QUESTION:
Could you tell me at what altitude the hst orbits?

ANSWER from Jack Leibee on March 20, 1996 :
 Currently, the HST is orbiting the earth at an altitude of 320 
nautical miles (nm).  (I'll leave it to you to convert to regular miles).  The 
orbit is nearly circular, so the highest and lowest points in the orbit differ 
by less than a thousand feet or so.  

Someone asked during the program the effect of solar cycles on 
HST.  The answer is that as the solar activity increases, its effect is to 
slightly expand the earth's atmosphere.  Since the HST is is just on the
edge of 
the atmosphere, this expansion causes the HST to slow down (caused by the very 
small friction between the HST and the atmosphere) and is called "atmosphereic 
drag. Consequently, the HST's orbital altitude is reduced.  From 1990 until
late 
1993, HST's altitude decreased by about 10 nautical miles.  During the 1993 
Servicing MIssion, the Space Shuttle lifted the HST up by about 6 nm.  The same 
thing will have to be done in 1999 to prevent the HST from re-entering and 
crashing to the ground.

Jack Leibee
HST Operations Manager