SpaceX called off a Falcon 9 countdown Wednesday due to the threat of lightning from thunderstorms along Florida’s Space Coast, pushing back the departure of a cargo mission for the International Space Station until Thursday.

SpaceX is replacing two engines on the Falcon 9 booster set to launch four astronauts next month on the company’s first operational Crew Dragon flight to the International Space Station, following an investigation that revealed a subcontractor failed to adequately clean out narrow vent ports on multiple engines across the company’s fleet, officials said Wednesday.

After a terminal countdown abort Sunday night, SpaceX launched a Falcon 9 rocket with the next 60 Starlink internet satellites Thursday at 3:24 a.m. EST (0824 GMT). The Falcon 9 took off from pad 39A at the Kennedy Space Center, and its first stage booster successfully landed on SpaceX’s offshore drone ship in the Atlantic Ocean.