NASA's Space Shuttle, officially called the Space Transportation System (STS), is the spacecraft currently used by the United States government for its human spaceflight missions. At launch, it consists of a rust-colored external tank (ET), two white, slender Solid Rocket Boosters (SRBs), and the orbiter, a winged spaceplane which is the space shuttle in the narrow sense.

The orbiter carries astronauts and payload such as satellites or space station parts into low earth orbit, into the Earth's upper atmosphere or thermosphere. Usually, five to seven crew members ride in the orbiter. The payload capacity is 22,700 kg (50,000 lb). When the orbiter's mission is complete it fires its Orbital Maneuvering System (OMS) thrusters to drop out of orbit and re-enters the lower atmosphere. During the descent and landing, the shuttle orbiter acts as a glider, and makes a completely unpowered ("dead stick") landing.

Description

The shuttle is the first orbital spacecraft designed for partial reusability. It carries payloads to low Earth orbit, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can also 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 ISS 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 man responsible for the design of the STS was Maxime Faget, who had also overseen the Mercury, Gemini and Apollo spacecraft designs. The crucial factor in the size and shape of the Shuttle Orbiter was the requirement that it be able to accommodate the largest planned commercial and classified satellites, and have the cross-range recovery range to meet classified USAF missions requirement for a one-around abort for a polar launch. Factors involved in opting for 'reusable' solid rockets and an expendable fuel tank included the desire of the Pentagon to obtain a high-capacity payload vehicle for satellite deployment, and the desire of the Nixon administration to reduce the costs of space exploration by developing a spacecraft with reusable components.

Six air-worthy shuttles have been built; the first orbiter, Enterprise, was not built for space flight, and was used only for testing purposes. Five space-worthy orbiters were built: Columbia, Challenger, Discovery, Atlantis, and Endeavour. Challenger disintegrated 73 seconds after launch in 1986, and Endeavour was built as a replacement. Columbia broke apart during re-entry in 2003.

Each Space Shuttle is a partially reusable launch system that is composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable external tank (ET), and the two partially-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.

At times, the orbiter itself is referred to as the space shuttle. Technically, this is a misnomer, as the actual "Space Transportation System" (space shuttle) is the combination of the orbiter, the external tank (ET), and the two partially-reusable solid rocket boosters. Combined, these are referred to as the "Stack".

Orbiter vehicle

The orbiter resembles an aircraft 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 50° 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 has a large payload bay measuring by comprising most of the fuselage.

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 orbiter structure is made primarily from aluminum alloy, although the engine thrust structure is made from titanium (alloy).

Solid Rocket Boosters

Two solid rocket boosters (SRBs) each provide 12.5 million Newtons (2.8 million lbf) of thrust at liftoff, which is 83% of the total thrust needed for liftoff. The SRBs are jettisoned two minutes after launch at a height of about 45.7 km (150,000 feet), and then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1.3 cm (½ inch) thick.

Flight systems

Early shuttle missions took along the GRiD Compass, arguably one of the first laptop computers. The Compass sold poorly, as it cost at least US$8000, but offered unmatched performance for its weight and size. NASA was one of its main customers.

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 Data Processing System (DPS).

The design goal of the shuttle's DPS is fail operational/fail safe reliability. After a single failure, the shuttle can still continue the mission. After two failures, it can still 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. Embedded system avionic software is developed under totally different conditions from public commercial software, the number of code lines is tiny compared to a public commercial software, 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 still fail, and the BFS exists for that contingency. And while BFS will run in parallel with PASS, to date, BFS has never been engaged to take over control from PASS during any shuttle mission.

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, and load software from magnetic 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.

Typography and graphic design

The typeface used on the Space Shuttle Orbiter is Helvetica. On the front lower corner of the cargo bay doors is the name of the orbiter, on the back lower corner of the cargo bay is the NASA 'Worm' logo. Below the NASA logo is the text 'United States' with a flag of the United States. Another United States flag appears on the right wing.

Upgrades

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 those of contemporary airliners like the Airbus A380 and Boeing 777. This is called a glass cockpit. Programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the orbiter's internal airlocks have been 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 (SSMEs) 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%. To clarify 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 the first two missions, 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 aluminum-lithium alloy. It weighs 3.4 tons (7,500 lb) 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. Design engineers added a third O-ring seal to the joints between the segments after the Space Shuttle Challenger disaster.

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. These rockets entered production in the early to mid-1990s to support the Space Station, but were later canceled to save money after the expenditure of $2.2 billion. The loss of the ASRB program resulted in 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.

STS-70 was delayed in 1995, when woodpeckers bored holes in the foam insulation of Discovery's external tank. Since then, NASA has installed commercial plastic owl decoys and inflatable owl balloons which must be removed prior to launch. The delicate nature of the foam insulation has been the cause of damage to the Thermal Protection System, the tile heat shield and heat wrap of the orbiter, during recent launches. NASA remains confident that this damage, while linked to the Space Shuttle Columbia disaster on February 1, 2003, will not jeopardize the objective of NASA to complete the International Space Station (ISS) in the projected time allotted.

A cargo-only, unmanned variant of the shuttle has been variously proposed, and rejected since the 1980s. It was called the Shuttle-C, and would have traded 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 modified U.S. Air Force high-altitude full-pressure suits, which included a full-pressure helmet during ascent and descent. From the fifth flight, STS-5, until the loss of Challenger, one-piece light blue nomex flight suits and partial-pressure helmets were worn. A less-bulky, partial-pressure version of the high-altitude pressure suits with a helmet was reinstated when shuttle flights resumed in 1988. The Launch-Entry Suit ended its service life in late 1995, and was replaced by the full-pressure Advanced Crew Escape Suit (ACES), which resembles the Gemini space suit worn in the mid-1960s.

To extend the duration that orbiters can stay docked at the ISS, the Station-to-Shuttle Power Transfer System (SSPTS) was installed. The SSPTS allows these orbiters to use power provided by the ISS to preserve their consumables. The SSPTS was first used successfully on STS-118.

Technical data

Orbiter specifications (for Endeavour, OV-105)

• Length: 37.24 m (122.17 ft)
• Wingspan: 23.79 m (78.06 ft)
• Height:
• Empty weight: 68,585 kg (151,205 lb)
• Gross liftoff weight: 109,000 kg (240,000 lb)
• Maximum landing weight: 104,000 kg (230,000 lb)
• Main engines: Three Rocketdyne Block IIA SSMEs, each with a sea level thrust of 1.75 meganewtons (MN) (393,800 pounds-force (lbf))
• Maximum payload:
• Payload bay dimensions: by
• Operational altitude: 100 to 520 nmi (185 to 960 km)
• Speed: 7,743 m/s (27,875 km/h, 25,404 ft/s, 17,321 mi/h)
• Crossrange: 2,009 km (1,085 nmi)
• Crew: Varies. The earliest shuttle flights had the minimum crew of two; many later missions a crew of five. Today, typically seven people fly (commander, pilot, several mission specialists, and rarely a flight engineer). On two occasions, eight astronauts have flown (STS-61-A, STS-71). Eleven people could be accommodated in an emergency mission (see STS-3xx).

External tank specifications (for SLWT)

• Length: 46.9 m (153.8 ft)
• Diameter: 8.4 m (27.6 ft)
• Propellant volume: 2,025 m³ (535,000 US gal)
• Empty weight:
• Gross liftoff weight: 756,000 kg (1,667,000 lb)

Solid Rocket Booster specifications

• Length:
• Diameter:
• Empty weight (per booster):
• Gross liftoff weight (per booster): 590,000 kg (1.3 million lb)
• Thrust (sea level, liftoff): 12.5 MN (2.8 million lbf)

System Stack specifications

• Height:
• Gross liftoff weight: 2 million kg (4.5 million lb)
• Total liftoff thrust: 30.16 MN (6.781 million lbf)

Mission profile

Launch

The Shuttle has not been launched if its flight will take it from one year to the next (December to January), a year-end rollover (YERO). Its flight software, designed in the 1970s, was not designed for this, and would require the orbiter's computers be reset through a change of year, which could cause a glitch while in orbit. In 2007, NASA engineers devised a solution to this, allowing Shuttle flights to cross the year-end boundary.

