Quote:
Originally Posted by Tervuren
How it works, is the airplane doesn't have to carry its own oxidizer(weight).
For the airplane it uses the atmosphere to get to that altitude, with initial velocity, and punching from a much thinner atmosphere the rocket doesn't have to carry as much fuel(weight).
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There is more to it. Rocket nozzles designed to work in atmosphere are not efficient shapes for near vacuum and the reverse is also true. By getting to 50-60K feet (10-12 miles, 15-18km), the atmosphere is thin enough that you don't have to make a compromise design. This further reduces the amount of propellant and oxidizer needed.