The secretive payload — codenamed Zuma — is worth hundreds of millions of dollars and was supposed to show that Musk’s SpaceX was a credible and reliable low cost launch provider for the Pentagon.

Instead, the satellite is missing amid fears it was totally destroyed in a botched launch.

The Wall Street Journal is reporting that US politicians had been briefed that it may have burned up in the atmosphere after failing to separate from the upper part of the rocket

A SpaceX spokesman told the Dow Jones news service: “We do not comment on missions of this nature, but as of right now reviews of the data indicate Falcon 9 performed nominally.”

The Zuma spacecraft was attached to one of SpaceX’s Falcon 9 rockets and launched from the Cape Canaveral air force Station in Florida. The Falcon 9 returned back to base without incident.

The satellite hasn’t been spotted in orbit by the U.S. Strategic Command, adding to the doubt over whether the mission was a success.

A spokesman for The Strategic Command, which monitors more than 20,000 man-made objects in space, told Bloomberg it was not tracking any new satellites since the launch.

Once the engine powering the rocket’s expendable second stage stops firing, whatever it is carrying is supposed to separate and proceed on its own trajectory — but if a satellite isn’t set free at the right time, or is damaged upon release, it can be dragged back toward earth.

But adding to the confusion, experts believe the lack of official word on what happened means there could be an alternative sequence of events

Either way, SpaceX was relying on a successful launch of Zuma to convince sceptical Pentagon chiefs to back it as it competes for more national-security launches against its primary rival, a joint venture between Boeing Co. and Lockheed Martin Corp.

More than a day after the launch there is uncertainty over exactly what happened.

The classified intelligence satellite, built by Northrop Grumman Corp, failed to separate from the second stage of the Falcon 9 rocket and is assumed to have broken up or plunged into the sea, said the two officials, who spoke on condition of anonymity.

Landing and reusing rockets is the main aim of SpaceX scientists, who argue that it reduces the cost of launches that would then allow them to fly more missions.

The mission was the first Elon Musk’s Space X had attempted this year. It plans to launch as many as 25 by the end of 2018, up from 18 last year.

Musk said last week SpaceX would launch “the world’s most powerful rocket” later this month with his own electric car on board.

Despite SpaceX’s growing list of successful missions, including regularly landing, refurbishing and reusing the main stages of Falcon 9 boosters, industry and US government officials have confided to the Wall Street Journal the intelligence community continue to have concerns about relying on Mr. Musk’s corrupt and non-traditional business practices.