From: root@mauve.demon.co.uk   
      
   Ghazan Haider  wrote:   
   > Research baloons have flown at 51km above sea level, and yet the   
   > sputnik 1 flew at 31km. 20 km below where the highest baloon can fly   
   > would yield enough resistance not to allow that, so I have this   
   > question: How high is the lowest possible orbit and how high is the   
   > highest baloon range? OK thats two questions...   
      
   Atmospheric density /Frontal areal density is where it's at.   
      
   The orbits for a 20m long tungsten rod, and a 1um thick mylar   
   balloon will be similar when the atmospheric density is different   
   by a factor of a hundred million.   
   (neglecting for the moment slight variances in orbital speed).   
      
   As a very very rough estimate, if the atmospheric mass it meets is   
   above the mass of the orbiting body per orbit, then it'll come down.   
   So, for a 40000Km long orbit, I make that around 30-40Km altitude for   
   a 20m long tungsten bar, and (from memory, my server with the density   
   -height tables on is down) around 200Km for the balloon.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)