Multiple independently targetable reentry vehicle

W78 type warheads as multiple warheads (MIRV) reentry vehicle Mk12A for an LGM-30G Minuteman III

Re-entry traces of eight MIRVs from an LG-118A Peacekeeper on Kwajalein

Multiple Independently targetable reentry vehicles (short MIRV ; English for independent zielbarer multiple re-entry ') are multiple warheads for intercontinental ballistic missiles (ICBM) and submarine-launched ballistic missile (SLBM). They make it possible to attack several targets at the same time with a single launcher and to make defensive measures more difficult due to the simultaneous penetration of many warheads. The first MIRV-equipped missiles were deployed by the United States in the early 1970s( Minuteman III ).

MIRV is the successor to the Multiple Reentry Vehicle (MRV) , in which the warheads could not be steered independently of one another.

General

Warheads from an LGM-118A Peacekeeper

MIRV systems are payloads of military ballistic missiles in which several re-entry bodies can be exposed on individual paths. In all systems deployed so far, the re-entry objects are nuclear warheads, even if there have been studies for re-entry objects with biological and chemical weapons and kinetic impactors. Due to their complexity and range of tasks, MIRVs are limited to strategic missile systems of medium and intercontinental range.

In the first strategic missile systems, which were developed by the Soviet Union, the USA and other countries in the 1950s and 1960s, the re-entry bodies sat directly on the last stage of the ballistic missile propulsion system. This means that when the warheads were deployed, they had reached their final course and speed and no more corrections could be made afterwards. Some missiles from these early generations of strategic weapons carried multiple warheads, but these were launched together and could only be aimed at a common target around which they were to strike in a scattered manner.

In a MIRV system, the re-entry bodies are no longer located directly on the last drive stage of the ballistic missile, but on a Post Boost Vehicle (PBV, in German about post-propulsion unit, also known as a bus for short ). After the topmost rocket stage is burned out, the bus with the warheads is separated from the stage. With the help of small control engines and an inertial navigation system, which is supported by star sensors in modern MIRV systems, the bus carries out small course and speed corrections and releases the re-entry bodies one after the other on optimal paths. This allows warheads to be aimed against individual targets within a certain area on the earth's surface with a single missile. How large this area is depends on the individual MIRV system, the planned range and the payload. The Poseidon C-3 SLBM, for example, with a full payload of 14 re-entry vehicles at a range of 1,800 nm, could not aim at any targets across the flight path. If the number of warheads was reduced to 10, the re-entry vehicles could be directed against targets a maximum of 150 nm across the direction of flight of the rocket (2,500 nm range), with only 6 re-entry vehicles this increased to 300 nm at a range of 3,000 nm.

The shape of the MIRV bus can vary depending on the respective technical requirements. If there are no restrictions on the dimensions, the diameter of the control and drive unit of the bus corresponds roughly to that of the top drive stage of the rocket and the re-entry bodies sit on top of the bus (e.g. on the Minuteman III). In many missile systems, however, the volume is tightly limited, e.g. B. SLBM, which are stationed on submarines or new missiles that are to replace older systems in silos with a given volume. The MIRV bus is often designed as a ring-shaped structure that surrounds a narrow upper rocket stage. This solution was chosen for the R-36MUTTH MIRV bus or the Trident II D5 bus, for example.

As far as is known, all previous MIRV systems carry re-entry bodies that follow a simple ballistic trajectory after being released by the bus. However, in principle, MARV ( Maneuverable reentry vehicle ) systems can also be used, in which the warheads can independently carry out course corrections. For example, the Mk.500 Evader was developed for the Trident I C4 at the end of the 1970s, which was able to change direction in the earth's atmosphere through changes in lift. In the Soviet Union, a MIRV warhead with final approach control was developed for the R-36M in about the same period. In both cases, however, there was no introduction.

MIRV systems have several advantages for military planners. Since a single missile could now carry several warheads, the construction of an effective missile defense system for the potential opponent became much more difficult and practically impossible to implement. Furthermore, the fine course corrections carried out with the MIRV bus can increase the accuracy of the weapon systems. In this way, the effectiveness of the weapons against "hard" targets such as bunkers can be increased while at the same time reducing the explosive power of the individual warheads. Furthermore, MIRV systems give the military and political planners a high degree of flexibility, since the number of re-entry vehicles on individual missiles can be adapted to the mission and the political environment. For example, the USA has reduced the number of warheads on the Minuteman III ICBM and Trident II D5 SLBM from the maximum possible number in order to meet the requirements of the START disarmament treaties, but could increase them again if necessary should the political environment change .

When MIRV systems were introduced in the early 1970s, they made a major contribution to the arms race in the field of strategic weapons between the Soviet Union and the United States. Although the number of strategic missiles on both sides has hardly increased since the late 1960s, the introduction of missiles with MIRV acted as a multiplier for the number of strategic nuclear weapons. Due to their comparatively high accuracy and the number of available warheads, they also fueled political and military debates about their own and opposing first strike strategies. For example, the introduction of powerful MIRV systems such as the R-36M in the Soviet Union in the mid-1970s led to fears in the US that a window of vulnerability had emerged, as it was believed that the Soviet ICBMs would now form a large part of the American Minuteman arsenal could turn off. This drove new armament projects in the USA such as the Peacekeeper ICBM or the Trident SLBM, to which the Soviet Union in turn responded with the development of mobile ICBM systems and improvements to its nuclear command and control system.

Take-off process with an LGM-30G Minuteman III

The most powerful MIRV system developed by the United States was the LGM-118A Peacekeeper, which could carry up to ten warheads, each with an explosive force of up to 300 kt TNT equivalent . The last of these systems were decommissioned in 2005.

The Soviet Union introduced several missiles with multiple warheads from the early 1970s. First these were the R-36 and UR-100 K missiles, each of which carried three non-individually controllable MRV warheads. These missiles were followed by the R-36M (eight to ten MIRV), MR UR-100 (four MIRV), UR-100N (six MIRV) and the RT-23 (ten MIRV). Up to 38 warheads were even planned. Two versions of these missiles, the R-36M2 and UR-100NUTTH, are still in service with the Russian missile forces today. They are to be replaced in the coming years by the MIRV variant of the Topol M ( RS-24 (rocket) , SS-27 Mod2) and a new medium-weight ICBM with MIRV that is being developed by Mekejew .

The Soviet Navy also introduced missiles with MIRV in the mid-1970s, these were the R-29 R, the R-29RM and the R-39 . Two sea-launched missiles with MIRVs are currently in production in Russia, the R-29RMU (in the Sineva and Liner versions with up to ten MIRVs) and the R-30 Bulava (with up to six MIRVs).

In addition, medium-range missiles with MIRV were in service in the Soviet Union from 1976 to 1989, the RSD-10 with up to three MIRV.

Great Britain and France also have sea-launched missiles with MIRV. Great Britain has Trident II D5 from Lockheed-Martin from the United States in service (but only with a maximum of three MIRVs), in France it is the M-45 and M-51 from EADS with up to six MIRVs.