Unmanned US Air Force plane completes 400 days in Earth orbit
The US Air Force's unmanned space plane X-37B has completed 400 days in Earth's orbit as part of its fifth secretive mission. The aircraft is orbiting at a height of around 320 km and is powered by solar cells with lithium-ion batteries. It was launched aboard one of Elon Musk's SpaceX Falcon 9 rocket at NASA's space centre in Florida. 