I like the semi-gibberish official explanation:<p><i>The orbiters "perform risk reduction, experimentation and concept-of-operations development for reusable space vehicle technologies," the Air Force has said without providing details. The cost of the program is also classified.</i><p>How, pray tell, does anything "perform risk reduction"? Does that phrase have any meaning in English, or any other terrestrial language?<p>"The cost of the program is also classified." - naturally! As someone much, much smarter than me noted, there's very few real state secrets, but there's tons of career-ending blunders, accounting mistakes, ridiculous overcharging and independent validation and verification companies that just happen to be owned by a distant relative. Those categories are not mutually exclusive.