Scientists in protective suits inspect the solar-powered craft prior to its mission
The U.S Air Force's highly secret unmanned space plane was supposed to stay in space for nine months, but it's now been there for a year and three days - and no one knows what it's doing.
The experimental craft has been circling Earth at 17,000 miles per hour and was due to land in California in December.
However the mission of the X-37B orbital test vehicle was extended - for unknown reasons.
The plane resembles a mini space shuttle and is the second to fly in space.
The first one landed last December at Vandenberg Air Force Base in California after more than seven months in orbit.
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.'
The X-37B sits on top of an Atlas V rocket as it's launched at Cape Canaveral Air Force Station in Florida
However, many sceptics think that the vehicle's mission is defence or spy-related.
There are rumours circulating that the craft has been kept in space to spy on the new Chinese space station, Tiangong.
However, analysts have pointed out that surveillance would be tricky, since the spacecraft would rush past each other at thousands of metres per second.
And Brian Weeden, from the Secure World Foundation, pointed out to the BBC: 'If the U.S. really wanted to observe Tiangong, it has enough assets to do that without using X-37B.'
Last May, amateur astronomers were able to detect the orbital pattern of the first X-37B which included flyovers of North Korea, Iraq, Iran, Pakistan and Afghanistan, heightening the suspicion that the vehicle was being used for surveillance.
Other industry analysts have speculated that the Air Force is just making use of the X-37B's amazing fuel efficiency and keeping it in space for as long as possible to show off its credentials and protect it from budget cuts.
After all, under budget cuts for 2013 to 2017 proposed by the Obama administration, the office that developed the X-37 will be shut down.
According to X-37B manufacturer Boeing, the space plane operates in low-earth orbit, between 110 and 500 miles above earth. By comparison, the International Space Station orbits at about 220 miles.
The current flight launched from Cape Canaveral, Florida, in March.