The United States Air Force (USAF), in collaboration with the company Northrop Grumman, has completed a full-scale qualification test of the solid rocket motor corresponding to the second stage of the LGM-35A Sentinel intercontinental ballistic missile (ICBM). The test was conducted on July 20 at the facilities of the 717th Test Squadron, within the Arnold Engineering Development Complex, in the state of Tennessee.
This technical evaluation, carried out in a vacuum chamber to simulate high-altitude conditions, allowed obtaining relevant data about the motor’s thrust, its combustion profile, and maneuvering capabilities through the thrust vector control system. The test marks a milestone in the process of modernizing the United States’ land-based nuclear deterrent.
The second-stage motor is one of the three segments that make up the Sentinel missile’s propulsion system. This test is part of a series designed to qualify the stage and validate predictive models developed in digital engineering environments. According to the information provided, the results will be used to adjust design elements and reduce technical risks before entering the production phase.
This progress follows the first-stage motor test conducted in March of this year at Northrop Grumman’s facilities in Promontory, Utah. That evaluation was also used to verify the motor’s performance and its correspondence with digital simulations, laying the groundwork for subsequent qualification stages.
The Sentinel program’s approach is based on using digital models to predict system behavior, improve the accuracy of performance calculations, and reduce reliance on physical prototypes. The Air Force, together with Northrop Grumman, will continue qualification tests of the second stage throughout the year, incorporating additional evaluations under various environmental conditions.
At the beginning of 2024, Northrop Grumman had completed a large-scale static test of the same second-stage motor, also at the Arnold Engineering Development Complex. On that occasion, conditions simulating the space environment faced by the missile during launch were recreated. The company highlighted that the accuracy of the obtained results strengthened confidence in the design and reduced the risk associated with system development.
However, the Sentinel program was subject to review in January of last year after a Nunn-McCurdy Act violation was reported, due to unit acquisition costs exceeding the legally stipulated budget by more than 25%. This situation forced the Department of Defense to initiate an investigation to determine the project’s continuation. Despite this, on July 8 of that same year, the Under Secretary of Defense for Acquisition and Sustainment, William A. LaPlante, formally authorized the continuation of the program after concluding that the Sentinel missile is fundamental to national security, that no viable alternatives with the same capabilities exist, and that current costs are acceptable based on a redistribution of funds from other programs.
The LGM-35A Sentinel aims to replace the current Minuteman III ballistic missile and is part of the United States’ efforts to maintain and modernize its nuclear triad.
*Cover image for illustrative purposes
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