From: kasow@panix.com   
      
   In article <50gZc.10673$5w4.2149@fe22.usenetserver.com>,   
   richie086   wrote:   
   >Hey..  I have a question.   
   >   
   >would the use of balloons to lift some sort of delivery vehicle or   
   >rocket into the very upper atmosphere work?  has this ever been attempted?   
      
   It has been attempted- it makes more sense for suborbital or very small   
   orbital vehicles than for large orbital craft.   
      
   >What got me thinking about this was a show about a US Air Force captain   
   >(joke kittenger) back in 1960, riding a balloon up to 100,000 feet and   
   >then jumping off of the platform he was sitting on.   I understand he   
   >was wearing a space suit and you would very easily die if exposed at   
   >such elevations.  After seeing the movie that was taken from a film   
   >camera attached to him somehow, it's very obvious that he was at the   
   >very edge of space.   
      
   > Isn't half the cost of putting the space shuttle up   
   >  or any rocket into orbit due to how much the fuel costs?   
      
   In the case of the space shuttle, most of the cost is not due to   
   fuel, which is fairly cheap, but to the salaries of the standing army of   
   technicians required to maintain, inspect, and ready the shuttles for   
   launch.   
      
   In any case, let us ignore those details and look at the energy   
   costs, which do relate more directly to the fuel costs.   
      
   The shuttle, like most rockets, basically goes straight up   
   and then turns over sideways and accelerates until it is moving   
   at orbital speed. The second part is the hard one- getting up to   
   altitude takes only about 1/32nd the energy of reaching the speed   
   required.   
      
   So, why does anyone bother with air launch? It's not so much because   
   you get to start from higher up, but because you get to start with   
   the air around you being thinner.   
      
   Obviously, it helps reduce air drag on your vehicle.   
   Not so obviously, it helps your engines also.   
      
   Rocket engines depend on the pressure difference between the   
   combustion chamber and the outside of the nozzle. To work at sea   
   level, the pressure at the output end of the rocket nozzle must be   
   greater than 14.7 psi. But in the vacuum of orbit, having the pressure   
   be 14.7psi would be a waste- you'd want to use a larger nozzle   
   that would drop the pressure as low as you practically could to   
   extract every bit of energy from your exhaust.   
      
   So an engine designed to work from, say, 100,000 feet altitude to   
   vacuum, could be more efficient that one designed to work from sea-level   
   to vacuum. And that could be a factor pushing towards an air launch.   
      
   	cheers,   
      
   		Steven   
      
   --   
   kasow@panix.com   
      
   "M-Theory is the unifying pachyderm of the five string theories."   
           - Brian Greene, _The Elegant Universe_   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)