Introduction
In the middle of the twentieth century, the Soviet Union launched the space vehicle Sputnik. That event helped start an international space race that culminated with the triumphant landing of Apollo 11 on the moon. After that, the United States, as well as other countries, continued to perform space missions, but there have been few great new undertakings in manned space missions since then. The International Space Station (ISS) is the one effort geared towards extending human presence in space. Currently, the United States uses two types of vehicles to get payloads into orbit and to get humans into space.
The main vehicle used by NASA to launch manned missions is the Space Shuttle. The Space Shuttle is a partially reusable, multi-stage launch platform. However, the Space Shuttle is very expensive to use. It costs approximately $500 million per launch, for a number of reasons. One reason is that the orbiter is decertified for flight after each mission, and so must undergo large amounts of maintenance. The engines are taken apart and rebuilt, the solid rocket boosters must be recovered, and a new external tank must be built. Also, recently, due to the Columbia incident, the Space Shuttle is no longer an operational vehicle; it is now classified as an experimental vehicle. The Space Shuttle has well served the need for a manned space vehicle for years, but with its large recurring costs, as well as its recent demotion to experimental status, a new vehicle would best serve a country actively reaching out into space.
Another type of vehicle used to launch payloads into orbit is the expendable rocket. Vehicles such as the Titan, Delta, and Atlas rockets are used to put satellites into orbit and to launch deep space probes. However, these rockets are fully expended during launch, and a new one must be built to be used for another launch. Also, these rockets cost a lot to build, and take a long time to construct and prep for flight.
In order to stimulate space exploration that has slowed down in the last 30 years, a new and cheaper space exploration vehicle must be found: a versatile vehicle that could perform both manned and unmanned launches, and could go to orbit with a single stage. A single-stage-to-orbit (SSTO) vehicle would eliminate any recurring rebuild or recovery costs, and help the vehicles achieve complete reusability as a reusable launch vehicle (RLV). Aerospace engineers have been working on the development of an SSTO rocket that is also an RLV. 10 years ago, a team in White Sands, New Mexico, built an experimental vehicle that proved that such a rocket is closer than it may have seemed [1].
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