Multiple independently targetable reentry vehicle
From Freepedia
A multiple independently targetable re-entry vehicle, or MIRV, is one of a collection of nuclear weapons carried on a single intercontinental ballistic missile (ICBM) or a submarine launched ballistic missile (SLBM). Using MIRVs, a single launched missile can strike several targets, or fewer targets redundantly.
The military purpose of a MIRV is twofold.
- To reduce or eliminate the effectiveness of an anti-ballistic missile system that relies on intercepting individual warheads. While a MIRVed attacking missile can have multiple (3-12 on various US missiles) warheads, interceptors can only have one warhead per missile. Thus, in both a military and practical sense, MIRVs render ABM systems less effective, as the costs of maintaining a workable defense against MIRVs would grow astronomically, and would require multiple defensive missiles for each offensive one.
- To reduce the number of missiles required to carry out an attack. With single warhead missiles, one missile must be launched for each target. The post-boost stage (or bus) of a MIRV can dispense the warheads against multiple targets across a broad area.
Mode of operation
In a MIRV, the main rocket motor, the booster, pushes a "bus" (See illustration) into a freely-falling ballistic flight path. At some time after boost, the bus maneuvers using on-board small rocket motors and a computerised inertial navigation system. It takes up a ballistic trajectory that will deliver a warhead to a target, and then releases a warhead on that trajectory. It then maneuvers to a different trajectory, and releases another warhead, and repeats the process for all warheads.
Details are closely-held military secrets, but it is thought that the bus' on-board fuel limits the distances between targets of individual warheads. Some buses may use small hypersonic airfoils at various times in the mission to gain additional cross-range distance, or higher accelerations. It is also thought possible that the buses can release decoys to confuse interception devices and radars, such as aluminized balloons or electronic noisemakers.
Accuracy is crucial, because doubling the accuracy decreases the needed warhead energy by a factor of four. Accuracy is limited by the accuracy of the navigation system, and the available geophysical information. Some writers believe that most government-supported geophysical mapping initiatives, such as GPS, and ocean satellite altitude systems such as Seasat, probably have a covert purpose to map mass concentrations and determine local gravitic anomalies, in order to improve accuracies of ballistic missiles.
Strategic missile systems are thought to use custom integrated circuits designed to calculate navigational differential equations thousands to millions of times per second in order to reduce navigational errors caused by calculation alone. These circuits are usually a network of binary addition circuits that continually recalculate the missile's position. The inputs to the navigation circuit are set by a general purpose computer according to a navigational input schedule loaded into the missile before launch.
See also
External links
- "MIRV: A BRIEF HISTORY OF MINUTEMAN and MULTIPLE REENTRY VEHICLES" by Daniel Buchonnet, Lawrence Livermore Laboratory, February 1976.
