The 29-foot, solar-powered craft had an original mission of 270 days.
The Air Force said the second mission was to further test the technology but the ultimate purpose has largely remained a mystery.
The vehicle’s systems program director, Lieutenant-colonel Tom McIntyre, told the Los Angeles Times in December: ‘We initially planned for a nine-month mission. Keeping the X-37 in orbit will provide us with additional experimentation opportunities and allow us to extract the maximum value out of the mission.’
It kind of looks like the space shuttle from the picture.