SpaceX has scored one of its biggest contracts yet with the US Air Force: launching the military’s secretive X-37B spaceplane on top of the company’s Falcon 9 rocket. The mission, set to happen sometime in August, will be the first one SpaceX does for the Air Force, as the company continues to break into the market of launching military spacecraft.

The mission was confirmed Tuesday at a hearing of the US Senate Armed Services Committee. “[The X-37B] will be going up again on top of a SpaceX launcher in August,” Air Force secretary Heather Wilson said at the hearing. SpaceX did not provide a comment on the news.

It’ll be the fifth mission for the mysterious spacecraft

Built by Boeing, the X-37B is the Air Force’s reusable spaceplane that looks a bit like a mini Space Shuttle. It’s meant to launch into space on top of a rocket and then return to Earth by landing on a runway. As far as what the vehicle does, that’s anybody’s guess. The X-37B has a payload bay that carries up secretive spacecraft into orbit, perhaps to test out new surveillance technologies or communications capabilities. On its most recent trip, the vehicle spent 718 days in space, conducting “on-orbit experiments” such as testing a new thruster technology. It just returned to Earth last month, without any heads up from the Air Force.

So far the X-37B, also known as the Orbital Test Vehicle, has made four trips into orbit, each time launching on top of one of the United Launch Alliance’s Atlas V rockets. In fact, ULA has essentially been the sole launch provider for military satellites and vehicles over the last decade. Yet SpaceX has been making headway in this area. The company became certified to launch military payloads in 2015, a move by the Air Force to create competition and potentially lower launch costs. “Competition is reducing the cost of launch services,” Wilson said at the hearing. “Currently we’ve got two providers for medium and heavy launch.” Still, it’s unclear if cost is the primary reason for switching to the Falcon 9 for this next mission, but Wilson did tout the potential cost savings offered by the commercial space industry during the hearing.

Since its certification, SpaceX has been publicly awarded two contracts to launch GPS satellites for the Air Force — though those launches won’t take place until 2018 at the earliest. The company did, however, conduct its first national security launch in May, when it launched a satellite for the National Reconnaissance Office. The Air Force has even said it’s open to the idea of launching its satellites on used Falcon 9 rockets — one of SpaceX’s main initiatives to lower the cost of getting to space.