Elon Musk’s SpaceX on Tuesday launched the first Falcon Heavy mission in over three years, a towering rocket that is the most robust in operation.

SpaceX’s rocket is taking charge of the classified USSF-44 mission for the U.S. Space Force, which is also the first operational national security mission for Falcon Heavy. Its most recent previous launch was the Space Test Program-2 (STP-2) mission in June 2019, which carried experimental satellites on a demonstration flight for the Pentagon.

The mission took off at 9:41 a.m. ET from a launchpad at NASA’s Kennedy Space Center in Florida.

While Falcon Heavy’s base is reusable, the firm landed just the side pair of the three rocket boosters – with the central core dropping into the ocean like traditional rockets do, to meet the Space Force’s high-performance requirement for this mission.

The hiatus in Falcon Heavy launches — the company has completed three since the rocket’s debut in February 2018 — is primarily due to customers' readiness for its schedule.

This USSF-44 mission was initially scheduled for late 2020, and two other Falcon Heavy missions scheduled for this year, another for the Space Force and the other for NASA, have customer payloads that are also not ready yet. There’s a backlog of about a dozen missions for Falcon Heavy still to come.