WASHINGTON — The first launch of United Launch Alliance’s Vulcan Centaur was also a successful demonstration of new solid rocket boosters developed by Northrop Grumman for the vehicle.

The Jan. 8 launch of Vulcan on the Cert-1 mission included two GEM 63XL solid rocket boosters that produced more than 900,000 pounds-force of thrust, nearly two-thirds of the vehicle’s overall thrust at liftoff. The strap-on boosters fired for nearly two minutes before burning out and being jettisoned.

The GEM 63XL is a stretched version of the GEM 63 booster used on ULA’s Atlas 5. It is the same diameter as the GEM 63 but is nearly two meters longer. The GEM 63XL is the largest monolithic, or non-segmented, solid rocket booster built.

A monolithic motor has several advantages. “Your thrust-to-mass ratio is certainly better,” said Bret Baldwin, Graphite Epoxy Motors program director at Northrop Grumman Propulsion Systems, in an interview before the launch. “Because you have less joints, you’re going to get a better performing motor that’s not as heavy.” He said the GEM 63XL offered 20% more thrust for 10% more mass compared to the GEM 63.

The lack of joints between booster segments also improves safety and reliability, he said. One challenge, though, is transportation, because of their length. “To try to transport them is a significant undertaking,” he said. Northrop developed special over-the-road transporters to haul the boosters from their Utah production facility to Cape Canaveral.

Northrop’s focus now is on ramping up production of the GEM 63XL. The company received a contract from ULA in 2022 worth more than $2 billion for what it said was “multiple years of high-rate production” of the booster for ULA’s backlog of Vulcan launches. Each Vulcan uses up to six of the boosters depending on mission requirements.

“We’re focused significantly on the scaling aspect of this program,” Baldwin said, an effort that will extend over three years. Northrop is investing in new buildings and other infrastructure for overall solid motor production, including the GEM 63XL. “W e’ll now have buildings that are big enough and designed for rockets that are this large, and we’re really looking forward to that.”

As the company ramps up production, it is looking at various improvements it can incorporate into the motors. That includes incorporating technologies tested through its Solid Motor Annual Rocket Technology Demonstrator, or SMART Demo, program, a new company initiative that included a test-firing of a new motor in December as part of an annual cycle of such tests.

“Any lessons learned that we can gain from the SMART motor program we are very open to,” he said, although he did not identify any specific capabilities he was looking to incorporate into the GEM 63XL. “We’ve already been talking about SMART Demo 2 and how that can apply to these boosters as well as other propulsion systems.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...