The US Air Force’s secret space plane has been up in orbit for nearly 500 days — a space endurance record. But nearly a year and a half into the mission, the Pentagon still won’t say what the is doing up there, or when it might come back.
At the time of its maiden launch, the (far right) was the smallest and lightest orbital spaceplane yet flown. Both the North American and SpaceShipOne were suborbital. Of the spaceplanes shown, only the and Buran conducted unmanned spaceflights.