The launch is a significant victory for billionaire Elon Musk's privately held rocket company, which has spent years trying to break into the lucrative market for military space launches.
The GPS III satellite, which has a lifespan of 15 years, is the first of 32 to be built by Lockheed in contracts worth a combined $12.6bn from the US Air Force.
SpaceX, along with Boeing, has a contract to ferry American astronauts to the International Space Station as part of what's known as the Commercial Crew programme with Nasa, but the timeline for the first flights has slipped repeatedly. "As more GPS III satellites join the constellation, it will bring better service at a lower cost to a technology that is now fully woven into the fabric of any modern civilization". SpaceX usually attempts to land Falcon 9 first stages shortly after liftoff for future reuse, but not today.
The satellite is one in a series of 10 third-generation satellites ordered by the Air Force with three times better accuracy, eight times improved anti-jamming capabilities, 25 percent longer spacecraft lifespan and the capability to broadcast signals compatible with other worldwide global navigation systems, including Europe's Galileo.
ULA has flown eight missions in 2018, and a ninth is scheduled for no earlier than 30 December from Vandenberg Air Force Base on California's central coast. Lockheed Martin is building the new satellites outside Denver.
The spacecraft's life will extend to 15 years, 25 percent longer than the newest Global Positioning System satellites on-orbit today. It completed Falcon 9's third launch and landing this year.
It is the first in a series, nicknamed Vespucci after the 15th-century Italian explorer who calculated Earth's circumference to within 80 kilometres. It helps the company to clear the airspace for launches, provides weather reports, and sets up road closures to make sure the public stays clear of the site.
This morning's launch was originally scheduled to occur on Tuesday (Dec. 18), but SpaceX called off that attempt after receiving an "out of family" reading from sensors on the Falcon 9's first stage.