The Planetary Society’s LightSail 2 spacecraft will spend at least four more months waiting to solar sail, due to a launch date slip for SpaceX’s second Falcon Heavy flight.

The launch, which was previously scheduled for June, will now take place no earlier than October 30, 2018, according to the U.S. Air Force.

LightSail 2 is currently at the Air Force Research Laboratory in Albuquerque, New Mexico. It was integrated into the Prox-1 spacecraft back in March. The two spacecraft will eventually undergo final environmental testing and acceptance before shipping to Cape Canaveral for launch.

Prox-1 and LightSail 2 are among 25 different spacecraft launching on STP-2, an Air Force-sponsored mission that will help certify the Falcon Heavy for Department of Defense missions. The triple-core rocket will use three Block 5 boosters—the new, upgraded variant of the company's Falcon 9 vehicle. The first Falcon 9 Block 5 rocket is scheduled to launch Friday, May 11.