From: henry@spsystems.net   
      
   In article ,   
   Rick Jones   wrote:   
   >> An ion drive can only work in a vacuum.   
   >   
   >Is there an atmosphere on Europa?  I figured that any ice   
   >melted/vaporized by the drive exhaust would simply vent into space. I   
   >see now with a bit of web searching that there is indeed atmosphere on   
   >Europa.  So much for that... :)   
      
   Europa's atmosphere is much too thin to be a significant issue, actually.   
   But the water vapor boiling off from the bottom of the hole will be coming   
   straight up into the ion engine; it doesn't dissipate into space instantly.   
      
   >> Europan ice might contain materials other than water, and may not be   
   >> free of solid debris...   
   >   
   >I'd not considered non-meltable debris in the ice.  That is a good   
   >point. That would indeed do a number on just melt and drop.  I wonder   
   >what the chances are of there being such stuff in the ice?   
      
   Probability pretty high, considering things like the assorted colors   
   seen on the surface.   
   --   
   MOST launched 30 June; science observations running     |   Henry Spencer   
   since Oct; first surprises seen; papers pending.        | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)