From: dietz@dls.net   
      
   Allen Meece wrote:   
      
   > <>   
   >      Remember, this vehicle is *floating* on air, thin air but still air. It   
   > therefore takes very little power to accelerate the vehicle, just enough to   
   > overcome the small drag of the thin air. As the balloon accelerates, it is   
   > nudged upwards a little, the air gets thinnner, the drag decreases, the   
   balloon   
   >  speeds up and repeats the process.   
      
   It's easy to see that bouyancy forces will be small compared to drag   
   forces at all but low speed (probably below Mach 1).   
      
   My take on this idea is that they aren't going to use ion engines as   
   such, but some higher thrust electric engine.  For example, a scheme   
   that applies an electric field along the passing airstream and accelerates   
   injected ions, which accelerate the air by ion/neutral collisions.   
   I also suspect their thrust/weight ratio is intended to be very high,   
   and they take a long time to reach orbit only because of limits on the speed   
   of the vehicle due to the extremely flimsiness of the design.   
      
   	Paul   
      
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