On the day of a launch, after the final hold in the countdown at T minus 9 minutes, the Shuttle goes through its final preparations for launch, and the countdown is automatically controlled by a special computer program at the Launch Control Center. This is known as the Ground Launch Sequencer (GLS), which stops the count if it senses a critical problem with any of the Shuttle's on-board systems. The GLS hands off the count to the Shuttle's on-board computers at T minus 31 seconds, in a process called auto sequence start.

At T minus 16 seconds, the massive sound suppression system (SPS) begins to drench the Mobile Launcher Platform (MLP) and SRB trenches with 300,000 U.S. gallons (1,100 m³) of water to protect the Orbiter from damage by acoustical energy and rocket exhaust reflected from the flame trench and MLP during liftoff.

At T-minus 10 seconds, hydrogen igniters are activated under each engine bell to quell the stagnant gas inside the cones before ignition. Failure to burn these gases can trip the onboard sensors and create the possibility of an overpressure and explosion of the vehicle during the firing phase. The main engine turbopumps are also commanded to begin charging the combustion chambers with liquid hydrogen and liquid oxygen at this time. The computers reciprocate this action by allowing the redundant computer systems to begin the firing phase.

The three Space Shuttle Main Engines (SSMEs) start at T minus 6.6 seconds. The main engines ignite sequentially via the shuttle's general purpose computers (GPCs) at 120 millisecond intervals. The GPCs require that the engines reach 90% of their rated performance to complete the final gimbal of the main engine nozzles to liftoff configuration. When the SSMEs start, the water from the sound suppression system flashes into a large volume of steam that shoots southward. All three SSMEs must reach the required 100% thrust within three seconds, otherwise the onboard computers will initiate an RSLS abort. If the onboard computers verify normal thrust buildup, at T minus 0 seconds, the SRBs are ignited. At this point the vehicle is committed to takeoff, as the SRBs cannot be turned off once ignited. After the SRBs reach a stable thrust ratio, pyrotechnic nuts are detonated by radio controlled signals from the shuttle's GPC's to release the vehicle. The plume from the solid rockets exits the flame trench in a northward direction at near the speed of sound, often causing a rippling of shockwaves along the actual flame and smoke contrails. At ignition, the GPC's mandate the firing sequences via the Master Events Controller, a computer program integrated with the shuttle's four redundant computer systems. There are extensive emergency procedures (abort modes) to handle various failure scenarios during ascent. Many of these concern SSME failures, since that is the most complex and highly stressed component. After the Challenger disaster, there were extensive upgrades to the abort modes.

After the main engines start, but while the solid rocket boosters are still clamped to the pad, the offset thrust from the Shuttle's three main engines causes the entire launch stack (boosters, tank and shuttle) to pitch down about 2 m at cockpit level. This motion is called the "nod", or "twang" in NASA jargon. As the boosters flex back into their original shape, the launch stack pitches slowly back upright. This takes approximately six seconds. At the point when it is perfectly vertical, the boosters ignite and the launch commences.

Shortly after clearing the tower the Shuttle begins a roll and pitch program to set its orbital inclination and so that the vehicle is below the external tank and SRBs, with wings level. The vehicle climbs in a progressively flattening arc, accelerating as the weight of the SRBs and main tank decrease. To achieve low orbit requires much more horizontal than vertical acceleration. This is not visually obvious, since the vehicle rises vertically and is out of sight for most of the horizontal acceleration. The near circular orbital velocity at the 380 km (236 statute miles) altitude of the International Space Station is 7.68 kilometers per second (27,650 km/h, 17,180 mph), roughly equivalent to Mach 23 at sea level. As the International Space Station orbits at an inclination of 51.6 degrees, the Shuttle has to set its inclination to the same value to rendezvous with the station.

Around a point called Max Q, where the aerodynamic forces are at their maximum, the main engines are temporarily throttled back to avoid overspeeding and hence overstressing the Shuttle, particularly in vulnerable areas such as the wings. At this point, a phenomenon known as the Prandtl-Glauert singularity occurs, where condensation clouds form during the vehicle's transition to supersonic speed.

126 seconds after launch, explosive bolts release the SRBs and small separation rockets push them laterally away from the vehicle. The SRBs parachute back to the ocean to be reused. The Shuttle then begins accelerating to orbit on the Space Shuttle main engines. The vehicle at that point in the flight has a thrust-to-weight ratio of less than one the main engines actually have insufficient thrust to exceed the force of gravity, and the vertical speed given to it by the SRBs temporarily decreases. However, as the burn continues, the weight of the propellant decreases and the thrust-to-weight ratio exceeds 1 again and the ever-lighter vehicle then continues to accelerate toward orbit.

The vehicle continues to climb and takes on a somewhat nose-up angle to the horizon it uses the main engines to gain and then maintain altitude while it accelerates horizontally towards orbit. At about five and three-quarter minutes into ascent, the orbiter rolls heads up to switch communication links from ground stations to Tracking and Data Relay Satellites.

Finally, in the last tens of seconds of the main engine burn, the mass of the vehicle is low enough that the engines must be throttled back to limit vehicle acceleration to 3 g (30 m/s²), largely for astronaut comfort.

The main engines are shut down before complete depletion of propellant, as running dry would destroy the engines. The oxygen supply is terminated before the hydrogen supply, as the SSMEs react unfavorably to other shutdown modes. Liquid oxygen has a tendency to react violently, and supports combustion when it encounters hot engine metal. The external tank is released by firing explosive bolts and falls, largely burning up in the atmosphere, though some fragments fall into the Indian Ocean. The sealing action of the tank plumbing and lack of pressure relief systems on the external tank helps it break up in the lower atmosphere. After the foam burns away during reentry, the heat causes a pressure buildup in the remaining liquid oxygen and hydrogen until the tank explodes. This ensures that any pieces that fall back to Earth are small.

To prevent the shuttle from following the external tank back into the lower atmosphere, the Orbital maneuvering system (OMS) engines are fired to raise the perigee higher into the upper atmosphere. On some missions (e.g., missions to the ISS), the OMS engines are also used while the main engines are still firing. The reason for putting the orbiter on a path that brings it back to Earth is not just for external tank disposal. It is one of safety; if the OMS malfunctions, or the cargo bay doors cannot open for some reason, the shuttle is already on a path to return to earth for an emergency abort landing.

Re-entry and landing

Almost the entire space shuttle re-entry, except for lowering the landing gear and deploying the air data probes, is normally performed under computer control. However, the re-entry can be flown entirely manually if an emergency arises. The approach and landing phase can be controlled by the autopilot, but is usually hand flown.

The vehicle begins re-entry by firing the Orbital maneuvering system engines, while flying upside down, backside first, in the opposite direction to orbital motion for approximately three minutes, which reduces the shuttle's velocity by about 200 mph (90 m/s). The resultant slowing of the Shuttle lowers its orbital perigee down into the upper atmosphere. The shuttle then flips over, by pulling its nose up (which is actually "down" because it's flying upside down). This OMS firing is done roughly halfway around the globe from the landing site.

