From: henry@spsystems.net   
      
   In article ,   
   Tim McDaniel  wrote:   
   >>And doing aerocapture -- shedding a *lot* of velocity with a single   
   >>pass, using a heatshield and active control -- is rather iffy ...   
   >>Nobody's used aerocapture even for Mars, yet.   
   >   
   >Mars Climate Orbiter.   
      
   Except that nobody actually knows whether MCO emerged from the atmosphere   
   still in solar orbit, in a very short-lived Mars orbit(*), or not at all.   
      
   I should have explained the terminology in more detail:  aerocapture   
   means ending up in *orbit*, not on the surface (and especially not on the   
   surface in little pieces :-)).  Going down to the surface by aerodynamic   
   braking straight from interplanetary trajectory is straightforward, as   
   witness Mars Pathfinder and the MERs.  But entering orbit that way is   
   very tricky.   
      
   (* For the first hour or so after MCO loss of signal, JPL was frantically   
   sending instructions for an emergency perigee-raising burn, because if   
   MCO's solar array had come off about when expected, there was a reasonable   
   chance for the rest of the spacecraft to end up more or less intact in a   
   low Mars orbit... except that the perigee(**) of the first orbit would have   
   been still deeper in the atmosphere, so without a burn there wasn't going   
   to be a second orbit.  Not that there was much left of the mission without   
   the array, but a few things might have been learned before MCO died.  Alas,   
   if MCO did emerge, it wasn't in good enough shape to report in. )   
      
   (** Technically "perigee" is correct only for an Earth orbit.  Tough. )   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)