For the second time in six months, SpaceX will deploy a US military satellite that was sitting in storage, waiting for a slot on United Launch Alliance’s launch schedule.

Space Systems Command, which oversees the military’s launch program, announced Monday that it is reassigning the launch of a Global Positioning System satellite from ULA’s Vulcan rocket to SpaceX’s Falcon 9. This satellite, designated GPS III SV-08 (Space Vehicle-08), will join the Space Force’s fleet of navigation satellites beaming positioning and timing signals for military and civilian users around the world.

The Space Force booked the Vulcan rocket to launch this spacecraft in 2023, when ULA hoped to begin flying military satellites on its new rocket by mid-2024. The Vulcan rocket is now scheduled to launch its first national security mission around the middle of this year, following the Space Force’s certification of ULA’s new launcher last month.

The “launch vehicle trade” allows the Space Force to launch the GPS III SV-08 satellite from Cape Canaveral, Florida, as soon as the end of May, according to a press release.

“Capability sitting on the ground”

With Vulcan now cleared to launch military missions, officials are hopeful ULA can ramp up the rocket’s flight cadence. Vulcan launched on two demonstration flights last year, and ULA eventually wants to launch Vulcan twice per month. ULA engineers have their work cut out for them. The company’s Vulcan backlog now stands at 89 missions, following the Space Force’s announcement last week of 19 additional launches awarded to ULA.

Last year, the Pentagon’s chief acquisition official for space wrote a letter to ULA’s owners—Boeing and Lockheed Martin—expressing concern about ULA’s ability to scale the manufacturing of the Vulcan rocket.

“Currently there is military satellite capability sitting on the ground due to Vulcan delays,” Frank Calvelli, the Pentagon’s chief of space acquisition, wrote in the letter.

Vulcan may finally be on the cusp of delivering for the Space Force, but there are several military payloads in the queue to launch on Vulcan before GPS III SV-08, which was complete and in storage at its Lockheed Martin factory in Colorado.

Col. Jim Horne, senior materiel leader of launch execution, said in a statement that the rocket swap showcases the Space Force’s ability to launch in three months from call-up, compared to the typical planning cycle of two years. “It highlights another instance of the Space Force’s ability to complete high-priority launches on a rapid timescale, which demonstrates the capability to respond to emergent constellation needs as rapidly as Space Vehicle readiness allows,” Horne said.