X-37B

The second flight of the U. S. Air Force's secretive unmanned space vehicle, the X-37B, is set for tomorrow afternoon from Cape Canaveral. Of course, keeping a space launch secret is next to impossible, so the USAF doesn't really try, but it doesn't share what the X-37B does in orbit. The vehicle, which resembles a small space shuttle, complete with payload bay, launches atop an Atlas 5 rocket, but glides home, landing itself on a runway. It can stay in space for months, generating its electricity through a solar power array, which would put an upper limit on the amount of energy it requires.

The program was originally pursued by NASA, but was shifted to the Defense Department, and on to the USAF, for budgetary reasons.