Space Shuttle Atlantis: Spacecraft profile

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Space Shuttle Atlantis (Orbiter Vehicle Designation: OV-104) is one of the three currently operational orbiters in the Space Shuttle fleet of NASA, the space agency of the United States. The other two are Discovery and Endeavour.

Space Shuttle Atlantis STS-122: Space Shuttle Atlantis with its crew of seven astronaut rise from Launch Pad 39A at NASA's Kennedy Space Center to start the STS-122 mission to the International Space Station. Photo credit: NASA/Jim GrossmannSpace Shuttle Atlantis STS-122: Space Shuttle Atlantis with its crew of seven astronaut rise from Launch Pad 39A at NASA's Kennedy Space Center to start the STS-122 mission to the International Space Station. Photo credit: NASA/Jim Grossmann

Atlantis was the fourth operational shuttle built. "Atlantis" is named after a two-masted sailing ship that operated from 1930 to 1966 for the Woods Hole Oceanographic Institute.

In early 2008, NASA officials decided to keep Atlantis flying until 2010, the projected end of the Shuttle program. This reversed a previous decision to retire Atlantis in 2008.

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.

Space Shuttle Atlantis STS-122: (7 Feb. 2008) --- The launch of the Space Shuttle Atlantis (STS-122) is seen through the louvered windows of the Launch Control Center Feb. 7, 2008, at the Kennedy Space Center in Cape Canaveral, Fla. The Shuttle lifted off from launch pad 39A at 2:45 p.m.(EST). Photo Credit: NASA/Bill IngallsSpace Shuttle Atlantis STS-122: (7 Feb. 2008) --- The launch of the Space Shuttle Atlantis (STS-122) is seen through the louvered windows of the Launch Control Center Feb. 7, 2008, at the Kennedy Space Center in Cape Canaveral, Fla. The Shuttle lifted off from launch pad 39A at 2:45 p.m.(EST). Photo Credit: NASA/Bill Ingalls

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.

Space Shuttle Atlantis STS-122: 8 Feb. 2008) --- Backdropped against a cloud-covered portion of Earth, the European Space Agency's Columbus laboratory and associated ESA hardware sit in the aft section of Space Shuttle Atlantis' cargo bay on the eve of the shuttle's scheduled docking to the International Space Station. The addition of Columbus to the orbital outpost is one of the primary tasks of the STS-122 mission.Space Shuttle Atlantis STS-122: 8 Feb. 2008) --- Backdropped against a cloud-covered portion of Earth, the European Space Agency's Columbus laboratory and associated ESA hardware sit in the aft section of Space Shuttle Atlantis' cargo bay on the eve of the shuttle's scheduled docking to the International Space Station. The addition of Columbus to the orbital outpost is one of the primary tasks of the STS-122 mission.

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 15 feet (4.6 m) by 60 feet (18.3 m) 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).

Space Shuttle Atlantis STS-122: (7 Feb. 2008) --- The Space Shuttle Atlantis and its seven-member STS-122 crew head toward Earth-orbit and a scheduled link-up with the International Space Station (ISS). Liftoff from Kennedy Space Center's launch pad 39A occurred at 2:45 p.m. (EST). The launch is the third attempt for Atlantis since December 2007 to carry the European Space Agency's (ESA) Columbus laboratory to the station. During the 11-day mission, the crew's prime objective is to attach the laboratory to the Harmony module, adding to the station's size and capabilities. Onboard are astronauts Steve Frick, commander; Alan Poindexter, pilot; Leland Melvin, Rex Walheim, ESA's Hans Schlegel, Stanley Love and ESA's Leopold Eyharts, all mission specialists. Eyharts will join Expedition 16 in progress to serve as a flight engineer aboard the ISS.Space Shuttle Atlantis STS-122: (7 Feb. 2008) --- The Space Shuttle Atlantis and its seven-member STS-122 crew head toward Earth-orbit and a scheduled link-up with the International Space Station (ISS). Liftoff from Kennedy Space Center's launch pad 39A occurred at 2:45 p.m. (EST). The launch is the third attempt for Atlantis since December 2007 to carry the European Space Agency's (ESA) Columbus laboratory to the station. During the 11-day mission, the crew's prime objective is to attach the laboratory to the Harmony module, adding to the station's size and capabilities. Onboard are astronauts Steve Frick, commander; Alan Poindexter, pilot; Leland Melvin, Rex Walheim, ESA's Hans Schlegel, Stanley Love and ESA's Leopold Eyharts, all mission specialists. Eyharts will join Expedition 16 in progress to serve as a flight engineer aboard the ISS.

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.

Space Shuttle Atlantis STS-122: Platforms are extended toward space shuttle Atlantis from the fixed service structure, at left, as processing begins following the shuttle's arrival at Launch Pad 39A. Photo credit: NASA/Kim ShiflettSpace Shuttle Atlantis STS-122: Platforms are extended toward space shuttle Atlantis from the fixed service structure, at left, as processing begins following the shuttle's arrival at Launch Pad 39A. Photo credit: NASA/Kim Shiflett

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.

