SpaceX launched its Falcon Heavy rocket late on Thursday, October 1, carrying a classified national security payload for the National Reconnaissance Office. The mission, designated NROL-97, lifted off at 11:54 p.m. ET from Launch Complex 39A at NASA’s Kennedy Space Center.

About eight minutes after liftoff, the rocket’s two side boosters returned to Landing Zones 1 and 2 at Cape Canaveral Space Force Station. Their synchronized landings produced the familiar double sonic booms that rattled windows across Florida’s Space Coast.

The boosters had flown before. They previously supported the GOES-U, Viasat-3 F3 and Nancy Grace Roman Space Telescope missions.

The launch capped one of SpaceX’s busiest days of the year. Just 13 hours earlier, a Falcon 9 had lifted NASA’s Crew-13 astronauts to the International Space Station from the same region, and another Falcon 9 launched from Vandenberg Space Force Base in California on the same day.

The NRO operates the United States’ reconnaissance satellites. Details of the NROL-97 payload remain classified.

The next Space Coast mission is expected to be NASA’s SpaceX CRS-35 cargo flight to the International Space Station, though its October date has not been announced.