The vehicle starts encountering more significant air density in the lower thermosphere at about 400,000 ft (120 km), at around Mach 25 (8.2 km/s). The vehicle is controlled by a combination of RCS thrusters and control surfaces, to fly at a 40 degree nose-up attitude, producing high drag, not only to slow it down to landing speed, but also to reduce reentry heating. In addition, the vehicle needs to bleed off extra speed before reaching the landing site. This is achieved by performing s-curves at up to a 70 degree roll angle.

The orbiter's maximum glide ratio/lift-to-drag ratio varies considerably with speed, ranging from 1:1 at hypersonic speeds, 2:1 at supersonic speeds and reaching 4.5:1 at subsonic speeds during approach and landing.

In the lower atmosphere, the orbiter flies much like a conventional glider, except for a much higher descent rate, over 10,000 feet per minute (50 m/s).

At approximately Mach 3, two air data probes, located on the left and right sides of the orbiter's forward lower fuselage, are deployed to sense air pressure related to the vehicle's movement in the atmosphere.

When the approach and landing phase begins, the orbiter is at a 3,000 m (10,000 ft) altitude, 12 km (7.5 miles) from the runway. The pilots apply aerodynamic braking to help slow down the vehicle. The orbiter's speed is reduced from 682 km/h (424 mph) to approximately 346 km/h (215 mph), (compared to 260 km/h (160 mph) for a jet airliner), at touch-down. The landing gear is deployed while the Orbiter is flying at 430 km/h (267 mph). To assist the speed brakes, a 12 m (40 ft) drag chute is deployed either after main gear or nose gear touchdown (depending on selected chute deploy mode) at about 343 km/h (213 mph). The chute is jettisoned once the orbiter slows to 110 km/h (69 mph).

After landing, the vehicle stands on the runway for several minutes to permit the fumes from poisonous hydrazine, used as a propellant for attitude control, to dissipate, and for the shuttle fuselage to cool before the astronauts disembark.

Landing sites

A list of other landing sites:

• Elmendorf Air Force Base, Alaska
• White Sands Space Harbor, New Mexico (actual landing site for STS-3)
• MCAS Yuma/Yuma International Airport, Arizona
• Plattsburgh Air Force Base, New York (Former site; now closed)
• Ben Guerir Air Base, Morocco
• Morón Air Base, Spain
• Banjul International Airport (Yundum), The Gambia
• Zaragoza Air Base, Spain
• Diosdado Macapagal International Airport, The Philippines (When it was still under U.S. Air Force Control)
• Kuala Lumpur International Airport, Malaysia
• RAAF Base Amberley, Australia
• Andersen AFB, Guam
• Amilcar Cabral International Airport, Cape Verde
• Hickam AFB, Hawaii
• Stockholm-Arlanda Airport, Sweden
• Istres AB, France
• Bangor International Airport, Maine
• Salina Municipal Airport, Kansas
• Westover Air Reserve Base, Massachusetts
• Gander International Airport, Canada
• Shannon International Airport, Ireland

A list of launch abort sites:

• Atlantic City International Airport, Atlantic City, New Jersey, USA
• RAAF Base Darwin, Darwin Australia
• Myrtle Beach International Airport, South Carolina, USA
• Dyess Air Force Base, Texas, USA
• Marine Corps Air Station Cherry Point, North Carolina, USA
• Ellsworth Air Force Base, South Dakota, USA
• Naval Air Station Oceana, Virginia Beach, Virginia, USA
• Esenboğa International Airport, Ankara, Turkey
• Dover Air Force Base, Delaware, USA
• Fort Wayne International Airport (Air Guard Station), Fort Wayne, Indiana, USA
• International Airport of Gran Canaria-Gando, Gran Canaria (Las Palmas), Canary Islands, Spain
• Otis Air National Guard Base, Massachusetts, USA
• Grant County International Airport, Washington, USA
• Pease ANGB, New Hampshire, USA
• Hao Airport, French Polynesia
• AFB Hoedspruit, South Africa
• Bermuda International Airport (former NAS Bermuda)
• King Khalid International Airport, Riyadh, Saudi Arabia
• Kinshasa International Airport, Congo-Kinshasa
• Cologne Bonn Airport, Germany
• Lajes Field, Azores, Portugal
• Lincoln Airport, Nebraska, USA
• Mountain Home Air Force Base, Idaho, USA
• Naval Air Station Bermuda, Bahamas
• NSA Souda Bay, Crete, Greece
• NSF Diego Garcia, Chagos Archipelago, British Indian Ocean Territory
• Orlando International Airport, Florida
• RAF Fairford, United Kingdom
• Roberts International Airport, Monrovia, Liberia
• Lehigh Valley International Airport, Allentown, PA
• Mataveri International Airport, Hanga Roa, Easter Island, Chile
• Halifax International Airport, Halifax, Nova Scotia, Canada
• Ben Guerir Air Base, Morocco
• Columbus Air Force Base, Mississippi

Fleet history

Below is a list of major events in the Space Shuttle orbiter fleet.

Retirement

In 2010, the Space Shuttle, after nearly 30 years of duty, will be retired from service. To fill the void left behind by the Shuttle's retirement a new spacecraft will be developed that will not only be capable of ferrying passengers and cargo to the ISS, but also beyond Earth's orbit to other worlds. This spacecraft has tentatively been dubbed the Crew Exploration Vehicle and the project has been dubbed Project Constellation. Atlantis will be the first of NASA's three space shuttles to be retired, most likely in 2008, as the shuttle program winds down in four years. The next-generation vehicles, the new Ares/Orion vehicles, won’t be operational until 2015 at the earliest. Therefore, NASA is confronting the possibility that there will only be Russian crew members on the International Space Station for that period of time. Under this dilemma, congressmen are discussing the possibility to postpone the retirement of the space shuttles. One of the proposals, which would cost about $10 billion, would have the shuttles make six or seven additional flights between 2010 and 2013 and speed up development of the Orion ships to be ready by then. A second proposal would keep the shuttles flying until 2015 and leave Orion's schedule alone.

See also

• Comparison of heavy lift launch systems
• Space Shuttle program
• Criticism of the Space Shuttle program
• GRiD Compass the early laptop carried aboard the shuttle.
• Human spaceflight
• List of human spaceflights
• NASA Space Shuttle decision
• Orbiter Processing Facility
• Shuttle Derived Launch Vehicle
• Shuttle SERV
• Space disaster
• Space exploration
• Space Shuttle abort modes
• Space Shuttle crews
• Shuttle Training Aircraft

Fiction and games

• Space shuttles in fiction
• Space Shuttle Mission 2007, latest Space Shuttle simulator for Windows XP and Vista PCs.
• Orbiter, a freeware simulator that allows users to fly various spacecraft including the shuttle.
• Space Shuttle America
• Shuttle, a Space Shuttle simulator for PC, Amiga & Atari ST.
• X-Plane, a flight simulator that allows players to fly the Space Shuttle's re-entry phase.

