Details About X-37B Payload Adapter Revealed After Record-Setting Mission

The sixth X-37B mission saw the uncrewed spaceplane fitted with a new service module to boost its payload capability.

byThomas Newdick|
U.S. Air Force photo by Staff Sgt. Adam Shank


For the first time, we’ve got to see the U.S. Space Force’s top-secret X-37B reusable spaceplane together with its service module, a bolt-on payload package that boosts the number of missions that this shadowy uncrewed orbital platform can undertake. The photo disclosure came soon after X-37B Orbital Test Vehicle-6, or OTV-6 — signaling its sixth mission — returned to Earth after a record 908 days (or roughly two and a half years) spent in orbit.

X-37B OTV-6 touched down at NASA’s Kennedy Space Center Shuttle Landing Facility on Saturday, at 5:22 AM local time, accompanied by sonic booms heard around Florida.

In line with the X-37B test missions, not a huge amount has been released regarding the nature of the experiments that were carried out while in orbit. There has long been widespread speculation that the two X-37Bs might also be used for gathering intelligence or other operational military missions of some kind.

We do know that its work on OTV-6 included examining the effects of cosmic radiation and other “space effects” on plant seeds and various material samples, as well as deploying a Naval Research Laboratory payload that’s capable of capturing solar power and beaming that energy back to Earth in the form of microwaves.

The mission, which began with a launch atop a United Launch Alliance Atlas V rocket at Cape Canaveral Space Force Station back in May 2020, also included “multiple NASA experiments,” and, very likely, highly classified ones in the military realm, too.

Among the photos released by Space Force after the conclusion of the OTV-6 mission is one that’s especially interesting, since it shows the ring-shaped service module attached to the rear of the X-37B. This was the first mission that saw the service module fitted and an accompanying statement explains that it “[expands] the number of experiments that can be hosted during a mission.”

X-37B orbital test vehicle ahead of its sixth mission, with the service module attached to its rear portion. U.S. Space Force

The module boosts the existing payload capacity of the X-37B, which comprises a truckbed-sized main payload bay, like that found on the much larger NASA Space Shuttle.

Due to the aerodynamic forces experienced by the X-37B vehicle on re-entry, the service module had to be separated before landing, leaving it in orbit. “In the coming weeks, the service module will be disposed of in accordance with best practices,” Space Force says.

The X-37B Orbital Test Vehicle-6 rests on the flight line at NASA’s Kennedy Space Center, Florida, on November 12, 2022, after it concluded its sixth successful mission that lasted 908 days. U.S. Air Force photo by Staff Sgt. Adam Shank

“The deliberate manner in which we conduct on-orbit operations to include the service module disposal speaks to the United States’ commitment to safe and responsible space practices, particularly as the issue of growing orbital debris threatens to impact global space operations,” Secretary of the Air Force Frank Kendall said.

Interestingly, the service module sounds like it has a lot in common with another item, the Evolved Expendable Launch Vehicle Secondary Payload Adapter Augmented Geosynchronous Laboratory Experiment, or EAGLE, from the Air Force Research Laboratory. Tested in 2018, EAGLE is a ring-shaped payload adapter that can maneuver by itself once reaching orbit and is capable of hosting six fixed or deployable payloads. We don’t know if EAGLE is also designed to be launched by the X-37B, but it’s notable that both EAGLE and the X-37B come under the jurisdiction of Space Force’s  Space Delta 9, a unit tasked with performing a mission set described as orbital warfare.

An artist’s conception of EAGLE. Orbital ATK

Lt. Col. Joseph Fritschen, the X-37B Program Director at the Department of the Air Force Rapid Capabilities Office, confirmed that “the addition of the service module on OTV-6 allowed us to host more experiments than ever before.”

“The X-37B continues to push the boundaries of experimentation, enabled by an elite government and industry team behind the scenes,” Fritschen added. “The ability to conduct on-orbit experiments and bring them home safely for in-depth analysis on the ground has proven valuable for the Department of the Air Force and scientific community.”

The X-37B Orbital Test Vehicle-6 sits at NASA’s Kennedy Space Center. U.S. Air Force photo by Staff Sgt. Adam Shank

Jim Chilton, the senior vice president of Boeing Space and Launch, echoed Fritschen’s words. “With the service module added, this was the most we’ve ever carried to orbit on the X-37B and we’re proud to have been able to prove out this new and flexible capability for the government and its industry partners,” Chilton said in a Boeing statement.

