Space Shuttle

The Space Shuttle is a retired spacecraft system that was partly reusable. It went to the International Space Station (ISS) and performed other missions in low Earth orbit. The U.S. National Aeronautics and Space Administration (NASA) operated it from 1981 to 2011 as part of the Space Shuttle program. Its official name was the Space Transportation System (STS). The name came from a 1969 plan led by U.S. vice president Spiro Agnew, in which the Space Shuttle was the only part funded for development.

The first of four orbital test flights, STS-1, took place in 1981. Operational flights, beginning with STS-5, started in 1982. Five complete orbiter vehicles were built and flown on a total of 135 missions. The shuttles launched from the Kennedy Space Center (KSC) in Florida. Their missions launched many satellites and interplanetary probes, and they carried the Hubble Space Telescope (HST) into space. They also performed science experiments, took part in the Shuttle-Mir program with Russia, and helped build and service the ISS. The fleet's total mission time was 1,323 days.

The Space Shuttle had three main parts. The Orbiter Vehicle (OV) had three RS-25 main engines made by Rocketdyne. Two solid rocket boosters (SRBs) could be recovered, and the external tank (ET) held liquid hydrogen and liquid oxygen and was not reused. The shuttle launched vertically, like a conventional rocket. The boosters were dropped before the vehicle reached orbit, and the external tank was dropped just before orbit insertion, which used the orbiter's two Orbital Maneuvering System (OMS) engines.

At the end of a mission, the orbiter fired its OMS engines to leave orbit and reenter the atmosphere. Its thermal protection system tiles protected it during reentry. It then glided as a spaceplane to a runway landing, usually at the Shuttle Landing Facility at KSC, or at Rogers Dry Lake in Edwards Air Force Base, California. If the shuttle landed at Edwards, it was flown back to KSC on top of the Shuttle Carrier Aircraft (SCA), a specially changed Boeing 747 built to carry the shuttle.

The first orbiter, Enterprise, was built in 1976 and used in Approach and Landing Tests (ALT), but it could not reach orbit. Four fully operational orbiters were built at first: Columbia, Challenger, Discovery, and Atlantis. Two of them were lost in mission accidents: Challenger in 1986 and Columbia in 2003, and 14 astronauts died in these accidents. Endeavour was built in 1991 to replace Challenger. The three remaining operational orbiters were retired after Atlantis's final flight on July 21, 2011. From then until the launch of the Crew Dragon Demo-2 mission in May 2020, the U.S. relied on the Russian Soyuz spacecraft to carry astronauts to the ISS.

Design and development

Long before the Shuttle, the German government started the "Amerikabomber" (America bomber) project in the late 1930s. Eugen Sänger and mathematician Irene Bredt proposed a winged rocket called the Silbervogel, which means "silver bird" in German. In the 1950s, the United States Air Force studied a reusable piloted glider, and in the late 1950s it began the partly reusable X-20 Dyna-Soar with NASA. Rising costs and the priority given to Project Gemini led to the program being cancelled in December 1963. The Air Force's studies also led to the aerospaceplane, a fully reusable spacecraft that never got past its first design stage. Starting in the early 1950s, NASA and the Air Force also tested lifting bodies, aircraft that got most of their lift from their bodies instead of wings. These included the NASA M2-F1, Northrop M2-F2, Northrop M2-F3, Northrop HL-10, Martin Marietta X-24A, and the Martin Marietta X-24B, and their tests helped shape the Shuttle's design. In 1966, NASA and the Air Force decided that a partly reusable system would be the most cost-effective solution. George Mueller announced the plan for a reusable shuttle in 1968, and NASA issued a request for proposal for designs. Companies including General Dynamics, Lockheed, McDonnell Douglas, and North American Rockwell received study contracts. A 1969 report, issued under U.S. vice president Spiro Agnew, called for a shuttle along with a space tug and a reusable nuclear upper stage. Max Faget, who had helped design the Mercury capsule, proposed a straight-winged design, but the Air Force said it could not handle the heat and stresses of reentry or carry the required payload. In 1971, NASA and the Air Force chose a reusable delta-wing orbiter. The Air Force wanted the Shuttle to reach a polar orbit, so NASA turned to the RS-25 engine, developed by Rocketdyne after the F-1 and J-2 engines from the Saturn rockets were judged insufficient. NASA chose reusable solid-propellant boosters because they were cheaper and easier to refurbish after landing in the ocean. In January 1972, President Richard Nixon approved the Shuttle. North American Rockwell built the orbiter, which was based on a full-scale model named Inspiration, and Morton Thiokol received the solid-rocket booster contract.

