FUTURE OF SPACECRAFT

FUTURE OF SPACECRAFT & AEROSPACE ENGINEERING:

LOOKING BACK AND AHEAD;

Opinions differ on the lessons of the Shuttle. While it was developed within the original development cost and time estimates given to President Richard M. Nixon in 1971, the operational costs, flight rate, payload capacity, and reliability have been worse than anticipated.

In general future designers look to less complex, more reliable launch systems with lower maintenance costs. One approach is Single Stage To Orbit (SSTO), which would be 100% reusable and use a single stage. NASA evaluated several concepts in the 1990s, and selected the X-33, which would eventually have been the Venturestar. During design that program increased in complexity and development cost, encountered problems and was finally cancelled.

Another variant of SSTO is a hypersonic, scramjet-powered, air breathing vehicle. This would be launched and landed horizontally like an airliner. It would achieve much of orbital velocity while still within the upper atmosphere. It was originally investigated by the U.S. Department of Defence, but passenger-carrying civilian versions were planned, sometimes called the "New Orient Express". The official name was the Rockwell X-30. Like the X-33, the X-30 encountered major technical difficulties, primarily due to the system complexity and materials required for hypersonic flight, and was also cancelled.

Another approach is lower cost expendable launch vehicles. NASA currently uses these for unmanned launches, and plans to use them for future manned launches. NASA plans on using modified shuttle components to build an expendable Shuttle Derived Launch Vehicle. This technology would be used to develop two separate launchers, one for manned missions and the other for unmanned heavy cargo. This contrasts with the current shuttle where astronauts and heavy cargo are launched in a single vehicle. Unlike the shuttle, this future launcher and associated crew exploration vehicle will have a launch escape system to save the crew in the event of a disaster.