The secretive U.S. Air Force X-37B space plane recently moved beyond 600 days in orbit as part of a classified test mission that doesn't have a scheduled end date in the near future. The space plane launched on Dec. 11, 2012 onboard an Atlas 5 rocket, and has spent almost one year and nine months in orbit.
Details about the X-37B's exact specifications - and what it is doing in space - remain unknown, but the aircraft is 29 feet in length and stands 9.5 feet tall, with a wingspan of almost 15 feet. Using solar panels, the aircraft is able to stay in space for longer durations, but is still nowhere near the longevity of many U.S. satellites currently in orbit.
"The Air Force continues to push the envelope of the solar-powered X-37B capabilities," said Joan Johnson-Freese, National Security Affairs professor at the U.S. Navy War College.
As nations invest more money into space militarization and counter-space programs, it's important for the United States to continue its own space ambitions, military officers have noted in the past.