SpaceX is preparing to send into space a satellite for the US government that is so secret the public cannot know even which branch of the administration commissioned the launch.

A weather report ahead of the launch released on Tuesday described the conditions as excellent.

Unlike the private aerospace company's previous classified launches for the military's National Reconnaissance Office and the super-secret space-plane it took into orbit for the Air Force, there is almost no information available about the "Zuma" payload.

Zuma is known to be a low Earth orbit satellite (orbiting within 2,000km) which is an orbit necessary both for spy and military communication satellites.