SpaceX’s Falcon Heavy used two side boosters during its first flight in February 2018.
Falcon Heavy is built from three Falcon 9-derived cores: a central core and two attached side boosters. Each core uses nine Merlin engines, giving the rocket 27 engines during liftoff.
The first flight launched from Kennedy Space Center’s Launch Complex 39A on February 6, 2018. Its payload was Elon Musk’s Tesla Roadster, with a mannequin nicknamed Starman in the driver’s seat. Both side boosters successfully landed at nearby Cape Canaveral landing sites.
The central core attempted to land on an autonomous drone ship in the Atlantic Ocean but did not complete the landing. Falcon Heavy’s configuration is therefore more than simply a Falcon 9 with one extra engine cluster: it combines three first-stage-derived cores and a separate upper stage.