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A reusable launch system (or reusable launch vehicle, RLV) is a launch system which is capable of launching a launch vehicle into space more than once. This contrasts with expendable launch systems, where each launch vehicle is launched once and then discarded. No true orbital reusable launch system is currently in use. The closest example was the partially reusable Space Shuttle. The orbiter, which included the Space Shuttle main engines, and the two solid rocket boosters, were reused after several months of refitting work for each launch. The external tank and launch vehicle load frame were discarded after each flight.〔〔 Orbital RLVs are thought to provide the possibility of low cost and highly reliable access to space. However, reusability implies weight penalties such as non-ablative reentry shielding and possibly a stronger structure to survive multiple uses, and given the lack of experience with these vehicles, the actual costs and reliability are yet to be seen. ==History== In the first half of the twentieth century, popular science fiction often depicted space vehicles as either single-stage reusable rocket ships which could launch and land vertically (SSTO VTVL), or single-stage reusable rocket planes which could launch and land horizontally (SSTO HTHL). The realities of early engine technology with low specific impulse or insufficient thrust-to-weight ratio to escape Earth's gravity well, compounded by construction materials without adequate performance (strength, stiffness, heat resistance) and low weight, seemingly rendered that original single-stage reusable vehicle vision impossible. However, advances in materials and engine technology have rendered this concept potentially feasible. Before VTVL SSTO designs came the partially reusable multi-stage NEXUS launcher by Krafft Arnold Ehricke. The pioneer in the field of VTVL SSTO, Philip Bono, worked at Douglas. Bono proposed several launch vehicles including: (ROOST ), (ROMBUS ), (Ithacus ), (Pegasus ) and SASSTO. Most of his vehicles combined similar innovations to achieve SSTO capability. Bono proposed: * Plug nozzle engines to retain high specific impulse at all altitudes. * Base first reentry which allowed the reuse of the engine as a heat shield, lowering required heat shield mass. * Use of spherical tanks and stubby shape to reduce vehicle structural mass further. * Use of drop tanks to increase range. * Use of in-orbit refueling to increase range. Bono also proposed the use of his vehicles for space launch, rapid intercontinental military transport (Ithacus), rapid intercontinental civilian transport (Pegasus), even Moon and Mars missions ((Project Selena ), (Project Deimos )). In Europe, Dietrich Koelle, inspired by Bono's SASSTO design, proposed his own VTVL vehicle named (BETA ). Before HTHL SSTO designs came Eugen Sänger and his Silbervogel ("Silverbird") suborbital skip bomber. HTHL vehicles which can reach orbital velocity are harder to design than VTVL due to their higher vehicle structural weight. This led to several multi-stage prototypes such as a suborbital X-15. Aerospaceplane being one of the first HTHL SSTO concepts. Proposals have been made to make such a vehicle more viable including: * Rail boost (e.g. 270 m/s at 3000 m on a mountain allowing 35% less SSTO takeoff mass for a given payload in one NASA study)〔(【引用サイトリンク】title=The Maglifter: An Advanced Concept Using Electromagnetic Propulsion in Reducing the Cost of Space Launch )〕 * Use of lifting body designs to reduce vehicle structural mass. * Use of in-flight refueling. Other launch system configuration designs are possible such as horizontal launch with vertical landing (HTVL) and vertical launch with horizontal landing (VTHL). One of the few HTVL vehicles is the 1960s concept spacecraft Hyperion SSTO, designed by Philip Bono.〔 〕 X-20 Dyna-Soar is an early example of a VTHL design, while the HL-20 and X-34 are examples from the 1990s. , the VTHL X-37 has completed initial development and flown an initial classified orbital mission of over seven months duration. Currently proposed VTHL manned spaceplanes include the Dream Chaser and Prometheus, both circa 2010 concept spaceplanes proposed to NASA under the CCDev program. The late 1960s saw the start of the Space Shuttle design process. From an initial multitude of ideas a two-stage reusable VTHL design was pushed forward that eventually resulted in a reusable orbiter payload spacecraft and reusable solid rocket boosters. The external tank and the launch vehicle load frame were discarded, and the parts that were reusable took a 10,000-person group nine months to refurbish for flight. So the space shuttle ended up costing a billion dollars per flight.