From: henry@spsystems.net   
      
   In article ,   
   Lawrence Gales   wrote:   
   >> No, it's less safe than any kind of docking, because now any failure in   
   >> stationkeeping can result in a collision.  Rendezvous & docking at least   
   >> is *over with* quickly.   
   >   
   >How about the  possibility of a special purpose tug docked at the space   
   >station.  A supply rocket comes within a few miles of the station and   
   >ejects a containerized module. The  tug then comes out and feteches it and   
   >docks with the station.   
      
   Putting a tug at the station makes *all kinds* of sense.  Even a tug of   
   quite modest capabilities has a bunch of uses.  Most notably, a supply   
   rocket can enter the lowest practical orbit, and then the *tug* can pick   
   up the cargo there and haul it up to the necessarily-higher station orbit.   
   This saves fuel and increases payload, even after you allow for part of   
   the cargo necessarily being tug fuel.  The improvement is particularly   
   marked if the supply rocket is reusable, which (as Larry notes) runs up   
   its dry mass, thus raising the fuel cost for *it* to go all the way up.   
      
   And this way, all station "proximity operations" are being done by a tug   
   which can be specially built for the job.   
      
   Unfortunately, it requires spending a bit of extra development money, and   
   that's been anathema to the station program for quite a while now.   
   --   
   "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)