The US Air Force Nuclear Weapons Center has flight-tested an unarmed Mk21A reentry vehicle from Vandenberg Space Force Base, California, aboard a Northrop Grumman Minotaur I rocket. Conducted on 9 October, the in-flight environmental test supports Lockheed Martin’s development of the vehicle for the future LGM-35A Sentinel intercontinental ballistic missile.
The Mk21A is being developed during Sentinel’s engineering and manufacturing development phase and is intended to carry the W87-1 nuclear warhead. It is based on the Mk21 reentry vehicle used by the Minuteman III, which Sentinel is designed to replace as the land-based component of the US nuclear triad.
The launch was overseen by the US Space Force’s Rocket Systems Launch Program. No nuclear warhead was carried, and the Air Force has not disclosed performance data, the trajectory, the impact area or whether specific test objectives were achieved. The flight followed a publicly reported Mk21A test in June 2024 and a failed attempt in July 2022.
The test comes as an inert Sentinel missile has been vertically assembled at Vandenberg ahead of the programme’s first planned flight test in 2027. A Critical Design Review for the Sentinel system is planned by March 2027. The Air Force has requested nearly $540 million for Mk21A development in fiscal 2027, $184 million more than in fiscal 2026, to support expanded integration and test activity.