Physics

• Atmospheric reentry
• Lifting body
• Reusable launch system
• Single-stage-to-orbit

Similar spacecraft

• Dyna-soar
• EADS Phoenix
• Hermes
• HOPE-X
• Kliper
• Military space shuttle
• Orion (Project Constellation)
• Soviet space shuttle Buran
• Lockheed Martin X-33
• DIRECT, a shuttle-derived vehicle proposed as an alternative for Project Constellation

References

Further reading

• Reference manual
• How The Space Shuttle Works
• NASA Space Shuttle News Reference - 1981 (PDF document)
• Orbiter Vehicles
• Lecture Series on the space shuttle from MIT OpenCourseWare

External links

• NASA Human Spaceflight - Shuttle: Current status of shuttle missions
• Video of current and historical missions (STS-1 thru Current)
• NASA TV: View live streaming of launch and mission coverage
• [news:sci.space.shuttle Space Shuttle Newsgroup - sci.space.shuttle]
• List of all Shuttle Landing Sites
• Map of Landing Sites
• Official NASA Human Space Flight Orbital Tracking system
• Congressional Research Service (CRS) Reports regarding the Space Shuttle
• Weather criteria for shuttle launch
• Newer images, audio, and video of the space shuttle program
• Older images of the space shuttle program
• The maiden launch of the space shuttle (Google Video)
• NASA Shuttle Gallery
• Different details and perspectives from the orbiter (Gallery drafts.de) (ger.)
• 04/16/07: Consolidated Launch Manifest: Space Shuttle Flights and ISS Assembly Sequence.
• NASA Further Updates Launch Schedule.
• GRiD Compass History at Hrothgar's Cool Old Junk Page
• NASA History Series Publications (many of which are on-line)
• Space Shuttle Endeavour Pictures at the ISS

NASA's Space Shuttle, officially called the Space Transportation System (STS), is the spacecraft currently used by the United States government for its human spaceflight missions. At launch, it consists of a rust-colored external tank (ET), two white, slender Solid Rocket Boosters (SRBs), and the orbiter, a winged spaceplane which is the space shuttle in the narrow sense.

The orbiter carries astronauts and payload such as satellites or space station parts into low earth orbit, into the Earth's upper atmosphere or thermosphere. Usually, five to seven crew members ride in the orbiter. The payload capacity is 22,700 kg (50,000 lb). When the orbiter's mission is complete it fires its Orbital Maneuvering System (OMS) thrusters to drop out of orbit and re-enters the lower atmosphere. During the descent and landing, the shuttle orbiter acts as a glider, and makes a completely unpowered ("dead stick") landing.

Description

The shuttle is the first orbital spacecraft designed for partial reusability. It carries payloads to low Earth orbit, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can also 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 ISS 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 man responsible for the design of the STS was Maxime Faget, who had also overseen the Mercury, Gemini and Apollo spacecraft designs. The crucial factor in the size and shape of the Shuttle Orbiter was the requirement that it be able to accommodate the largest planned commercial and classified satellites, and have the cross-range recovery range to meet classified USAF missions requirement for a one-around abort for a polar launch. Factors involved in opting for 'reusable' solid rockets and an expendable fuel tank included the desire of the Pentagon to obtain a high-capacity payload vehicle for satellite deployment, and the desire of the Nixon administration to reduce the costs of space exploration by developing a spacecraft with reusable components.

Six air-worthy shuttles have been built; the first orbiter, Enterprise, was not built for space flight, and was used only for testing purposes. Five space-worthy orbiters were built: Columbia, Challenger, Discovery, Atlantis, and Endeavour. Challenger disintegrated 73 seconds after launch in 1986, and Endeavour was built as a replacement. Columbia broke apart during re-entry in 2003.

Each Space Shuttle is a partially reusable launch system that is composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable external tank (ET), and the two partially-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.

At times, the orbiter itself is referred to as the space shuttle. Technically, this is a misnomer, as the actual "Space Transportation System" (space shuttle) is the combination of the orbiter, the external tank (ET), and the two partially-reusable solid rocket boosters. Combined, these are referred to as the "Stack".

Orbiter vehicle

The orbiter resembles an aircraft 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 50° 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 has a large payload bay measuring by comprising most of the fuselage.

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 orbiter structure is made primarily from aluminum alloy, although the engine thrust structure is made from titanium (alloy).

Solid Rocket Boosters

Two solid rocket boosters (SRBs) each provide 12.5 million Newtons (2.8 million lbf) of thrust at liftoff, which is 83% of the total thrust needed for liftoff. The SRBs are jettisoned two minutes after launch at a height of about 45.7 km (150,000 feet), and then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1.3 cm (½ inch) thick.

Flight systems

Early shuttle missions took along the GRiD Compass, arguably one of the first laptop computers. The Compass sold poorly, as it cost at least US$8000, but offered unmatched performance for its weight and size. NASA was one of its main customers.

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 Data Processing System (DPS).

The design goal of the shuttle's DPS is fail operational/fail safe reliability. After a single failure, the shuttle can still continue the mission. After two failures, it can still 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. Embedded system avionic software is developed under totally different conditions from public commercial software, the number of code lines is tiny compared to a public commercial software, 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 still fail, and the BFS exists for that contingency. And while BFS will run in parallel with PASS, to date, BFS has never been engaged to take over control from PASS during any shuttle mission.

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, and load software from magnetic 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.

Typography and graphic design

The typeface used on the Space Shuttle Orbiter is Helvetica. On the front lower corner of the cargo bay doors is the name of the orbiter, on the back lower corner of the cargo bay is the NASA 'Worm' logo. Below the NASA logo is the text 'United States' with a flag of the United States. Another United States flag appears on the right wing.

Upgrades

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 those of contemporary airliners like the Airbus A380 and Boeing 777. This is called a glass cockpit. Programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the orbiter's internal airlocks have been 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 (SSMEs) 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%. To clarify 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 the first two missions, 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 aluminum-lithium alloy. It weighs 3.4 tons (7,500 lb) 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. Design engineers added a third O-ring seal to the joints between the segments after the Space Shuttle Challenger disaster.

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. These rockets entered production in the early to mid-1990s to support the Space Station, but were later canceled to save money after the expenditure of $2.2 billion. The loss of the ASRB program resulted in 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.

STS-70 was delayed in 1995, when woodpeckers bored holes in the foam insulation of Discovery's external tank. Since then, NASA has installed commercial plastic owl decoys and inflatable owl balloons which must be removed prior to launch. The delicate nature of the foam insulation has been the cause of damage to the Thermal Protection System, the tile heat shield and heat wrap of the orbiter, during recent launches. NASA remains confident that this damage, while linked to the Space Shuttle Columbia disaster on February 1, 2003, will not jeopardize the objective of NASA to complete the International Space Station (ISS) in the projected time allotted.

A cargo-only, unmanned variant of the shuttle has been variously proposed, and rejected since the 1980s. It was called the Shuttle-C, and would have traded 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 modified U.S. Air Force high-altitude full-pressure suits, which included a full-pressure helmet during ascent and descent. From the fifth flight, STS-5, until the loss of Challenger, one-piece light blue nomex flight suits and partial-pressure helmets were worn. A less-bulky, partial-pressure version of the high-altitude pressure suits with a helmet was reinstated when shuttle flights resumed in 1988. The Launch-Entry Suit ended its service life in late 1995, and was replaced by the full-pressure Advanced Crew Escape Suit (ACES), which resembles the Gemini space suit worn in the mid-1960s.

To extend the duration that orbiters can stay docked at the ISS, the Station-to-Shuttle Power Transfer System (SSPTS) was installed. The SSPTS allows these orbiters to use power provided by the ISS to preserve their consumables. The SSPTS was first used successfully on STS-118.

Technical data

Orbiter specifications (for Endeavour, OV-105)

• Length: 37.24 m (122.17 ft)
• Wingspan: 23.79 m (78.06 ft)
• Height:
• Empty weight: 68,585 kg (151,205 lb)
• Gross liftoff weight: 109,000 kg (240,000 lb)
• Maximum landing weight: 104,000 kg (230,000 lb)
• Main engines: Three Rocketdyne Block IIA SSMEs, each with a sea level thrust of 1.75 meganewtons (MN) (393,800 pounds-force (lbf))
• Maximum payload:
• Payload bay dimensions: by
• Operational altitude: 100 to 520 nmi (185 to 960 km)
• Speed: 7,743 m/s (27,875 km/h, 25,404 ft/s, 17,321 mi/h)
• Crossrange: 2,009 km (1,085 nmi)
• Crew: Varies. The earliest shuttle flights had the minimum crew of two; many later missions a crew of five. Today, typically seven people fly (commander, pilot, several mission specialists, and rarely a flight engineer). On two occasions, eight astronauts have flown (STS-61-A, STS-71). Eleven people could be accommodated in an emergency mission (see STS-3xx).

