From: marmiteNOTSPAM@dualboot.net   
      
   Henry Spencer wrote:   
   > The fast answer is that there is no crossover point:  aerodynamic braking   
   > is *always* a lot cheaper in mass than doing the same braking with rocket   
   > fuel.  That's not quite 100% true when you start examining specialized   
   > situations, but for normal reentry from orbit you can take it as given.   
      
   That depends very heavily on the ratio between   
   delta V and rocket exhaust velocity, as you know.   
   Currently rocket exhaust velocities are so much   
   lower than useful delta vees that this ratio is   
   almost always greater than 1, which is definitely   
   the wrong side of that exponential to be on.   
   But in the long term, if we have rockets with   
   very high exhaust velocities then this ratio could   
   be much lower, and the behavior would be more   
   linear with respect to delta V and mass ratio.   
   High performance gas core nuclear thermal rockets   
   can just about reach the performance levels to do   
   multiples of Earth-to-LEO delta V, NSWR or Orion   
   would certainly have that capability with   
   reasonable mass ratios.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)