A Northrop Grumman official on Monday attributed the explosive projected cost growth of the U.S. Air Force’s next intercontinental ballistic missile to the service’s design changes, including to the nuclear missile’s silo and connecting cables.

The Air Force’s original plan for modernizing its ICBM enterprise included keeping nearly all its existing copper cabling in place to be reused for the upcoming LGM-35A Sentinel. That’s roughly 7,500 miles’ worth of copper cabling, connecting 450 half-century-old Minuteman III ICBM silos scattered through the Great Plains region with launch control centers and other facilities.

But the company official, who spoke with reporters on the condition that he be identified only as an official familiar with the Sentinel program, said the Air Force concluded it is necessary to upgrade the copper cables with a higher-performing fiber-optic network. That decision apparently came after the service awarded the engineering and manufacturing development contract to Northrop Grumman in 2020, and during the company’s work on the program’s early design phase.

The Air Force also realized that the original designs for Sentinel’s launch facilities — the massive concrete-encased silos from which the missiles would launch — would not work and had to be changed, the Northrop official said. Those original concepts were drawn up during the technology maturation and risk-reduction phase as well as the early engineering and manufacturing development step.

And with hundreds of launch facilities dotting the Great Plains region, often in 1-acre plots, and thousands of miles of cable stretching across farmland and other privately held property that now must be dug up, the cost of these changes swiftly added up, the Northrop official said.

“As we’ve worked through those changes. That’s led to a design that’s different than the one that they [the Air Force] started with,” the official explained. “When you multiply that by 450, if every silo is a little bit bigger or has an extra component, that actually drives a lot of cost because of the sheer number of them that are being updated.”

In a statement to Defense News, the Air Force said the Pentagon is still studying what exactly caused the severe cost overruns, which triggered a review process known as a critical Nunn-McCurdy breach.

“In accordance with statute, [the Office of the Secretary of Defense] will determine what factors caused the cost growth that led to a critical breach via the Nunn-McCurdy process, which is currently underway,” an Air Force spokesperson said. “Early estimates indicate that a large portion of the Sentinel program’s cost growth is in the command and launch segment, which is the most complex segment of the Sentinel program.”

‘Unknown unknowns’ on $96B program

Sentinel is a massive program to replace the Air Force’s aging LGM-30G Minuteman III ICBMs, which now make up the land-based portion of the U.S. military’s nuclear triad. In 2020, Northrop Grumman received a $13.3 billion cost-plus-incentive-fee contract for Sentinel’s engineering and manufacturing development phase.

The program was expected to run about $96 billion, with the total per-unit cost amounting to $118 million when its most recent cost, schedule and performance goals were set in 2020. But the price tag has skyrocketed at least 37%, and the per-unit cost is now about $162 million.

In a congressional hearing this month, Rep. John Garamendi, D-Calif., pegged Sentinel’s current cost at more than $130 billion.

That triggered the Nunn-McCurdy breach, and the Pentagon is now reviewing Sentinel to figure out how to get it back on track as well as where to find funds to keep it going. Top Air Force officials have publicly said that with Minuteman III well past its originally expected life span, the service has no choice but to replace it with a new, more reliable model — and will find money to pay for it.

Sentinel, which was originally supposed to reach initial operational capability in 2029, is now expected to fall two years behind schedule. The nuclear missile’s first flight test, which had been expected to take place in fiscal 2024, is now likely to come in February 2026, according to the Air Force’s budget documents.

The Air Force said in an email to Defense News that the Sentinel’s first flight was pushed back due to longer lead times for components in its guidance computer. But the delayed flight test is not a factor in the program’s Nunn-McCurdy breach, the service said.

In a March hearing held by the House Armed Services Committee’s sea power and projection forces panel, Garamendi voiced his displeasure to Air Force officials over the Sentinel’s cost overruns, as well as the service’s inability to explain potential “trade-offs” to keep the program alive.

Garamendi questioned the need for the United States to spend vast sums of money on Sentinel, arguing the belief that the nation must maintain a triad of nuclear weapons has become a “religious issue, having very little to do with the world in which we’re now living.”

The Northrop Grumman official told reporters Monday that the company’s work on Sentinel continues, despite the Nunn-McCurdy breach and ensuing review process.

“We don’t have a pause on our EMD [engineering and manufacturing development] work,” the official said. “We’re continuing to make progress on developing the missile and iterating the designs for all the facilities.”

In a discussion last fall, Air Force Secretary Frank Kendall said given it’s been so long since the service created an ICBM, early cost estimates for Sentinel were based on “a huge uncertainty.”

“There are unknown unknowns that are surfacing, that are affecting the program,” Kendall said during a November 2023 event with Center for a New American Security think tank. Kendall also said the Sentinel program was “struggling.”

The Northrop Grumman official highlighted such comments — including Kendall’s about the uncertainty that went into the program’s cost estimates — and said some estimates that went into the 2020 baseline review turned out to be incorrect.

Mock-up silo

Northrop also said the company’s effort to game out how a conversion process might work also showed problems with the original plan.

Before it received the Sentinel contract in September 2020, the firm started building a full-scale mock-up of a Minuteman III silo in Promontory, Utah, which it completed in spring 2021. The project was a major undertaking, and on Northrop Grumman’s dime. But the company saw it as a worthwhile investment in its bid to win the lucrative Ground Based Strategic Deterrent contract, as the program was then known.

