From: henry@spsystems.net   
      
   In article <4021CF77.448A9CCD@shaw.ca>,   
     wrote:   
   >I would like to know why we don't travel to Mars by first lifting many   
   >loads of fuel to the space station.  The actual spaceship would be   
   >assembled in space, at the space station, from parts that are lifted   
   >there the same as the fuel is lifted, by conventional rockets...   
      
   The idea is an old one -- early studies simply *assumed* that even a lunar   
   expedition, never mind one to Mars, would have to be done that way -- and   
   things will undoubtedly be done that way (using some space station, not   
   necessarily the current one) eventually.  The question is whether it's   
   worth doing this for initial, relatively modest expeditions.   
      
   The answer depends quite sensitively on the assumptions you make, like   
   whether the current space station is used (it's in a poor orbit and is not   
   equipped for the job), just how big your expedition is, and whether your   
   goal is a one-shot program like what Apollo became, or something with an   
   orderly growth path.   
      
   There are two classical problems with this concept.  First, it incurs some   
   up-front investment which isn't repaid quickly, so it scores poorly by the   
   standards of people who propose one-shot programs (some of whom don't   
   realize that that is what they are proposing...).  Second, it involves you   
   immediately with the extremely expensive and inefficient bureaucracy that   
   runs current US manned spaceflight, and some advocates of NASA Mars   
   expeditions fantasize that their schemes can somehow avoid such   
   involvement if only they avoid using the shuttle and the station.   
      
   >...the thrust required might be only   
   >1/20 of what it would be if launched from earth, so a small propulsive   
   >system will do the job.   
      
   Yes and no.  There are still efficiency losses if thrust is too low, so   
   you don't want to make the propulsion system too small.   
   --   
   MOST launched 30 June; science observations running     |   Henry Spencer   
   since Oct; first surprises seen; papers pending.        | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
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