[jaydubya2]

Thanks Jack,

So, based on your comment, and what I read on the web, Altitude is not a factor in calculating the speed of sound. Temperature (density) is the determining factor. So, at 120k ft @ -94F, the speed of sound is 638.97 mph.

[mamelukesabre]

Altitude *IS* a factor. The higher up you go in the column of air, the lower the weight of the atmosphere above it.

[Jack Hydrazine]

That sounds about right.

If you want to see what it is like to drop from 94,000+ feet watch this video.
http://www.youtube.com/watch?v=Pl2OIQMbZhg

I think what would be a fun project to do is make an R/C skydiving dummy that you would drop from a balloon. Once it gets into range pop the chute and guide it back for a landing.

[Melas]

So, based on your comment, and what I read on the web, Altitude is not a factor in calculating the speed of sound. Temperature (density) is the determining factor. So, at 120k ft @ -94F, the speed of sound is 638.97 mph.

Yeah, but how aren't temperature and density related to altitude? For all practical purposes, the two are one and the same. The higher you go, the colder and less dense the atmosphere. Even the thermosphere isn't really an exception. You might find molecules and atoms exited to temperatures that would melt concrete, but the molecules are so far apart (kilometers) that you'd flash freeze if you stepped out into it. Even if you came into contact with any of the superheated gasses, the total amount of energy would be so slight, that you couldn't physically detect it without advanced instruments.