W87 (nuclear weapon)

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W87 thermonuclear weapons are the current warheads on LGM-30 Minuteman III intercontinental ballistic missiles. They replaced W78 warheads, which had previously been the Minuteman III standard before arms reduction treaties removed multiply independently targetable reentry vehicles from these land-based ICBMs. The W87, a relatively new warhead introduced in 1986, came from the single-warhead LGM-117 Peacekeeper single-warhead ICBMs, which were bei[ng retired as a result of other arms control treaties.

Schematic of W87 by Howard Morland

In the illustration, there is a spherical secondary at the top, while at the bottom is a spherical primary. The outer casing (blue/purple) is that of a MIRV warhead reentry vehicle. The "physics package" of the primary and secondary is surrounded by a uranium-238 reflector casing (gray), inside of which is filled with polystyrene foam (tan) which aids in the transfer of radiation from the primary to compress the secondary. The primary (bottom) is a tamper of some sort (gray), followed by precisely arranged high explosives (yellow), followed by a plutonium core (blue), filled with tritium gas (green). The spherical secondary is a uranium-235 or uranium-238 tamper (blue), followed by lithium deuteride fusion fuel (red), followed by a uranium-235 or plutonium "sparkplug" (blue),

A warhead refurbishment program is scheduled to extend their service life to at least 2025.[1]

Effects

The warheads are enclosed in Mark 21 reentry vehicles. Their basic yield is 300 kilotons (KT), but they can have uranium rings added to increase it to 475 KT.

Current LGM-30G Minuteman missiles are estimated to have a circular error probability of 120 meters.

Deployment

Before the 2010 New START arms control treaty, the U.S. kept 450 warheads on Minuteman III's at 450 F.E. Warren Air Force Base, Malmstrom Air Force Base and Minot Air Force Base. The new agreement reduces the total number of national deployed nuclear weapons from 2200 to 1600. The Obama Administration has not yet announced which specific launchers will be cut, but there are indications that the number of (dispersed) bases will stay constant, but there will be fewer missiles at each base.

Safeguards

Safeguards for the warhead proper include enhanced electrical isolation, LX-17 insensitive high explosive (IHE) and a fire-resistant pit. It meets the one-point safe criterion. The LX-17 has exhibited, in laboratory tests, some stiffening and crystallization, but remains within design limits. The W87, and the retired W84, are the only warheads that contain only IHE with no conventional boosters.[2]

References

  1. Fact Sheet: U.S. Nuclear Modernization Programs, Arms Control Association, 27 April 2010
  2. Safe Handling of Insensitive High Explosive Weapon Subassemblies at the Pantex Plant, Defense Nuclear Facilities Safety Board, September 1999, DNFSB/TECH-24, p. 4-1