with thermal jackets which reduce the effect of uneven
temperature on the barrel. For instance, if it were to rain on a tank barrel the top would
cool faster than the bottom, or a breeze on the left might cause the left side to cool
faster then the right. This uneven cooling will cause the barrel to bend slightly and will
affect long range accuracy.
Usually, tanks carry other armament for short range defence against infantry or targets
where the use of the main weapon would be ineffective or wasteful. Typically, this is a
small calibre (7.62 to 12.7 mm) machine gun mounted coaxially with the main gun. However, a
couple of French tanks such as the AMX-30 and AMX-40 carry a coaxial 20mm cannon that has a
high rate of fire and can destroy lightly armoured vehicles. Additionally, many tanks carry
a roof-mounted or commander's cupola machine gun for close-in ground or limited air defence.
The 12.7-mm and 14.5-mm machine guns commonly carried on U.S. and Russian tanks and the
French Leclerc are also capable of destroying lightly-armoured vehicles at close range.
Some tanks have been adapted to specialised roles and have had unusual main armament such as
flame-throwers. These specialised weapons are now usually mounted on the chassis of an
armoured personnel carrier.
Fire control
Historically, tank weapons were aimed through simple optical sights and laid onto target by
hand, with windage estimated or assisted with a reticule. Range to the target was estimated
with the aid of a reticule (markings in the gun sight which are aligned to frame an object
of known size, in this case a tank). Consequently, accuracy was limited at long range and
concurrent movement and accurate shooting were largely impossible. Over time these sights
were replaced with stereoscopic range-finders. These were eventually replaced by Laser
range-finders.
Most modern main battle tanks in the armies of industrialised countries use laser
range-finders but optical and reticule range-finders are still in use in older and less
sophisticated vehicles. Modern tanks have a variety of sophisticated systems to make them
more accurate. Gyroscopes are used to stabilise the main weapon; computers calculate the
appropriate elevation and aim-point, taking input from sensors for wind speed, air
temperature, humidity, the gun-barrel temperature, warping and wear, the speed of the target
(calculated by taking at least two sightings of the target with the range-finder), and the
movement of the tank. Infrared, light-amplification, or thermal night vision equipment is
also commonly incorporated. Laser target designators may also be used to illuminate targets
for guided munitions. As a result modern tanks can fire reasonably accurately while moving.
[edit]
Ammunition
There are several types of ammunition designed to defeat armour, including High explosive
squash head (HESH, also called high explosive plastic, HEP), High explosive antitank (HEAT),
and kinetic energy penetrators (KEP, or armour-piercing discarding sabot APDS). For
accuracy, shells are spun by gun-barrel rifling, or fin-stabilized (APFSDS, HEAT-FS, etc.).
Some tanks, including the M551 Sheridan, T-72, T-64, T-80, T-90, T-84, and PT-91 can fire
ATGMs (anti-tank guided missile) through their gun barrel or from externally mounted
launchers. This functionality can extend the effective combat range of the tank beyond the
range afforded by conventional shells, depending on the capabilities of the ATGM system. It
also provides the tank with a useful weapon against slow, low-flying airborne targets like
helicopters. The United States has abandoned this concept, phasing the M551 and M60A2 out of
their forces in favour of helicopters and aircraft for long range anti-tank roles, but CIS
countries continue to employ gun-missile systems in their main battle tanks.
Protection
The main battle tank is the most heavily armoured vehicle in modern armies. Its armour is
designed to protect the vehicle and crew against a wide variety of threats. Commonly,
protection against kinetic energy penetrators fired by other tanks is considered the most
important. Tanks are also vulnerable to antitank guided missiles; antitank mines, larger
bombs, and direct artillery hits, which can disable or destroy them. Tanks are especially
vulnerable to airborne threats. Most modern MBTs do offer near complete protection from
artillery fragmentation and lighter antitank weapons such as rocket propelled grenades. The
amount of armour needed to protect against all conceivable threats from all angles would be
far too heavy to be practical, so when designing an MBT much effort goes into finding the
right balance between protection and weight.
Armour
Main article: vehicle armour
Most armoured fighting vehicles are manufactured of hardened steel plate, or in some cases
aluminium. The relative effectiveness of armour is expressed by comparison to rolled
homogeneous armour.
Most armoured vehicles are best-protected at the front, and their crews always try to keep
them pointed toward the likeliest direction of the enemy. The thickest and best-sloped
armour is on the glacis plate and the turret front. The sides have less armour and the rear,
belly and roof are least protected. World War II American M4 Medium tank crews found the
German Tigers to be practically invulnerable from the front, and were forced to employ flank
attacks. Today, tanks are vulnerable to specialised top-attack missile weapons and air
attack. During WW2, aircraft rockets earned a formidable reputation, especially in France
after the Normandy landings (Operation Neptune); post-war analysis revealed many reported
kills were near-misses. Aircraft cannon firing armour-piercing ammunition, such as the
Hurribomber's 40mm or Stuka's 37mm, could be effective, also. Even a simple Molotov cocktail
on the engine deck, however, may disable most tanks.
Before the Second World War, several tank designers tried sloping the armour on experimental
tanks. The most famous and successful example of this approach at the time was the T-34.
