The US Air Force’s top-secret, unmanned X37-B space plane successfully touched down at Vanderberg Air Force Base in California on Saturday (video below), ending a 469-day marathon mission. The flight was nearly 200 days longer than originally planned, and more than twice as long as the inaugural mission in 2010, which lasted a mere 224 days.

NASA originally started the X-37B project in 1999, but the jet it envisioned was never built, and control transferred to the Defense Advanced Research Projects Agency (DARPA) in 2004. Since so little is known about the plane, speculation about its design runs the gamut from a simple transport vehicle to possible military applications. Whatever the case, we're just hoping the development of smaller, lighter vehicles will lead to cheaper space tour tickets.