After weeks of delays, a covert military spaceplane was finally launched into orbit last night by SpaceX’s Falcon Heavy rocket, albeit very little information about the operation has been made public.

At 8:07 PM Eastern, the Falcon Heavy blasted out from NASA’s Kennedy Space Center on its covert mission. The only payload aboard the enormous rocket was the X-37B space plane, a reusable vehicle used by the United States Space Force as a classified testbed for space experiments.

Much remains unknown about this mission, as it did for the other six unmanned X-37B operations. Numerous payloads, the mission’s duration, and the target orbit are all classified. The tiny spacecraft has blacked-out windows too.

One of the big mysteries of this particular mission is the Space Force’s choice to book a triple-boosted Falcon Heavy. Falcon Heavy has previously taken off on SpaceX’s smaller Falcon 9 and United Launch Alliance’s Atlas V rocket, but this is the first time the military has chosen the spacecraft for an X-37B mission.

Although the space plane’s mission profile is kept under wraps, the additional boost might indicate that the mission is moving toward farther orbits. The Boeing-built X-37B, which looks like a miniature space shuttle, will eventually return to Earth and land on a runway similar to a conventional aircraft.

The mission, known as USSF-52, is tasked with “operating the reusable spaceplane in new orbital regimes, experimenting with future space domain awareness technologies, and investigating the radiation effects on materials provided by NASA,” according to a statement from the Space Force. The last of these goals is the only known payload, a NASA experiment called Seeds-2 that will investigate what happens to plants exposed to the extreme radiation of space.

This is not only SpaceX’s ninth launch of a Falcon Heavy rocket since 2018, but also its fifth this year. Following more than two weeks of delays—first because of bad weather, then again because of problems that weren’t made public—the launch was successfully completed. It was SpaceX’s 97th launch of the year (it launched its 98th, a batch of Starlink birds, on a Falcon 9 just hours later, at approximately 11 PM Eastern).