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航天飞机

2005-12-28 00:00Wikipedia

Space Shuttle


The Space Shuttle Columbia seconds after engine ignition, 1981 (NASA). For the first two missions only, the external fuel tank spray-on foam insulation (SOFI) was painted white. Subsequent missions have featured an unpainted tank thus exposing the orange/rust colored foam insulation. This resulted in a weight saving of over 1,000 lb (450 kg), a savings that translated directly to added payload capacity to orbit

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    航天飞机,又称为太空梭、穿梭机,是一种有翼、可重复使用的航天器,由辅助的运载火箭发射脱离大气层,作为往返于地球与外层空间间的交通工具,外形酷似飞机。

    虽然世界上有许多国家都陆续进行过航天飞机的开发,但只有美国与前苏联实际成功发射并回收过这种交通工具,而由于苏联瓦解,相关的设备由哈萨克斯坦接收后,由于没有足够经费维持运作,因此目前仅有美国的航天飞机机队可以实际使用并执行任务。

    (This article is about the NASA Space Shuttle)

    NASA's Space Shuttle, officially called Space Transportation System (STS), is the United States government's sole manned launch vehicle currently in service. The Space Shuttle orbiter was manufactured by North American Rockwell, now part of the Boeing Company. Martin Marietta (now part of Lockheed Martin) designed the external fuel tank and Morton Thiokol (now part of Alliant Techsystems (ATK)) designed the solid rocket boosters.

    The Shuttle is the first orbital spacecraft designed for partial reusability. It carries large payloads to various orbits, provides crew rotation for the International Space Station (ISS), and performs servicing missions. While the vehicle was designed with the capacity to recover satellites and other payloads from orbit and return them to Earth, this capacity has not been used often; it is, however, an important use of the Space Shuttle in the context of the ISS program, as only very small amounts of experimental material, hardware needing to be repaired, and trash can be returned by Soyuz.

    Each Shuttle was designed for a projected lifespan of 100 launches or 10-years operational life.

    The program started in the late 1960s and has dominated NASA's manned operations since the mid-1970s. According to the Vision for Space Exploration, use of the Space Shuttle will be focused on completing assembly of the ISS in 2010, after which it will be replaced by the yet-to-be-developed Crew Exploration Vehicle (CEV). However, following the STS-114 return-to-flight mission in August 2005, the Shuttle program is currently grounded pending repairs and the solution of outstanding safety issues.

    Further aggravating the shuttle's return to space, also in August 2005, the Space Shuttle external tank construction site, Michoud Assembly Facility located in New Orleans, Louisiana was damaged by Hurricane Katrina, with all work shifts cancelled up to September 26, 2005. This could potentially set back further Shuttle flights by more than two months.

    The NASA Chief Administrator Michael Griffin has recently suggested the decision to develop the Space Shuttle and International Space Station was a mistake by saying, It is now commonly accepted that was not the right path. We are now trying to change the path while doing as little damage as we can.

Space Shuttles


American
  • Enterprise (test)
  • Pathfinder (mockup)
  • Columbia (destroyed 2003)
  • Challenger (destroyed 1986)
  • Discovery (active)
  • Atlantis (active)
  • Endeavour (active)

    Soviet/ Russian

  • Buran (retired, destroyed 2002)
  • Ptichka (unfinished)
  • 2.01 (unfinished)
  • 2.02 (dismantled)
  • 2.03 (dismantled)
  • Baikal (hoax)

History


    The Shuttle decision

    NASA had conducted a series of paper projects throughout the 1960s on the topic of reusable spacecraft to replace their expedient one-off systems like Mercury, Gemini, and Apollo. Meanwhile, the U.S. Air Force had a continuing interest in smaller systems with more rapid turn-around times, and were involved in their own spaceplane project, the X-20 Dyna-Soar. In several instances groups from both worked together to investigate the state of the art.

    With the major Apollo development effort winding down in the second half of the 1960s, NASA started looking to the future of the space program. They envisioned an ambitious program consisting of a large space station being launched on huge boosters, served by a reusable logistics space shuttle, both providing services for a permanently manned Lunar colony and eventual manned missions to Mars.

