It's been five years since the first launch of the Air Force's X-37B mini-shuttle, and outside observers-meaning those who lack the proper security clearances-still know little more about this mysterious unmanned vehicle than they did in 2010 (see "Space Shuttle Jr.," Dec. 2009/Jan. 2010). But after three completed flights and a fourth launch last May (the spaceplane was still in orbit as of mid-December), they're at least able to make educated guesses.
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