Northrop didn’t have direct access to the Minuteman III silos — and likely won’t until the government hands them over for conversion into Sentinel silos — since the missiles must remain ready for launch at all times. And so the company considered its construction project the best way to understand how the massive retrofitting process might work — and to find where the biggest risks might lie.

The company’s team, alongside the Air Force, pored through the nonoperational mock-up and started to lay out components akin to what Sentinel would require. But as they did so, the Northrop official said, the group found some of the original conversion plans weren’t going to work.

Other design processes, including computer-aided design work, also helped the Sentinel team map out how much square footage various configurations would take up. In the process, some of the unknown factors that led to the original shaky estimates were cleared up. Still, it became clearer that the costs would be much higher than originally believed.

“They learned, along with us, things that needed to be potentially different or changed from the design,” the official said.

Five programs in one

In January, top Air Force official Kristyn Jones compared the Sentinel project to five major acquisition programs rolled into one. But the nuclear missile itself “is not an area of concern,” said Jones, who is performing the duties of undersecretary of the Air Force.

The Northrop official said the Sentinel missile will not just be a new iteration of the Minuteman series of ICBMs — “it’s not a Minuteman IV,” the official said — but a brand-new weapon top to bottom.

Its solid-rocket motors will be made of composite materials instead of the steel used on the Minuteman III, he explained, and it will have a more advanced guidance system.

Its design also includes modular components that allow the Air Force and Northrop Grumman to more easily add new technology as it becomes available.

And airmen are expected to be able to more easily maintain the Sentinel than its predecessor, with key components accessible without the need to delve too deeply into the missile and bring along a massive security detail while it is opened up.

Sentinel will be slightly larger and lighter than the Minuteman III, which will allow it to carry more propellant and payload, he said. And it is being designed to last until at least 2075 — far longer than the decade Minuteman III was originally supposed to last.

The infrastructure for Sentinel — including the silos themselves, the launch control centers where airmen control the ICBMs, and supporting infrastructure — will also be refurbished.

That portion — which Jones called “essentially a civil works program” — is especially challenging, particularly with issues such as inflation, the supply chain and labor force shortages.

The service and Northrop Grumman plan to reuse the existing Minuteman III silos as much as possible. But that will require a great deal of new construction and equipment updates to ensure the Sentinel silos can keep operating through disruptions such as power outages.

Old computers in launch centers — some of them 1980s-era terminals with green screens — will receive updates with modern equipment.

But not all Minuteman III silos were built in the same configuration, the Northrop official said, which will further complicate their conversions.

With the nation’s roughly 400 Minuteman IIIs spread out across nearly 32,000 square miles in Wyoming, Montana, North Dakota, Colorado and Nebraska, that makes the Sentinel program a massive real estate project, requiring the government to negotiate easements and, in some cases, property purchases with numerous landowners.

All of that adds up to “one of the most large, complex programs I’ve ever seen,” Kendall said of Sentinel in November 2023. “It’s probably the biggest thing, in some ways, that the Air Force has ever taken on.”

There’s also another factor at play: What happens if the Air Force and Northrop Grumman look deeper within the existing Minuteman III silos and find they’re in worse shape than expected?

The condition of the silos is a potentially high-risk area for the program, the Northrop official acknowledged, but the program still expects to be able to reuse existing ones. A “handful” of LiDAR — or light detection and ranging — scans of current ICBM sites already took place, he said, and there have been reviews of silos decommissioned in the 2000s.

But deeper, destructive testing — “breaking apart the concrete to see what’s behind it and what the conditions are” — has not occurred on existing silos, the official said, since they have to remain operational.

Minuteman III silos have concrete liners as well as mechanical launch tubes and missile suspension systems that hold the current ICBMs. The tubes and suspension systems will be replaced, the official said, and the concrete liners underneath will undergo inspection to determine if repairs need done and what is reusable.

The government has contingency plans if the silos’ foundations prove to be seriously cracked or damaged, the official said. That could include remediation work such as patching cracks or replacing portions of the concrete.

If a site is too far gone to fix, however, drilling may have to take place for an entirely new silo.

“There’s currently no plan to dig new holes,” the official said. “But given the site conditions of the land, [there is] certainly the potential that when they get to investigating more of the silos, they may find that [reusing] some of them might not be possible.”

Though the Nunn-McCurdy review process is still underway, the Northrop official said the company is talking to the Air Force about ways to bring down costs. One idea under discussion, he noted, is potentially changing the way mechanical rooms are constructed to build them in a more modular way, which could lower expenses.

But no matter how difficult or expensive Sentinel becomes, or what trade-offs are made to pay for it, the Air Force is adamant it must happen.

Lt. Gen. Richard Moore, the service’s deputy chief of staff for plans and programs, said at the January appearance alongside Jones that extending the Minuteman III missile significantly longer is “not a viable option.”

“We will find the money,” Moore said. “Sentinel is going to be funded. We’ll make the trades to make that happen.”

Stephen Losey is the air warfare reporter for Defense News. He previously covered leadership and personnel issues at Air Force Times, and the Pentagon, special operations and air warfare at Military.com. He has traveled to the Middle East to cover U.S. Air Force operations.

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