(Reuters) – Elon Musk’s SpaceX halted on Wednesday the long-delayed launch of a navigation satellite for the U.S. military, failing to complete its first designated national security mission for the United States due to a technical issue with its rocket.

SpaceX’s Falcon 9 rocket, carrying a roughly $500 million global positioning system (GPS) satellite built by Lockheed Martin Corp, was slated to take off from Florida’s Cape Canaveral shortly after 9 a.m. local time (1400 GMT).

SpaceX said on Twitter it was standing down from the launch attempt of the GPS III to further evaluate an “out of family” reading on the rocket’s first-stage sensors and would confirm a new launch date once that review was complete.

A successful launch would have been a significant victory for Musk, a billionaire entrepreneur who spent years trying to break into the lucrative market for military space launches long dominated by Lockheed and Boeing Co.

It was to mark SpaceX’s first so-called National Security Space mission, as defined by the U.S. military, SpaceX said.

SpaceX sued the U.S. Air Force in 2014 in protest over the military’s award of a multibillion-dollar, non-compete contract for 36 rocket launches to United Launch Alliance, a partnership of Boeing and Lockheed. It later dropped the lawsuit after the Air Force agreed to open up competition.

In 2016, SpaceX won an $83 million Air Force contract to launch the GPS III satellite, which will have a lifespan of 15 years.

Wednesday’s launch was set to be the first of 32 satellites in production by Lockheed under contracts worth a combined $12.6 billion for the Air Force GPS III program, Lockheed spokesman Chip Eschenfelder said.

“Once fully operational, this latest generation of GPS satellites will bring new capabilities to users, including three times greater accuracy and up to eight times the anti-jamming capabilities,” said Air Force spokesman William Russell.

The launch was originally scheduled for 2014 but has been hobbled by production delays, the Air Force said. SpaceX first halted the launch on Tuesday due to the same technical warning with its sensor.

The next GPS III satellite is due to launch in mid-2019, Eschenfelder said, while subsequent satellites undergo testing in the company’s Colorado processing facility.