USAF Sentinel Design Matures And Tests Continue Ahead Of Key Decision

The U.S. Air Force’s Sentinel program is still undergoing a restructuring process that began more than two years ago—following massive cost growth and the rescinding of a key milestone—but the effort has charged ahead with major changes and tests in the meantime.

Top Air Force and Northrop Grumman leaders argue that the extended process has further clarified the program’s scale, scope and importance. The restructuring is finally expected to conclude within the next three months with a new Milestone B decision that will restart engineering and manufacturing development.

• A new production decision is expected within months
• Critical subsystems are on track for the initial flight test in 2027

“We’ve set a good program plan in place,” Amanda Davis, Northrop Grumman’s vice president and general manager of strategic deterrent systems, told Aviation Week at the Air & Space Forces Association’s National Convention in National Harbor, Maryland, in mid-September. “We’ve learned a lot in the past six years and through the restructuring process, and making sure we have the right requirements set. . . . We’re balancing that cost, schedule and capability and putting that plan in place.”

The program sparked a Nunn-McCurdy breach in 2024 as the Pentagon reported major cost growth—81% over the original projection at about $141 billion. Although the Pentagon recertified the need for the program, Milestone B was rescinded, and the Air Force was required to begin the restructuring plan. At the time, service leaders projected the process would take 18-24 months. While that target has passed, top leaders say the restructuring has been effective, and a new Milestone B is planned by year-end.

Gen. Dale White, the Air Force’s direct reporting program manager for major acquisition efforts including the Sentinel, told reporters Sept. 14 that new cost figures are not ready yet, but he does not see any surprises in that area.

“We’re learning as we go along because of just the sheer amount of data we have now,” White said. “It’s so much more mature than when we did this five years ago.”

As part of the restructuring and new approach, White set a series of milestones to keep the program progressing. This includes the Sept. 14 announcement that the program completed a vertical stacking of the inert missile for the first time at Vandenberg SFB, California. The assembly showed that critical subsystems are on track for the initial flight test in 2027. The Air Force Test Center also completed a flight test design review to ensure the design maturity and hardware testing satisfy safety and performance requirements for the first flight test.

Davis said the program also completed a structural trial of the missile’s payload reentry system in August. “It’s really just everything hitting those marks, and there’s just a few things left that we will do for those tests that get us to that flight test,” she said.

The program has also conducted three sled tests of the missile’s navigation system to subject it to flight conditions, iterating the design based on lessons from each. The most recent was conducted in June.

“It’s one thing to have something on paper,” Davis said. “It’s quite another to have hardware that we can show good progress on.”

The design and assembly of a new ICBM is no simple task, but it has gone smoothly and quickly compared to the overall Sentinel program’s biggest issue: construction.

The Sentinel is an overhaul of the Air Force’s entire ICBM infrastructure, including new missile silos, alert facilities and other support complexes across vast areas of the Mountain West and Northern Plains. For silos alone, the program must deliver a new structure at a pace of every eight days to meet the overall timeline, Davis said.

In August, the program and the U.S. Army Corps of Engineers established a new group, Joint Task Force Castle, focused on the construction. The goal of this is “really focused on making sure we get the infrastructure part of this program and making sure it does not become the thing that prevents us from succeeding,” White said.

As part of the restructuring, top Air Force and U.S. Strategic Command leaders had to determine how many facilities are needed in how much space. They held quarterly meetings on the requirements, he said.

“We have since pretty much locked down the majority of the design to that, which was the first step, and then that allows a little more flexibility in terms what we had to do.” White said.

After the program decided that it would not reuse Minuteman III silos, Northrop Grumman and construction partner Bechtel created a prototype silo at the site in Promontory, Utah, to evaluate the design.

Davis said the program is setting up hubs for the work and changing the construction methodology to focus more on a deterministic cost and schedule. Under the modular approach, staff will work largely at central hubs on large components  that will be constructed at the remote silos.

“What’s a good way to make a big megaproject?” Davis remarked. “You want to modularize. Make something that you can replicate a lot of and then use that as kind of Lego blocks to build something up.

“That’s what we’re doing on the silo,” she added. “Instead of doing things that are very site-specific, now they will be something that we can replicate a lot. That gives us a lot more cost certainty, a lot more schedule certainty, and we’re testing those.”