U.S. Air Force, Lockheed Martin Conduct Mk21A Reentry Vehicle Test

The U.S. Air Force and Lockheed Martin conducted the first flight test of the unarmed, developmental Mk21A reentry vehicle over the Pacific Ocean on June 17.

This test, launched from Vandenberg Space Force Base, aimed to evaluate the design components and advanced technologies integrated into Lockheed Martin’s Mk21A reentry vehicle. The test utilized a Minotaur I rocket to propel the vehicle.

The Mk21A is intended for deployment on the forthcoming Sentinel intercontinental ballistic missile (ICBM) weapon system. The Mk21A represents an updated version of the Mk21, which is currently mounted on the Minuteman III ICBM.

The test was executed under Lockheed Martin’s Engineering and Manufacturing Development contract with the Air Force Nuclear Systems Center, with gathered data set to inform further Mk21A design and testing activities.

In October 2023, the Air Force Nuclear Weapons Center awarded Lockheed Martin a $996 million contract for the development of the Mk21A. These reentry vehicles will eventually be armed with nuclear warheads and integrated into the Sentinel ICBM. During deployment, the reentry vehicle is released near the apex of the missile’s flight path and descends back through the atmosphere toward its designated target.

Despite this progress, the Sentinel program has encountered significant cost and schedule overruns, leading to a critical program review following a Nunn-McCurdy breach. This breach, declared in April, indicated that cost increases had surpassed the 25% threshold over initial baseline estimates.

While the Mk21A program is technically separate, Air Force budget documents reveal plans to procure 426 reentry vehicles, with deliveries slated to commence in fiscal 2028 and extend through 2039. Concurrently, the Air Force is investing in research and development for a next-generation reentry vehicle.

The Minotaur I rocket that launched the Mk21A on June 17 is part of a family of systems derived from the Peacekeeper and Minuteman rocket motors, according to Space Launch Delta 30. Recent Sentinel ICBM-related tests include a shroud fly-off test and a missile stack test by Northrop Grumman in February, as well as a test of the missile’s second stage solid-rocket motor in January.

The Air Force plans to procure over 600 Sentinel missiles to replace the aging Minuteman III missiles, which have been in operation for several decades and have surpassed their projected service life. The goal is to field the new ICBMs by 2030.