SpaceShipTwo Tests Its Rocket Engine and Goes Supersonic

Nope, no X-plane ever made it into orbit. They were very-high-altitude rocket planes, and were much too small to contain enough fuel to reach orbit. More fuel would necessitate a bigger plane to contain it, and hence a bigger motor to propel it, and hence more fuel to run the bigger motor, etc... That's why rockets get around this problem with multiple stages. They jettison excess mass on the way to orbit. A true "space plane" that lands and takes off on a runway and doesn't dump stages along the way would need to be Single-Stage-To-Orbit (SSTO). So far, there are no true SSTO vehicles, even rockets. A space plane would need to haul along landing gear, wings, conventional engines, etc, and would be much more difficult to do than a simple SSTO rocket.

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/1iehqCp_YLc/story01.htm

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