|
The Space Shuttle program, officially called the Space Transportation System (STS), was the United States government's manned launch vehicle program from 1981 to 2011, administered by NASA and officially beginning in 1972. The winged Space Shuttle orbiter—which was launched with two reusable solid rocket boosters and a disposable external fuel tank—usually carried four to seven astronauts (though crews as small as two and as large as eight have been carried) and up to 50,000 lb (22,700 kg) of payload into low Earth orbit (LEO). When its mission was complete, the Shuttle could independently move itself out of orbit using its maneuvering system and re-enter the Earth's atmosphere. During descent and landing the orbiter acted as a re-entry vehicle and a glider, using its reaction control system and flight control surfaces to maintain attitude until it made an unpowered landing at either Kennedy Space Center or Edwards Air Force Base. The Shuttle is the only winged manned spacecraft to have achieved orbit and land, and the only reusable manned space vehicle that has ever made multiple flights into orbit (the Russian shuttle Buran was very similar and had the same capabilities but made only one unmanned spaceflight before it was cancelled). Its missions involved carrying large payloads to various orbits (including segments to be added to the International Space Station (ISS)), providing crew rotation for the space station, and performing service missions. The orbiter also recovered satellites and other payloads (e.g., from the ISS) from orbit and returned them to Earth, though its use in this capacity was rare. Each vehicle was designed with a projected lifespan of 100 launches, or 10 years' operational life, though original selling points on the shuttles were over 150 launches and over a 15-year operational span with a 'launch per month' expected at the peak of the program, but extensive delays in the development of the International Space Station 〔(【引用サイトリンク】title=International Space Station Historical Timeline )〕 never created such a peak demand for frequent flights. Although the concept had been explored since the late 1960s, the program formally commenced in 1972, and was the sole focus of NASA's manned operations after the final Apollo and Skylab flights in the mid-1970s. The Shuttle was originally conceived of and presented to the public in 1972 as a 'Space Truck' which would, among other things, be used to build a United States space station in low Earth orbit during the 1980s and then be replaced by a new vehicle by the early 1990s. The stalled plans for a U.S. space station evolved into the International Space Station and was formally initiated in 1983 by U.S. President Ronald Reagan, but the ISS suffered from long delays, design changes and cost over-runs 〔 and forced the service life of the Space Shuttle to be extended several times until 2011 when it was finally retired — serving twice as long than it was originally designed to do. In 2004, according to the President George W. Bush's Vision for Space Exploration, use of the Space Shuttle was to be focused almost exclusively on completing assembly of the ISS, which was far behind schedule at that point. The first experimental orbiter ''Enterprise'' was a high-altitude glider, launched from the back of a specially modified Boeing 747, only for initial atmospheric landing tests (ALT). ''Enterprises first test flight was on February 18, 1977, only five years after the Shuttle program was formally initiated; leading to the launch of the first space-worthy shuttle ''Columbia'' on April 12, 1981 on STS-1. The Space Shuttle program finished with its last mission, STS-135 flown by ''Atlantis'', in July 2011, retiring the final Shuttle in the fleet. The Space Shuttle program formally ended on August 31, 2011. Retirement of the Shuttle ended the era in which all of America's varied space activities were performed by one craft -or even one organization. Functions performed by the Shuttle for 30 years will be done by not one but many different spacecraft currently flying or in advanced development. Secret military missions are being flown by the US Air Force's "highly successful" unmanned mini-space plane, the X-37B. By 2012, cargo supply to the International Space Station began to be flown by privately owned commercial craft under NASA's Commercial Resupply Services by SpaceX's successfully tested and partially reusable Dragon spacecraft, followed by Orbital Sciences' Cygnus spacecraft in late 2013. Crew service to the ISS will be flown exclusively by the Russian Soyuz while NASA works on the Commercial Crew Development program. For missions beyond low Earth orbit, NASA is building the Space Launch System and the Orion spacecraft. ==Conception and development== (詳細はApollo 11 moon landing in 1969, NASA began early studies of space shuttle designs. 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.〔Hepplewhite, T.A. (''The Space Shuttle Decision: NASA's Search for a Reusable Space Vehicle'' ). Washington, DC: National Aeronautics and Space Administration, 1999.〕 The goal, as presented by NASA to Congress, was to provide a much less-expensive means of access to space that would be used by NASA, the Department of Defense, and other commercial and scientific users.〔General Accounting Office. Cost Benefit Analysis Used in Support of the Space Shuttle Program. Washington, DC: General Accounting Office, 1972.〕 During early shuttle development there was great debate about the optimal shuttle design that best balanced capability, development cost and operating cost. Ultimately the current design was chosen, using a reusable winged orbiter, reusable solid rocket boosters, and an expendable external fuel tank for the orbiter's main engines.〔 The 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 stated goals of "transforming the space frontier...into familiar territory, easily accessible for human endeavor" was to be achieved by launching as many as 50 missions per year, with hopes of driving down per-mission costs. The prime contractor for the program was North American Rockwell (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 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''.〔Brooks, Dawn (date unknown). ''The Names of the Space Shuttle Orbiters''. Washington, DC: National Aeronautics and Space Administration. Retrieved on 2006-07-26 from http://www.hq.nasa.gov/osf/shuttle/orbiters.html.〕 Amid great fanfare, ''Enterprise'' (designated OV-101) was rolled out on September 17, 1976, and later conducted a successful series of glide-approach and landing tests in 1977 that were the first real validation of the design. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Space Shuttle program」の詳細全文を読む スポンサード リンク
|