The aircraft, resembling a miniature space shuttle
and known as the Orbital Test Vehicle or X-37B,
spent 674 days in orbit around the planet.
It was the unmanned plane’s third space flight, but
its mission has been shrouded in mystery.
A theory that it was taking a look at China’s space
lab has been downplayed by experts.
Air Force officials have only told US media the
aircraft performs “risk reduction, experimentation
and concept-of-operations development for
reusable space vehicle technologies”.
The X-37B programme, started in 1999 and is
currently run by the Air Force’s Rapid Capabilities
The first plane flew in April 2010 and returned after
eight months. The second launched in March 2011
and remained in space for 15 months.
The current aircraft – built by Boeing – uses solar
panels for power in orbit, measures over 29ft (9m)
long, has a wingspan of nearly 15ft and a weight of
11,000lbs (4,989 kg).
It looks like a mini space shuttle and can glide back
down through the atmosphere to land on a runway,
just like Nasa’s re-usable manned spaceplane used
to do before its retirement.