Northrop Grumman successfully tested the second stage solid-rocket motor of the LGM-35A Sentinel intercontinental ballistic missile at the Air Force’s Arnold Engineering Development Complex at Tullahoma, Tenn., the company announced Jan. 16.
“The test was conducted in a vacuum chamber simulating real-world flight environmental conditions the solid-rocket motor would experience during high-altitude and space flight,” the company said in a press release.
Northrop Grumman did not disclose the exact date or duration of the burn and could not be reached for comment.
The test follows a successful trial of the first stage, carried out at the company’s Promontory, Utah, facilities in March 2023. That test was a full-scale static test fire with the rocket also mounted on a stand, but fired outdoors, since it will burn within the atmosphere. Sentinel is a three-stage missile, and Northrop will build stages one and two.
Test data are being analyzed “to determine how motor performance matched digitally engineered model predictions, critical to maturing the design and lowering risk,” the company said. Following this development effort, Northrop “will begin a series rocket motor qualification testing for both stages.”
The test “moves us forward for qualification testing in partnership with the Air Force,” Northrop vice president and Sentinel program manager Sarah Willoughby said in a statement. The test provides “an accurate reading of our design’s performance and now informs our modeling and designs,” lowering risk and building confidence in the design, she said.
The test comes as a welcome step forward for the $13.3 billion Sentinel development program, which Pentagon officials say may be headed for schedule slips and cost overruns. Though the missile design was vetted through what USAF officials have touted as “millions” of iterations in its digital design phase, numerous officials and watchdogs have warned that its staggering scope puts its planned initial operational capability—in late spring of 2030—in doubt.
Brig. Gen. Colin J. Connor, head of Global Strike Command’s ICBM Modernization Directorate, said in late November that a new program schedule would be developed by the end of 2023.
Global Strike commanders and Air Force Secretary Frank Kendall have said reaching initial operational capability by Fall 2030 is a “no fail” date that must be met if the U.S. strategic deterrent is to be maintained at current strength.
Kendall said in a November event of the Center for New American Security that Sentinel is “quite honestly, struggling a little bit” but declined to say more because he is recused from program actions due to his prior employment. Kendall said he’s “nervous” about the sprawling program, which calls for replacing more than 400 Minuteman III ICBMs with all-new missiles in refurbished and modernized silos across five states, along with an all-new command-and-control system. Sentinel is “probably the biggest thing … the Air Force has ever taken on,” he said.
The Government Accountability Office assessed in June that Sentinel is probably a year behind schedule, “due to staffing shortfalls, delays with clearance processing, and classified information technology infrastructure challenges,” as well as “supply chain disruptions.”
The program’s master schedule contains “many deficiencies,” the GAO said, and should be discarded in favor of a new plan.
Sentinel is currently projected to cost about $85 billion. Kendall and the GAO agreed that early cost estimates suffered from the Air Force not having attempted a program of such magnitude since the 1970s and thus being out of practice in understanding the costs and challenges involved.
Critical design review for the Sentinel is expected in the spring, but Pentagon officials have warned that may slip.