Space Shuttle Endeavour: Spacecraft profile

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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.

Space Shuttle Endeavour STS-113: STS-113 Space Shuttle Endeavour landing at KSCSpace Shuttle Endeavour STS-113: STS-113 Space Shuttle Endeavour landing at KSC

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.

Space Shuttle Endeavour (Orbiter Vehicle Designation: OV-105) 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 Atlantis.) Endeavour was the fifth and final NASA space shuttle to be built.

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 Endeavour STS-111: STS-111 Endeavour launch from Launch Pad 39ASpace Shuttle Endeavour STS-111: STS-111 Endeavour launch from Launch Pad 39A

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.

NASA has announced that the Space Shuttle, which was first launched in 1981, will be retired after mission STS-133 in 2010. From 2015 on it will be replaced by Orion, a new vehicle designed to take humans to the Moon and beyond along with its partner rockets, the Ares I and Ares V Rockets, although keeping it flying until Ares is ready has not been ruled out. Michael D. Griffin has stated "The shuttle is an inherently risky design. We currently assess the per-mission risk as about one in 75 of having a fatal accident. If one were to ... fly the shuttle for an additional five years - say two missions a year - the risk would be about one in 12 that we would lose another crew." Since Orion is meant primarily for manned space flights, ESA's Automated Transfer Vehicle, with its 7,667 kg payload, has been suggested as an alternative for tasks like supplying space stations.

Space Shuttle Endeavour STS-113: STS-113 Endeavour rollout to Launch Complex 39ASpace Shuttle Endeavour STS-113: STS-113 Endeavour rollout to Launch Complex 39A

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".

Space Shuttle Endeavour STS-126: Under a waning full moon at NASA's Kennedy Space Center, Space Shuttle Endeavour makes its way to the launch pad atop the mobile launcher platform and massive crawler-transporter. For the first time since July 2001, two shuttles are on the launch pads at the same time at the center. Space Shuttle Endeavour will stand by at pad B in the unlikely event that a rescue mission is necessary during space shuttle Atlantis' upcoming mission to repair NASA's Hubble Space Telescope. After Space Shuttle Endeavour is cleared from its duty as a rescue spacecraft, it will be moved to Launch Pad 39A for the STS-126 mission to the International Space Station. Image credit: NASA/Dimitri Gerondidakis.Space Shuttle Endeavour STS-126: Under a waning full moon at NASA's Kennedy Space Center, Space Shuttle Endeavour makes its way to the launch pad atop the mobile launcher platform and massive crawler-transporter. For the first time since July 2001, two shuttles are on the launch pads at the same time at the center. Space Shuttle Endeavour will stand by at pad B in the unlikely event that a rescue mission is necessary during space shuttle Atlantis' upcoming mission to repair NASA's Hubble Space Telescope. After Space Shuttle Endeavour is cleared from its duty as a rescue spacecraft, it will be moved to Launch Pad 39A for the STS-126 mission to the International Space Station. Image credit: NASA/Dimitri Gerondidakis.

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 Endeavour STS-113: STS-113 Endeavour rollover to VAB in preparation for launchSpace Shuttle Endeavour STS-113: STS-113 Endeavour rollover to VAB in preparation for launch

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.

Space Shuttle Endeavour STS-126: After rollout from the Vehicle Assembly Building at NASA's Kennedy Space Center, Space Shuttle Endeavour is secure on the launch pad. First motion from the VAB was at 11:15 p.m. Sept. 18. At left of the shuttle is the open rotating service structure with the payload changeout room revealed. Behind it is the fixed service structure with the 80-foot lightning mast on top. Space Shuttle Endeavour is set to launch on mission STS-126 to the International Space Station. Image credit: NASA/Jim Grossmann.Space Shuttle Endeavour STS-126: After rollout from the Vehicle Assembly Building at NASA's Kennedy Space Center, Space Shuttle Endeavour is secure on the launch pad. First motion from the VAB was at 11:15 p.m. Sept. 18. At left of the shuttle is the open rotating service structure with the payload changeout room revealed. Behind it is the fixed service structure with the 80-foot lightning mast on top. Space Shuttle Endeavour is set to launch on mission STS-126 to the International Space Station. Image credit: NASA/Jim Grossmann.

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.

Space Shuttle Endeavour STS-113: STS-113 Space Shuttle Endeavour landing at KSCSpace Shuttle Endeavour STS-113: STS-113 Space Shuttle Endeavour landing at KSC

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.

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.

Space Shuttle Endeavour STS-111: STS-111 Endeavour launch from Launch Pad 39ASpace Shuttle Endeavour STS-111: STS-111 Endeavour launch from Launch Pad 39A

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.

