Smallest robotic spaceplane

The Boeing X-37B is an unmanned spaceplane which launches on an Atlas V rocket and returns to Earth as a glider, much like the retired space shuttles, before touching down on wheels. Measuring 8.9 m long with a wingspan of 4.5 m and a loaded mass of around 4,990 kg, it is only the second type of space vehicle to land unmanned on wheels, after the Soviet Buran shuttle. Two X-37Bs exist to date, the first was launched into orbit on 22 April 2010 and landed on 5 December 2010. The mission for a second vehicle began on 5 March 2011 and, in November 2011, the US Air Force announced that it would be extended beyond the initial design of 270 days. The mission and payload of both flights are secret.