Hi Rich, as I understand it, the energy requirements to put SS1 at 100 kilometers are pretty modest. There are not a few fairly safe fuel/oxidizer combinations and Rutan exploited that. NASA must boost much heavier loads to much higher speeds, so must use fuel/oxidizer combinations with the highest energy release (I think it's called specific impulse, jeez physics class was a long time ago. In the last century.) and those are usually the nastiest. The tourist/private space industry won't be able to run on controlled tire-fires forever, I suspect, though that does on the surface seem to kill two birds with one stone!
Chuck,
An amateur rocket friend of mine was telling me yesterday at lunch that Rutan's rocket ran on recycled tire rubber and laughing gas! Doesn't sound too exotic or expensive to me, but I'm sure he was oversimplifying it just a bit. Can you (or others in the know on this list) tell me more about it (risks, costs, etc.)? Sounds very interesting to me.
-Rich
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