Early on Sunday, the US Air Force announced that its X-37B space plane had returned to Earth, touching down at Kennedy Space Center’s Shuttle Landing Facility in Florida. The uncrewed space plane had spent 779 days, 17 hours in space, breaking its own long-duration record.
During four previous missions dating back to 2010, the X-37B had previously flown for as long as 717 days, 20 hours—during a period from May, 2015 through May, 2017.
The latest mission launched on September 7, 2017 aboard a Falcon 9 rocket.
As ever, the biggest question surrounding the Air Force’s space plane concerned what it was up to during its long flight in low-Earth orbit. “The spaceplane conducted on-orbit experiments,” an Air Force news release stated, blandly. “The distinctive ability to test new systems in space and return them to Earth is unique to the X-37B program and enables the US to more efficiently and effectively develop space capabilities necessary to maintain superiority in the space domain.”
According to Randy Walden, Air Force Rapid Capabilities Office director, this fifth flight of the X-37B successfully hosted Air Force Research Laboratory experiments, as well as providing a ride for small satellites. (It is not clear whether the space vehicle deployed these satellites. If so, the lack of disclosure may violate the United Nations Registration Convention satellite expert Jonathan McDowell noted on Twitter).
The X-37B resembles NASA’s space shuttle, but at less than 10 meters in length it is considerably smaller. The vehicle’s cargo bay can hold something about the size of a standard refrigerator. Sources have suggested it serves several purposes for the Air Force, including as an in-orbit test bed for developing advanced surveillance sensors.
It is part of the Air Force’s goal of developing more nimble, responsive capabilities in space. Reusable space planes such as the X-37B and rapid-launch capabilities are among the needs the military sees as it confronts space as a “warfighting” domain in the 21st century. In this case, almost all of this mission was reusable, as the Falcon 9 rocket’s first stage landed safely shortly after its launch.
The Air Force said it will launch a sixth mission of the space plane sometime in 2020 from Cape Canaveral Air Force Station in Florida.