PORT CANAVERAL, Fla. — The main booster core of the Falcon Heavy rocket that lifted off from Kennedy Space Center several days ago fell off the drone ship and was lost at sea, SpaceX says.

SpaceX said Monday that the center booster, which landed on the company's drone ship in the Atlantic, "was unable to remain upright" in 8- to 10-foot seas on the way back to Port Canaveral and toppled over.

The crew tasked with bringing back the booster to port is fine, SpaceX said.

Consisting of three boosters and 27 engines, the Falcon Heavy is one of the world's most powerful rockets. The second Falcon Heavy to launch blasted off from Pad 39A at KSC on Thursday evening carrying the 13,000-pound Arabsat 6A satellite.

Less than 10 minutes after liftoff, the two side boosters landed successfully on landing zones at Cape Canaveral Air Force Station, while the larger main booster core landed on the drone ship.

In February 2018, during the Falcon Heavy's first flight, the main core crashed into the ocean on its landing and damaged the drone ship.