Mysterious robotic plane hits 500 days in space; what's it doing?

A robotic space plane is speeding in low Earth orbit at this very moment. Some say it's a weapon; others, a data-gathering mission. There's one fact most agree on as the plane hits 500 days in space: Its real purpose is a mystery.

The Boeing-built X-37B Orbital Space Vehicle, constructed in California, is one-fourth the size of the Endeavour Space Shuttle.

Whatever its real purpose, the X-37B has very real capabilities. It travels low in orbit, staying around 110 to 500 miles above the Earth at a cruising speed of about 17,500 mph. It's equipped with special heat-shield tiles for re-entry, which are billed by Boeing as tougher than Endeavour's.

But the government's treatment of the project poses questions. Though it's advertised as a secret project, Boeing releases pictures and more than two pages of details on the X-37B. In contrast, the secret, super-fast Lockheed SR-71 Blackbird was not declassified until decades after it had been used in the Vietnam War.