ULA Confirms Successful GEM 63XL Static Fire as Vulcan SRB Investigation Drags On and Space Force Pause Holds
ULA says Northrop Grumman ran a successful GEM 63XL solid rocket booster static fire on April 15, but the Vulcan rocket remains grounded for national security launches three months after a nozzle anomaly on USSF-87, with Amazon expected to anchor a return-to-flight by year-end.
Overview
United Launch Alliance said on May 14 that Northrop Grumman performed a successful static fire of a Graphite Epoxy Motor (GEM) 63XL Solid Rocket Booster on April 15, a key milestone in clearing the Vulcan rocket to fly again after a nozzle anomaly on the USSF-87 mission grounded the vehicle for national security launches. According to Spaceflight Now, the test was intended to demonstrate nozzle design enhancements and an advanced propellant technology for future solid rocket motors, but the investigation into the February 12 incident is still open and the Space Force has not lifted its pause on Vulcan missions.
What We Know
The trouble began during the launch of USSF-87 on February 12, 2026. As reported by Space.com, Gary Wentz — then ULA’s vice president of Atlas and Vulcan Programs — said the team “observed a significant performance anomaly on one of the four solid rocket motors” early during the flight. Despite the failure, Space.com reported that Vulcan was “carrying two spy satellites aloft for the U.S. Space Force” and “delivered the spacecraft directly to geosynchronous orbit.”
In his most recent comments to Spaceflight Now, Wentz — now identified as vice president of Government and Commercial Programs at ULA — described how the rocket coped with the asymmetric load. “There was some asymmetric thrust when we had that solid motor fail, it reduced performance,” Wentz said. “The BE-4s and our avionics system gimbaled to control that. We did see some roll, and the BE-4s were able to compensate to arrest that roll.”
The Space Force responded quickly. On February 25, at the Air Force Association’s Warfare Symposium, Col. Eric Zarybnisky — Program Executive Officer for Assured Access to Space — announced the service would halt Vulcan launches until the cause was understood, according to Space.com. “We are going to work through this anomaly until we launch again on Vulcan. Until this anomaly is solved we will not be launching Vulcan missions,” Zarybnisky said, characterizing the work ahead as “a many-months process.” Space.com noted that ULA had booked its Vulcan Centaur rocket for more than two dozen national security launches.
The April 15 static fire is the most visible technical milestone since the pause. Spaceflight Now reported that the GEM 63XL test was meant to validate nozzle design enhancements that were already in work and an advanced propellant technology intended for future solid motors. Wentz told the outlet that “Vulcan’s going to get back to flight by the end of the year,” and indicated that the return-to-flight customer would more than likely be Amazon, which has been waiting on Vulcan to start lofting its Leo broadband constellation.
In the near term, ULA is leaning on the venerable Atlas V to keep the Amazon manifest moving. According to Spaceflight Now, “Amazon Leo’s next flight is scheduled to be the Leo Atlas 07 (LA-07) mission, which is scheduled for no earlier than May 22.” Satellites are already stacked for the first Leo Vulcan mission (LV-01) and subsequent Vulcan flights, the outlet noted.
Context: The October 2024 Echo
The February USSF-87 anomaly is the second time a Vulcan SRB nozzle has failed in flight. As Space.com recounted, Vulcan’s October 2024 second certification flight saw “a manufacturing defect caused on one of the solid rocket booster nozzles to fall off,” causing the rocket to veer slightly before recovering. Spaceflight Now reported that then-ULA chief executive Tory Bruno traced the 2024 problem to a manufacturing defect in one of the internal parts of the nozzle, and that the Space Force certified Vulcan for national security missions in late March 2025 after a static-fire qualification.
Whether the February 2026 nozzle problem shares the same underlying mechanism has not been confirmed by either ULA or Space Force officials. ULA’s recovery efforts have been constrained by where the debris fell. Spaceflight Now reported that Wentz said the pieces of the SRB nozzle landed in water that was likely too deep for recovery, denying engineers the chance to inspect the failed hardware directly.
What We Don’t Know
ULA has not published a root-cause finding for the USSF-87 nozzle failure, and the Space Force has not signaled when the pause might be lifted. ULA’s own framing has consistently been that return-to-flight will arrive “by the end of the year,” but Zarybnisky’s “many-months” timeline from late February has not been revised in public. Whether the GEM 63XL design enhancements tested on April 15 will be incorporated into the SRBs already stacked for LV-01, or whether those boosters will need to be unstacked and rebuilt, has not been disclosed in the cited reporting.
The identity of the LV-01 payload has also not been clarified beyond Wentz’s comment that Amazon is the likely return-to-flight customer. With more than two dozen national security launches still on Vulcan’s books, per Space.com, every additional week of grounding compounds the manifest pressure on the vehicle.