LGM-118 Peacekeeper

LGM-118 Peacekeeper
Test launch of a Peacekeeper ICBM by the 1st Strategic Aerospace Division (1 STRAD), Vandenberg AFB, CA (USAF)
Type	Intercontinental ballistic missile
Place of origin	United States
Service history
In service	December 1986 (1986-12)[1] — 12 September 2005 (2005-09-12)[2]
Used by	United States Air Force
Production history
Manufacturer	Boeing Martin Marietta TRW Denver Aerospace
Unit cost	US$70,000,000 (equivalent to $194,571,949 in 2023)
Specifications
Mass	87,750 kg 193,460 lb[3]
Length	21.8 m 72 ft[3]
Diameter	2.34 m 7.7 ft[3]
Warhead	Up to 11 Avco Mk21 re-entry vehicles each carrying a 300 kt W87-0 warhead (though in practice, only 10 were carried); or 12 Avco Mk12A re-entry vehicles each carrying a 335–350 kt W78 warhead (never deployed)[4] plus decoys
Detonation mechanism	Ground-burst and/or air-burst fusing modes
Engine	Three-stage solid-fuel rocket First stage: Thiokol SR118 solid-fuel rocket motor Second stage: Aerojet General SR119 solid-fuel rocket motor Third stage: Hercules SR120 solid-fuel rocket motor Post-boost vehicle: Rocketdyne restartable liquid-propellant rocket motor; storable hypergolic fuel First stage: 500,000 pounds-force (2.2 MN)
Operational range	6,000 mi (9,600 km)[5]: 288 [3]-8,700 mi (14,000 km)[6][7]
Maximum speed	Approximately 15,000 miles per hour (Mach 20; 24,000 km/h) at burnout[1]
Guidance system	Inertial (AIRS)
Accuracy	130 ft (40 m)[8][9]-300 ft (90 m) CEP[3]
Launch platform	Fixed silo

The LGM-118 Peacekeeper, originally known as the MX for "Missile, Experimental", was a MIRV-capable intercontinental ballistic missile (ICBM) produced and deployed by the United States from 1985 to 2005. The missile could carry up to twelve Mark 21 reentry vehicles (although treaties limited its actual payload to 10), each armed with a 300-kiloton W87 warhead. Initial plans called for building and deploying 100 MX ICBMs, but budgetary concerns limited the final procurement; only 50 entered service. Disarmament treaties signed after the Peacekeeper's development led to its withdrawal from service in 2005.

Studies on the underlying concept started in the 1960s. The idea was to allow the US to absorb a sneak attack by the USSR with enough warheads surviving to attack the remaining Soviet missile silos. To do so, the missiles had to be highly accurate, be based in such a way that enough would survive a nuclear attack, carry a large number of warheads so the survivors would still inflict massive damage, and be able to rapidly re-target so they could be aimed at only those missiles the Soviets had not yet fired. Over its development through the 1970s, MX emerged as a highly accurate, rapid-firing, and quickly retargeted system. Ultimately, the only problem that was never completely solved was the issue of basing.

Initial development began in 1971, with full-scale development starting in 1974. President Jimmy Carter ordered initial production in 1979 but was overturned by Congress. After considerable debate about the system, in October 1982, President Ronald Reagan announced that 50 of the newly named Peacekeepers would be put into service in existing LGM-30 Minuteman silos, a temporary measure until final basing was decided. The first flight test took place in 1983, which included the successful launch of six inert re-entry vehicles, each hitting pre-planned targets. It was the first US ICBM to use a cold launch system.

Peacekeeper reached initial operational capability in 1986. At this time, the United States and the Soviet Union were negotiating the START II treaty, under which ICBMs were allowed to carry only a single warhead each. Because the Minuteman could carry a single warhead for far less money, the United States agreed to remove the Peacekeeper from their nuclear force in this treaty. Despite the US withdrawal from the Anti-Ballistic Missile Treaty and the subsequent Russian withdrawal from the START II on 14 June 2002, the last Peacekeeper missile was deactivated on 19 September 2005. Their advanced W87 warheads were moved to the Minuteman III.

The private launch firm Orbital Sciences Corporation has developed the Minotaur IV, a four-stage civilian expendable launch system using old Peacekeeper components. As of 2020^[update], seven Minotaur IV flights have been made.