Angling armour plates greatly increases their effectiveness against projectiles, by
increasing the effective perpendicular thickness of the armour, and by increasing the chance
of deflection. German tank crews were said to be horrified to find that shots fired at the
angled plates of T-34s would sometimes simply ricochet.
Even light infantry antitank weapons can immobilise a tank by damaging its suspension or
track. Many tracked military vehicles have side skirts, protecting the suspension.
High explosive antitank weapons (HEAT), such as the bazooka, were a new threat in the Second
World War. These weapons carry a warhead with a shaped charge, which focuses the force of an
explosion into a narrow penetrating stream. Thin plates of spaced armour, steel mesh "RPG
screens", or rubber skirts, were found to cause HEAT rounds to detonate too far from the
main armour, greatly reducing their penetrating power.
Some antitank ammunition (HESH or HEP) uses flexible explosive material, which squashes
against a vehicle's armour, and causes dangerous spalling of material inside the tank when
the charge explodes. This may kill the crew without penetrating the armour, still
neutralizing the tank. As a defence, some vehicles have a layer of anti-spall material
lining their insides.
Since the 1970s, some tanks have been protected by more complex composite armour, a sandwich
of various alloys and ceramics. One of the best types of passive armour is the
British-developed Chobham armour, which is comprised of spaced ceramic blocks contained by a
resin-fabric matrix between layers of conventional armour. A form of Chobham armour is
encased in depleted uranium on the very well-protected M1A1 Abrams MBT.
The Israeli Merkava tank takes the design of protection systems to an extreme, using the
engine and fuel tanks as secondary armour.
[edit]
Grenade launchers, smoke and passive defences
Most armoured vehicles carry smoke grenade launchers which can rapidly deploy a smoke screen
to visually shield a withdrawal from an enemy ambush or attack. The smoke screen is very
rarely used offensively, since attacking through it blocks the attacker's vision and gives
the enemy an early indication of impending attack. Modern smoke grenades work in the
infrared as well as visible spectrum of light.
Some smoke grenades are designed to make a very dense cloud capable of blocking the laser
beams of enemy target designators or range finders and of course obscuring vision, reducing
probability of a hit from visually aimed weapons, especially low speed weapons, such as
antitank missiles which require the operator to keep the tank in sight for a relatively long
period of time. In many MBTs, such as the French-built Leclerc, the smoke grenade launchers
are also meant to launch tear gas grenades and anti-personnel fragmentation grenades. Many
Israeli tanks contain small vertical mortar tubes which can be operated from within the
tank, enhancing the anti-personnel capabilities and allowing it to engage targets which are
behind obstacles. There have been proposals to equip other tanks with dual-purpose
smoke/fragmentation grenade launchers that can be reloaded from the interior.
Prior to the widespread introduction of thermal imaging the most common smoke grenade in AFV
launchers was white phosphorus which created a very rapid smoke screen as well as having a
very useful incendiary effect against any infantry in the burst area (e.g., infantry
attempting to close with hand placed charges or mines).
Since the advent of thermal imagers most tanks carry a smoke grenade that contains a plastic
or rubber compound whose tiny burning fragments provide better obscurant qualities against
thermal imagers.
Some tanks also have smoke generators which can generate smoke continuously, rather than the
instantaneous, but short duration of smoke grenades. Generally smoke generators work by
injecting fuel into the exhaust, which partially burns the fuel, but leaves sufficient
unburned or partially burned particles to create a dense smoke screen.
Modern tanks are increasingly being fitted with passive defensive systems such as laser
warning devices, which activate an alarm if the tank is "painted" by a laser range-finder or
designator.
Other passive defences include radio warning devices, which provide warning if the tank is
targeted by radar systems that are commonly used to guide antitank weapons such as
millimetre and other very short wave radar.
[edit]
Countermeasures
Passive countermeasures, like the Russian Shtora system, attempt to jam the guidance systems
of incoming guided missiles.
Explosive reactive armour, or ERA, is another major type of protection against high
explosive antitank weapons, in which sections of armour explode to dissipate the focussed
explosive force of a shaped charge warhead. Reactive armour is attached to the outside of an
MBT in small, replaceable bricks.
Active protection systems go one step further than reactive armour. An APS uses radar or
other sensing technology to automatically react to incoming projectiles. When the system
detects hostile fire, it calculates a firing resolution and directs an explosive-launched
counter-projectile to intercept or disrupt the incoming fire a few metres from the target.
Cranes
Cranes, in one form or another, have been around since ancient times. From the pyramids to medieval cathedrals to modern day skyscrapers, cranes are an integral part of the construction process. Cranes usually use some type of pulley system which enables heavy materials to be lifted into the air or lowered to the ground. Usually construction cranes are driven by an operator. However, remote operation by infrared or radio signals is also possible. Through a series of signals, cranes can position materials with an astounding degree of accuracy. Because they are used in the construction and destruction process of building only, cranes must be mobile to some extent and be able to be transported from one site to another.
Cranes come in many different sizes and forms depending upon their intended use. Some common types of industrial cranes include boom, tower, ship, mobile, gantry, overhead, crawler, floating and jib cranes.
