After a pause in deliveries for the military’s next-generation missile tracking and warning system, a Falcon rocket at Vandenberg Space Force Base launched the next batch of satellites Thursday afternoon.

The SpaceX rocket blasted off at 1:32 p.m. from Space Launch Complex-4 with 21 satellites on board for the third delivery in the Defense Department‘s Space Development Agency’s Tranche 1. The first-stage booster successfully landed on the droneship, completing its fourth flight.

Two hours after the liftoff, SDA representatives dubbed the mission successful.

“This launch continues to expand warfighting capability to deliver persistent tactical satellite communication for the warning and tracking of advanced missile threats,” SDA Director GP Sandhoo said.

The spacecraft, built by York Space Systems, were part of the data transport layer for the constellation designed to detect and track just-launched missiles.

The system represents the military’s new approach, or Proliferated Warfighter Space Architecture, of developing and launching hundreds of satellites to do the job previously performed by several humongous, and costly, craft. The prior method meant a launch or satellite failure doomed the mission, and replacement took years.

Development and delivery of the new satellite constellation will occur in phases, or what the military called tranches.

However, the SDA paused the deliveries following the pair of Tranche 1 launches from Vandenberg in September and October because of glitches spotted on orbit for the satellites built by York plus Lockheed Martin Corp.

“We took a decent pause on at least fixing all of the known issues that we had,” Sandhoo said during a media roundtable earlier this week.

Most of the previously launched satellites were “functioning” although weren’t necessarily in the ideal location because of orbit-raising issues.

The SDA initially intended to conduct Tranche 1 launches about once a month but delayed future liftoffs after encountering troubles involving the first satellites placed in space.

“The goal here is not to launch on a monthly cadence …,” Sandhoo said. “The goal is to get operational as quickly as possible once we get on orbit.”

Rather than experiencing months of delays readying the orbiting satellites to begin operating, Sandhoo said the SDA decided to deal with weeks of delays for launches to more easily fix glitches on the ground.

Earlier this year, a General Accountability Office report, “Missile Warning Satellites: Space Development Agency Should Be More Realistic and Transparent About Risks to Capability Delivery,” criticized aspects of the effort and made six recommendations.

While the first satellites experienced troubles, Sandhoo said early aircraft leaving the assembly line also had issues.

“It’s just the reality of building complicated systems,” he said. “We think we have addressed most of the ones that we knew. Our plan and our current schedule is these checkouts should not be as long as the first couple of launches were.”

One of the first satellites remained out of contact with ground controllers, Sandhoo said, calling it “the nature of this business.”

Along with fixing software glitches, the contractors have implemented hardware changes, Sandhoo said. Taking risks is part of technology development, he added, referring to the early space programs.

“That’s the kind of mindset we are taking. That’s what I think the nation needs right now to face the threat that we are in,” Sandhoo said. 

U.S. military forces and allies have faced regular missile launch attack attempts during Operation Epic Fury, or the war against Iran. 

“We are doing everything we can technically to solve these technical challenges to get these systems on orbit so we can deliver these capabilities,” he said. 

Thursday’s delivery means one-half of transport layer satellites have arrived in obit, with three more expected plus four tracking layer satellites making up Tranche 1, which is expected to become operational in 2027.

The “deployment of Tranche 1’s proliferated capability will soon deliver continuous overwatch — neutralizing any first-mover advantage by delivering data to warfighters around the world, nearly instantaneously,” Sandhoo said.

In total, Tranche 1 will have 154 satellites with 126 for the data transport layer and 28 for tracking capabilities plus four missile-defense demonstration satellites.