NASA X37B: Secret US space plane lands itself

The return of a robotic space plane to Earth last week marked a milestone for US space capabilities, but did nothing to lift the veil of secrecy surrounding the vehicle's mission.

After spending more than seven months in orbit, the US Air Force's X-37B spacecraft returned safely to Earth on Friday, landing at Vandenberg Air Force Base in California.

The vehicle is the first in the history of the US space programme to reach orbit and return autonomously to a runway, the BBC reports.

The 9-metre-long plane, which resembles the space shuttle but is roughly a quarter the size, carries a shuttle-like cargo bay that is about the size of the bed of a pickup truck. Its ability to land on a runway means it has the potential to be used to routinely loft instruments to space and bring them back, or even to retrieve objects already in orbit.

In all likelihood, space analysts say, such planes will be used to carry sensors or deploy satellites that can be used to spy on Earth. But little information has been forthcoming about the nature of the X-37B's first mission or the plane's intended purpose.

That's raised some concerns that the plane could have a dual use, carrying instruments that could zap satellites belonging to other countries.