From: henry@spsystems.net   
      
   In article ,   
   John Bartley  I solved my XP problems w/ Service Pack Linux  wrote:   
   >> No outsider has yet been able to make the numbers add up for the system as   
   >> described.  It seems to assume impossibly good aerodynamics...   
   >   
   >The analysis does include their three-element system (# 1 ship,   
   >ground-to-station / station in the stratosphere / #2 ship, station to   
   >LEO), right?   
      
   Right.  The problem is that the orbiter appears to need an impossibly good   
   L/D ratio to support itself (its buoyancy is helpful only briefly) while   
   spending several days accelerating to orbital velocity on low-thrust   
   propulsion.  Real-life hypersonic L/D is generally pretty lousy, and while   
   this thing *is* rather unconventional by hypersonic-vehicle standards,   
   nobody can see any reason why it would have a radically improved L/D.   
      
   >Does it also consider the possibility of using hydrogen in the #2   
   >ship; hydrogen, lighter than He, is not very flammable at the low   
   >pressures 20 miles up.   
      
   Hydrogen does not, alas, increase the lift very *much* -- it gives 93% of   
   the lift that vacuum would, while helium gives 86%.  The difference is not   
   big enough to be worth a lot of trouble; the main reason early balloons   
   and airships used hydrogen was that it's a whole lot cheaper and easier to   
   get.  (The Hindenberg was designed for helium, but used hydrogen because   
   the US -- which controls most of the world's helium supply -- refused to   
   sell bulk helium to Nazi Germany.)   
      
   >...they've got a track record with their PongSats, so perhaps   
   >they don't need any Unobtanium to make it work.   
      
   Yeah, if it was just *anybody* proposing this, they'd simply have been   
   written off as crazies.  JP clearly has its act together on dealing with   
   lesser technical challenges, so insanity is not a convincing explanation   
   in this case.  Hence people are puzzled.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
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