Mobile cranes are one of the most basic types of crane and consist of a boom mounted on a mobile platform. The mobile platform is usually a truck and therefore mobile cranes are also routinely called truck cranes. The mobile platform enables the mobile crane to move from site to site with ease. Mobile cranes can also be fitted with adapters and additions in order to satisfy a variety of uses including demolition and earth moving.
Tower cranes are also very common and popular in modern construction. A tower crane is a type of balance crane and is used in the erection of tall buildings. Routinely, tower cranes are set up within a shaft in the inside of the building which will be converted to elevators when the building is completed. A horizontal arm is then balanced asymmetrically across the top of the tower. The long side of the arm maintains the lifting gear while the short arm counterbalances the load.
The most common type of crane for aquatic construction is the floating crane. This crane is used to build bridges, ports, ship loading and unloading and ship salvage. These cranes are mounted on a pontoon platform and are therefore able to move over the water to wherever they are needed.
Buying or renting a crane can be confusing. Sometimes cranes are included within a building contract and sometimes they will need to be purchased or rented separately. The inclusion or exclusion of an industrial crane can have a big affect on the cost of construction. It is important to find out and understand what type of crane will satisfy your needs and how the crane will be provided.
Cranes come in many different sizes and forms depending upon their intended use. Some common types of industrial cranes include boom, tower, ship, mobile, gantry, overhead, crawler, floating and jib cranes.
Mobile cranes are one of the most basic types of crane and consist of a boom mounted on a mobile platform. The mobile platform is usually a truck and therefore mobile cranes are also routinely called truck cranes. The mobile platform enables the mobile crane to move from site to site with ease. Mobile cranes can also be fitted with adapters and additions in order to satisfy a variety of uses including demolition and earth moving.
Tower cranes are also very common and popular in modern construction. A tower crane is a type of balance crane and is used in the erection of tall buildings. Routinely, tower cranes are set up within a shaft in the inside of the building which will be converted to elevators when the building is completed. A horizontal arm is then balanced asymmetrically across the top of the tower. The long side of the arm maintains the lifting gear while the short arm counterbalances the load.
The most common type of crane for aquatic construction is the floating crane. This crane is used to build bridges, ports, ship loading and unloading and ship salvage. These cranes are mounted on a pontoon platform and are therefore able to move over the water to wherever they are needed.
Buying or renting a crane can be confusing. Sometimes cranes are included within a building contract and sometimes they will need to be purchased or rented separately. The inclusion or exclusion of an industrial crane can have a big affect on the cost of construction. It is important to find out and understand what type of crane will satisfy your needs and how the crane will be provided.
Boiler
A boiler is a closed vessel in which water or other fluid is heated under pressure. The
steam or hot fluid is then circulated out of the boiler for use in various process or
heating applications. A safety valve is required to prevent over pressurisation and possible
explosion of a boiler.
Overview
Construction of boilers is mainly limited to copper, steel and cast iron. In Live steam
toys, brass is often used.
Sources of heat for the boiler can be the combustion of fuels such as wood, coal, oil or
natural gas. Electric boilers use resistance or immersion type heating elements. Nuclear
fission is also used as a heat source for generating steam. Waste-heat boilers, or HRSGs use
the heat rejected from other processes such as gas turbines.
Boilers can also be classified into fire-tube, water-tube boilers or cast iron sectional
depending on whether the heat source is inside or outside the tubes or in the case of the
cast iron sectional the design and manufacture of the boiler. The goal in all cases is to
maximize the heat transfer between the water and the hot gases heating it. For example,
steam locomotives have fire-tube boilers, where the fire is inside the tube and the water on
the outside. These usually take the form of a set of straight tubes passing through the
boiler through which hot combustion gases flows.
In water-tube boilers the water flows through a large number of narrow tubes around the
fire. The tubes frequently have a large number of bends and sometimes fins to maximize the
surface area. This type of boiler is generally preferred in high pressure applications since
the high pressure water/steam is contained within narrow pipes which can contain the
pressure with a thinner wall.
In a cast iron sectional boiler, sometimes called a "pork chop boiler" the water is
contained inside cast iron sections. These sections are mechanically assembled on site to
create the finished boiler.
There are other types of boilers, largely of historical interest. For example, the Cornish
boiler developed around 1812 by Richard Trevithick for generating steam for steam engines.
This was both stronger and more efficient than the simple boilers which preceded it. It was
a cylindrical water tank around 27 feet long and 7 feet in diameter, and had a coal furnace
placed in a single cylindrical tube about three feet wide which passed centrally along the
long axis of the tank. The fire was tended from one end and the hot gases from it travelled
along the tube and out of the other end, to be circulated back along flues running along the
outside of the boiler before being expelled via the chimney. This was later improved upon in
the Lancashire boiler which had a pair of furnaces in separate tubes side-by-side. This was
an important improvement since each furnace could be stoked at different times, allowing one
to be cleaned whilst the other was operating. These designs are really primitive fire tube
boilers, and led on to the Scotch boiler which was a popular fire tube design.
Supercritical boilers
Supercritical boilers are used for the generation of electric power. They operate at
"supercritical pressure". In contrast to a "subcritical boiler", a supercritical boiler has
no water - steam separation. There is no generation of steam because the pressure is
regulated above the "critical pressure" at which steam bubbles can form. Thus, the fluid
generated is called "supercritical fluid". It passes below the critical point as it does
work in the high pressure turbine and enters the generator's condensor. This is more
efficient resulting in slightly less fuel use and therefore less greenhouse gas production.
