Space Shuttle orbiter

Space Shuttle forward reaction control thrusters

The Reaction Control System (RCS) was composed of 44 small liquid-fueled rocket thrusters and their very sophisticated fly-by-wire flight control system, which utilized computationally intensive digital Kalman filtering. This control system carried out the usual attitude control along the pitch, roll, and yaw axes during all of the flight phases of launching, orbiting, and re-entry. This system also executed any needed orbital maneuvers, including all changes in the orbit's altitude, orbital plane, and eccentricity. These were all operations that required more thrust and impulse than mere attitude control.

The forward rockets of the Reaction Control System, located near the nose of the Space Shuttle orbiter, included 14 primary and two vernier RCS rockets. The aft RCS engines were located in the two Orbital Maneuvering System (OMS) pods at the rear of the orbiter, and these included 12 primary (PRCS) and two vernier (VRCS) engines in each pod. The PRCS system provided the pointing control of the Orbiter, and the VRCS was used for fine maneuvering during the rendezvous, docking, and undocking maneuvers with the International Space Station, or formerly with the Russian Mir space station. The RCS also controlled the attitude of the orbiter during most of its re-entry into the Earth's atmosphere – until the air became dense enough that the rudder, elevons and body flap became effective.[2]

During the early design process of the orbiter, the forward RCS thrusters were to be hidden underneath retractable doors, which would open once the orbiter reached space. These were omitted in favor of flush-mounted thrusters for fear that the RCS doors would remain stuck open and endanger the crew and orbiter during re-entry.[3]

Space Shuttle glass cockpit

A window on Endeavour's aft flight deck

The orbiter crew cabin consisted of three levels: the flight deck, the mid-deck, and the utility area. The uppermost of these was the flight deck, in which sat the Space Shuttle's commander and pilot, with up to two mission specialists seated behind them. The mid-deck, which was below the flight deck, had three more seats for the rest of the crew members.

The galley, toilet, sleep locations, storage lockers, and the side hatch for entering and exiting the orbiter were also located on the mid-deck, as well as the airlock. The airlock had an additional hatch into the payload bay. This airlock allowed two or three astronauts, wearing their Extravehicular Mobility Unit (EMU) space suits, to depressurize before a walk in space (EVA), and also to repressurize and re-enter the orbiter at the conclusion of the EVA.

The utility area was located under the floor of the mid-deck and contained air and water tanks in addition to the carbon dioxide scrubbing system.

Atlantis 's main engines during launch

Three Space Shuttle Main Engines (SSMEs) were mounted on the orbiter's aft fuselage in the pattern of an equilateral triangle. These three liquid-fueled engines could be swiveled 10.5 degrees vertically and 8.5 degrees horizontally during the rocket-powered ascent of the orbiter in order to change the direction of their thrust. Hence, they steered the entire Space Shuttle, as well as providing rocket thrust towards orbit. The aft fuselage also housed three auxiliary power units (APU). The APUs chemically converted hydrazine fuel from a liquid state to a gas state, powering a hydraulic pump which supplied pressure for all of the hydraulic system, including the hydraulic sub-system that pointed the three main liquid-fueled rocket engines, under computerized flight control. The hydraulic pressure generated was also used to control all of the orbiter's "flight control surfaces" (the elevons, rudder, speed brake, etc.), to deploy the landing gear of the orbiter, and to retract the umbilical hose connection doors located near the rear landing gear, which supplied the orbiter's SSMEs with liquid hydrogen and oxygen from the external tank.

Two Orbital Maneuvering System (OMS) thrusters were mounted in two separate removable pods on the orbiter's aft fuselage, located between the SSMEs and the vertical stabilizer. The OMS engines provided significant thrust for course orbital maneuvers, including insertion, circularization, transfer, rendezvous, deorbit, abort to orbit, and to abort once around.[4] At lift-off, two solid rocket boosters (SRBs) were used to take the vehicle to an altitude of roughly 140,000 feet.[5]

Electric power for the orbiter's subsystems was provided by a set of three hydrogen-oxygen fuel cells which produced 28 volt DC power and was also converted into 115 volt 400 Hz AC three-phase electric power (for systems that used AC power).[6] These provided power to the entire Shuttle stack (including the SRBs and ET) from T-minus 3m30s up through the end of the mission. The hydrogen and oxygen for the fuel cells was kept in pairs of cryogenic storage tanks in the mid-fuselage underneath the payload bay liner, and a variable number of such tanks could be installed (up to five) depending on the requirements of the mission. The three fuel cells were capable of generating 21 kilowatts of power continuously (or a 15-minute peak of 36 kilowatts) with the orbiter consuming an average of about 14 kilowatts of that power (leaving 7 kilowatts for the payload).

