The Air Force's top-secret space plane just celebrated its one-year anniversary of space flight.
As of May 20, the X-37B hads been in orbit for one year, the third time the craft has accomplished such a goal.
The space plane launched on its first mission in April 2010, staying in orbit for 224 days. The second and third missions in 2011 and 2012, respectively, both lasted longer than a year.
Now the fourth mission has hit the one-year mark as well, with no announced plans to bring the plane back to Earth anytime soon.
Service officials told Air Force Times simply that they're "excited for this fourth flight and look forward to learning from it."
There are actually two X-37 aircraft, according to the Air Force. Each is about 29 feet long and nine 9 feet high, with a 14-foot wingspan, and they weigh in at 11,000 pounds each. The program began at NASA in 1999 and transferred to the Pentagon in 2004.
The Air Force, however, has remained tight-lipped about what the space planes actually do. An oft-repeated statement from the service says the craft are testing out "advanced guidance, navigation and control, thermal protection systems, avionics, high temperature structures and seals, conformal reusable insulation, lightweight electromechanical flight systems, advanced propulsion systems, and autonomous orbital flight, reentry, and landing."
But experts have also noted the Air Force could likely be testing out systems to disable enemy satellites or rapidly replace U.S. satellites if they're destroyed.
The Air Force said it would not discuss whether the X-37’s fourth mission has had different objectives than its first three.
