Mystery spaceplane blasts off

CAPE CANAVERAL, Fla. - The military's small, top-secret version of the space shuttle rocketed into orbit Tuesday for a repeat mystery mission, two years after making the first flight of its kind.

The Air Force launched the unmanned spacecraft Tuesday hidden on top of an Atlas V rocket. As if on cue, clouds quickly swallowed up the rocket as it disappeared out over the ocean.

It is the second flight for this original X-37B spaceplane. The craft 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 known as OTV-3, or Orbital Test Vehicle, flight No. 3.

But one scientific observer, Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics, speculates that the spaceplane is carrying sensors designed for spying and likely is serving as a test bed for future satellites. He dismisses rumors of "exotic ideas" for the X-37B as weaponry or shadowing a Chinese satellite.

While acknowledging he does not know what the spaceplane is carrying, McDowell said that onboard sensors could be capable of imaging or intercepting transmissions of electronic emissions from terrorist training sites in Afghanistan or other hot spots. "All the sorts of things that spy satellites generally do," he said.

The beauty of a reusable spaceplane is that it can be launched on short notice based on need, McDowell said.