The US Air Force's secret Space Plane has been up in the air continuously for almost 500 days, but the Pentagon refuses to say still what the spacecraft, X-37B, is doing up there. There's not even an estimation of when it may come back.
The Daily Beast reports that the rocket was boosted into the air in December of 2012, and has since orbited the Earth thousands of times. The Daily Beast also notes that its trajectory has flown over such places of interest as North Korea and Iran.
The equipment onboard remains shrouded in mystery as well, with some speculating that the X37-B might be employed to assist US soldiers and war efforts around the world. The craft lacks a crew and has no cockpit windows that might give a clue to the goings-on inside, and has a payload bay no largers than the bed of a pickup truck.
As the Daily Mail notes, the craft recently broke the record for the longest X37-B by surpassing the previous record of 469 days.
The X37-B began as a Nasa project to create an unmanned space project, but the project soon passed into the hands of the Air Force. Air Force official tout the X37-B as a great technological achievement but refuses to give insight into the goals of such a long time spend in the air.
As such, there's been much speculation on the mission. The most prominent explanations include that it picks up transmissions from other satellites for intelligence gathering, or drops bombs from an orbital height, or interferes with other satellites. None of these claims have been substantiated with evidence.