External tank specifications (for SLWT)

• Length: 46.9 m (153.8 ft)
• Diameter: 8.4 m (27.6 ft)
• Propellant volume: 2,025 m³ (535,000 US gal)
• Empty weight:
• Gross liftoff weight: 756,000 kg (1,667,000 lb)

Solid Rocket Booster specifications

• Length:
• Diameter:
• Empty weight (per booster):
• Gross liftoff weight (per booster): 590,000 kg (1.3 million lb)
• Thrust (sea level, liftoff): 12.5 MN (2.8 million lbf)

System Stack specifications

• Height:
• Gross liftoff weight: 2 million kg (4.5 million lb)
• Total liftoff thrust: 30.16 MN (6.781 million lbf)

Mission profile

Launch

The Shuttle has not been launched if its flight will take it from one year to the next (December to January), a year-end rollover (YERO). Its flight software, designed in the 1970s, was not designed for this, and would require the orbiter's computers be reset through a change of year, which could cause a glitch while in orbit. In 2007, NASA engineers devised a solution to this, allowing Shuttle flights to cross the year-end boundary.

On the day of a launch, after the final hold in the countdown at T minus 9 minutes, the Shuttle goes through its final preparations for launch, and the countdown is automatically controlled by a special computer program at the Launch Control Center. This is known as the Ground Launch Sequencer (GLS), which stops the count if it senses a critical problem with any of the Shuttle's on-board systems. The GLS hands off the count to the Shuttle's on-board computers at T minus 31 seconds, in a process called auto sequence start.

At T minus 16 seconds, the massive sound suppression system (SPS) begins to drench the Mobile Launcher Platform (MLP) and SRB trenches with 300,000 U.S. gallons (1,100 m³) of water to protect the Orbiter from damage by acoustical energy and rocket exhaust reflected from the flame trench and MLP during liftoff.

At T-minus 10 seconds, hydrogen igniters are activated under each engine bell to quell the stagnant gas inside the cones before ignition. Failure to burn these gases can trip the onboard sensors and create the possibility of an overpressure and explosion of the vehicle during the firing phase. The main engine turbopumps are also commanded to begin charging the combustion chambers with liquid hydrogen and liquid oxygen at this time. The computers reciprocate this action by allowing the redundant computer systems to begin the firing phase.

The three Space Shuttle Main Engines (SSMEs) start at T minus 6.6 seconds. The main engines ignite sequentially via the shuttle's general purpose computers (GPCs) at 120 millisecond intervals. The GPCs require that the engines reach 90% of their rated performance to complete the final gimbal of the main engine nozzles to liftoff configuration. When the SSMEs start, the water from the sound suppression system flashes into a large volume of steam that shoots southward. All three SSMEs must reach the required 100% thrust within three seconds, otherwise the onboard computers will initiate an RSLS abort. If the onboard computers verify normal thrust buildup, at T minus 0 seconds, the SRBs are ignited. At this point the vehicle is committed to takeoff, as the SRBs cannot be turned off once ignited. After the SRBs reach a stable thrust ratio, pyrotechnic nuts are detonated by radio controlled signals from the shuttle's GPC's to release the vehicle. The plume from the solid rockets exits the flame trench in a northward direction at near the speed of sound, often causing a rippling of shockwaves along the actual flame and smoke contrails. At ignition, the GPC's mandate the firing sequences via the Master Events Controller, a computer program integrated with the shuttle's four redundant computer systems. There are extensive emergency procedures (abort modes) to handle various failure scenarios during ascent. Many of these concern SSME failures, since that is the most complex and highly stressed component. After the Challenger disaster, there were extensive upgrades to the abort modes.

After the main engines start, but while the solid rocket boosters are still clamped to the pad, the offset thrust from the Shuttle's three main engines causes the entire launch stack (boosters, tank and shuttle) to pitch down about 2 m at cockpit level. This motion is called the "nod", or "twang" in NASA jargon. As the boosters flex back into their original shape, the launch stack pitches slowly back upright. This takes approximately six seconds. At the point when it is perfectly vertical, the boosters ignite and the launch commences.

Shortly after clearing the tower the Shuttle begins a roll and pitch program to set its orbital inclination and so that the vehicle is below the external tank and SRBs, with wings level. The vehicle climbs in a progressively flattening arc, accelerating as the weight of the SRBs and main tank decrease. To achieve low orbit requires much more horizontal than vertical acceleration. This is not visually obvious, since the vehicle rises vertically and is out of sight for most of the horizontal acceleration. The near circular orbital velocity at the 380 km (236 statute miles) altitude of the International Space Station is 7.68 kilometers per second (27,650 km/h, 17,180 mph), roughly equivalent to Mach 23 at sea level. As the International Space Station orbits at an inclination of 51.6 degrees, the Shuttle has to set its inclination to the same value to rendezvous with the station.

Around a point called Max Q, where the aerodynamic forces are at their maximum, the main engines are temporarily throttled back to avoid overspeeding and hence overstressing the Shuttle, particularly in vulnerable areas such as the wings. At this point, a phenomenon known as the Prandtl-Glauert singularity occurs, where condensation clouds form during the vehicle's transition to supersonic speed.

126 seconds after launch, explosive bolts release the SRBs and small separation rockets push them laterally away from the vehicle. The SRBs parachute back to the ocean to be reused. The Shuttle then begins accelerating to orbit on the Space Shuttle main engines. The vehicle at that point in the flight has a thrust-to-weight ratio of less than one the main engines actually have insufficient thrust to exceed the force of gravity, and the vertical speed given to it by the SRBs temporarily decreases. However, as the burn continues, the weight of the propellant decreases and the thrust-to-weight ratio exceeds 1 again and the ever-lighter vehicle then continues to accelerate toward orbit.

The vehicle continues to climb and takes on a somewhat nose-up angle to the horizon it uses the main engines to gain and then maintain altitude while it accelerates horizontally towards orbit. At about five and three-quarter minutes into ascent, the orbiter rolls heads up to switch communication links from ground stations to Tracking and Data Relay Satellites.

Finally, in the last tens of seconds of the main engine burn, the mass of the vehicle is low enough that the engines must be throttled back to limit vehicle acceleration to 3 g (30 m/s²), largely for astronaut comfort.

The main engines are shut down before complete depletion of propellant, as running dry would destroy the engines. The oxygen supply is terminated before the hydrogen supply, as the SSMEs react unfavorably to other shutdown modes. Liquid oxygen has a tendency to react violently, and supports combustion when it encounters hot engine metal. The external tank is released by firing explosive bolts and falls, largely burning up in the atmosphere, though some fragments fall into the Indian Ocean. The sealing action of the tank plumbing and lack of pressure relief systems on the external tank helps it break up in the lower atmosphere. After the foam burns away during reentry, the heat causes a pressure buildup in the remaining liquid oxygen and hydrogen until the tank explodes. This ensures that any pieces that fall back to Earth are small.

To prevent the shuttle from following the external tank back into the lower atmosphere, the Orbital maneuvering system (OMS) engines are fired to raise the perigee higher into the upper atmosphere. On some missions (e.g., missions to the ISS), the OMS engines are also used while the main engines are still firing. The reason for putting the orbiter on a path that brings it back to Earth is not just for external tank disposal. It is one of safety; if the OMS malfunctions, or the cargo bay doors cannot open for some reason, the shuttle is already on a path to return to earth for an emergency abort landing.

Re-entry and landing

Almost the entire space shuttle re-entry, except for lowering the landing gear and deploying the air data probes, is normally performed under computer control. However, the re-entry can be flown entirely manually if an emergency arises. The approach and landing phase can be controlled by the autopilot, but is usually hand flown.