Additionally, the fuel cells provided potable water for the crew during the mission.

The orbiter's computer system consisted of five identical IBM AP-101 avionics computers, which redundantly controlled the vehicle's on-board systems. The specialized HAL/S programming language was used for orbiter systems.[7][8]

Discovery's ventral thermal protection system

The orbiters were protected by Thermal Protection System (TPS) materials (developed by Rockwell Space Systems) inside and out, from the orbiter's outer surface to the payload bay.[9] The TPS protected it from the cold soak of −121 °C (−186 °F) in space to the 1,649 °C (3,000 °F) heat of re-entry.

The orbiter's structure was made primarily from aluminium alloy, although the engine thrust structure was made from titanium alloy. The later orbiters (Discovery, Atlantis and Endeavour) substituted graphite epoxy for aluminum in some structural elements in order to reduce weight. The windows were made of aluminum silicate glass and fused silica glass, and comprised an internal pressure pane, a 1.3-inch-thick (33 mm) optical pane, and an external thermal pane.[10] The windows were tinted with the same ink used to make American banknotes.[11]

Atlantis's landing gear are deployed following STS-122

The Space Shuttle orbiter had three sets of landing gear which emerged downwards through doors in the heat shield. As a weight-saving measure, the gear could not be retracted once deployed. Since any premature extension of the landing gear would very likely have been catastrophic (because it opened through the heat shield layers), the landing gear could only be lowered by manual controls, and not by any automatic system.

Similarly, since the Shuttle landed at high speed and could not abort its landing attempt, the gear had to deploy reliably on the first try every time. The gear were unlocked and deployed by triple redundant hydraulics, with the gear doors actuated by mechanical linkages to the gear strut. If all three hydraulic systems failed to release the landing gear uplocks within one second of the release command, pyrotechnic charges automatically cut the lock hooks and a set of springs deployed the gear.

During landing, the Shuttle nose wheel could be steered with the rudder pedals in the cockpit. During the construction of Space Shuttle Endeavour, an improved nose wheel steering system was developed which allowed easier and better nose wheel steering. After Endeavour's roll-out, the system was installed on the other shuttles except Challenger, during their overhauls in the early 1990s.

The Space Shuttle orbiter did not carry anti-collision lights, navigational lights, or landing lights, because the orbiter always landed in areas that had been specially cleared by both the Federal Aviation Administration and the Air Force. The Orbiter nearly always landed at either Edwards Air Force Base (California) or at the Kennedy Space Center Shuttle Landing Facility (Florida), although one mission – STS-3 – landed at the White Sands Space Harbor in New Mexico. Similar special clearances (no-fly zones) were also in effect at potential emergency landing sites, such as in Spain and in West Africa during all launches.

When an orbiter landing was carried out at night, the runway was always strongly illuminated with light from floodlights and spotlights on the ground, making landing lights on the orbiter unnecessary and also an unneeded spaceflight weight load. A total of 26 landings took place at night, the first being STS-8 in September 1983.[12]

The Space Shuttle orbiter ranks second among the world's first spaceplanes, preceded only by the North American X-15 and followed by the Buran, SpaceShipOne, and the Boeing X-37.

Enterprise displaying the orbiter markings

The typeface used on the Space Shuttle Orbiter was Helvetica.[13]

The prototype orbiter Enterprise originally had a flag of the United States on the upper surface of the left wing and the letters "USA" in black on the right wing. The name "Enterprise" in black was painted on the payload bay doors just above the forwardmost hinge and behind the crew module; on the aft end of the payload bay doors was the NASA "worm" logotype in gray. Underneath the rear of the payload bay doors on the side of the fuselage just above the wing was the text "United States" in black with a flag of the United States ahead of it.

