DOD’s X-37B to Test Aerobraking

The U.S. Space Force said today the ultra-secretive X-37B spaceplane, in orbit since December, will test aerobraking maneuvers to change its orbit with a minimum amount of fuel. In the process, it will also shed the service module attached to the spacecraft and safely dispose of it in conformance with space debris mitigation standards.

DOD’s X-37B is on its seventh flight, which began on December 28, 2023.

Looking like small space shuttles, the two Boeing-built X-37Bs actually began as a part of NASA’s Orbital Space Plane program to create a vehicle to transport and rescue International Space Station crews. The agency terminated the OSP program in 2004 after President George W. Bush announced a strategy shift for the human spaceflight program that included cancelling the Space Shuttle once construction of the ISS was completed. NASA transferred X-37B to the Defense Advanced Research Projects Agency (DARPA) and it was later taken over by the Air Force’s Rapid Capabilities Office.

DOD shares very little information about what X-37B does on its increasingly long durations in orbit. This is the seventh flight, Orbital Test Vehicle-7 (OTV-7), and how long it will stay in orbit is unclear. Each flight has remained in space for longer and longer durations. OTV-6 reached two-and-a-half years.

First flight: 2010, 224 days
Second flight: 2011-2012, 469 days
Third flight: 2012-2014 674 days
Fourth flight: 2015-2017, 718 days
Fifth flight: 2017-2019, 780 days
Sixth flight: 2020-2022, 908 days

OTV-6 was the first to incorporate a service module that enabled the mission to host additional experiments.  In that case, the service module separated from the spacecraft just before reentry and was “disposed of in accordance with best practices” weeks later.

This time they are separating the service module after just 10 months. OTV-7 is about to execute “a series of novel maneuvers, called aerobraking, to change its orbit … and safely dispose of its service module components in accordance with recognized standards for space debris mitigation.”  It will then resume its mission.

Why the Space Force decided to separate the service module now, and publicize it, even allowing Boeing to put out its own press release and a flashy video, adds to the mystery.

Boeing Vice President of Space Mission Systems Michelle Parker said: “Space is a vast and unforgiving environment where testing technologies is critical to the success of future endeavors” and “there is no other space platform as capable, flexible and maneuverable as the X-37B, and its next demonstration will be another proof point that this test vehicle sets the pace of innovation.”

U.S. Space Force Chief of Space Operations B. Chance Salzman added: “This first-of-a kind maneuver from the X-37B is an incredibly important milestone for the United States Space Force as we seek to expand our aptitude and ability to perform in this challenging domain.”

Aerobraking is not a new concept. NASA uses the technique to put probes into orbit around or land on Mars, for example. The drag from a planet’s atmosphere is used to slow down a spacecraft while expending a minimum amount of propellant.

In this case the X-37B will not be landing, only separating the service module. Afterwards it will “resume its test and experimentation objectives until they are accomplished,” the Space Force said.

DOD provides extremely little information about what the X-37B spaceplanes do. Today’s Space Force statement said only that OTV-7 has been conducting radiation effect experiments and “testing Space Domain Awareness technologies in a Highly Elliptical Orbit.”

At the time of launch, the Space Force didn’t say what orbit they were putting OTV-7 into, but the use of SpaceX’s powerful Falcon Heavy prompted speculation that it might be headed for HEO instead of a low Earth orbit (LEO) used for previous missions. HEO orbits come close to Earth (perigee) over one hemisphere, but swing high (apogee) over the other hemisphere allowing the satellite to linger over that part of the world for hours instead of minutes as illustrated in this COMSPOC video.

Amateur observers soon found it in HEO and have been tracking it ever since. Dutch observer Marco Langbroek is one of them and posted on X today that back in February he hypothesized that OTV-7 would end by using aerobraking, but acknowledged the Space Force’s wording today leaves open the possibility it may remain in space for “days, weeks, or months” in a more typical LEO orbit.

New blogpost:
“X-37B Spaceplane OTV 7 to lower orbit by aerobraking”.
My discussion on what this practically might mean:https://t.co/eJkurxrSDZ

— Dr Marco Langbroek (@Marco_Langbroek) October 10, 2024

As with all the X-37B flights, only time will tell what the future holds.