The vehicle begins re-entry by firing the Orbital maneuvering system engines, while flying upside down, backside first, in the opposite direction to orbital motion for approximately three minutes, which reduces the shuttle's velocity by about 200 mph (90 m/s). The resultant slowing of the Shuttle lowers its orbital perigee down into the upper atmosphere. The shuttle then flips over, by pulling its nose up (which is actually "down" because it's flying upside down). This OMS firing is done roughly halfway around the globe from the landing site.

The vehicle starts encountering more significant air density in the lower thermosphere at about 400,000 ft (120 km), at around Mach 25 (8.2 km/s). The vehicle is controlled by a combination of RCS thrusters and control surfaces, to fly at a 40 degree nose-up attitude, producing high drag, not only to slow it down to landing speed, but also to reduce reentry heating. In addition, the vehicle needs to bleed off extra speed before reaching the landing site. This is achieved by performing s-curves at up to a 70 degree roll angle.

The orbiter's maximum glide ratio/lift-to-drag ratio varies considerably with speed, ranging from 1:1 at hypersonic speeds, 2:1 at supersonic speeds and reaching 4.5:1 at subsonic speeds during approach and landing.

In the lower atmosphere, the orbiter flies much like a conventional glider, except for a much higher descent rate, over 10,000 feet per minute (50 m/s).

At approximately Mach 3, two air data probes, located on the left and right sides of the orbiter's forward lower fuselage, are deployed to sense air pressure related to the vehicle's movement in the atmosphere.

When the approach and landing phase begins, the orbiter is at a 3,000 m (10,000 ft) altitude, 12 km (7.5 miles) from the runway. The pilots apply aerodynamic braking to help slow down the vehicle. The orbiter's speed is reduced from 682 km/h (424 mph) to approximately 346 km/h (215 mph), (compared to 260 km/h (160 mph) for a jet airliner), at touch-down. The landing gear is deployed while the Orbiter is flying at 430 km/h (267 mph). To assist the speed brakes, a 12 m (40 ft) drag chute is deployed either after main gear or nose gear touchdown (depending on selected chute deploy mode) at about 343 km/h (213 mph). The chute is jettisoned once the orbiter slows to 110 km/h (69 mph).

After landing, the vehicle stands on the runway for several minutes to permit the fumes from poisonous hydrazine, used as a propellant for attitude control, to dissipate, and for the shuttle fuselage to cool before the astronauts disembark.

Landing sites

A list of other landing sites:

• Elmendorf Air Force Base, Alaska
• White Sands Space Harbor, New Mexico (actual landing site for STS-3)
• MCAS Yuma/Yuma International Airport, Arizona
• Plattsburgh Air Force Base, New York (Former site; now closed)
• Ben Guerir Air Base, Morocco
• Morón Air Base, Spain
• Banjul International Airport (Yundum), The Gambia
• Zaragoza Air Base, Spain
• Diosdado Macapagal International Airport, The Philippines (When it was still under U.S. Air Force Control)
• Kuala Lumpur International Airport, Malaysia
• RAAF Base Amberley, Australia
• Andersen AFB, Guam
• Amilcar Cabral International Airport, Cape Verde
• Hickam AFB, Hawaii
• Stockholm-Arlanda Airport, Sweden
• Istres AB, France
• Bangor International Airport, Maine
• Salina Municipal Airport, Kansas
• Westover Air Reserve Base, Massachusetts
• Gander International Airport, Canada
• Shannon International Airport, Ireland

A list of launch abort sites:

• Atlantic City International Airport, Atlantic City, New Jersey, USA
• RAAF Base Darwin, Darwin Australia
• Myrtle Beach International Airport, South Carolina, USA
• Dyess Air Force Base, Texas, USA
• Marine Corps Air Station Cherry Point, North Carolina, USA
• Ellsworth Air Force Base, South Dakota, USA
• Naval Air Station Oceana, Virginia Beach, Virginia, USA
• Esenboğa International Airport, Ankara, Turkey
• Dover Air Force Base, Delaware, USA
• Fort Wayne International Airport (Air Guard Station), Fort Wayne, Indiana, USA
• International Airport of Gran Canaria-Gando, Gran Canaria (Las Palmas), Canary Islands, Spain
• Otis Air National Guard Base, Massachusetts, USA
• Grant County International Airport, Washington, USA
• Pease ANGB, New Hampshire, USA
• Hao Airport, French Polynesia
• AFB Hoedspruit, South Africa
• Bermuda International Airport (former NAS Bermuda)
• King Khalid International Airport, Riyadh, Saudi Arabia
• Kinshasa International Airport, Congo-Kinshasa
• Cologne Bonn Airport, Germany
• Lajes Field, Azores, Portugal
• Lincoln Airport, Nebraska, USA
• Mountain Home Air Force Base, Idaho, USA
• Naval Air Station Bermuda, Bahamas
• NSA Souda Bay, Crete, Greece
• NSF Diego Garcia, Chagos Archipelago, British Indian Ocean Territory
• Orlando International Airport, Florida
• RAF Fairford, United Kingdom
• Roberts International Airport, Monrovia, Liberia
• Lehigh Valley International Airport, Allentown, PA
• Mataveri International Airport, Hanga Roa, Easter Island, Chile
• Halifax International Airport, Halifax, Nova Scotia, Canada
• Ben Guerir Air Base, Morocco
• Columbus Air Force Base, Mississippi

Fleet history

Below is a list of major events in the Space Shuttle orbiter fleet.

Retirement

In 2010, the Space Shuttle, after nearly 30 years of duty, will be retired from service. To fill the void left behind by the Shuttle's retirement a new spacecraft will be developed that will not only be capable of ferrying passengers and cargo to the ISS, but also beyond Earth's orbit to other worlds. This spacecraft has tentatively been dubbed the Crew Exploration Vehicle and the project has been dubbed Project Constellation. Atlantis will be the first of NASA's three space shuttles to be retired, most likely in 2008, as the shuttle program winds down in four years. The next-generation vehicles, the new Ares/Orion vehicles, won’t be operational until 2015 at the earliest. Therefore, NASA is confronting the possibility that there will only be Russian crew members on the International Space Station for that period of time. Under this dilemma, congressmen are discussing the possibility to postpone the retirement of the space shuttles. One of the proposals, which would cost about $10 billion, would have the shuttles make six or seven additional flights between 2010 and 2013 and speed up development of the Orion ships to be ready by then. A second proposal would keep the shuttles flying until 2015 and leave Orion's schedule alone.

See also

• Comparison of heavy lift launch systems
• Space Shuttle program
• Criticism of the Space Shuttle program
• GRiD Compass the early laptop carried aboard the shuttle.
• Human spaceflight
• List of human spaceflights
• NASA Space Shuttle decision
• Orbiter Processing Facility
• Shuttle Derived Launch Vehicle
• Shuttle SERV
• Space disaster
• Space exploration
• Space Shuttle abort modes
• Space Shuttle crews
• Shuttle Training Aircraft

Fiction and games

• Space shuttles in fiction
• Space Shuttle Mission 2007, latest Space Shuttle simulator for Windows XP and Vista PCs.
• Orbiter, a freeware simulator that allows users to fly various spacecraft including the shuttle.
• Space Shuttle America
• Shuttle, a Space Shuttle simulator for PC, Amiga & Atari ST.
• X-Plane, a flight simulator that allows players to fly the Space Shuttle's re-entry phase.