Hydronic boilers
Hydronic boilers are used in generating heat typically for residential uses. They are the
typical power plant for central heating systems fitted to houses in northern Europe, as
opposed to the forced air furnaces or wood burning stoves more common in North America. The
hydronic boiler operates by way of heating water/fluid to a preset temperature and
circulating that fluid throughtout the home typically by way of radiators, baseboard heaters
or through the floors. The fluid can be heated by any means....gas, wood, fuel oil, etc, but
in built-up areas where piped gas is available, natural gas is currently the most economical
and therefore the usual choice. The fluid is in an enclosed system and circulated throughout
by means of a motorized pump. These hydronic systems are being used more and more in new
construction in North America as they are more economical than forced air furnaces and make
it easier to construct smaller diameter water pipes as it is the larger ventilation piping.
Most new systems are fitted with condensing boilers for greater efficiency. "Boiler" is
clearly a misnomer for this kind of device, which is really nothing but a large water heater
in which the water is never intended to boil; but the name is universal and unlikely ever to
change.
Accessories
Boiler fittings
* Safety valve
* Water column: to help the operator tell if there is a satisfactory level of fluid in
the boiler, a water gauge or water column is provided.
* Bottom blowdown valves
* Surface blowdown line
* Circulating pump
Feedwater accessories
* Feedwater pressure regulator
* Vacuum pump
* City water makeup
* Low water cut-off switch
* Backflow preventer
* condensat
Steam accessories
* Main steam stop valve
* Steam traps
Combustion accessories
* Fuel oil system
* Gas system
* Coal system
* Automatic combustion systems
Controlling draft
steam or hot fluid is then circulated out of the boiler for use in various process or
heating applications. A safety valve is required to prevent over pressurisation and possible
explosion of a boiler.
Overview
Construction of boilers is mainly limited to copper, steel and cast iron. In Live steam
toys, brass is often used.
Sources of heat for the boiler can be the combustion of fuels such as wood, coal, oil or
natural gas. Electric boilers use resistance or immersion type heating elements. Nuclear
fission is also used as a heat source for generating steam. Waste-heat boilers, or HRSGs use
the heat rejected from other processes such as gas turbines.
Boilers can also be classified into fire-tube, water-tube boilers or cast iron sectional
depending on whether the heat source is inside or outside the tubes or in the case of the
cast iron sectional the design and manufacture of the boiler. The goal in all cases is to
maximize the heat transfer between the water and the hot gases heating it. For example,
steam locomotives have fire-tube boilers, where the fire is inside the tube and the water on
the outside. These usually take the form of a set of straight tubes passing through the
boiler through which hot combustion gases flows.
In water-tube boilers the water flows through a large number of narrow tubes around the
fire. The tubes frequently have a large number of bends and sometimes fins to maximize the
surface area. This type of boiler is generally preferred in high pressure applications since
the high pressure water/steam is contained within narrow pipes which can contain the
pressure with a thinner wall.
In a cast iron sectional boiler, sometimes called a "pork chop boiler" the water is
contained inside cast iron sections. These sections are mechanically assembled on site to
create the finished boiler.
There are other types of boilers, largely of historical interest. For example, the Cornish
boiler developed around 1812 by Richard Trevithick for generating steam for steam engines.
This was both stronger and more efficient than the simple boilers which preceded it. It was
a cylindrical water tank around 27 feet long and 7 feet in diameter, and had a coal furnace
placed in a single cylindrical tube about three feet wide which passed centrally along the
long axis of the tank. The fire was tended from one end and the hot gases from it travelled
along the tube and out of the other end, to be circulated back along flues running along the
outside of the boiler before being expelled via the chimney. This was later improved upon in
the Lancashire boiler which had a pair of furnaces in separate tubes side-by-side. This was
an important improvement since each furnace could be stoked at different times, allowing one
to be cleaned whilst the other was operating. These designs are really primitive fire tube
boilers, and led on to the Scotch boiler which was a popular fire tube design.
Supercritical boilers
Supercritical boilers are used for the generation of electric power. They operate at
"supercritical pressure". In contrast to a "subcritical boiler", a supercritical boiler has
no water - steam separation. There is no generation of steam because the pressure is
regulated above the "critical pressure" at which steam bubbles can form. Thus, the fluid
generated is called "supercritical fluid". It passes below the critical point as it does
work in the high pressure turbine and enters the generator's condensor. This is more
efficient resulting in slightly less fuel use and therefore less greenhouse gas production.
Hydronic boilers
Hydronic boilers are used in generating heat typically for residential uses. They are the
typical power plant for central heating systems fitted to houses in northern Europe, as
opposed to the forced air furnaces or wood burning stoves more common in North America. The
hydronic boiler operates by way of heating water/fluid to a preset temperature and
circulating that fluid throughtout the home typically by way of radiators, baseboard heaters
or through the floors. The fluid can be heated by any means....gas, wood, fuel oil, etc, but
in built-up areas where piped gas is available, natural gas is currently the most economical
and therefore the usual choice. The fluid is in an enclosed system and circulated throughout
by means of a motorized pump. These hydronic systems are being used more and more in new
construction in North America as they are more economical than forced air furnaces and make
it easier to construct smaller diameter water pipes as it is the larger ventilation piping.
