After three successes, a leftover SpaceX rocket booster crashed Wednesday while trying to land on an ocean barge.
The attempt came minutes after the Falcon 9 rocket successfully launched two satellites from Cape Canaveral, Florida.
SpaceX chief Elon Musk said via Twitter that there was a problem with one of the three engines used to slow the first-stage booster for landing. He said it may be the hardest crash of all. Early attempts also failed.
SpaceX's first successful landing on the platform off Florida's east coast came in April, with two more last month. It also landed a 15-story booster in December on land at Cape Canaveral Air Force Station.
Musk plans to recycle boosters to lower launch costs. They normally are discarded in the ocean.