U.S. Air Force Tests Mk21A Reentry Vehicle for Future Sentinel Intercontinental Ballistic Missile

The United States Air Force flight-tested an unarmed Mk21A reentry vehicle on October 9, 2026, using a Minotaur I rocket launched from Vandenberg Space Force Base. The test exposed the future Sentinel intercontinental ballistic missile payload carrier to launch, separation and atmospheric-flight conditions, allowing engineers to collect performance and environmental data. Mk21A is being developed for the LGM-35A Sentinel program, which is intended to replace the aging Minuteman III strategic missile force. The launch was a developmental risk-reduction event, not a flight of a complete Sentinel missile or a nuclear-armed weapon.