Space Shuttle Endeavor: History

The United States Congress authorized the construction of Endeavour in 1987 to replace Challenger, which was lost in an accident in 1986. Structural spares from the construction of Discovery and Atlantis, two of the three remaining operating shuttles at the time, were used in its assembly. The decision to build Endeavour was favored over refitting Enterprise on cost grounds.

Endeavour was named through a national competition involving students in elementary and secondary schools. Entries included an essay about the name, the story behind it and why it was appropriate for a NASA shuttle, and the project that supported the name. Endeavour was the most popular entry, accounting for almost one-third of the state-level winners. For example, Utah's state level winner, Nolan Butcher, a sixth grade student from Nibley Park Elementary school located in Salt Lake City Utah, selected Endeavour because some definitions of the word mean to be bold and put forth great effort. The national winners were Senatobia Middle School in Senatobia, Miss., in the elementary division and Tallulah Falls School in Tallulah Falls, Ga., in the upper school division. The national winners were selected based on the quality of the project submitted with their entries. They were honored at several ceremonies in Washington, D.C., including a White House ceremony where then-President George H.W. Bush presented awards to each school.

The orbiter is named after HM Bark Endeavour, the ship commanded by 18th century explorer James Cook; the name also honored Endeavour, the Command Module of Apollo 15. This is why the name is spelled in the British English manner, rather than the American English spelling of "Endeavor." This has caused confusion, most notably when NASA themselves misspelled a sign on the launch pad in 2007.

Endeavour was delivered by Rockwell International in May 1991 and first launched a year later, in May 1992, on STS-49. Rockwell International claimed that it had made no profit on Space Shuttle Endeavour, despite it costing $2.2 billion USD. On its first mission, it captured and redeployed the stranded INTELSAT VI communications satellite.

In 1993, it made the first service mission to the Hubble Space Telescope. Endeavour was withdrawn from service for eight months in 1997 for a retrofit, including installation of a new airlock. In December 1998, it delivered the Unity Module to the International Space Station. Endeavour completed its latest Orbiter Major Modification period, which began in December 2003, and ended on Thursday, October 6, 2005. During this time, the Orbiter received major hardware upgrades, including a new, multi-functional, electronic display system, often referred to as glass cockpit, and an advanced GPS receiver, along with safety upgrades recommended by the Columbia Accident Investigation Board (CAIB) for Shuttle return to flight after the disintegration of sister-ship Columbia during re-entry on February 1, 2003.

The STS-118 mission, the first for Endeavour following a lengthy refit, included astronaut Barbara Morgan, formerly assigned to the Educator Astronaut program, but now a full member of the Astronaut Corps, as part of the crew. Morgan was the backup for Christa McAuliffe on the ill-fated STS-51-L mission.

Upgrades and features

Endeavour features new hardware designed to improve and expand orbiter capabilities. Most of this equipment was later incorporated into the other two orbiters during out-of-service major inspection and modification programs. Endeavour's upgrades include:

* A 40-foot (12 m) diameter drag chute that is expected to reduce the orbiter's rollout distance by 1,000 to 2,000 feet (300 to 600 m).

* The plumbing and electrical connections needed for Extended Duration Orbiter (EDO) modifications to allow up to 28-day missions (although a 28-day mission has never yet been attempted; the current record is 17 days, which was set by Columbia).

* Updated avionics systems that include advanced general purpose computers, improved inertial measurement units and tactical air navigation systems, enhanced master events controllers and multiplexer-demultiplexers, a solid-state star tracker and improved nose wheel steering mechanisms.

* An improved version of the Auxiliary Power Units (APUs) that provide power to operate the Shuttle's hydraulic systems.

Modifications resulting from a 2005-2006 refit of Endeavour include:

* The Station-to-Shuttle Power Transfer System (SSPTS), which converts 8 kilowatts of DC power from the ISS main voltage of 120VDC to the orbiter bus voltage of 28VDC. This upgrade will allow Endeavour to remain on-orbit while docked at ISS for an additional 3- to 4-day duration. The corresponding power equipment was added to the ISS during the STS-116 station assembly mission, and Endeavour flew with SSPTS capability during STS-118.

Decommissioning of Space Shuttle Endeavour

According to NASA, Space Shuttle Endeavour will be decommissioned in 2010, after 18 years of service, along with Discovery and Atlantis. NASA expects to have the Orion spacecraft ready no later than 2014. Based on the current (as of August 2007) consolidated launch manifest, Endeavour may be the last Orbiter to fly, contingent on the optional STS-133 mission to the International Space Station, which will carry the final components in the ISS assembly sequence, the EXPRESS Logistics Carrier ELC5 and ELC1, to orbit.

Source: wikipedia.org

More photos: Space Shuttle Endeavour photo gallery

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