The mysterious US Air Force X-37B space plane has now spent over 600 days in orbit. Designated USA-277, the mission is the fifth flight of the X-37B’s program.
Resembling a small space shuttle orbiter, the X-37B was launched aboard a SpaceX Falcon 9 on September 7, 2017. Although the exact nature of the mission and the majority of the payloads carried aboard the X-37B are classified, the Air Force has revealed that it’s carrying the Advanced Structurally Embedded Thermal Spreader II, a payload that measures the performance of an oscillating heat pipe. Additionally, it is believed that the X-37B also carried a number of small satellites, although there has been no official confirmation.
USA-277 surpassed 600 days in orbit early this week. Prior to the launch of USA-277, only two other X-37B missions had surpassed 600 days. USA-240 was launched in December 2012 and completed 674 days in orbit. The following mission, USA-261 was launched in May 2015 and completed 717 days in orbit. These milestones were achieved in consecutive order hinting that USA-277 may remain in orbit well past the 700-day mark.
Once its mission is completed, the X-37B will return to Earth and touchdown horizontally like a traditional plane ready to be reused again.