https://techcrunch.com/2020/05/07/air-force-gives-a-rare-look-at-the-research-going-to-orbit-in-its-x-37b-spaceplane/

The X-37B spaceplane sounds like something out of a sci-fi novel, and its mysterious past is equally evocative. What does the military put in this long-term orbital vehicle? Turns out it’s exactly the kind of neat, but not mind-blowing, science you’d expect to find in such a thing — though solar-powered masers do sound pretty cool.

Also known as the Orbital Test Vehicle, the Boeing -designed X-37B has performed five prior missions, amounting to a total of nearly eight years in orbit; The last mission alone was 780 days. But while the craft’s owners (the Air Force, though it is used by many others) are proud to tout its remarkable longevity and reliability, they rarely if ever admit what they’re sending up, or what (if anything) it brings down.