As part of ensuring the land-based leg of the nuclear triad is ready and capable of responding to attack, the United States usually conducts four to five ICBM test launches per year. If the U.S. continued this pace of testing, it would run out of extra weapons to launch by 2035, forcing it to either halt test launches indefinitely or start shaving operational weapons off the inventory to be used for these tests. 

Yet, the Air Force contends that there are several other challenges it would have to face to keep the Minuteman III alive for the foreseeable future. The first and most prominent is the aging out of the rocket motors meant to carry the weapons to their targets. Rocket motor lifespans are determined by destructively testing a small number of them and measuring the degradation of physical, chemical, and mechanical properties to create statistical models that can be used to determine when the motor’s functionality would fall below operational thresholds. In other words, they subject these rockets to immense stresses, measure the damage, and then use that data to extrapolate an expiration date for when the rocket will no longer work well enough to accomplish its mission. 

Based on the Air Force’s rocket lifespan modeling, the three boosters in the Minuteman III will begin to expire in 2029. 

The next technical hurdle another service life extension program would need to overcome is the weapons guidance system also aging out of service. The Minuteman III originally came equipped with the NS-20 Missile Guidance System, which had already aged out of relevance by the 1990s, prompting the branch to kick off the Minuteman III Guidance Replacement Program midway through the decade. This program saw the NS-20 swapped out for the more modern and accurate NS-50 system. This cost some $1.6 billion in 1995 currency, or roughly $3.34 billion today, and would extend the lifespan of these guidance systems out to 2020. 

By 2012, the Federation of American Scientists reported that the Defense Department had already invested a total of $7 billion into various Minuteman III service life extension efforts – roughly $9.7 billion in today’s dollars, and it certainly didn’t end there. 

Then, 2020 came and went without a Minuteman III replacement, and the Air Force had to award several subsequent contracts to Boeing to stretch their lifespans out to 2030 and beyond – when the Minuteman III’s replacement was meant to come online. 

While not a conclusive list of these life-extending costs, public records exist for a $51.2 million contract award to Boeing for the job in January 2015 ($68.83 million today), followed by at least two contract modifications to add an additional $15.6 million the following February and an additional $8.1 million in July (a combined $31.43 million today for a total of $100.26 million). 

But even with all this invested, the Minuteman III still faces a laundry list of systems that are not only aging out of relevance but aging out of being feasible to maintain and support. 

A 2019 analysis conducted by the conservative think tank Hudson Institute posited that between 2031 and 2033, as many as 50 missiles might age out of service due to motor or onboard systems falling below the operational threshold, and by 2037, the operational Minuteman III fleet could be as small as 100 weapons. However, the Air Force awarded Boeing another $1.6 billion in February 2023 for Minuteman III “guidance subsystem support,” which is likely to curtail at least a portion of these losses, even if it did mean eclipsing the $10 billion mark on service life extensions. 

As the Pentagon sees it, continuing to funnel billions of dollars into keeping these Kirk-and-Spock-era weapons in service simply isn’t sustainable from either financial or strategic perspectives. 

As Lt. General Andrew Gabera, deputy chief of staff for Strategic Deterrence and Nuclear Integration explained, the Air Force has already modeled out the costs of keeping the Minuteman III relevant, but even those projections have limited value because they simply don’t know what the future may hold. Adapting to unforeseen threats would objectively be simpler (and cheaper) with a fully modern system. 

In 2021, the head of U.S. Strategic Command, U.S. Navy Admiral Charles Richard, did not mince words regarding the future of the Minuteman III, saying it was simply no longer logical to pursue more service life extensions for the weapon, and issuing harsh criticisms for external calls to do so. 

“I don’t understand frankly how someone in a think tank who doesn’t have their hands on the missile, looking at the parts, the cables, all of the pieces inside that. I was out at Hill Air Force Base looking at this. That thing is so old that in some cases the drawings don’t exist anymore. Or where we do have drawings they’re six generations behind the industry standard. There’s not only not anybody working that can understand them, they’re not alive anymore,” he said. 

The admiral went on to highlight concerns about cyber vulnerabilities, saying the U.S. needed to replace what was “ basically a circuit switch system with a modern cyber defendable up-to-current standards command and control system.”

“Just to pace the cyber threat alone, GBSD is a necessary step forward,” he argued. 

He also highlighted the changing threat environment, one of the factors the 2014 Rand analysis acknowledged would justify an ICBM replacement. 

“This nation has never before had to face the prospect of two, peer, nuclear-capable adversaries who have to be deterred differently and actions to deter one have an impact on the other. This is way more complicated than it used to be,” Richard said. 

The LGM-35A Sentinel ICBM program

But if replacing the Minuteman III was supposed to be the budget-friendly solution, that appears to have backfired. Originally, Northrop Grumman and Boeing were competing for the opportunity to design and field this new missile, with both firms planning to use solid rocket motors produced by Orbital ATK. However, Northrop Grumman purchased the rocket maker in 2019, giving them the ability to procure their rocket motors at cost, while Boeing would have to buy them at market rate. This allowed Northrop Grumman to significantly undercut Boeing’s proposal, and recognizing that, Boeing bowed out, leaving Northrop to pursue the contract uncontested. 

The Air Force ultimately awarded the company a $13.3 billion developmental contract for the Ground Based Strategic Deterrent (GBSD) that would become the Sentinel ICBM in September of 2020, with a projected overall program cost of $77.7 billion by the time a new fleet of missiles, silos, and launch facilities had been constructed and put into service. 

Of course, it wasn’t long before that projected $77 billion price tag began to climb. By February of 2021, the projected program cost has already risen to $100 billion, a figure that held until 2023, when the Pentagon acknowledged that the program’s cost had risen so substantially that even a “reasonably modified” version of the ongoing missile program, meant to reduce overall costs, would still likely ring in at roughly $140.1 billion — representing an 81% cost overrun over the effort’s initial projections. More recent estimates from earlier this month saw another roughly $800 million increase, bringing the current total to $140.9 billion.

While cost overruns are pretty commonplace among the Defense Department’s highest-priority efforts, an increase this substantial is not — in fact, the Sentinel’s budget woes are so severe that the program ran the risk of being canceled by law until just a few weeks ago. 

Significant cost overruns in the 1980s associated with programs like the H-60 Series Black Hawk helicopter and MIM-104 Patriot Air Defense System prompted Senator Sam Nunn and Representative David McCurdy to sponsor what has come to be known as the Nunn-McCurdy Act, which mandated public reporting to Congress when Defense acquisition costs began to skyrocket. 

This law has seen at least nine amendments since, with today’s Nunn-McCurdy laws identifying two types of budgetary breaches separated by severity. Significant Breaches occur when a weapon system or platform’s per-unit cost exceeds 15 percent or more of the current baseline cost, or when overall program costs grow more than 30 percent above their original baseline estimate. More severe Critical Breaches occur when costs increase 25 percent or more over current baseline estimates or 50 percent more than the original baseline estimate. 

As of 2009, any program that meets the criteria for a Critical Breach is considered legally canceled unless certified otherwise by the Secretary of Defense, which is generally accompanied by a plan to restructure the program and a full written explanation of the problems — and intended solutions — for Congress. 

At 81 percent above the original program cost estimate, the LGM-35 certainly met the criteria to be classified as a Critical Breach, prompting a Defense Department review of issues the program is facing and potential alternatives to continuing its development. 

The results of that review were released to the public on July 8, with the Pentagon certifying the program to continue despite its immense cost for a number of reasons that could truly all be boiled down to one: The Air Force simply doesn’t have any other option.