The Air Force faces software design challenges for Northrop Grumman’s future LGM-35A Sentinel intercontinental ballistic missile (ICBM), according to the Government Accountability Office (GAO).
“Sentinel is software-intensive, and development progress remains slower than anticipated,” the new GAO two-page ‘national security snapshot‘ on Sentinel said. “These delays have raised concerns from program officials about the prime contractor’s ability to complete the program’s software in a timely manner.”
The report added that “software risks remain because, notwithstanding how long the program has been in development, the Air Force and Sentinel contractor have yet to finalize software design or software development metrics, and are re-planning the delivery schedule.”
Additionally, “Sentinel program officials expect that Sentinel will provide the nation with a significantly more capable ICBM system with modular capacity to adapt as threats and technology evolve,” according to GAO. “Further, officials stated that the Air Force and the Office of the Secretary of Defense are actively mitigating risks to ensure there are no capability gaps during the Minuteman III to Sentinel transition.”
The release of the Sentinel update by GAO came a day after the Air Force said that it would start construction this month of a prototype Sentinel silo at Northrop Grumman’s Promontory, Utah, site and that the service expected to conduct the first flight test of Sentinel from a pad at Vandenberg Space Force Base, Calif. next year.
The GAO notes, however, that the first full flight test of Sentinel from a silo is not until March 2028.
“The program’s first flight of the Sentinel missile has slipped about 4 years from original estimates and is now planned to occur in March 2028,” GAO said in the Wednesday update.
Last year, GAO said that the Air Force had pushed back the first flight test from 2025 until 2028, but Air Force Deputy Chief of Staff for Strategic Deterrence and Nuclear Integration Lt. Gen. Andrew Gebara said in August that the first Sentinel flight test would be “well prior to” 2028.
“The first full flight test (from a Sentinel representative silo) is still scheduled for the [2028] time frame we reported,” Joseph Kirschbaum, the author of the GAO update and the agency’s director of defense capabilities and management, wrote in an email last week to Exchange Monitor affiliate Defense Daily. “The Air Force has added a number of pad launch tests before this, each of which use varying amounts of actual Sentinel hardware/software. They are looking for ways to buy down risk for the first in-silo test. We are not sure where they are on finalizing software design.”
The Air Force said on Tuesday that it expects Pentagon acquisition chief Michael Duffey will re-approve Sentinel for engineering and manufacturing development (EMD) this year–months ahead of the Air Force’s earlier estimate of early to mid-2027.
The Defense Department approved Sentinel to enter EMD in 2020, but then rescinded that decision in 2024 after a critical Nunn-McCurdy unit cost breach.
Initial operational capability for Sentinel was May 2029, but that shifted to the end of 2033.
On Tuesday, the Air Force did not mention 2033 but instead said that it planned “an initial capability targeted for the early 2030s.”
The 659 Sentinel missiles–including 25 for test–are to replace the 450 Boeing Minuteman IIIs–400 deployed and 50 reserve–fielded in the 1970s. The Air Force will likely have a mixed fleet of Sentinel missiles and Minuteman IIIs initially.
Exchange Monitor affiliate Defense Daily first published a version of this story.