Physics

• Atmospheric reentry
• Lifting body
• Reusable launch system
• Single-stage-to-orbit

Similar spacecraft

• Dyna-soar
• EADS Phoenix
• Hermes
• HOPE-X
• Kliper
• Military space shuttle
• Orion (Project Constellation)
• Soviet space shuttle Buran
• Lockheed Martin X-33
• DIRECT, a shuttle-derived vehicle proposed as an alternative for Project Constellation

References

Further reading

• Reference manual
• How The Space Shuttle Works
• NASA Space Shuttle News Reference - 1981 (PDF document)
• Orbiter Vehicles
• Lecture Series on the space shuttle from MIT OpenCourseWare

External links

• NASA Human Spaceflight - Shuttle: Current status of shuttle missions
• Video of current and historical missions (STS-1 thru Current)
• NASA TV: View live streaming of launch and mission coverage
• [news:sci.space.shuttle Space Shuttle Newsgroup - sci.space.shuttle]
• List of all Shuttle Landing Sites
• Map of Landing Sites
• Official NASA Human Space Flight Orbital Tracking system
• Congressional Research Service (CRS) Reports regarding the Space Shuttle
• Weather criteria for shuttle launch
• Newer images, audio, and video of the space shuttle program
• Older images of the space shuttle program
• The maiden launch of the space shuttle (Google Video)
• NASA Shuttle Gallery
• Different details and perspectives from the orbiter (Gallery drafts.de) (ger.)
• 04/16/07: Consolidated Launch Manifest: Space Shuttle Flights and ISS Assembly Sequence.
• NASA Further Updates Launch Schedule.
• GRiD Compass History at Hrothgar's Cool Old Junk Page
• NASA History Series Publications (many of which are on-line)
• Space Shuttle Endeavour Pictures at the ISS

NASA's Space Shuttle, officially called Space Transportation System (STS), is the United States government's current manned launch vehicle. The winged Space Shuttle orbiter is launched vertically, usually carrying five to seven astronauts (although eight have been carried) and up to 50,000 lb (22 700 kg) of payload into low earth orbit. When its mission is complete, the Shuttle can independently move itself out of orbit (by means of its maneuvering thrusters) and re-enter the Earth's atmosphere. During descent and landing, the Shuttle Orbiter acts as a glider and makes a completely unpowered landing.

The Shuttle is the only winged manned spacecraft to achieve orbit and land, and the only reusable space vehicle that has ever made multiple flights into orbit. Its missions involve carrying large payloads to various orbits (including segments to be added to the International Space Station), providing crew rotation for the International Space Station, and performing service missions. The orbiter can also recover satellites and other payloads from orbit and return them to Earth, but its use in this capacity is rare. However, the Shuttle has previously been used to return large payloads from the ISS to Earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each vehicle was designed with 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 by 2010, after which it will be retired from service, and eventually replaced by the new Orion spacecraft (now expected to be ready in about 2014). On Saturday, August 30th, 2008 it was reported by the Orlando Sentinel that than an internal NASA E-Mail was leaked which stated NASA director Michael Griffin ordered a study to determine if the shuttle could fly until 2015. "We want to focus on helping bridge the gap of U.S. vehicles traveling to the ISS (International Space Station) as efficiently as possible," wrote John Coggeshall, manager of manifest and schedules at Johnson Space Center. The letter's authenticity was confirmed by NASA.

Conception

Even before the Apollo 11 moon landing in 1969, NASA began early studies of space shuttle designs. The early studies beginning in October, 1968 were denoted "Phase A." Further studies resulted in "Phase B" in June 1970. These plans were much more detailed and more specific.

In 1969 President Richard Nixon formed the Space Task Group, chaired by vice president Spiro T. Agnew. This group evaluated the shuttle studies to date, and recommended a national space strategy including building a space shuttle.

In October 1969, at a Space Shuttle symposium held in Washington, George Mueller (NASA's deputy administrator) presented opening remarks:

The goal we have set for ourselves is the reduction of the present costs of operating in space from the current figure of $1,000 a pound for a payload delivered in orbit by the Saturn V, down to a level of somewhere between $20 and $50 a pound. By so doing we can open up a whole new era of space exploration. Therefore, the challenge before this symposium and before all of us in the Air Force and NASA in the weeks and months ahead is to be sure that we can implement a system that is capable of doing just that. Let me outline three areas which, in my view, are critical to the achievement of these objectives. One is the development of an engine that will provide sufficient specific impulse, with adequate margin to propel its own weight and the desired payload. A second technical problem is the development of the reentry heat shield, so that we can reuse that heat shield time after time with minimal refurbishment and testing. The third general critical development area is a checkout and control system which provides autonomous operation by the crew without major support from the ground and which will allow low cost of maintenance and repair. Of the three, the latter may be a greater challenge than the first two.

The 1972 NASA/GAO REPORT TO THE CONGRESS, Cost-Benefit Analysis Used In Support Of The Space Shuttle Program states:

NASA has proposed that a space shuttle be developed for U.S. Space Transportation needs for NASA, the Department of Defense (DOD), and other users in the 1980s.The primary objective of the Space Shuttle Program is to provide a new space transportation capability that will:

• reduce substantially the cost of space operations and
• provide a future capability designed to support a wide range of scientific, defense, and commercial uses.

Development

The Space Shuttle program was formally launched on January 5, 1972, when President Nixon announced that NASA would proceed with the development of a reusable Space Shuttle system. The final design was less costly to build and less technically ambitious than earlier fully reusable designs. The initial design parameters included a larger external fuel tank, which would have been carried to orbit, where it could be used as a section of a space station, but this idea was killed due to budgetary and political considerations.

The prime contractor for the program was North American Aviation (later Rockwell International, now Boeing), the same company responsible for building the Apollo Command/Service Module. The contractor for the Space Shuttle Solid Rocket Boosters was Morton Thiokol (now part of Alliant Techsystems), for the external tank, Martin Marietta (now Lockheed Martin), and for the Space shuttle main engines, Rocketdyne (now Pratt & Whitney Rocketdyne, part of United Technologies).

The first complete orbiter was originally planned to be named Constitution, but a massive write-in campaign from fans of the Star Trek television series convinced the White House to change the name to Enterprise. Amid great fanfare, the Enterprise was rolled out on September 17, 1976, and later conducted a successful series of glide-approach and landing tests that were the first real validation of the design.

The first fully functional Shuttle Orbiter was the Columbia, built in Palmdale, California. It was delivered to Kennedy Space Center on March 25, 1979, and was first launched on April 12, 1981—the 20th anniversary of Yuri Gagarin's space flight—with a crew of two. Challenger was delivered to KSC in July 1982, Discovery in November 1983, and Atlantis in April 1985. Challenger was destroyed during ascent due to O-Ring failure on the right SRB on January 28, 1986, with the loss of all seven astronauts on board. Endeavour was built to replace Challenger (using spare parts originally intended for the other orbiters) and delivered in May 1991; it was first launched a year later. Seventeen years after Challenger, Columbia was lost, with all seven crew members, during reentry on February 1, 2003, and has not been replaced. Out of the five fully functional shuttle orbiters built, three remain.

Shuttle applications

• Crew rotation and servicing of Mir and the International Space Station (ISS)
• Manned servicing missions, such as to the Hubble Space Telescope (HST)
• Manned experiments in Low Earth orbit (LEO)
• Carried to LEO:
• Large satellites — including the HST
• Components for the construction of the ISS
• Supplies in Spacehab modules or Multi-Purpose Logistics Modules
• Carried satellites with a booster, the Payload Assist Module (PAM-D) or the Inertial Upper Stage (IUS), to the point where the booster sends the satellite to:
• A higher Earth orbit; these have included:
• Chandra X-ray Observatory
• Many TDRS satellites
• Two DSCS-III (Defense Satellite Communications System) communications satellites in one mission
• A Defense Support Program satellite
• An interplanetary orbit; these have included:
• Magellan probe
• Galileo spacecraft
• Ulysses probe

Flight statistics

Other shuttles

Disasters

As of April 2008, two Shuttles have been destroyed in 123 missions, both with the loss of the entire crew (14 astronauts total):

• Challenger — lost 73 seconds after liftoff, STS-51-L, January 28, 1986
• Columbia — lost approximately 16 minutes before its expected landing, STS-107, February 1, 2003

This gives a 2% death rate per astronaut-flight, and an average failure rate of nearly 1 in every 60 missions. The original disaster potential, though disaster is not defined as fatal or non-fatal, was estimated during Shuttle development at one every 75 missions. 87 successful missions were flown between STS-51-L and STS-107.

