SpaceX will launch the Space Force's mysterious X-37B space plane on a Falcon Heavy rocket Dec. 7

The X-37B has previously launched atop the smaller Falcon 9 rocket.

The U.S. Space Force's shadowy X-37B is set for launch atop a SpaceX rocket.

The reusable space plane will launch atop a SpaceX Falcon Heavy rocket from NASA's Kennedy Space Center in Florida on Dec. 7 for its seventh overall mission, designated USSF-52. 

This marks the first time that the X-37B will launch on a Falcon Heavy, according to a Space Force statement. Little is known about the capabilities and operations of the space plane, but Space Force says the mission will follow previous flights that used the X-37B as a test bed for launching experimental payloads and returning them to Earth.

"We are excited to expand the envelope of the reusable X-37B's capabilities, using the flight-proven service module and Falcon Heavy rocket to fly multiple cutting-edge experiments for the Department of the Air Force and its partners," said Lt. Col. Joseph Fritschen, program director for the X-37B, in the statement.

Related: US Space Force's 1st official painting shows military space plane intercepting adversary satellite

It isn't known why the X-37B is launching atop a Falcon Heavy for the USSF-52 mission. Five of the space plane's previous missions launched on United Launch Alliance Atlas V rockets, while its fifth mission, USA-277, took off on top of SpaceX's smaller rocket, the Falcon 9 (Falcon Heavy consists of three Falcon 9 boosters strapped together). 

Such a change could suggest that the space plane is carrying heavier payloads or is sporting a new hardware configuration. So far, Space Force has only stated that the mission will "expand the United States Space Force's knowledge of the space environment by experimenting with future space domain awareness technologies," according to the statement.

However, Space Force's statement adds that the mission will carry a NASA experiment known as Seeds-2 that will test the effects that space-based radiation has on plant seeds during a long-duration spaceflight.

The X-37B was built by Boeing and made its first flight in 2010. It's previous flight saw the space plane spend 908 days in orbit before landing at Kennedy Space Center on Nov. 12, 2022.

Space Force released its first official painting last month that depicts a space plane somewhat similar to the X-37B engaging an adversary satellite in orbital combat. Space Force says the painting is purely fiction and shows a "futuristic intercept vehicle" derived from historical space plane concepts and the artist's imagination.