Construction of the first orbiter began in 1974, and the test vehicle Enterprise was moved to Edwards Air Force Base in 1976 to begin testing. Engineers tested the engines and structures at the National Space Technology Laboratory and elsewhere. The engine work faced delays, and Pratt & Whitney challenged the contract that had been given to Rocketdyne. Engine problems were also found during testing. The heat shield was another challenge. Earlier spacecraft used ablative heat shields that could not be reused, so NASA chose ceramic tiles on a lightweight aluminum frame, which could be replaced one at a time. The orbiter Columbia was delivered in 1979, but many of its tiles had to be replaced before it could fly. NASA then ordered more orbiters, named Discovery, Atlantis, and Endeavour, and limited the fleet to four orbiters in 1983. Enterprise was used in tests with the Shuttle Carrier Aircraft, and later in Approach and Landing Tests and at the Marshall Space Flight Center and LC-39. On April 12, 1981, the Shuttle made its first launch, flown by John Young and Robert Crippen on STS-1. Some tiles had fallen off Columbia, but satellite images showed no damage. In 1982, STS-4, flown by Ken Mattingly and Henry Hartsfield, landed on a runway, and Ronald Reagan and Nancy met the crew. After this flight, NASA declared its Space Transportation System operational. After the loss of Challenger, NASA resumed production of Endeavour in 1987.

Description

The Space Shuttle was the first operational orbital spacecraft designed for reuse. Each orbiter was designed for a projected lifespan of 100 launches or ten years of operation, although this was later extended. At launch, the Space Shuttle had three main parts: the orbiter, which held the crew and payload, the external tank (ET), and two solid rocket boosters (SRBs). Responsibility for these parts was shared among several NASA centers. The KSC handled launch, landing, and turnaround for equatorial orbits, the only orbit type actually used. The U.S. Air Force at Vandenberg Air Force Base handled polar orbit operations, although these were never used. The Johnson Space Center was the central point for all Shuttle operations, the MSFC was responsible for the main engines, external tank, and solid rocket boosters, the John C. Stennis Space Center tested the main engines, and the Goddard Space Flight Center managed the global tracking network.

The orbiter combined features of both a rocket and an aircraft. It could launch upright and then land like a glider. Its three-part fuselage supported the crew compartment, cargo bay, flight surfaces, and engines. The orbiter was protected from the heat of reentry by a heat shield designed to be used many times, because the orbiter was built to be reused. The external tank was the only major part that was not reused, and the solid rocket boosters provided 71.4% of the Space Shuttle's thrust during liftoff and ascent.

Main article: Canadarm

Main article: Spacelab

Main article: RS-25

Mission profile

See also: Launch commit criteria

The Space Shuttle was prepared for launch mainly in the VAB at the KSC. Its solid rocket boosters were attached to the external tank, and the orbiter was prepared at the Orbiter Processing Facility (OPF) before being lifted into place against the tank. The complete stack was carried 5.6 km (3.5 mi) to Launch Complex 39 by one of the crawler-transporters. Launches were planned to avoid lightning, because the exhaust could give lightning a path to the ground, as happened on Apollo 12. Weather was checked against the launch commit criteria, and conditions also had to be acceptable at a Transatlantic Abort Landing site. During the countdown, the Launch Control Center (LCC) and the crew completed system checks. The Launch Processing System handed control to the orbiter's computers, which could stop the countdown if they sensed a serious problem. Water was poured onto the launch area to protect the orbiter from acoustical energy, and the RSLS abort could stop the launch if the engines did not perform well enough. At launch, the frangible nuts holding the boosters to the pad were set off, and the Mission Control Center took over control of the flight. The engines were eased back at Max Q to reduce stress on the vehicle. About two minutes after launch, the boosters separated, reached an apogee of 67,000 meters (220,000 ft), and parachuted into the Atlantic Ocean. Early missions kept in contact with a tracking station in Bermuda, but later missions, starting with STS-87, used a tracking and data relay satellite system instead. Early missions used two firings of the Orbital Maneuvering System to reach orbit, while missions after STS-38 used the main engines for most of the climb. The orbits varied from 220 to 620 km (120 to 335 nmi), depending on the mission.

