New Sentinel ICBM’s Nose Shroud Separation Test A Flying Success

The safe separation of the Sentinel ICBM’s top ‘shroud,’ under which the nuclear warhead sits, is an essential part of how the missile works.

byJoseph Trevithick|
Northrop Grumman says it has successfully conducted a shroud fly-off test as part of the development of the new LGM-35 intercontinental ballistic missile for the U.S. Air Force.
Northrop Grumman


Northrop Grumman has released a striking visual of the top section for the U.S. Air Force's new LGM-35 Sentinel intercontinental ballistic missile (ICBM) flying off in a test. This is a critical part of how the missile functions, with this "shroud" needing to safely detach before the nuclear warhead underneath can be released onto its target. The successful test comes as the Sentinel program has been facing serious challenges and billions of dollars in cost overruns, though these issues are largely tied to infrastructure modernization demands and not the missile itself.

A rendering of a complete LGM-35 Sentinel intercontinental ballistic missile. Northrop Grumman

The successful LGM-35 shroud "fly-off" test took place at the U.S. Navy's sprawling Naval Air Weapons Station China Lake test base in California, according to a press release put out today. Additional testing involving the upper and lower stages of the Sentinel missile has also recently occurred at Northrop Grumman's Strategic Missile Test and Production Complex in Promontory, Utah, the release added. In addition to the shroud test, this included a "stack test" demonstrating how lower stages of the missile would be expected to perform during an actual flight. This all follows other successful testing of the Sentinel's rocket motors and other components of the missile in the past year.

A picture showing a LGM-35A Sentinel stage-one solid rocket motor at the Northrop Grumman test facility in Promontory, Utah, on March 2, 2023. Northrop Grumman

"Working with the Air Force and our team of suppliers, we put key elements of the missile’s hardware to the test to mature our design and lower risk," Sarah Willoughby, Northrop Grumman Vice President and Program Manager for Sentinel, said in a statement "The shroud fly-off test proved our modeling predictions are solid, while the missile stack test demonstrated inflight missile performance, helping validate assumptions and fine-tune models."

Sentinel is still in development, but the goal is for these new ICBMs to begin replacing older LGM-30G Minuteman III ICBMs in the 2030s. The Air Force currently has approximately 400 Minuteman IIIs deployed in silos spread across five states.

An infrared image of an LGM-30G Minuteman III ICBM launched during a routine test. USAF

The shroud fly-off specifically verified that "the shroud did not strike enclosed payload, critical to mission success," according to the press release. The picture that Northrop Grumman released shows that the shroud is 'spun off' from the top of the missile with the help of a pair of rocket motors.

At present, each LGM-35 is expected to be armed with a single W87-1 nuclear warhead inside a Mk 21A re-entry vehicle attached to a payload bus under the shroud on top. During a real launch, the Sentinel's top stage would first be lofted outside of the Earth's atmosphere. At a designated point, the shroud would then separate from the rest of the missile. The payload bus would then maneuver into position and release the warhead. Modern ICBMs typically carry decoys and have other countermeasures to complicate any attempt at an intercept, and otherwise hamper defenders.

The U.S. Air Force video below gives a good general look at how the payload bus on a typical ICBM, loaded with a mixture of warheads and penetration, functions.

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The exact yield of the W87-1 is unclear, but the original W87 warhead has a reported baseline yield of 300 kilotons that could be increased to 475 kilotons through a modification to the weapon's second stage. The W87 and its Mk 21 re-entry vehicle were originally developed for the LGM-118 Peacekeeper ICBM, which entered service in the 1980s. The last of the Peacekeepers were removed from service in 2005 as a result of U.S.-Russian arms control agreements. The warheads from those missiles were subsequently adapted for use on older LGM-30G Minuteman IIIs, which are the only ICBM in U.S. inventory today.

The Air Force has said that it is prepared to arm the LGM-35s with multiple warheads – a configuration referred to as multiple independently targetable reentry vehicles, or MIRV – should such a decision be made in the future. The existing Minuteman III can be employed in a MIRV configuration, but each of these missiles are loaded today with just a single warhead due to arms control agreements.

The total number of nuclear warheads the U.S. military can deploy at any one time, including those on top of ICBMs, is currently limited by the provisions of the New START treaty. In 2021, U.S. and Russian authorities agreed to extend this deal through 2026. However, Russia's government suspended its participation in New START last year ostensibly over the United States' continued support for Ukraine.

Air Force personnel maneuver reentry vehicles on a payload bus for the Minuteman III ICBM. As a result of arms control agreements, deployed Minuteman III missiles today are loaded with only one warhead. USAF

There have also been past discussions about the potential for arming Sentinels with highly maneuverable unpowered hypersonic boost-glide vehicles instead of warheads inside traditional re-entry vehicles.

Unfortunately, while the development of the LGM-35 missile itself looks to be progressing steadily, the Air Force has admitted the overall program has been struggling. Sentinel's overall estimated cost was originally pegged at just under $96 billion, but this has now grown by some 37 percent to just over $125 billion, according to a report in January from Air & Space Forces Magazine. The program is also looking at a two year delay at least. A full reassessment of the program cost and schedule is now underway.

However, "one of the things that we've learned is that the missile aspect of the [Sentinel] program is not where we're seeing a sizable amount of growth," Kristyn Jones, the senior official currently performing the duties of the Under Secretary of the Air Force, told The War Zone and other outlets at a media roundtable on the sidelines of the 2024 Air & Space Forces Association Warfare Symposium last week. "It's primarily in the civil works aspects of the program. This is a massive undertaking."

In addition to the development and acquisition of the LGM-35 missiles, the Sentinel program also includes the modernization of the hundreds of existing silos and launch control facilities, as well as other infrastructure and command and control-related improvements.

"We're starting to see some things that we thought could be reused that don't look like they can be [now]," Jones explained. "Then there's the macroeconomic factors with inflation, supply chain, labor costs, those kinds of things."

A rendering of a future Sentinel silo, which also highlights that much of the facility is expected to be entirely new. Northrop Grumman

Jones added that a full analysis of where Sentinel's cost growth is coming from remains underway.

The Air Force also announced last year that it had found unsafe levels of carcinogenic materials in ICBM launch control facilities. This could be tied to a significant number of cancer diagnoses among current and former members of the service's missile community.

Air Force officials have made clear they see no alternative to Sentinel and that the ICBM program remains critical to U.S. national security in the long term. At the same time, it remains to be seen how Sentinel's woes will impact the rest of the Air Force's future plans and budgets.

"I can't take anything off the table right now," Secretary of the Air Force Frank Kendall said at the same media roundtable last week as Jones spoke. "If we have to pay a certain amount of money for Sentinel, that will limit the amount of money we have for everything else. ... the primacy of the mission I think says a lot."

Altogether, what the full cost of the Sentinel program might ultimately be and how long it takes to complete very much remain to be seen. The newly announced shroud fly-off test does show that work on the missile itself does appear to be continuing apace.

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