Solid rocket motors for the first five Air Force flight tests of the Northrop Grumman LGM-35A Sentinel future intercontinental ballistic missile (ICBM) are in construction, the company said on Monday.
“Every propulsive element of the Sentinel missile has been prototyped and tested,” according to the company press release. “Northrop Grumman has assembled the first three-stage Sentinel booster, verifying design, processes and technologies, and solid rocket motors for the first five flight tests are already in production.”
In addition, “two interstage separation tests were conducted to demonstrate the ability of the missile to cleanly separate the spent solid rocket motor stages one and two from the rest of the vehicle,” Northrop Grumman said. “A shroud fly-off test tested and validated the design of the shroud–a protective cover for the missile’s payload.”
Finally, according to the company, Sentinel’s guidance and control hardware “was stress tested through an initial mass model sled test which exposed the Navigation Inertial Measurement System hardware to flight-like conditions to evaluate performance.”
“Passing this test means the hardware will survive the environmental stresses induced during the missile’s flight, critical for Sentinel’s accuracy and overall mission success,” Northrop Grumman said.
The Sentinel missile will replace the Boeing Minuteman III intercontinental ballistic missile. The National Nuclear Security Administration’s plutonium pit production program at Los Alamos National Laboratory plans to make the fissile cores for the W87-1 warhead, which will top the Sentinel missile.
The first full flight test of Sentinel from a silo is not until March 2028 – four years later than the Air Force had planned.
The Air Force has said that it expects Pentagon acquisition chief Michael Duffey to re-certify 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The Defense Department approved Sentinel to enter EMD in 2020, but then rescinded that decision in 2024 after a critical Nunn-McCurdy unit cost breach.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.
In February, construction of a prototype Sentinel silo began at Northrop Grumman’s Promontory, Utah, site, and the Air Force said it expected to conduct the first flight test of Sentinel from a pad at Vandenberg Space Force Base, Calif., next year.
In the last year, the service decided to build new silos for Sentinel, rather than re-using those housing Minuteman IIIs. Environmental factors in the Minuteman III silos include asbestos, lead paint, and tilting in a small number of silos due to variations in their concrete thickness.
A Sentinel program official said in February that variability in the condition of the Minuteman III silos and a desire to reduce cost were key in the Air Force’s decision to build new ones.
The official said that the Sentinel missile is a “little bit larger” than Minuteman III and that “there are some things that come along with that, heavily focused on how we transport it, how it’s emplaced is different that Minuteman III, what vehicles are required to try to make sure that it is transportable on commercial roads and bridges, that we’ve got vehicles that don’t need special handling and things of that nature.”
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.