In the dead of night, a space plane landed at Nasa’s Kennedy Space Center after over two years in orbit. Although the US Air Force seems to be pleased with how this mission ended, it has been tight-lipped about what it was for.

At only 2.7 metres tall with a 4.2m wingspan, the unmanned Boeing X-37B orbital test vehicle looks like a smaller version of the Nasa space shuttle. It orbited the Earth for 780 days, performing secret experiments for the Air Force before returning home autonomously.

The Air Force says that these experiments “benefit the national space community” and concern areas such as advanced guidance, navigation and control, and reentry and landing. What we don’t know is why this plane was launched into space, or what it learned up there.

Nor likely will you know. To read more, click here.