Private space company Sierra Nevada Corporation announced today that its mini-spaceplane, the Dream Chaser, will launch into orbit on top of the United Launch Alliance’s future Vulcan Centaur rocket. The Dream Chaser has yet to see space, but once it’s operational, it will help ferry cargo and science experiments to the astronauts on board the International Space Station between 2021 and 2024.

The Sierra Nevada Corporation (SNC) is one of three companies tasked by NASA to periodically launch to the ISS to make sure the station is fully stocked with supplies. The cargo missions are all part of NASA’s Commercial Resupply Services Program, one of a few initiatives at the space agency that’s meant to offload space transportation to the private aerospace industry. The other two companies in the program, SpaceX and Northrop Grumman, have already been launching cargo to the station since 2012, thanks to an initial round of contracts. But NASA awarded a second round of contracts in 2016, adding SNC to the supplier pool.

In development since 2004, the Dream Chaser looks a lot like a miniature Space Shuttle. The plan is for the spaceplane to fly into orbit vertically on top of a rocket and then meet up with the ISS. The astronauts on board the station will then use the robotic arm to grab hold of the spaceplane and place it on an available docking port. Once all of the cargo it’s carrying has been offloaded and the mission is complete, the Dream Chaser will separate from the ISS and then reenter the Earth’s atmosphere. Unlike other space capsules that use parachutes to land, the Dream Chaser will land akin to an airplane, gliding down horizontally onto a runway.

“It truly provides a very unique capability, different than anything else available in the world today and in the foreseeable future,” SNC CEO Fatih Ozmen said during a press conference announcing the selection of Vulcan.

Originally, the company envisioned launching the Dream Chaser on ULA’s Atlas V to carry astronauts to and from the ISS for NASA, and the team even received initial development funding from the space agency to work on a crewed vehicle. But NASA ultimately awarded contracts to SpaceX and Boeing to send humans to the space station. So SNC decided to rework the Dream Chaser to just carry cargo, and the company is now tasked with launching a total of 12,000 pounds of cargo on a minimum of six supply missions for NASA. The company maintains there is still the possibility of flying people on Dream Chaser in the future.

In fact, SNC maintains that the cargo Dream Chaser could carry people if absolutely necessary since it has some life support and temperature control systems. “You could actually, in an emergency even today, bring people down If you had to,” John Curry, the program director for Dream Chaser’s cargo missions, said at the press conference. “I’m not saying that NASA has asked us to do that. I’m just saying that the capability is there. So the bridge to a crewed vehicle is not that far.”

SNC has other plans for its Dream Chaser, including launching international payloads to space for the United Nations as early as 2021. But there’s still quite a lot of work to be done before Dream Chaser is shooting upward on a Vulcan rocket. For one thing, the Vulcan has to start flying first. ULA has already started bending metal for the rocket, which is derived from the company’s already operational Atlas V rocket. But the first flight isn’t supposed to take place until 2021. The Dream Chaser will fly on the second flight of the Vulcan.

“I have been a fan and a supporter and a cheerleader of this amazing vehicle from the first moment I saw it,” ULA CEO Tory Bruno said during today’s press conference. “And so to be able to make Vulcan’s sort of commercial debut with this block of missions underneath a Dream Chaser is just truly exciting.”

In the meantime, SNC has been doing tests on the Dream Chaser, and it performed the vehicle’s second free flight in 2017, demonstrating that the spaceplane can land successfully from a super high altitude. The flight was much more successful than the first test in 2013 when the vehicle’s landing gear failed and caused the spaceplane to skid off the runway on touchdown. More tests are scheduled for the years ahead as SNC gets ready for the Dream Chaser’s first launch.

Update August 14th, 3:15PM ET: This article was updated to include additional information from an SNC press conference.