I guess a little basic flight school is called for here.

Airspeed at sea level (ASL) is a constant. The same as groundspeed. As altitude increases the air thins. The aircraft is traveling through less air for a given distance traveled over the ground than it would at a lower altitude. Although indicated airspeed (IAS) is one thing at sea level and the same thing at altitude, you must compensate for thinning air at altitude by increasing ground speed. If you are traveling through air at 2200 mph indicated air speed in sea level pressure of APX 14 psi then your ground speed is 2200 mph. If you are traveling through air at half sea level preasure of 7 psi with an indicated air speed of 2200 mph then your groundspeed is 4400 mph etc. While the airspeed of sound decreases slightly at altitude, its ground speed increases the same way.

One might propose that the stated (official) speed is a ground speed measurement(as its officialy stated range indicates (speed 2200mph/endurance 1 hour).) .This proposal would not work, as, if its groundspeed is 2200 mph and its altitude is 85,000 feet then its indicated airspeed would be 220 mph. Now just between you me and whoever might be reading this, the SR-71 looks to me like it can go through the air at better than 220 mph IAS at sea level and better than 220 IAS at 85,000 feet. In fact I think I could find references to some boats that can do better than that at sea level and so can you.

The atlas facts I got here:

http://www.hq.nasa.gov/office/pao/Hi...d/programs.htm

<font size=-1>[ This Message was edited by: SAMU on 2002-08-22 02:48 ]</font>