From: k_meinhard@gmx.de   
      
   Hallo frank scrooby,   
      
      
   > Rule of thumb with hydrogen as a lifting gas is that you need one   
   > liter per gram that you want to lift.   
   >   
   > So 30,000,000 liters of hydrogen (which I think is about 135 kgs of   
   > hydrogen).   
   >   
   > 30,000,000 liters is 30,000 cubic meters.   
   >   
   > Assuming a spherical envelope: volume = 4/3 * pi * r^3   
   >   
   > My untidy (and very poorly exercised) math  says:   
   >   
   >   
   > 90,000 = 4* pi * r^3 90,000 / (4 * pi) = r^3 7162.183 = r^3 r =   
   > 19.27m   
   >   
   > A balloon 40 meters in diameter doesn't sound that big... but I'm   
   > not a balloon man.   
      
   I didn't check the math, but I think you forgot the expansion of the gas   
   with height, which will be extreme at stratospheric heights.   
      
   There are some nice pictures and numbers at   
      
      
   > Now if the balloon is aluminium covered mylar then it will certainly   
   > stand out on radar. If it is something less obvious, with a layer of   
   > radar absorbing material (like the F-117 was painted with) it might   
   > be able to avoid detection.   
      
   If the envelope is not silvered by aluminium, it won't reflect radar   
   very well. No need for stealthing that. The rocket is radar-reflective,   
   of course.   
      
      
      
   --   
   Mit freundlichen Grüßen,   
      
   Klaus Meinhard   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)