(NewsNation) — Space X and the U.S. Space Force are set to launch a top-secret plane into space Thursday, weather permitting. But what happens next remains a mystery.

The X-37B space plane is set to be launched from Kennedy Space Center atop a Falcon Heavy rocket. The unmanned plane has been flying top-secret missions since 2010, but this is the one everyone is curious about.

One big question is why the launch is using the Falcon Heavy rocket rather than the Falcon 9, which has been used in previous launches.

There isn’t a lot of information about the plane’s activity in orbit, which has remained classified. Space Force has disclosed some information on previous payloads and has repeatedly said it is testing out technology for future spacecraft and carrying out varying experiments, including harnessing and transferring solar power energy from space back to Earth.

This mission does include one unclassified experiment, NASA’s Seed Two project, which is seeking to understand how the high radiation in space would affect seeds.

The X-37B is about the size of a small bus, and is built by Boeing. The plane has been on six previous missions and has spent 3,774 days in space. Previous experiments include testing space exposure on organic material and helping to launch a spacecraft designed by Air Force Cadets.

Another space shuttle launched last week, not from the U.S. but from China, highlighting a space race between the two countries.

“It’s not just the United States that’s operating space,” said retired Lt. Gen. Richard Newton. “There’s a whole host of other countries, including China. We have to maintain that leading edge where we were, and I still believe strongly we’re the best in space but there are other competitors coming very close.”

Newton told NewsNation China’s recent launch demonstrates they’re focused on learning to operate and maneuver spacecraft in a variety of orbits above Earth.

The launch of the X-37B has been rescheduled a few times previously, due to technical difficulties and weather.