From: utzoo!decvax!cca!John@sri-unix
Newsgroups: net.space
Title: rocket planes
Article-I.D.: sri-unix.1847
Posted: Tue Jun 22 10:27:54 1982
Received: Sun Jun 27 02:25:54 1982

The 4000 mph that the X-15 could do is a long way from the 18,000 mph
needed for earth orbit.  At that speed the X-20 would have faced the same 
problem that the shuttle has: how to protect the craft from the heat of 
re-entry.  The Boeing designers could have used Von Braun's solution, ablative
shields, but with expendable shields and expendable boosters the only
reusable part of the craft would be the cockpit.  The only advantage I can
see to that sort of design is being able to land it at different locations.
This was more useful for military programs than civilian ones, which is
probably why they ultimately decided not to bother.
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