The Air Force's mysterious robotic space plane returned to the earth over the weekend, renewing speculation about its mission and capabilities.
For the record, the 29-foot craft, better known as the X-37B, spent 469 days orbiting the earth, far exceeding the 270-day mark set by its sister ship in 2010. The spacecraft landed safely at Vandenburg AFB, California early Saturday, but the service remains mum on what it accomplished during 15 months in space.
However, there is no shortage of theories about the X-37B and what it might be up to.
Popular Science speculated earlier this year that the mini-shuttle was being used to spy on China's new space station:
We know that Tiangong-1--which was launched back in September and is slated to host a manned crew sometime later this year--is in an orbit with an inclination of 42.78 degrees at an altitude of roughly 186 miles. And we know--not from the Pentagon but from a group of vigilant amateur space trackers--that the X-37B is orbiting at about the same altitude and at an inclination of 42.79 degrees. Not only is that orbit strange for a military recon satellite--they usually have polar orbits that offer better access to the entire globe--but it would periodically bring the two orbiters very close together.