The United States Air Force recently completed a full-scale qualification test of the Stage 2 solid-rocket motor for the LGM-35A Sentinel intercontinental ballistic missile (ICBM).
The evaluation, carried out with manufacturer Northrop Grumman in July 2025, took place in a vacuum chamber at Arnold Air Force Base in Tennessee. The chamber, which allows for the simulation of high-altitude conditions, provided data on the motor’s thrust, burn and steering capabilities via its thrust vector control system, according to a news release from the Air Force Nuclear Weapons Center (AFNWC).
“This test reflects our disciplined digital-engineering approach and the continued momentum behind the Sentinel program,” U.S. Air Force Brig. Gen. William Rogers, program executive officer for ICBMs and director of the ICBM Systems Directorate, AFNWC, said in a news release. “We’re not just testing hardware — we’re proving that our models are accurate, our development timeline is achievable, and the system will be ready to deliver when called upon.”
The test of the Stage 2 motor — the middle segment of the missile’s three solid-fuel stages — is part of a series focusing on specific components. The Sentinel program uses a “model-based design approach [that] allows engineers to simulate system behavior, improve accuracy in performance predictions and reduce reliance on costly hardware prototypes,” according to the AFNWC news release. The Air Force and Northrop Grumman said Stage 2 qualification testing will continue throughout 2025.
The Sentinel testing is part of the effort to replace legacy Minuteman III missiles and modernize the land-based segment of the U.S. nuclear triad. There are 400 Minuteman in hardened silos across five states in the western U.S. The Sentinel program includes upgrading or replacing launch facilities, communication systems and support infrastructure. The Department of Energy’s National Nuclear Security Administration (NNSA) is developing a new warhead, the W87-1, for the Sentinel, according to a June 2025 Congressional Research Service (CRS) report.
In addition to ICBMs, the U.S. nuclear triad consists of air (strategic bombers) and sea components ballistic missile submarines, or SSBNs). The modernization of those segments includes the B-21 Raider stealth bomber and Columbia-class SSBN programs.
“Modernization is not a matter of ‘Can we?’ It is a matter of ‘We must.’ Our nation’s security, and the security of our allies and partners for whom we provide extended deterrence, depends on it,” U.S. Air Force Gen.
Anthony Cotton, Commander of U.S. Strategic Command (USSTRATCOM), said in a February 2024 interview with Joint Force Quarterly, a journal published by the National Defense University. USSTRATCOM’s responsibilities include strategic deterrence, nuclear command, control and communications, and global strike operations.
The Air Force says the Sentinel improves on the Minuteman system in several areas. These, according to a March 2024 CRS report, include:
- An open-system architecture that allows the Air Force, which will control the intellectual property and source code, to perform upgrades and improvements. A modular design allows components to be replaced in a safer and more accessible manner during maintenance.
- Lighter composite materials give the missile an increased throw weight and the capability to carry different payloads. (Throw weight is a measure of the weight of the payload that the missile can deliver to a