From: schillin@spock.usc.edu   
      
   ghazan@ghazan.haider.name (Ghazan Haider) writes:   
      
   >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...   
      
   You are in error w/re Sputnik 1.  That spacecraft's orbit was an ellpise   
   with the perigee at 227 km and apogee at 945 km.  It only ever flew at   
   31 km in the sense that it flew at every altitude between 1 and 226 km,   
   which is to say very briefly with a big-ass rocket underneath to lift   
   the whole thing as quickly as possible to the 227+ km destination orbit.   
      
   >Building and launching baloons are the currently cheapest way to send   
   >payload high above. A rocket launched horizontally and then detaching   
   >could further push the payload to the lowest orbit. I would imagine   
   >for a 1kg payload, the rocket can be pretty small and maybe a single   
   >stage solid fuel, which is legal for amateur rocketry in many places.   
      
   The highest altitude for balloons is about 50 km, the lowest altitude   
   for anything resembling an orbit is about 150 km, and you aren't the   
   first to suggest balloons might be used as a first step to orbit.   
      
   But keep in mind, going up is only ~15% of the problem.  ~85% of the   
   difficulty of getting to orbit is the going very fast horizontally   
   part, and since the balloon only handles 1/3 of the "going up" part   
   of the problem, the rocket is going to be doing 95% of the work in   
   any event.   
      
      
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