Most new systems are fitted with condensing boilers for greater efficiency. "Boiler" is
clearly a misnomer for this kind of device, which is really nothing but a large water heater
in which the water is never intended to boil; but the name is universal and unlikely ever to
change.
Accessories
Boiler fittings
* Safety valve
* Water column: to help the operator tell if there is a satisfactory level of fluid in
the boiler, a water gauge or water column is provided.
* Bottom blowdown valves
* Surface blowdown line
* Circulating pump
Feedwater accessories
* Feedwater pressure regulator
* Vacuum pump
* City water makeup
* Low water cut-off switch
* Backflow preventer
* condensat
Steam accessories
* Main steam stop valve
* Steam traps
Combustion accessories
* Fuel oil system
* Gas system
* Coal system
* Automatic combustion systems
Controlling draft
Machine Gun
General Overview: Calibers
There are two main different definitions of the upper limit of caliber for machine guns —
larger than 12.7 mm (.50 caliber) and larger than 20 mm — at which point they are generally
referred to as autocannons. In-between, there are weapons that have been called by either
name depending other traits; for instance, there have been weapons of roughly 15 mm that
were variably referred to as autocannons and machine guns.
Another factor is whether the weapon fires conventional rounds or explosive rounds.
Automatic weapons firing large-caliber explosive rounds are generally either autocannons or
automatic grenade launchers ("grenade machine guns"). Machine guns tend to share a very high
ratio of caliber to barrel length (a long barrel for a small caliber).
There have been two main machine gun eras: the era of manual machine guns and the era of
automatic machine guns. The technical development itself is marked by a series of
developments of specific automatic features, as well as technical developments (such as
linked ammunition). The era of manual multi-shot devices extends back hundreds of years
(such as manual volley guns), but the development of manual and automatic machine guns takes
place almost entirely in the latter half of the 1800s. Manual machine guns are
manually-powered, e.g., a crank must be turned to power reloading and firing, as opposed to
simply holding down a trigger, as with automatic machine guns. There are many other notable
features, but this is one of the most significant to allowing higher rates of fire common to
machine guns.
Manual machine guns, as well as manual volley guns, saw their first major use in the
American Civil War. The Gatling gun and "coffee gun" both used manually-powered automatic
loading, fed via a hopper filled with cartridges. The Gatling gun — a manually-powered
rotary machine gun — would be the major type of the late 19th century, though there were
many other manual designs with varying degrees of use (e.g. the Nordenfelt machine gun). The
first automatic machine gun was the recoil-operated Maxim gun, which used linked (belt)
ammunition, as well as a single barrel and automatic loading. This concept of using bullet
energy would also drive the development all nearly all other semi and fully-automatic
firearms of 20th century.
The two major operation systems of modern automatic machine guns are gas operation (which
uses the gas generated from the burning powder to cycle the action), or recoil operation
(which uses the recoil generated from the ejecting bullet to cycle the action). The first
gas-operated machine gun was the Colt-Browning M1895. Another (minor) type is the
externally-powered machine gun. Rather than human manual power or bullet energy, a third
source (such as an electric motor) is used; these types are now called by more specific
names (see Minigun, Chaingun). The most common type of modern machine gun remains the
automatic, recoil-operated and belt-fed type. Eletrical and Gatling-type machine guns are
common on fighting aircraft and other vehicles.
Overview of modern automatic machine guns
Unlike semi-automatic firearms, which require one pull per bullet fired, a machine gun is
designed to fire bullets as long as the trigger is held down and ammunition is fed into the
weapon. Although the term "machine gun" is often used to describe all fully-automatic
weapons, in military usage the term is restricted to relatively heavy weapons fired from
some sort of support rather than hand-held, able to provide continuous or frequent bursts of
automatic fire for as long as ammunition lasts. Machine guns are normally used against
unprotected or lightly-protected personnel, or to provide suppressive fire.
Some machine guns have in practice maintained suppressive fire almost continuously for
hours; other automatic weapons overheat after sometimes less than a minute of use. Because
they become very hot, practically all machine guns fire from an open bolt, to permit air
cooling from the breech between bursts. They also have either a barrel cooling system, or
removable barrels which allow a hot barrel to be replaced.
Although subdivided into "light", "medium", "heavy" or "general purpose", even the lightest
machine guns tend to be substantially larger and heavier than other automatic weapons. Squad
automatic weapons (SAWs) are a variation of light machine guns and only require one operator
(sometimes with an assistant to carry ammunition). Medium and heavy machine guns are either
mounted on a tripod or on a vehicle; when carried on foot, the machine gun and associated
equipment (tripod, ammunition, spare barrels) require additional crew members.
The majority of machine guns are belt-fed, although some light machine guns are fed from
drum or box magazines, and some vehicle-mounted machine guns are hopper-fed.
Other automatic weapons are subdivided into several categories based on the size of the
bullet used, and whether the cartridge is fired from a positively locked closed bolt, or a
non-positively locked open bolt. Fully automatic firearms using pistol-caliber ammunition
are called machine pistols or submachine guns (largely on the basis of size); selective fire
rifles firing a full-power rifle cartridge from a closed bolt are called automatic rifles,
while those using a reduced-power rifle cartridge are called assault rifles.
