Article Posted on : - Dec 12, 2012

The Atlas V rocket blasts off from Space Launch Complex-41 with the US Air Force's third Orbital Test Vehicle (OTV-3). A ULA photo

CAPE CANAVERAL (AP): A top-secret mini-space shuttle has blasted off from Cape Canaveral in the US.

The Air Force launched the unmanned spacecraft Tuesday aboard 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 mystery machines are about one-quarter the size of NASA's old space shuttles, and they can land automatically on a runway.

The military isn't saying much, if anything, about this new secret mission. 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.

The two previous secret flights were in orbits roughly 200 miles (321 kilometres) high.