The first operational orbiter, Columbia, originally had the same markings as Enterprise, although the letters "USA" on the right wing were slightly larger and spaced farther apart. Columbia also had black tiles which Enterprise lacked on its forward RCS module, around the cockpit windows, and on its vertical stabilizer. Columbia also had distinctive black chines on the forward part of its upper wing surfaces, which none of the other orbiters had.

Gray NASA "worm" logotype used on the orbiters from 1982 to 1998

Challenger established a modified marking scheme for the shuttle fleet that would be matched by Discovery, Atlantis and Endeavour. The letters "USA" in black above an American flag were displayed on the left wing, with the NASA "worm" logotype in gray centered above the name of the orbiter in black on the right wing. Also, the name of the orbiter was inscribed not on the payload bay doors, but on the forward fuselage just below and behind the cockpit windows. This would make the name visible when the orbiter was photographed in orbit with the doors open. Challenger also had black tiles on the tip of its vertical stabilizer much like Columbia, which the other orbiters lacked.

In 1983, Enterprise had its wing markings changed to match Challenger, and the NASA "worm" logotype on the aft end of the payload bay doors was changed from gray to black. Some black markings were added to the nose, cockpit windows and vertical tail to more closely resemble the flight vehicles, but the name "Enterprise" remained on the payload bay doors as there was never any need to open them. Columbia had its name moved to the forward fuselage to match the other flight vehicles after STS-61-C, during the 1986–88 hiatus when the shuttle fleet was grounded following the loss of Challenger, but retained its original wing markings until its last overhaul (after STS-93), and its unique black chines for the remainder of its operational life.

NASA "meatball" insignia used on the operational Space Shuttle orbiters after 1998

Beginning in 1998, the flight vehicles' markings were modified to incorporate the NASA "meatball" insignia. The "worm" logotype, which the agency had phased out, was removed from the payload bay doors and the "meatball" insignia was added aft of the "United States" text on the lower aft fuselage. The "meatball" insignia was also displayed on the left wing, with the American flag above the orbiter's name, left-justified rather than centered, on the right wing. The three surviving flight vehicles, Discovery, Atlantis and Endeavour, still bear these markings as museum displays. Enterprise became the property of the Smithsonian Institution in 1985 and was no longer under NASA's control when these changes were made, hence the prototype orbiter still has its 1983 markings and still has its name on the payload bay doors.

With the end of the Shuttle program, plans were made to place the three remaining Space Shuttle orbiters on permanent display. NASA Administrator Charles Bolden announced the disposition location of the orbiters on April 12, 2011, the 50th anniversary of the first human space flight and the 30th anniversary of the first flight of Columbia. Discovery went to the Smithsonian's Steven F. Udvar-Hazy Center, replacing Enterprise which was moved to the Intrepid Sea, Air & Space Museum in New York City. Endeavour went to the California Science Center in Los Angeles arriving on October 14, 2012. Atlantis went to the Kennedy Space Center Visitor Complex on November 2, 2012. Hundreds of other shuttle artifacts will be put on display at various other museums and educational institutions around the US.[14]

One of the Crew Compartment Trainer Flight and mid-deck training hardware is on display at the National Museum of the U.S. Air Force,[15] while the other is on display at the JSC.[16] The Full Fuselage Trainer , which includes the payload bay and aft section but no wings, is on display at the Museum of Flight in Seattle, Washington.[17] The Mission Simulation and Training Facility's Shuttle Mission Simulator Fixed Base Simulator originally went to the Adler Planetarium in Chicago, Illinois[18] but was later transferred to the Stafford Air & Space Museum in Weatherford, Oklahoma.[19] The Motion Base Simulator was transferred to the Texas A&M Aerospace Engineering Department in College Station, Texas,[20] and the Guidance and Navigation Simulator went to the Wings of Dreams Aviation Museum in Starke, Florida.[21] NASA also made approximately 7,000 TPS tiles available to schools and universities.[22]