Minimum altitude
Wed, 29 Nov 1995 17:07:26 -0500

     In response to the question, "at what altitude (above earths surface) 
     does a satellite begin to "re-enter" what I mean by this is when can 
     it not sustain an orbit anymore, when it begins actually coming down 
     to earth..."
     This ought to raise a lot of discussion, depending on how precise an 
     answer is sought.
     The minimum altitude to complete one orbit is generally considered to 
     be 89 - 93 miles. 
     Of course, that assumes a circular orbit and an average interaction 
     with the earth's atmosphere.  The density of the atmosphere at 90 
     miles is not constant.  It varies due to daily and periodic solar 
     influences.  It also varies with latitude so the inclination of the 
     orbiting satellite is an issue.  In fact, the force of gravity around 
     the world isn't even constant.  
     Anybody else?
     Jeff Barker