Current status

The second "Return to Flight" mission, STS-121, launched on July 4, 2006, at 2:37:55 p.m. (EDT), after two previous launches were scrubbed because of lingering thunderstorms and high winds around the launch pad and the launch took place despite objections from its chief engineer and safety head. A five-inch (13 cm) crack in the foam insulation of the external tank gave cause for concern; however, the Mission Management Team gave the go for launch. This mission increased the ISS crew to three. Discovery touched down successfully on July 17, 2006 at 9:14:43 a.m. (EDT) on Runway 15 at Kennedy Space Center.

Following the success of STS-121, eight missions have been completed without major foam problems, and the construction of ISS has resumed. (During the STS-118 mission in August 2007, the orbiter was again struck by a foam fragment on liftoff, but this was a very small damage compared to the damage sustained to Columbia.)

On October 31, 2006, NASA announced approval of a shuttle servicing mission to the Hubble Space Telescope. This mission is designated STS-125 and is scheduled for October 8, 2008.

The Shuttle program is scheduled for mandatory retirement in 2010. The Shuttle's planned successor is Project Constellation with its Ares I and Ares V launch vehicles and the Orion Spacecraft. NASA plans to launch 8 to 10 more shuttle missions before the program ceases.

U.S. Representative Dave Weldon has introduced H.R. 4837, known as the SPACE Act. This legislation would keep the Space Shuttle flying past 2010 at a reduced rate until the Orion spacecraft is ready to replace it. It would allow both the Alpha Magnetic Spectrometer as well as the completed-but-unused Centrifuge Accommodations Module to be launched to the ISS, which the current schedule does not allow. The bill is currently in committee.

In an internal e-mail sent August 18, 2008 to NASA managers (published September 6, 2008 in the Orlando Sentinel), Griffin flatly stated his belief that the current US administration is has made no viable plan for US crews to participate in the ISS beyond 2011, and that OMB and OSTP are actually seeking its demise. Griffin believes the only reasonable solution is to extend the operation of the Space Shuttle beyond 2010, but notes that Executive Policy (ie, the White House) is firm that there will be no extension of the shuttle retirement date, and thus no US capability to launch crews into orbit until the Ares I/Orion system becomes operational in 2014 at the very earliest. He does not see purchase of Russian launches for NASA crews as politically viable following the 2008 South Ossetia war, and hopes the new US administration will resolve the issue in 2009 by extending shuttle operations beyond 2010.

From September 2005 until early 2008, the manager of the Space Shuttle program was Wayne Hale. Hale then became NASA's deputy associate administrator for strategic partnerships. John Shannon, who had been Hale's deputy since November 2005, succeeded him as the Space Shuttle Program manager.

Costs

Per-launch costs can be measured by dividing the total cost over the life of the program (including buildings, facilities, training, salaries, etc) by the number of launches. With 115 missions (as of 6 August 2006), and a total cost of $150 billion ($145 billion as of early 2005 + $5 billion for 2005, this gives approximately $1.3 billion per launch. Another method is to calculate the incremental (or marginal) cost differential to add or subtract one flight — just the immediate resources expended/saved/involved in that one flight. This is about $60 million.

Early cost estimates of $118 per pound ($260/kg) of payload were based on marginal or incremental launch costs, and based on 1972 dollars and assuming a 65,000 pound (30 000 kg) payload capacity. Correcting for inflation, this equates to roughly $36 million incremental per launch costs. Compared to this, today's actual incremental per launch costs are about two thirds more, or $60 million per launch.

Criticism

After both the Challenger disaster and the Columbia disaster, high profile boards convened to investigate the accidents with both committees returning praise and serious critiques to the program and NASA management. One of the most famous of these criticisms came from Nobel Prize winner Richard Feynman.

Terrestrial transportation vehicles

• The Crawler-Transporter carries the Mobile Launcher Platform and the Space Shuttle from the Vehicle Assembly Building to Launch Complex 39.
• The Shuttle Carrier Aircraft are two modified Boeing 747s. Either can fly an orbiter from alternative landing sites back to Cape Canaveral.
• A 36-wheeled transport trailer, the Orbiter Transfer System, originally built for the U.S. Air Force's launch facility at Vandenberg Air Force Base in California (since then converted for Delta IV rockets) that would transport the orbiter from the landing facility to the launch pad, which allowed both "stacking" and launch without utilizing a separate VAB-style building and crawler-transporter roadway. Prior to the closing of the Vandenberg facility, orbiters were transported from the OPF to the VAB on its undercarriage, only to be raised when the orbiter was being lifted for attachment to the SRB/ET stack. The trailer allows the transportation of the orbiter from the OPF to either the SCA-747 "Mate-Demate" stand or the VAB without placing any additional stress on the undercarriage.
• The Crew Transport Vehicle (CTV), a modified airport "People Mover", is used to assist astronauts to egress from the orbiter after landing. Upon entering the CTV, astronauts can take off their launch and re-entry suits then proceed to chairs and beds for medical checks before being transported back to the crew quarters in the Operations and Checkout Building.
• The AstroVan is used to transport astronauts from the crew quarters in the Operations and Checkout Building to the launch pad on launch day. It is also used to transport astronauts back again from the Crew Transport Vehicle at the Shuttle Landing Facility.

See also

• Human spaceflight
• List of human spaceflights
• List of space shuttle missions
• NASA Space Shuttle decision
• Shuttle Derived Launch Vehicle
• Shuttle SERV
• Space disaster
• Space exploration
• Space Shuttle abort modes
• Space Shuttle crews

Fiction

• Space shuttles in fiction
• 'Shuttle' Game DOS-based shuttle simulator from the 1990s.
• Orbiter a freeware simulator that allows users to fly various spacecraft including the Shuttle.

Physics

• Atmospheric reentry
• Lifting body
• Reusable launch system
• Single-stage-to-orbit

Similar spacecraft

• EADS Phoenix
• Hermes
• HOPE-X
• Kliper
• Military space shuttle
• Project Constellation
• Shuttle Buran program
• Martin Marietta Spacemaster

Notes

Further reading

• Reference manual
• NASA Space Shuttle News Reference - 1981 (PDF document)
• Orbiter Vehicles
• Shuttle Program Funding 1992 - 2002
• Shuttle development costs and history, CAIB transcript 4-23-03
• R.A.Pielke, "Space Shuttle Value open to Interpretation", Aviation Week Magazine, issue 26. July 1993, p.57 (PDF file):

External links

• Official NASA Mission Site
• NASA Johnson Space Center Space Shuttle Site
• Official Space Shuttle Mission Archives
• NASA Space Shuttle Multimedia Gallery & Archives
• Shuttle audio, video, and images – searchable archives from STS-67 (1995) to present
• Kennedy Space Center Media Gallery – video/audio/photos of shuttle pre-launch, launch, landing, and behind-the-scenes shuttle processing activities
• Congressional Research Service (CRS) Reports regarding the Space Shuttle
• U.S. Space Flight History: Space Shuttle Program
• Weather criteria for Shuttle launch
• Consolidated Launch Manifest: Space Shuttle Flights and ISS Assembly Sequence