VANDENBERG SPACE FORCE BASE, Calif., — The U.S. Air Force launched an unarmed Mk21A reentry vehicle aboard a Minotaur I rocket from Vandenberg Space Force Base on October 9, conducting an in-flight environmental test to support development of the system for the next-generation LGM-35A Sentinel intercontinental ballistic missile (ICBM).
The test provided additional flight data to mature the Mk21A design. Developed by Lockheed Martin, the vehicle is currently in the engineering and manufacturing development phase and is designed to carry the modernized W87-1 nuclear warhead on the Sentinel.
Maj. Gen. William Rogers, the Air Force portfolio acquisition executive for ICBMs and director of ICBM systems at the Air Force Nuclear Weapons Center (AFNWC), said the Mk21A is crucial to modernizing U.S. ICBMs in response to the changing global threat environment. He said its development would support a safe, secure and effective nuclear deterrent. Brig. Gen. Amanda Okeson, program manager for the AFNWC ICBM Systems Directorate, added that ICBM modernization remains an Air Force priority.
Mk21A Testing and Development
The latest launch follows a successful Mk21A test flight over the Pacific Ocean on June 17, 2024. An earlier attempt on July 6, 2022, failed when the Minotaur II+ rocket carrying the vehicle exploded approximately 11 seconds after liftoff from Vandenberg.
Northrop Grumman supplied the Minotaur I rocket for the latest test, which was overseen by the U.S. Space Force’s Rocket Systems Launch Program. Minotaur rockets are used to demonstrate and test payload technologies in operationally realistic flight environments. Northrop Grumman is also developing the Sentinel ICBM.
A reentry vehicle houses a missile’s warhead and must withstand high speeds and intense atmospheric heat during reentry. Lockheed Martin adapted the existing Mk21 design for the Mk21A using digital engineering, modeling and simulation.
Lockheed Martin began work on the programme in October 2019 under a $108.3 million technology maturation and risk reduction contract. On October 30, 2023, it received a follow-on contract worth approximately $996 million for engineering, manufacturing and development. Subsequent modifications increased the cumulative contract value to about $1.48 billion by late 2025. Work is being conducted in King of Prussia, Pennsylvania, and other locations.
The AFNWC leads the Mk21A acquisition effort, coordinating nuclear materiel management for Air Force Materiel Command in support of Air Force Global Strike Command.
Sentinel ICBM Programme
The LGM-35A Sentinel is intended to replace the U.S. Air Force’s Minuteman III ICBM fleet. Initial Sentinel missiles are planned to use existing Mk21 reentry vehicles and W87-0 warheads before transitioning to the Mk21A and modernized W87-1 warhead.
The Air Force plans to procure 642 Sentinel missiles, including 400 for one-for-one replacement of Minuteman III missiles, with the remainder intended for operational reserve and testing. Sentinel has a targeted operational entry date of 2029, with initial flight testing scheduled for 2027.
The Air Force has also completed the vertical stacking of an inert Sentinel vehicle at Vandenberg to verify critical subsystems ahead of flight testing.
Looking beyond the Mk21A, the Air Force issued a request for information in April 2023 for a Next Generation Reentry Vehicle intended eventually to replace both the Mk21 and Mk21A. Further details about the future system have not been released.
The October 9 test adds to the data supporting Mk21A development as the Air Force continues work on its next-generation land-based nuclear deterrent.
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