From: johnhare@tampabay.rr.com   
      
   "Kelly St"  wrote in message   
   news:20040126205838.04554.00000829@mb-m10.aol.com...   
   > I was interested in seeing if you could do it with current equipment, not   
   > searching for a justification for a new one.   
   >   
   > I'm not saying a new engine with better perfomance wouldn't make things,   
   but   
   > I'm not at all clear Its needed to get the job done.  A first generation   
   craft   
   > that could drop cost to orbit by a order of magnitude or two, and greatly   
   > increase flexibility, would get the ball runing and later bankroll the dev   
   of   
   > better engines.   
      
   I should have put some numbers on my other reply to clarify my points a   
   bit better. An all rocket VTVL SSTO is probably feasible at this time.   
   The margins will be tight with no slack for extra systems that don't pull   
   their own weight. Adding any current airbreathing engine to the projected   
   VTVL SSTO will cut into the payload for a given dry mass.   
      
   Take a theoretical VTVL SSTO at 100,000 lbs GLOW. At mass ratio of   
   16, there will be 6,250 lbs mass in orbit. If you add some hypothetical jet   
   which cuts the GLOW to 80,000 lbs and increases the mass in orbit to   
   7,250 lbs for the same payload, you have lost. The 1,000 lb jet you added   
   could cost something on the order of $1M. That $1M will buy 20,000,000   
   lbs of the LOX you replaced. That is 1,000 launches to reach break even   
   all else being equal.   
      
   All else is seldom equal. That 1,000 lb jet must be accelerated all the way   
   to   
   orbit, reentered, and landed. Most studies would seem to indicate that   
   adding   
   the jet will prevent SSTO operation without seriously advanced tech across   
   the board. Increasing the reentry mass and landing mass also increases the   
   cost of the vehicle. 1 lb of hardware at $1,000 lb will buy 20,000 lbs   
   of LOX.   
      
   For HTHL, you are lifting wings and landing gear sized for GLOW all the   
   way to orbit and back. Add all the weights of HTHL and you don't reach   
   SSTO mass ratio requirements. Add a second type all up propulsion system to   
   the required rockets and it becomes more difficult yet. You are forced into   
   some form of air tow or refueling to even attempt making it to orbit. Most   
   of the papers I have read assume one or more advanced technologies to   
   make this happen.   
      
   If you go TSTO, then many possibilities open up. Air breathing becomes   
   more feasible in several of them. I am basing on SSTO because it is a useful   
   math model. If pure rocket SSTO is feasible, and adding jets requires an   
   additional stage, then the jets hamper performance. You shouldn't add   
   systems that hamper performance without a very good reason. I would   
   like to find the point where the operational flexibilities possible with an   
   airbreathing engine do not cost performance in real terms.   
      
      
   > Kelly Starks   
   > KellySt@aol.com   
   >   
   > "Humans are a race of compassionate predators."   
   >   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)