Robot spaceplane returns from hush-hush mission

Craft touches down on the Kennedy Space Centre runway where the now retired space shuttle landed 78 times from 1984 to 2011

The US Air Force's X-37B robotic space plane landed on 7 May after 718 days in orbit. This was the unmanned spacecraft's fourth trip into space and, as before, the precise details of the sojourn are classified.

The only payloads that the military revealed upon the vehicle's launch on 20 May 2015, were a new form of "ion engine", which is an extremely efficient thruster that could extend the life of communications or spy satellites; and a pallet of around 100 samples that were to be exposed to space to see how they degenerate.