dsinc sends this quote from an AP report about the U.S. Air Force's X-37B spaceplane
"The Air Force launched the unmanned spacecraft Tuesday hidden on top of an Atlas V rocket. It's the second flight for this original X-37B spaceplane. It circled the planet for seven months in 2010. A second X-37B spacecraft spent more than a year in orbit. These high-tech mystery machines — 29 feet long — are about one-quarter the size of NASA's old space shuttles and can land automatically on a runway. The two previous touchdowns occurred in Southern California; this one might end on NASA's three-mile-long runway once reserved for the space agency's shuttles. The military isn't saying much, if anything, about this new secret mission. In fact, launch commentary ended 17 minutes into the flight. But one scientific observer, Harvard University's Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics, speculates the spaceplane is carrying sensors designed for spying and likely is serving as a testbed for future satellites."