Mach (speed)

http://en.wikipedia.org/wiki/Mach_number

Mach number (Ma or M)is the speed of an object moving through air, or any fluid substance, divided by the speed of sound as it is in that substance. It is commonly used to represent an object's (such as an aircraft or missile) speed, when it is travelling at (or at multiples of) the speed of sound.

Speed of sound

http://en.wikipedia.org/wiki/Speed_of_sound

True airspeed

http://en.wikipedia.org/wiki/True_airspeed

NASA on Shuttle
http://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html

List of unusual units of measurement

http://en.wikipedia.org/wiki/List_of_unusual_units_of_measurement

Astronomy Answers

http://www.astro.uu.nl/~strous/AA/en/antwoorden/ruimtereizen.html