From: root@mauve.demon.co.uk   
      
   Allen Meece  wrote:   
   > Ian Stirling wrote:   
   >> At 100Km, and at orbital speeds, the pressure exerted by the atmosphere   
   >> on the vehicle is around 2Kg force/square meter.   
   >> This will cause a balloon to slow at around 20000m/s (it'll effectively come   
   >> to a stop in half a second and drift down)   
      
   As a further note, to increase the atmospheric density by a million fold, you   
   need to drop down from 100Km to around 22Km.   
      
   This means that to get an orbit similar to one at 100Km at 22Km, you need   
   a million times the density per unit area.   
      
   I was assuming that the average sectional density was around a gram   
   a square meter for the balloon, and there was no lift.   
      
   >   JP Aerospace may not agree with this pessimistic view of balloon behavior   
   in   
   > orbit. Balloons can be built streamlined to have lift and they can assume an   
   > angle of attack that will be forced upward by the high speed slipstream.   
      
   A lot of people think that JP Aerospace are on really, really good drugs,   
   to believe this.   
      
   >   I  think they'll want to avoid all air molecules and orbit higher than 200   
   > km altitude though.   
      
   There is significant atmosphere (for very low density satellites)   
   to be significant at 200Km.   
      
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