Robert Bussard's Aspen SSTO Concept

This idea for this discussion was obtained from The Nuclear Rocket, by James Dewar.

Dewar said nobody has studied Bussard's concept since 1971.  However, that is incorrect.


The linked pdf study was done in 2001 and concluded that the idea seems impractical for now.  Perhaps, it is because of the use of scramjets, which have poor thrust to weight ratios.

The idea occurred to me that you could use Skylon's engines for the ASPEN.  Replace the scramjets and take it up to Mach 5.5, then switching Skylon's engines to conventional rocket mode.  Here's a twist though.  Instead of using the scramjet trajectory, you are now free to use a sounding rocket trajectory.  The sounding rocket, using Skylon's converted to conventional rocket, can get the vehicle well above the atmosphere, where it can then power the rocket to orbital velocity.  It is hoped that the use of a trajectory like this will save onboard oxygen ( and weight penalty) because, as a sounding rocket, it won't need full power.  Sounding rockets only get altitude, not velocity.

It will have the added benefit of avoiding NASA's prohibition on using an atomic rocket in the atmosphere.  Once high enough, say at the Karman line, the nuclear rocket can then be used to gain orbital velocity.  A similar technique is proposed by Parkins in his beamed microwave concept.

Why do this at all if the Skylon will achieve orbital velocity without the need for nuclear thermal technology?  Well, the motive is to improve upon its performance.  Nuclear thermal rocketry can achieve higher ISP's than conventional rockets.  Dewar believes the payload fractions could be increased significantly.  If he's right, this could be way to get cheaper access to space.

Another possibility would be to carry a small vehicle in the payload bay, and deploy it at the Karman line.

It would weigh much more than the Skylon is designed for, but the Skylon won't be going to orbit, so it may be able to handle the weight.  Or the payload could be downsized.  This is a bit harder, though.

If we stick to ASPEN, then we will have to borrow Skylon's engines.  Alan Bond may not agree to that proposition.

You'd like to combine the two concepts for a more powerful concept.