〔http://www.ted.com/talks/elon_musk_the_mind_behind_tesla_spacex_solarcity/transcript?utm_content=buffer5c917&utm_medium=social&utm_source=facebook.com&utm_campaign=buffer〕 Early studies from 1980 and 1982 proposed in-space uses for the tank to be re-used in space for various applications〔() 〕〔(【引用サイトリンク】title=STS External Tank Station )〕 but NASA never pursued those options beyond the proposal stage. During the 1970s further VTVL and HTHL SSTO designs were proposed for solar power satellite and military applications. There was a VTVL SSTO (study ) by Boeing. HTHL SSTO designs included the Rockwell (Star-Raker ) and the Boeing (HTHL SSTO study ). However the focus of all space launch funding in the United States on the Shuttle killed off these prospects. The Soviet Union followed suit with Buran. Others preferred expendables for their lower design risk, and lower design cost. Eventually the Shuttle was found to be expensive to maintain, even more expensive than an expendable launch system would have been. The cancellation of a Shuttle-Centaur rocket after the loss of Challenger also caused an hiatus that would make it necessary for the United States military to scramble back towards expendables to launch their payloads. Many commercial satellite customers had switched to expendables even before that, due to unresponsiveness to customer concerns by the Shuttle launch system. In 1986 President Ronald Reagan called for an airbreathing scramjet plane to be built by the year 2000, called NASP/X-30 that would be capable of SSTO. Based on the research project copper canyon the project failed due to severe technical issues and was cancelled in 1993. This research may have inspired the British HOTOL program, which rather than airbreathing to high hypersonic speeds as with NASP, proposed to use a precooler up to Mach 5.5. The program's funding was canceled by the British government when the research identified some technical risks as well as indicating that that particular vehicle architecture would only be able to deliver a relatively small payload size to orbit. When the Soviet Union collapsed in the early nineties, the cost of Buran became untenable. Russia has only used pure expendables for space launch since. The 1990s saw interest in developing new reusable vehicles. The military Strategic Defense Initiative ("Star Wars") program "Brilliant Pebbles" required low cost, rapid turnaround space launch. From this requirement came the McDonnell Douglas Delta Clipper VTVL SSTO proposal. The DC-X prototype for Delta Clipper demonstrated rapid turnaround time and that automatic computer control of such a vehicle was possible. It also demonstrated it was possible to make a reusable space launch vehicle which did not require a large standing army to maintain like the Shuttle. In mid-1990, further British research and major reengineering to avoid deficiencies of the HOTOL design led to the far more promising Skylon design, with much greater payload. From the commercial side, large satellite constellations such as Iridium satellite constellation were proposed which also had low cost space access demands. This fueled a private launch industry, including partially reusable vehicle players, such as Rocketplane Kistler, and reusable vehicle players such as Rotary Rocket. The end of that decade saw the implosion of the satellite constellation market with the bankruptcy of Iridium. In turn the nascent private launch industry collapsed. The fall of the Soviet Union eventually had political ripples which led to a scaling down of ballistic missile defense, including the demise of the "Brilliant Pebbles" program. The military decided to replace their aging expendable launcher workhorses, evolved from ballistic missile technology, with the EELV program. NASA proposed riskier reusable concepts to replace Shuttle, to be demonstrated under the X-33 and X-34 programs. The 21st century saw rising costs and teething problems lead to the cancellation of both X-33 and X-34. Then the Space Shuttle Columbia disaster and another grounding of the fleet. The Shuttle design was now over 20 years old and in need of replacement. Meanwhile, the military EELV program churned out a new generation of better expendables. The commercial satellite market is depressed due to a glut of cheap expendable rockets and there is a dearth of satellite payloads. Against this backdrop came the Ansari X Prize contest, inspired by the aviation contests made in the early 20th century. Many private companies competed for the Ansari X Prize, the winner being Scaled Composites with their reusable HTHL SpaceShipOne. It won the ten million dollars, by reaching 100 kilometers in altitude twice in a two-week period with the equivalent of three people on board, with no more than ten percent of the non-fuel weight of the spacecraft replaced between flights. While SpaceShipOne is suborbital like the X-15, some hope the private sector can eventually develop reusable orbital vehicles given enough incentive. SpaceX is a recent player in the private launch market which is working to convert its Falcon 9 expendable launch vehicle into a partially-reusable vehicle by returning the first stage for reuse. On 23 November 2015, Blue Origin New Shepard rocket became the first proven Vertical Take-off Vertical Landing (VTVL) rocket which can reach space, by passing Kármán line (100 kilometres), reaching 329,839 feet (100.5 kilometers). Previous VTVL record was in 1994, the McDonnell Douglas DC-X ascended to an altitude of about 3.1 kilometers before successfully landing. 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「Reusable launch system」の詳細全文を読む スポンサード リンク
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