    However, in reality, NASA found itself with a rapidly plunging budget. Rather than trying to adapt their long-term future to their dire financial situation, they attempted to save as many of the individual projects as possible. The mission to Mars was rapidly dismissed, but the Space Station and Shuttle conserved. Eventually only one of them could be saved, so it stood to reason that a low-cost Shuttle system would be the better option, because without it a large station would never be affordable.

    A number of designs were proposed, but many of them were complex and varied widely in their systems. An attempt to re-simplify was made in the form of the DC-3 by one of the few people left in NASA with the political importance to accomplish it, Maxime Faget, who had designed the Mercury capsule, among other vehicles. The DC-3 was a small craft with a 20,000-pound (9 tonne) (or less) payload, a four-man capacity, and limited maneuverability. At a minimum, the DC-3 provided a baseline workable (but not significantly advanced) system by which other systems could be compared for price/performance compromises.

    Shuttle launch of Atlantis at sunset in 2001. The sun is behind the camera, and the shadow of the plume is cast across the vault of the sky, intersecting the moon.

    The defining moment for NASA was when they, in desperation to see their only remaining project saved, went to the Air Force for its blessing. NASA asked that the USAF place all of their future launches on the Shuttle instead of their current expendable launchers (like the Titan II), in return for which they would no longer have to continue spending money upgrading those designs ¡ª the Shuttle would provide more than enough capability.

    The Air Force reluctantly agreed, but only after demanding a large increase in capability to allow for launching their projected spy satellites (mirrors are heavy). These were quite large, weighing an estimated 40,000 pounds (18 tonnes), and needed to be put into polar orbits, which require higher energies than lower inclination orbits; and since the Air Force also wanted to be able to abort after a single orbit (as did NASA), and in addition land at the launch site (unlike NASA), the spacecraft would also require the ability to maneuver significantly to either side of its orbital track to adjust for launch-point rotational drift while in polar orbit ¡ª for example, in a 90-minute orbit, Vandenberg AFB would drift over 1,000 miles (1,600 km), whereas in more equatorially aligned orbits, the required cross-range would be less than 250 mi/400 km. This large cross-range capability for polar orbits meant the craft had to have a greater lift-to-drag ratio than originally planned, requiring the addition of bigger, heavier wings.

    The result was that the simple DC-3 was clearly irrelevant because it had neither the cargo capacity nor the cross-range the Air Force demanded. In fact, all existing designs were far too small, as a 40,000-pound (18 tonnes) delivery to polar orbit equates to a 65,000-pound (29 tonne) delivery to an eastwardly launched orbit with typical 28-degree inclination. Additionally, any design using simple straight or foldout wings was not going to meet the cross-range requirements, so any future design would require a more complex, heavier delta wing.

    Of further concern, any increase in the weight of the upper portion of a launch vehicle, which had just occurred, required an even bigger increase in the capability of the lower stage used to launch it. Suddenly, the two-stage system had grown in size to something larger than the Saturn V, and the complexity and costs to develop it soared.

    While all of this was going on, others were suggesting a completely different approach to the future. They stated that NASA would fare better using the existing Saturn to launch their space station, supplied and manned using modified Gemini capsules on top of the Air Force's newer Titan II-M. The cost of development for this looked to be considerably less than the Shuttle alone, and would have a large space station in orbit earlier.

    In reply, advocates of the Shuttle answered that given enough launches, a reusable system would more than pay for the cost of development when compared with the launch costs of disposable rockets. Another factor in the cost-benefit analysis was inflation, and in the 1970s this was high enough that the payback from the development had to happen very quickly to see a positive return. Hence, a high launch rate was needed to make the system economically feasible.

    But it was infeasible that a space station or Air Force payloads could demand such rates (roughly one or two a week), so they insisted and suggested that all future U.S. launches would take place on the Shuttle, once built. In order to do this, the cost of launching the Shuttle would have to be lower than any other system, with the exception of very small rockets, ignored for practical reasons, and very large boosters, which were rare and excessively expensive in any case.

    With a baseline project now gelling, NASA started to work through the process of obtaining stable funding for the five years the project would take to develop. Once again, they found themselves in an increasingly deplorable situation.

