WASHINGTON, Jan. 7 (Xinhua) -- U.S. space firm SpaceX on Sunday launched a top secret payload into space for the U.S. government, known only by the codename Zuma.

The payload took off at 8 p.m. EST (0100 GMT) on a Falcon 9 rocket from the Cape Canaveral Air Force Station in Florida.

Northrop Grumman, an American aerospace and defense technology company, acknowledged that it arranged the launch on the U.S. government's behalf and said the payload will be launched into a low-Earth orbit.

However, very little is known about the nature of the Zuma mission, as no U.S. government agency has claimed responsibility for it so far.

SpaceX has already launched two classified payloads for the U.S. government during the past year.

Launched in May, the NROL-76 spy satellite was for the National Reconnaissance Office. The other was an uncrewed X-37B space plane for the U.S. Air Force, which lifted off in September.

As usual, SpaceX once again landed Falcon 9's first stage back to Earth during Sunday's mission.

The company's launch webcast showed the first stage touched down at Landing Zone 1 at Cape Canaveral just eight minutes after liftoff.

Such landings are part of SpaceX's efforts to develop fully reusable rockets, which the company believes could bring down spaceflight costs.