The machine gun's primary role in ground combat is to provide suppressive fire on an
opposing force's position, forcing the enemy to take cover and reducing the effectiveness of
his fire. This either halts an enemy attack or allows friendly forces to attack enemy
positions with less risk.
To this end, most light machine guns and general purpose machine guns are not designed for
high accuracy, as would be expected of a rifle. Most are designed with a small degree of
inaccuracy, referred to as the "cone of fire", because the rounds spread out as they travel
towards the target area. Light machine guns usually have simple iron sights. A common aiming
system is to alternate solid ("ball") rounds and tracer ammunition rounds (usually one
tracer round for every four ball rounds), so shooters can see the trajectory and "walk" the
fire into the target, and direct the fire of other soldiers.
Assault rifles are a compromise between the pistol-caliber submachine gun and a traditional
rifle firing a full-power cartridge, allowing single-shot, burst and full-automatic fire
options.
Many heavy machine guns, such as the Browning M2 .50 caliber machine gun, are accurate
enough to engage targets at great distances. During the Vietnam War, Carlos Hathcock set the
record for a long-distance shot at 7382 ft (2250 m) with a .50 caliber heavy machine gun he
had equipped with a telescopic sight. This led to the introduction of .50 caliber
anti-material sniper rifles, such as the Barrett M82.
Components
All machine guns require the following components:
1. A feed system to load the firing chamber. Cartridges can be fed into the chamber by a
variety of methods, the most common being spring-fed magazines or ammunition belts.
2. A trigger mechanism to fire the round. This includes the actual trigger, a trigger
sear to catch the bolt, a bolt and a firing pin, as well as other components. Typically, the
act of pulling the trigger causes something to strike the primer on the round in the chamber
and disengages the sears. This allows continual cycling of the bolt until the trigger is
released. A sear then grabs the bolt or firing pin. This stops the machine gun at some point
in its cycle.
3. An extractor system to eject the spent or misfired cartridge. Usually this is fairly
simple. A pin on the side of the bolt catches a ridge on the cartridge and flicks it out an
ejection port.
These components form a mechanism which must be powered by something. If powered by a spring
absorbing the recoil of a fired cartridge, it is called recoil operated. If powered by the
expanding gases of a fired cartridge, it is called gas actuated. If it powered by an
external force, such as a motor, it is usually called a chain gun.
Operation
All machine guns follow a cycle:
* Removing the spent cartridge through an ejection port.
* Cocking the trigger mechanism so the weapon can be fired again.
* Loading the next round into the firing chamber. Usually spring tension or a cam forces
the new round and bolt back into the firing chamber.
A mechanism makes the firing pin fire the cartridge, activating the ejection and reloading
steps. The cycle repeats. This full cycle takes a fraction of a second and can thus occur
many times per second. The operation is basically the same, regardless of the means of
activating these mechanisms. Some examples:
* Machine pistols and submachine guns (like the World War II "grease gun," MAC-10 or the
Uzi) are usually blowback operated.
* Most assault rifles and squad automatic weapons are gas actuated. Some weapons, such
as the AR-15/M16, integrate the piston with the bolt. Others, such as the M15 and AK
patterns, attach the piston to a bolt carrier that unlocks and operates the bolt.
* A recoil-actuated machine gun uses the recoil to first unlock and then operate the
action. Heavy machine guns, such as the M2 .50 and Browning .50, are of this type. These can
be recognized by a large cocking lever needed to feed the first round.
* An externally actuated machine gun uses an external power source, such as an electric
motor or even a hand crank to move its mechanism through the firing sequence. Most modern
weapons of this type are called chain guns in reference to their driving mechanism. Gatling
guns and revolver cannon have several barrels or chambers on a rotating carousel and a
system of cams that load, cock, and fire each mechanism progressively as it rotates through
the sequence. The continuous nature of the rotary action allows for an incredibly high
cyclic rate of fire, often several thousand rounds per minute. Not all chain guns use
multiple barrels or chambers, though. Chain guns are less prone to jamming than a gun
operated by gas or recoil, as the external power source will eject misfired rounds with no
further trouble. This is not possible if the force needed to eject the round comes from the
round itself. Chain guns are generally used with large shells, 20 mm in diameter or more,
though some, such as the M134 Minigun, fire smaller cartridges. They offer benefits of
reliability and firepower, though the weight and size of the power source and driving
mechanism makes them impractical for use outside of a vehicle or aircraft mount.
Heavy machine guns are often water cooled or have interchangeable barrels, which must be
changed periodically to avoid overheating. The higher the rate of fire, the more often
barrels must be changed and allowed to cool. To minimize this, most air-cooled guns are
fired only in short bursts or at a reduced rate of fire.
Not all machine guns strike the primer in the same way. In blowback machine guns, the act of
seating the round also fires the round. In gas operated and recoil-operated guns, a separate
step in the firing sequence is needed to strike the round. In a progressive-fire gun, the
firing pin is cycled by cams. In some automatic cannon, the primer is fired electrically.