    With the budgets being pressed by inflation in the U.S. and the Vietnam War abroad, Congress and the Administration were generally uninterested in long-term projects such as space exploration. Some members were therefore looking to further cut NASA's budget; but with a single long-term project confirmed, they could do little in terms of cutting whole projects ¡ª the Shuttle was the single one left, and its cancellation would mean that there would be no U.S. manned space program by 1980.

    Instead, they looked to reduce the year-to-year costs of development to a stable figure. That is, they wished to see the development budgets spread out over several more years. This was somewhat impractical and in conflict with the planned funding and development. The result was another intense series of redesigns in which the reusable booster was eventually abandoned due to its high price. Unsurprisingly, some designs for reusable boosters amounted to vehicles the size of the then-new Boeing 747, which would have to fly faster than the record-holding ¡ª and considerably smaller ¡ª X-15 rocket plane. Instead, a series of simpler rockets would launch the system and then drop away for recovery. Another change was that the fuel for the Shuttle itself was placed in an external tank instead of internal tanks as in the previous designs. This allowed a larger payload bay in an otherwise much smaller craft, although it also meant throwing away the tankage after each launch.

    The last remaining debate was over the nature of the boosters. NASA had been looking at no less than four solutions to this problem: one a development of the existing Saturn lower stage, another using simple pressure-fed liquid-fuel engines of a new design, and finally either a large, single solid rocket, or two (or more) smaller ones. The decision was eventually made on the smaller solids due to their lower development costs (a decision that had been echoed throughout the whole Shuttle program). While the liquid-fueled systems provided better performance and enhanced safety, delivery capability to orbit is much more a function of the upper-stage performance and weight than the lower; the money was hence spent elsewhere.

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Shuttle Orbiter, showing Shuttle main engines

    Development

    The Shuttle program was launched on January 5, 1972, when President Richard M. Nixon announced that NASA would proceed with the development of a reusable, low-cost Space Shuttle system.

    The project was already to take longer than originally anticipated due to the year-to-year funding caps. Nevertheless, work started quickly and several test articles were available within a few years.

    Most notable among these was the first complete Orbiter, originally to be known as Constitution. However, a massive write-in campaign from fans of the Star Trek television series convinced the White House to change the name to Enterprise. Amid great fanfare, the Enterprise was rolled out on September 17, 1976, and later conducted a successful series of glide-approach and landing tests that were the first real validation of the design.

    The first fully functional Shuttle Orbiter, built in Palmdale, California, was the Columbia, which was delivered to Kennedy Space Center on March 25, 1979, and was first launched on April 12, 1981¡ªthe 20th anniversary of Yuri Gagarin's space flight¡ªwith a crew of two. Challenger was delivered to KSC in July 1982, Discovery was delivered in November 1983, and Atlantis was delivered in April 1985. The Shuttle was meant to visit Space Station Freedom, announced in 1984, an ambitious and much-delayed project later downsized and merged into the International Space Station program. Challenger was destroyed in an explosion during launch on January 28, 1986, with the loss of all seven astronauts on board. Endeavour was built to replace it (using spare parts originally intended for the other Orbiters) and delivered in May 1991. Columbia was lost, with all seven crew members, during reentry on February 1, 2003, and has not been replaced.

Description


    The Shuttle has a large 60 by 15 ft (18 by 4.6 m) payload bay, filling most of the fuselage. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while the Shuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm used to retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missions where it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for Shuttle flights, it will probably be included on all future flights.

    The Space Shuttle system has undergone numerous improvements over the years.

    The Orbiter has changed its thermal protection system several times in order to save weight and ease workload. The original silica-based ceramic tiles need to be removed for inspection for damage after every flight, and they also soak up water and thus need to be protected from the rain. The latter problem was initially fixed by spraying the tiles with Scotchgard, but a custom solution was adopted. Later, many of the tiles on the cooler portions of the Shuttle were replaced by large blankets of insulating feltlike material, which means huge areas (notably the cargo bay area) no longer have to be inspected as often.