Current status

Atlantis is currently in the vehicle assemby building following a return from pad 39A due to a delay in mission STS 125

Space Shuttle Atlantis STS-122: (7 Feb. 2008) --- The Space Shuttle Atlantis and its seven-member STS-122 crew head toward Earth-orbit and a scheduled link-up with the International Space Station (ISS). Liftoff from Kennedy Space Center's launch pad 39A occurred at 2:45 p.m. (EST). The launch is the third attempt for Atlantis since December 2007 to carry the European Space Agency's (ESA) Columbus laboratory to the station. During the mission, the crew's prime objective is to attach the laboratory to the Harmony module, adding to the station's size and capabilities. Onboard are astronauts Steve Frick, commander; Alan Poindexter, pilot; Leland Melvin, Rex Walheim, ESA's Hans Schlegel, Stanley Love and ESA's Leopold Eyharts, all mission specialists. Eyharts will join Expedition 16 in progress to serve as a flight engineer aboard the ISS.Space Shuttle Atlantis STS-122: (7 Feb. 2008) --- The Space Shuttle Atlantis and its seven-member STS-122 crew head toward Earth-orbit and a scheduled link-up with the International Space Station (ISS). Liftoff from Kennedy Space Center's launch pad 39A occurred at 2:45 p.m. (EST). The launch is the third attempt for Atlantis since December 2007 to carry the European Space Agency's (ESA) Columbus laboratory to the station. During the mission, the crew's prime objective is to attach the laboratory to the Harmony module, adding to the station's size and capabilities. Onboard are astronauts Steve Frick, commander; Alan Poindexter, pilot; Leland Melvin, Rex Walheim, ESA's Hans Schlegel, Stanley Love and ESA's Leopold Eyharts, all mission specialists. Eyharts will join Expedition 16 in progress to serve as a flight engineer aboard the ISS.

History

The first flight of Atlantis, STS-51-J, took place during October 1985. The mission was one of five flights during which crews conducted classified military activities. Atlantis flew one other mission, STS-61-B, before the Space Shuttle Challenger disaster temporarily grounded the shuttle fleet in 1986.

Atlantis was used for ten flights between 1988 and 1992. Two of these, both flown in 1989, deployed planetary probes (Magellan on STS-30 and Galileo on STS-34). Another mission, STS-37 flown in 1991, deployed the Compton Gamma Ray Observatory.

Beginning in 1995 with STS-71, Atlantis made seven straight flights to Mir (a Russian space station) as part of the Shuttle-Mir Program.

After STS-86, the seventh flight of Atlantis to Mir, the orbiter underwent a series of refitting operations. From November 1997 to July 1999, about 165 modifications were made to Atlantis, including the installation of the Multifunction Electronic Display System, or glass cockpit. In May 2000 Atlantis returned to service for STS-101, a flight to the International Space Station (ISS).

The first mission flown by Atlantis after the Space Shuttle Columbia disaster was STS-115, conducted during September 2005. The mission carried the P3/P4 truss segments and solar arrays to the ISS.

The longest mission flown using Atlantis -- STS-117 during June 2007 -- lasted almost 14 days. Because Atlantis is not equipped to take advantage of the Station-to-Shuttle Power Transfer System, missions cannot be extended by making use of power provided by ISS.

NASA had planned to withdraw Atlantis from service in 2008, as the orbiter would have been due to undergo the scheduled Orbiter Maintenance Down Period (OMDP); this is a major program of refit and maintenance which would have lasted at least a year. Because of the final retirement of the shuttle fleet in 2010, this was deemed uneconomic. It was planned that Atlantis would be kept in near flight condition to be used as a parts hulk for Discovery and Endeavour. However, with the significant planned flight schedule up to 2010, the decision was taken to extend the time between OMDPs, allowing Atlantis to be retained for operations. Atlantis has been swapped for one flight of each of the other orbiters in the flight manifest. As of March 2008, Atlantis is now projected to fly at least three more missions prior to the end of the shuttle program:

* STS-125 - final Hubble servicing mission

* STS-128 - ISS logistics mission (Multi-Purpose Logistics Module Leonardo)

* STS-131 - ISS logistics mission (Multi-Purpose Logistics Module Raffaello)

Flights

Atlantis has completed 28 flights, spent 220.40-days in space, completed 3,468 orbits, and flown 89,908,732 nautical miles (166,510,972 km) in total, as of September 2006. Among the five Space Shuttles flown in space, Atlantis has conducted a subsequent mission in the shortest time after the previous mission when it launched in November, 1985, only 50 days after its previous mission.

Aging

NASA announced that 24 helium and nitrogen gas tanks, named Composite Overwrap Pressure Vessels, in Atlantis are older than their designed lifetime (designed for 10 years, later cleared for another 10 years but in service now for 22 years). NASA said it cannot guarantee any longer that the vessels on Atlantis will not burst or explode under full pressure. Therefore, the vessels will only be at 80 percent pressure as close to the launch countdown as possible, and the launch pad will be cleared of all but essential personnel when pressure is increased to 100 percent. A launch pad explosion could damage parts of the shuttle and even wound or kill ground personnel. An in-flight failure to the vessels could even result in the loss of the orbiter and its crew. Because the original vendor is no longer available, the vessels cannot be rebuilt before 2010, when the shuttles are scheduled to be retired. NASA analyses originally assumed that the vessels would leak before they burst, but new tests showed that they would burst before they leak. The new launch procedure, of clearing the launch pad of all but the essential personnel and pressurizing the tanks to 100 percent as late as possible, will now be conducted during the remaining Atlantis launches if no other resolution is found. Atlantis will have to fly at least one more time in this setting. It is unclear, but possible, that Discovery, which will launch another five or six times, has the same problems and if the same launch procedure needs to be conducted with Discovery. Since Endeavour, which will launch another six or seven times, was built much later, around 1990, it is possible that Endeavour does not have the same problem.

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