From: henry@spsystems.net   
      
   In article ,   
   David Given   wrote:   
   >There are people here with more technical knowledge than I, but I do know   
   >that the shuttle's main engines aren't restartable. (Do they even have   
   >on-board fuel tanks?)   
      
   Not for the main engines.  Which, as you note, are not restartable.   
   (There is no fundamental reason why they couldn't be, but there is no   
   requirement for it, and so various details of setup for engine start are   
   handled with the help of ground equipment.)   
      
   >How about fitting the shuttle out with a lifeboat? Stick it somewhere in   
   >the cargo bay. If a shuttle gets sufficiently damaged that it can't   
   >reenter, you use the capsule to get the crew down.   
      
   It's been proposed many times.  It presents some problems of physical   
   layout, its mass puts a considerable dent in the payload capacity... and   
   note that it wouldn't have saved Columbia's crew, since they didn't know   
   something was badly wrong until too late.  (Nor is there any plausible   
   scenario where they would have.  Suspicions about TPS damage were focused   
   on the tiles, not the RCC leading edge, and no plausible imaging -- from   
   the ground or from elsewhere in space -- would have been at all likely to   
   notice a small dark hole in a black surface.)   
      
   >Depending on whether the capsule had its own thruster system, you would   
   >get the choice of putting the shuttle onto a reentry trajectory and then   
   >bailing out, or leaving the shuttle on orbit and just returning in the   
   >capsule.   
      
   You'd want the capsule to do its own maneuvering, partly so that entering   
   it and separating wouldn't be time-critical operations, partly to cover   
   cases like the orbiter being unable to do its own deorbit burn.  This   
   isn't that big a deal; a deorbit burn isn't large.   
      
   >...You'd also have to outfit the shuttle   
   >with an automated station-keeping facility using the OMS; you wouldn't   
   >want it to accidentally fall on someone.   
      
   The orbiter will be dead and uncontrolled within days anyway:  when its   
   fuel cells run out of reactants, it loses power.   
      
   >(What's the lightest-weight way of getting a single human down from orbit?   
   >Could you build something like an orbital parachute? If so, would that be   
   >more appropriate than a combined capsule?)   
      
   There have been various proposals for "orbital bailout" kits.  But a shared   
   capsule is probably better:  it keeps the crew together, it can serve as   
   shelter or boat, it simplifies providing sizable amounts of survival gear   
   and electronics, it greatly simplifies cases where someone is injured.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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