In weapons where the round seats and fires at the same time, mechanical timing is essential
for operator safety, to prevent the round from firing before it is seated properly. This is
especially important in weapons like the 40 mm grenade launcher, where high explosives are
present in the rounds being fired.
Machine guns are controlled by one or more mechanical sears. When a sear is in place, it
effectively stops the bolt at some point in its range of motion. Some sears stop the bolt
when it is locked to the rear. Other sears stop the firing pin from going forward after the
round is locked into the chamber.
Almost all weapons have a "safety" sear, which simply keeps the trigger from engaging.
There are two main different definitions of the upper limit of caliber for machine guns —
larger than 12.7 mm (.50 caliber) and larger than 20 mm — at which point they are generally
referred to as autocannons. In-between, there are weapons that have been called by either
name depending other traits; for instance, there have been weapons of roughly 15 mm that
were variably referred to as autocannons and machine guns.
Another factor is whether the weapon fires conventional rounds or explosive rounds.
Automatic weapons firing large-caliber explosive rounds are generally either autocannons or
automatic grenade launchers ("grenade machine guns"). Machine guns tend to share a very high
ratio of caliber to barrel length (a long barrel for a small caliber).
There have been two main machine gun eras: the era of manual machine guns and the era of
automatic machine guns. The technical development itself is marked by a series of
developments of specific automatic features, as well as technical developments (such as
linked ammunition). The era of manual multi-shot devices extends back hundreds of years
(such as manual volley guns), but the development of manual and automatic machine guns takes
place almost entirely in the latter half of the 1800s. Manual machine guns are
manually-powered, e.g., a crank must be turned to power reloading and firing, as opposed to
simply holding down a trigger, as with automatic machine guns. There are many other notable
features, but this is one of the most significant to allowing higher rates of fire common to
machine guns.
Manual machine guns, as well as manual volley guns, saw their first major use in the
American Civil War. The Gatling gun and "coffee gun" both used manually-powered automatic
loading, fed via a hopper filled with cartridges. The Gatling gun — a manually-powered
rotary machine gun — would be the major type of the late 19th century, though there were
many other manual designs with varying degrees of use (e.g. the Nordenfelt machine gun). The
first automatic machine gun was the recoil-operated Maxim gun, which used linked (belt)
ammunition, as well as a single barrel and automatic loading. This concept of using bullet
energy would also drive the development all nearly all other semi and fully-automatic
firearms of 20th century.
The two major operation systems of modern automatic machine guns are gas operation (which
uses the gas generated from the burning powder to cycle the action), or recoil operation
(which uses the recoil generated from the ejecting bullet to cycle the action). The first
gas-operated machine gun was the Colt-Browning M1895. Another (minor) type is the
externally-powered machine gun. Rather than human manual power or bullet energy, a third
source (such as an electric motor) is used; these types are now called by more specific
names (see Minigun, Chaingun). The most common type of modern machine gun remains the
automatic, recoil-operated and belt-fed type. Eletrical and Gatling-type machine guns are
common on fighting aircraft and other vehicles.
Overview of modern automatic machine guns
Unlike semi-automatic firearms, which require one pull per bullet fired, a machine gun is
designed to fire bullets as long as the trigger is held down and ammunition is fed into the
weapon. Although the term "machine gun" is often used to describe all fully-automatic
weapons, in military usage the term is restricted to relatively heavy weapons fired from
some sort of support rather than hand-held, able to provide continuous or frequent bursts of
automatic fire for as long as ammunition lasts. Machine guns are normally used against
unprotected or lightly-protected personnel, or to provide suppressive fire.
Some machine guns have in practice maintained suppressive fire almost continuously for
hours; other automatic weapons overheat after sometimes less than a minute of use. Because
they become very hot, practically all machine guns fire from an open bolt, to permit air
cooling from the breech between bursts. They also have either a barrel cooling system, or
removable barrels which allow a hot barrel to be replaced.
Although subdivided into "light", "medium", "heavy" or "general purpose", even the lightest
machine guns tend to be substantially larger and heavier than other automatic weapons. Squad
automatic weapons (SAWs) are a variation of light machine guns and only require one operator
(sometimes with an assistant to carry ammunition). Medium and heavy machine guns are either
mounted on a tripod or on a vehicle; when carried on foot, the machine gun and associated
equipment (tripod, ammunition, spare barrels) require additional crew members.
The majority of machine guns are belt-fed, although some light machine guns are fed from
drum or box magazines, and some vehicle-mounted machine guns are hopper-fed.
Other automatic weapons are subdivided into several categories based on the size of the
bullet used, and whether the cartridge is fired from a positively locked closed bolt, or a
non-positively locked open bolt. Fully automatic firearms using pistol-caliber ammunition
are called machine pistols or submachine guns (largely on the basis of size); selective fire
rifles firing a full-power rifle cartridge from a closed bolt are called automatic rifles,
while those using a reduced-power rifle cartridge are called assault rifles.
The machine gun's primary role in ground combat is to provide suppressive fire on an
opposing force's position, forcing the enemy to take cover and reducing the effectiveness of
his fire. This either halts an enemy attack or allows friendly forces to attack enemy
positions with less risk.
