Corrected entry: Near the beginning of the book, the X-33 airplane travels at Mach 15, "hurtling through space at 11,000 miles per hour." There's a slight problem with this, however: 11,000 miles per hour at this altitude (60,000 feet) is actually over Mach 16, because the speed of sound decreases with altitude.
redbaron2000
11th May 2006
Correction: In fact there is no problem at all. Mach 1, when used as a measure of aircraft speed, is defined as 'the speed of sound in air at sea level at one atmosphere'. It does not alter with the local speed of sound, so ironically a high flying aircraft witll break 'the sound barrier' while flying at about Mach 0.92.