The Falcon 9 carrying "Zuma" lifts off from a SpaceX launch pad at Kennedy Space Center.
A SpaceX Falcon 9 rocket carrying the secret Zuma spacecraft for the USA government launches Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida on January 7, 2018 in this still from a SpaceX video.
This will be SpaceX's first launch of 2018.
"The U.S. government asked the aerospace and defense company Northrop Grumman to procure a launch vehicle, in this case the Falcon 9, for the Zuma launch", a company spokesperson said in November. SpaceX has done classified launches for the Air Force and National Reconnaissance Office before, but this is the first time that the name of the government agency behind the spacecraft being launched is not even known.
The Zuma mission was first revealed to the public in October, when NASA reported that SpaceX has requested authorization for the mysterious "Mission 1390".
Falcon 9 rocket stage lands back at Cape Canaveral. SpaceX said it needed to review a potential issue with the Falcon 9 rocket's nose cone that cropped up in testing.
CEO Elon Musk says the heavy-lift launcher's debut test flight - carrying his own Tesla Roadster sports auto into space - is possible from KSC before the end of this month. The exact time of the launch has yet to be set, though SpaceX has set a two-hour window beginning at 12 AEDT. The Wing could potentially support more than 30 launches.