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.’

via Secret mission accomplished: America’s secret space plane to land after a YEAR in orbit – and no one knows what it did up there | Mail Online.

It kind of looks like the space shuttle from the picture.