The US military's small, top-secret version of the space shuttle has rocketed into orbit for another mystery mission, two years after making the first flight of its kind.
The air force launched the unmanned spacecraft hidden on top of an Atlas V rocket.
It is the second flight for this X-37B spaceplane, which 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 the US space agency's old space shuttles and can land automatically on a runway.
The military is not saying much, if anything, about this new mission. Launch commentary ended 17 minutes into the flight.
But one scientific observer, Harvard University's Jonathan McDowell of the Harvard-Smithsonian Centre for Astrophysics, speculated the spaceplane is carrying sensors designed for spying and is probably serving as a testbed for future satellites.
While acknowledging he does not know what the spaceplane is carrying, Mr McDowell said on-board sensors could be capable of imaging or intercepting transmissions of electronic emissions from terrorist training sites in Afghanistan or other hot spots.
The beauty of a reusable spaceplane is that it can be launched on short notice based on need, Mr McDowell said.
The two previous secret flights were in orbits roughly 200 miles high, circling at roughly 40-degree angles to the equator. That means the craft flew over the swath between 40 degrees or so north latitude and 40 degrees or so south latitude.