From: root@mauve.demon.co.uk   
      
   Mike Miller  wrote:   
   > Scott Moore  wrote in message news:...   
   >> If you can forgive a dumb space question or two:   
   >>   
   >> 1. assuming the next "big prize" would be an orbital vehicle, what is the   
   lowest   
   >> altitude an object can be orbited at, if only for a circuit or so ?   
   >   
   > At 90-100 miles, drag should be low enough to complete one orbit.   
      
   It depends somewhat on the density of the object.   
      
   If it's really low (a balloon) then it'll need to orbit much higher than   
   if it's a solid 100m long bar of tungsten.   
      
   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) but the bar of tungsten by only   
   a billionth of a the same amount, and it'd take some 15 years to slow   
   as much.   
   (though as it slows down, it drops, so it'll come in faster, maybe a   
   few months.)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)