From: g_d_pusch_remove_underscores@xnet.com   
   Copy: ghazan@ghazan.haider.name   
      
   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   
      
   I suggest you go back and check your facts. A near-trivial google search   
   for "sputnik-1 perigee apogee"" found that Sputnik 1 had a perigee of   
   142 miles (229 km), and an apogee of 588 miles (946 km).   
      
      
   > would yield enough resistance not to allow that, so I have this   
   > question: How high is the lowest possible orbit   
      
   Zero meters --- since every time you drop something, it's in free fall,   
   and therefore in orbit. (Oh, you meant _stable_ orbit?  They don't exist.   
   You will need to first to specify how _long_ you want the orbit to last   
   before re-entry, and the mass to frontal area ratio of your satellite...)   
      
      
   > and how high is the highest baloon range?   
      
   43 km has been achieved, as you could have easily found by googling for   
   "balloon altitude record." However, in principle, the upper limit is   
   determine by the strongest, lightest balloon fabric or membrane available,   
   and it is not obvious what this limit will be.   
      
      
   > Building and launching baloons are the currently cheapest way to send   
   > payload high above.   
      
   It is very easy to get to a high altitude --- even a single-stage rocket   
   can exceed 100 km. Less than 5% of the total energy put into a satellite   
   is used to lift it to its orbital altitude; more than 95% of the energy   
   is spent accelerating it to a large enough horizontal velocity to _stay_   
   at that altitude for any significant length of time.   
      
      
   > 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.   
      
   You are very, VERY, =VERY= much mistaken; you will only reduce the total   
   delta-vee requirement by a small amount.   
      
   The major benefit of launching from altitude is that your rocket won't   
   need an altitude-compensating nozzle; however, it will be nearly as big as   
   if you launched it from the ground.   
      
      
   > I'm also curious about the atm pressure at the highest baloon altitude.   
      
   For all practical purposes it is a good vacuum. The record-holding manned   
   balloon flights required full pressure suits, just like an astronaut would.   
      
      
   > What kind of a suit will I need if I tie an ankle to a cheap huge nylon   
   > baloon with lots of hydrogen?   
      
   That depends on how big the balloon is. But you better wear nomex fire   
   coveralls outside it, to protect you when a stray spark causes your   
   hydrogen balloon to do a "Hindenburg" on you...   
      
      
   -- Gordon D. Pusch   
      
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