While we don’t know everything that the X-37B was carrying on its payload adapter and inside its payload bay, we do know the basics of at least some of the items.

Of these, we have already looked in detail at the Naval Research Laboratory’s aforementioned Photovoltaic Radiofrequency Antenna Module. According to Space Force, “This experiment successfully harnessed solar rays outside of Earth’s atmosphere and aimed to transmit power to the ground in the form of radio frequency microwave energy.” From that statement, it’s unclear if the experiment achieved its goals, although previous statements from the Navy sounded a lot more upbeat.

An October 2019 demonstration of the Navy’s power-beaming capabilities at the Naval Surface Warfare Center in Bethesda, Maryland:

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Overall, the Photovoltaic Radiofrequency Antenna Module could end up being highly significant. As we have pointed out before, a microwave system of this kind could be a game-changer for many military-related applications, including bringing closer the prospect of near-continuous unmanned flight throughout the atmosphere.

OTV-6 also deployed the U.S. Air Force Academy’s FalconSat-8, which was put into orbit last October. According to the Air Force Academy, this satellite is being used for five different tests and demonstrations, namely, “[testing] the latest generation of plasma thruster, a metamaterials antenna, a carbon nanotubes experiment, an energy surge and control device, and a joint payload with the Air Force Institute of Technology for a low-cost camera.” All these experiments are being conducted by cadets, providing valuable experience before they enter active duty as space operators. FalconSat-8 is currently still in orbit.

Among the NASA experiments deployed on OTV-6 was Materials Exposure and Technology Innovation in Space, or METIS-2, which tested thermal control coatings, printed electronic materials, and candidate radiation shielding materials. In the previous METIS-1, which was part of OTV-5, the samples for testing were mounted on the outside of the X-37B vehicle.

The even longer duration of OTV-6 will have helped provide useful data for METIS-2 and the same is true for another NASA experiment, which studied the effect of long-duration space exposure on seeds. Ultimately, data gathered from this could help provide food for future interplanetary missions and for permanently inhabited bases in space.

The statement from the Space Force did not disclose which of the experiments undertaken during OTV-6 involved the service module specifically. However, a statement from Boeing confirmed that the module “successfully carried experiments for [the] Naval Research Laboratory, U.S. Air Force Academy, and other partners.” That suggests that both the Photovoltaic Radiofrequency Antenna Module and FalconSat-8 relied upon the module in some way, but that there’s a distinct possibility that other undisclosed tests were conducted using this new addition to the X-37B and also the original payload bay.

The mysterious X-37B spaceplane, which looks somewhat like a scaled-down version of the Space Shuttle, was first launched in 2010. While OTV-6 was the longest duration so far, the spaceplane has flown previous missions of prodigious length. In 2019, it returned to Earth after its fifth mission, having spent 780 days in orbit.

U.S. Air Force personnel examine the X-37B after it landed following the completion of OTV-5 in 2019. USAF

On the whole, though, the bulk of the work that the X-37B has done has remained unpublicized, with the Air Force being notably reluctant to reveal significant details about its “experiments” with the spaceplane.

As well as being able to launch and recover objects in space, the X-37B has a unique capability to remain in orbit for prolonged periods, so far having flown over 1.3 billion miles and spent a total of 3,774 days in space. Having the option to have payloads in space for such a long time and then bring them back safely to Earth for further study (or reuse) has significant implications for government and industry alike. This includes providing relatively low-cost access to space.

This is of particular relevance for the United States, as well as potential adversaries, who are increasingly exploring new options for getting payloads into space using methods that are faster, more flexible, and less predictable. China, in particular, is also forging ahead with a spaceplane design similar to the X-37B. According to Chinese state media reports, its reusable spaceplane was launched for the second and most recent time on the night of August 4-5, 2022, via a Long March 2F rocket, and successfully entered orbit. You can read our analysis of that event here.

With a record-breaking sixth flight now under its belt, the X-37B seems to be very much at the cutting edge of developing new and advanced space-related capabilities for the Space Force, Air Force, and other agencies. With the service module now also proven, the spaceplane is very likely to become an even more important and flexible element to U.S. space operations, military and otherwise.

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