The mission type decided which orbit the shuttle entered. Early missions often carried satellites, but after the Challenger disaster, many commercial payloads moved to expendable rockets such as the Delta II. Later missions focused on science, including the Hubble Space Telescope, Spacelab, and the Galileo spacecraft. Starting with STS-71, the shuttle docked with the Mir space station, and in its final decade it helped build the International Space Station. Most missions lasted several days to two weeks, though the Extended Duration Orbiter pallet made longer missions possible. The longest mission was STS-80, which lasted 17 days and 15 hours. Before landing, the crew prepared the orbiter, which turned tail-first and fired its engines to slow down. The orbiter then entered the atmosphere nose-first, and the reaction control system jets were emptied of fuel. A speed brake opened at 46 km (150,000 ft) to help control speed. The orbiter's glide ratio/lift-to-drag ratio changed a great deal with speed, from 1.3 at hypersonic speeds to 4.9 at slower speeds. The main landing site was the Shuttle Landing Facility at KSC, where 78 of the 133 successful landings took place. Edwards AFB was the main backup, used for 54 landings. STS-3 landed at the White Sands Space Harbor in New Mexico, where the sand was gypsum-rich and needed extra cleaning. Landings at other airfields meant the orbiter had to be flown back to Cape Canaveral. There were also 85 agreed-upon emergency landing sites, though they were never used. These sites needed a long enough runway and suitable TACAN or DME equipment to be chosen. After landing, ground crews checked the air for hydrogen, hydrazine, nitrogen tetroxide, and ammonia before approaching. A flight surgeon checked the crew, and the orbiter was towed to the OPF for inspection, repair, and preparation for the next mission. This work included removing the Orbital Maneuvering System and Reaction Control System pods for maintenance at the Hypergol Maintenance Facility.

Space Shuttle program

The Space Shuttle flew from April 12, 1981, until July 21, 2011. During the program it flew 135 missions, and 133 of them returned safely. It was used for scientific research and to deploy commercial, military, and scientific payloads. It also helped build and operate Mir and the ISS. The Space Shuttle was the only U.S. vehicle that launched astronauts until the launch of Crew Dragon Demo-2 on May 30, 2020. The overall NASA budget for the program has been estimated at $221 billion (in 2012 dollars). The developers hoped that reusing the Space Shuttle would save money, but the costs of each launch ended up being higher than first predicted.

Main article: Criticism of the Space Shuttle program

Partial reusability was one of the main design goals, but it meant the Space Shuttle could carry less cargo per launch. NASA had planned to fly 24 missions a year, but it did not reach that number. The Space Shuttle was first meant to deploy satellites, but cheaper rockets that could be thrown away after use became the main way to launch satellites. A key customer was the National Reconnaissance Office, which runs spy satellites. The Challenger and Columbia disasters showed that the Space Shuttle could be dangerous for its crew. Unlike the Apollo and Soyuz capsules, the Shuttle had few ways for the crew to escape during a problem. Its retirement was announced in January 2004. George W. Bush said the Shuttle would be retired after it finished building the ISS, as part of his Vision for Space Exploration. The final launch was planned as STS-134, but after the Columbia disaster, extra orbiters were prepared for launch on need. Its last flight became STS-135, which launched on July 8, 2011. After that, American astronauts flew on Russian Soyuz spacecraft until 2020. The retired orbiters were made safe and displayed. Atlantis is at the Kennedy Space Center Visitor Complex in Florida, Discovery is at the Steven F. Udvar-Hazy Center in Virginia, Endeavour is at the California Science Center in Los Angeles, and Enterprise is at the Intrepid Museum in New York. Parts were also reused, such as engines for the Space Launch System and the Artemis program. Some of these engines were built in the early 1980s.