Originally Posted by Larry Jacks

Just as an aside, I'm a bit surprised that a sonic boom would be heard from 80,000 feet. I would have thought that the air would be too thin to produce a boom at ground level. What is the maximum altitude that can produce a sonic boom?

I don't know the answer to your question, but I've read many times that the SR-71 (traveling at Mach 3+ and up to 85,000 feet) left sonic booms in its wake. Loud ones.

As for the Shuttle, as its speed decays to the supersonic to sonic ranges, the glide ratio is very steep (as much as 20 degrees nose down). It glides like an anvil. You'd probably have to be pretty close to the Cape to see it.