Lockheed Martin and the U.S. Air Force successfully completed a developmental flight test of the unarmed Mk21A reentry vehicle, an advanced component designed for the U.S. military’s future LGM-35A Sentinel intercontinental ballistic missile (ICBM). Launched from Vandenberg Space Force Base in California, the vehicle flew over the Pacific Ocean, marking another milestone in developing America’s next-generation land-based nuclear deterrent. The Mk21A is designed to accommodate the W87-1 nuclear warhead and will eventually replace the legacy Mk21 reentry vehicle.

Northrop Grumman’s Sentinel missile is expected to reach speeds of about 15,000 mph at burnout. The Mk21A must protect its payload from extreme heat and mechanical stresses during atmospheric reentry while keeping its onboard systems functional. The latest test evaluated the vehicle’s architecture and advanced technologies without carrying a nuclear warhead. Engineers are also using digital engineering, high-fidelity simulations, and data from previous tests to refine the design and accelerate development, according to Interesting Engineering.

The Mk21A program is being developed under a military contract valued at more than $1 billion, with upcoming work focused on design refinements and a system-level Critical Design Review. The successful test represents progress in the broader modernization of the U.S. nuclear deterrent, although the Sentinel program continues to face development delays and cost increases. Continued testing and development will be important to the Air Force’s long-term plan to replace its aging Minuteman III missile fleet.