SpaceX successfully launched the U.S. Space Force’s X-37B Orbital Test Vehicle (OTV) on a Falcon Heavy rocket on Monday, Dec. 10, 2023, marking the first time the reusable spaceplane has flown on the powerful launcher.

The Falcon Heavy lifted off from Launch Complex 39A at NASA’s Kennedy Space Center in Florida at 8:14 p.m. EST (0114 UTC), after a 24-hour delay due to a ground issue. The rocket’s three boosters, two of which had flown four times before, separated and returned to land at nearby landing zones and on a drone ship in the Atlantic Ocean.

The X-37B, a classified spacecraft that resembles a miniature space shuttle, was deployed into orbit about 30 minutes after liftoff. The mission, designated USSF-52, is the seventh flight of the OTV program, which began in 2010 and is managed by the U.S. Space Force’s Rapid Capabilities Office.

The details of the X-37B’s mission are shrouded in secrecy, but the U.S. Space Force said in a statement that the spaceplane will “expand the X-37B flight envelope, launching into a new orbital regime, and enabling unique experimentation opportunities for the X-37B.”

The X-37B has a wingspan of 14.9 feet (4.5 meters) and a length of 29.3 feet (8.9 meters). It can carry a payload bay of about 7 feet by 4 feet (2.1 by 1.2 meters), where it can host various experiments and technologies. It can also change its orbit and perform maneuvers in space, making it hard to track by ground observers.

The X-37B has demonstrated the ability to stay in orbit for long durations, ranging from 224 days to 779 days. The total time spent in space by the OTV program is 3,363 days. The previous six missions of the X-37B were launched by United Launch Alliance’s Atlas V rocket, with the fifth mission being the only one to fly on a SpaceX Falcon 9 rocket.

The Falcon Heavy is the most powerful operational rocket in the world, capable of lifting more than 140,000 pounds (63,500 kilograms) to low Earth orbit. It consists of three Falcon 9 first stages strapped together, with a single second stage on top. The rocket has flown five times since its debut in 2018, carrying payloads for NASA, the U.S. military, and private customers.

SpaceX has two more Falcon Heavy missions scheduled for 2024, one for NASA’s Psyche asteroid mission and one for the U.S. Space Force’s Space Test Program-3. The company is also developing a next-generation rocket called Starship, which is intended to eventually replace the Falcon 9 and Falcon Heavy.

SpaceX’s launch of the X-37B on a Falcon Heavy rocket was a historic achievement for both the company and the U.S. Space Force, demonstrating their capabilities and collaboration in the field of space exploration and security.