An exterior of the SpaceX headquarters in Hawthorne, California, US, May 29, 2014. REUTERS/Mario Anzuoni/Files

MIAMI: SpaceX is poised to launch on Thursday a secretive payload known as Zuma for the US government, though the nature of the mission and the agency behind it remain a mystery.

The launch atop a Falcon 9 rocket is scheduled from Cape Canaveral, Florida sometime between 8 and 10 PM (0100-0300 GMT Friday).

SpaceX and the Pentagon did not respond to requests for comment about the nature of the mission.

Northrup Grumman ? the maker of the payload ? said it was for the US government and would be delivered to low-Earth orbit, but offered no other details, according to Space.com.

SpaceX is no stranger to national security launches.

Earlier this year, the California-based company headed by billionaire entrepreneur Elon Musk launched a spy satellite for the National Reconnaissance Office and an X-37B space plane for the US Air Force.

After liftoff, SpaceX will attempt to return the first stage portion of its Falcon 9 rocket to Earth for a controlled landing on solid ground near Cape Canaveral.

If successful, it will be the 20th upright touchdown for a Falcon 9 since the company began its effort to recycle costly rocket parts and make spaceflight more affordable.