To this end, most light machine guns and general purpose machine guns are not designed for
high accuracy, as would be expected of a rifle. Most are designed with a small degree of
inaccuracy, referred to as the "cone of fire", because the rounds spread out as they travel
towards the target area. Light machine guns usually have simple iron sights. A common aiming
system is to alternate solid ("ball") rounds and tracer ammunition rounds (usually one
tracer round for every four ball rounds), so shooters can see the trajectory and "walk" the
fire into the target, and direct the fire of other soldiers.
Assault rifles are a compromise between the pistol-caliber submachine gun and a traditional
rifle firing a full-power cartridge, allowing single-shot, burst and full-automatic fire
options.
Many heavy machine guns, such as the Browning M2 .50 caliber machine gun, are accurate
enough to engage targets at great distances. During the Vietnam War, Carlos Hathcock set the
record for a long-distance shot at 7382 ft (2250 m) with a .50 caliber heavy machine gun he
had equipped with a telescopic sight. This led to the introduction of .50 caliber
anti-material sniper rifles, such as the Barrett M82.
Components
All machine guns require the following components:
1. A feed system to load the firing chamber. Cartridges can be fed into the chamber by a
variety of methods, the most common being spring-fed magazines or ammunition belts.
2. A trigger mechanism to fire the round. This includes the actual trigger, a trigger
sear to catch the bolt, a bolt and a firing pin, as well as other components. Typically, the
act of pulling the trigger causes something to strike the primer on the round in the chamber
and disengages the sears. This allows continual cycling of the bolt until the trigger is
released. A sear then grabs the bolt or firing pin. This stops the machine gun at some point
in its cycle.
3. An extractor system to eject the spent or misfired cartridge. Usually this is fairly
simple. A pin on the side of the bolt catches a ridge on the cartridge and flicks it out an
ejection port.
These components form a mechanism which must be powered by something. If powered by a spring
absorbing the recoil of a fired cartridge, it is called recoil operated. If powered by the
expanding gases of a fired cartridge, it is called gas actuated. If it powered by an
external force, such as a motor, it is usually called a chain gun.
Operation
All machine guns follow a cycle:
* Removing the spent cartridge through an ejection port.
* Cocking the trigger mechanism so the weapon can be fired again.
* Loading the next round into the firing chamber. Usually spring tension or a cam forces
the new round and bolt back into the firing chamber.
A mechanism makes the firing pin fire the cartridge, activating the ejection and reloading
steps. The cycle repeats. This full cycle takes a fraction of a second and can thus occur
many times per second. The operation is basically the same, regardless of the means of
activating these mechanisms. Some examples:
* Machine pistols and submachine guns (like the World War II "grease gun," MAC-10 or the
Uzi) are usually blowback operated.
* Most assault rifles and squad automatic weapons are gas actuated. Some weapons, such
as the AR-15/M16, integrate the piston with the bolt. Others, such as the M15 and AK
patterns, attach the piston to a bolt carrier that unlocks and operates the bolt.
* A recoil-actuated machine gun uses the recoil to first unlock and then operate the
action. Heavy machine guns, such as the M2 .50 and Browning .50, are of this type. These can
be recognized by a large cocking lever needed to feed the first round.
* An externally actuated machine gun uses an external power source, such as an electric
motor or even a hand crank to move its mechanism through the firing sequence. Most modern
weapons of this type are called chain guns in reference to their driving mechanism. Gatling
guns and revolver cannon have several barrels or chambers on a rotating carousel and a
system of cams that load, cock, and fire each mechanism progressively as it rotates through
the sequence. The continuous nature of the rotary action allows for an incredibly high
cyclic rate of fire, often several thousand rounds per minute. Not all chain guns use
multiple barrels or chambers, though. Chain guns are less prone to jamming than a gun
operated by gas or recoil, as the external power source will eject misfired rounds with no
further trouble. This is not possible if the force needed to eject the round comes from the
round itself. Chain guns are generally used with large shells, 20 mm in diameter or more,
though some, such as the M134 Minigun, fire smaller cartridges. They offer benefits of
reliability and firepower, though the weight and size of the power source and driving
mechanism makes them impractical for use outside of a vehicle or aircraft mount.
Heavy machine guns are often water cooled or have interchangeable barrels, which must be
changed periodically to avoid overheating. The higher the rate of fire, the more often
barrels must be changed and allowed to cool. To minimize this, most air-cooled guns are
fired only in short bursts or at a reduced rate of fire.
Not all machine guns strike the primer in the same way. In blowback machine guns, the act of
seating the round also fires the round. In gas operated and recoil-operated guns, a separate
step in the firing sequence is needed to strike the round. In a progressive-fire gun, the
firing pin is cycled by cams. In some automatic cannon, the primer is fired electrically.
In weapons where the round seats and fires at the same time, mechanical timing is essential
for operator safety, to prevent the round from firing before it is seated properly. This is
especially important in weapons like the 40 mm grenade launcher, where high explosives are
present in the rounds being fired.
Machine guns are controlled by one or more mechanical sears. When a sear is in place, it
effectively stops the bolt at some point in its range of motion. Some sears stop the bolt
when it is locked to the rear. Other sears stop the firing pin from going forward after the
round is locked into the chamber.
Almost all weapons have a "safety" sear, which simply keeps the trigger from engaging.
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