SpaceX has test-fired the center booster of its new Falcon Heavy rocket for the first time, the company announced May 9.

The “center core” test occurred the week of May 1 at the company’s facility in McGregor, Texas, SpaceX tweeted. The Falcon Heavy’s first stage has three boosters, or cores, each of which has nine Merlin engines.

SpaceX plans to conduct Falcon Heavy’s first flight test in summer 2017 and use the heavy-lift rocket to send a privately crewed Dragon spacecraft around the moon in late 2018.