    Internally the Shuttle remains largely similar to the original design, with the exception that the avionics continue to be improved. The original systems were hardened IBM 360 computers connected to analog displays in the cockpit similar to contemporary airliners like the DC-10. Today the cockpits have been replaced with all glass systems and the computers themselves are many times faster. The computers use the HAL/S programming language. In the Apollo-Soyuz Test Project tradition, programmable calculators are carried as well (originally the HP-41C). In addition to the glass cockpit, several improvements have been made for safety reasons after the Challenger explosion, including a crew escape system for use in a narrow range of situations that require the Orbiter to ditch. With the coming of the Space Station, the Orbiter's internal airlocks are being 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 have had several improvements to enhance reliability and power. This is why during launch you may hear curious phrases such as Go to throttle-up at 106%. This does not mean the engines are being run over limit. The 100% figure is the power level for the original main engines. The actual engine contract requirement was for 109%. The original flight engines could handle 102%. The 109% number was finally reached in flight hardware with the Block II engines in 2001.

    For 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. This saved considerable weight, and thereby increases the payload the Orbiter can carry into 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 7,500 lb (3.4 t) less than the last run of lightweight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been tested on operational flights.

    And, of course, the SRBs (Solid Rocket Boosters) have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident.

    A number of 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 which was to have entered production in the early to mid-1990s to support the Space Station, but was later cancelled to save money after the expenditure of $2.2 billion. The loss of the ASRB program forced the development of the 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 design using a filament-wound system, but this too was cancelled.

    A cargo-only, unmanned variant of the Shuttle has been variously proposed and rejected since the 1980s. It is called the Shuttle-C and would trade re-usability for cargo capability with large potential savings from reusing technology developed for the Space Shuttle.

    Components

    The Space Shuttle consists of three main components: the reusable Orbiter itself, a large, brown, expendable external fuel tank, and a pair of white, reusable solid-fuel booster rockets. The fuel tank and booster rockets are jettisoned during ascent, so only the Orbiter goes into orbit.
The reusable Orbiter Vehicle (OV), with a large payload bay and three main engines (fed from the external tank) and an orbital maneuvering system with two smaller engines (used after jettisoning the external tank). There are currently three orbiters, rotated between missions.
A large expendable external fuel tank (ET) containing liquid oxygen and liquid hydrogen (at the forward and aft ends, respectively) for the three main engines of the Orbiter; it is discarded 8.5 minutes after launch at an altitude of 60 nautical miles (111 km) and breaks up in the atmosphere upon reentry. The pieces fall in the ocean and are not recovered.
A pair of reusable solid-fuel rocket boosters (SRB); the propellant consists mainly of ammonium perchlorate (oxidizer, 70% by weight) and aluminum (fuel, 16 %); they are separated two minutes after launch at a height of 36 nautical miles (67 km) and are recovered after landing in the ocean, their fall slowed by parachutes.

    Initial plans for the so-called Space Transportation System included space tugs and extra fuel tanks for the orbital-maneuvering-system engines, among many other concepts. None of this hardware has actually ever been built.

    Technical data 

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Space Shuttle Atlantis transported by a Boeing 747 Shuttle Carrier Aircraft (SCA), 1998 (NASA)
  • System stack height: 184.2 ft (56.14 m)
  • Orbiter length: 122.17 ft (37.236 m)
  • Wingspan: 78.06 ft (23.79 m)
  • Gross liftoff: 4.5 million lb (2,040,000 kg)
  • ET: 1.7 million lb (751,000 kg)
  • SRBs: 1.3 million lb (590,000 kg) each (x 2)
  • Orbiter: 240,000 lb (109,000 kg)
  • Total liftoff thrust: 7.82 million lbf (34.8 MN)
  • SSMEs: 400,000 lbf (1.8 MN) each (x 3) = 1.2 million lbf (5.3 MN)
  • SRBs: 3.30 million lbf (14.7 MN) each (x 2) = 6.61 million lbf (29.4 MN)
  • Maximum landing: 230,000 lb (104,000 kg)
  • Maximum launch payload: 63,500 lb (28,800 kg)
  • Operational altitude: 100 to 520 nmi (185 to 1000 km)
  • Speed: 25,404 ft/s (7743 m/s, 27 875 km/h, 17 321 mi/h)
  • Passenger capacity: 10 Astronauts (crews other than 5 to 7 are uncommon)

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