Multiple Independently Targetable Reentry Vehicle (Missiles)

A multiple independently targetable reentry vehicle (MIRV) is a ballistic missile payload containing several warheads each capable of hitting one of a group of targets. By contrast a unitary warhead is a single warhead on a single missile.

In a MIRV, the main rocket motor (or booster) pushes a "bus" into a free-flight suborbital ballistic flight path. After the boost phase the bus maneuvers using small on-board rocket motors and a computerized inertial guidance system. It takes up a ballistic trajectory that will deliver a reentry vehicle containing a warhead to a target, and then releases a warhead on that trajectory. It then maneuvers to a different trajectory, releasing another warhead, and repeats the process for all warheads.

Accuracy is expressed as circular error probable (CEP). This is simply the radius of the circle that the warhead has a 50 percent chance of falling into when aimed at the center. CEP is about 90–100 m for the Trident II and Peacekeeper missiles.

MIRV launch sequence: 1. The missile launches out of its silo by firing its first stage boost motor (A). 2. About 60 seconds after launch, the 1st stage drops off and the second stage motor (B) ignites. The missile shroud (E) is ejected. 3. About 120 seconds after launch, the third stage motor (C) ignites and separates from the 2nd stage. 4. About 180 seconds after launch, third stage thrust terminates and the Post-Boost Vehicle (D) separates from the rocket. 5. The Post-Boost Vehicle maneuvers itself and prepares for reentry vehicle (RV) deployment. 6. While the Post-Boost Vehicle backs away, the RVs, decoys, and chaff are deployed (although the figure shows this happening during descent, this may occur during ascent instead). 7. The RVs and chaff reenter the atmosphere at high speeds and are armed in flight. 8. The nuclear warheads detonate, either as air bursts or ground bursts.