Science Fair Project Encyclopedia
It is a guided missile, with three solid-fuel stages, and in addition, in the post-boost stage ("bus"), a liquid-fuel propulsion system rocket engine used to fine-tune the trajectory of the reentry vehicle and/or dispense individual warheads to separate targets across a broad area. The missile has a gimballed inertial guidance system.
With START II’s ban on multiple independently targetable reentry vehicles (MIRVs) now a dead letter, earlier plans to reduce the number of warheads per missile to one have been revised: the United States is now considering keeping 800 warheads on the Minuteman force.
The Minuteman III missile entered service in 1970, with weapon systems upgrades included during the production run from 1970 to 1978 to increase accuracy and payload capacity. 1998 USAF plans are to operate it until 2025.
Operational test launches are performed by the men and women of the 576th Flight Test Squadron at Vandenberg AFB, California. This squadron is also the home of "Top Hand", a board-selected professional development program for launch officers, deemed to be "America's Best Missileers."
The Minuteman had two innovations that gave it a long practical service life: a solid rocket booster, and a digital flight computer. This computer was one of the very first recognizably modern embedded systems.
The solid rocket booster made the Minuteman faster to launch than other ICBMs, which used liquid fuels. A crucial innovation in this area was to include a valve to release the booster pressure, and permit effective throttling of the booster.
A reprogrammable inertial guidance system was a major risk in the original program. When first proposed, no one had built a digital computer that would fit in a missile. One program, the Navaho supersonic cruise missile, had already failed to produce such a system.
A digital computer was essential to obtain the accuracy gains that kept this weapon effective throughout the cold war. As the Defense Mapping Agency more accurately mapped mass concentrations in the Earth, the inertial guidance software could be updated and loaded into the missiles to make them ever more accurate by having them compensate for these sources of gravity.
Another gain that persuaded program managers to accept the risk of the computer was that the computer could also be used to test the missile. This saved a large amount of weight in cables and connectors.
The Minuteman I Autonetics D-17 flight computer used a rotating magnetic disk for about 4KB of primary storage. Unlike modern computers, which use descendants of that technology for secondary storage on hard disk, this was the active computer memory. At the time, this was a small and inexpensive method to store data, although it was extremely slow by modern standards. The 5ms average access time is about 100,000 times slower than the PC133 SDRAM commonly used as main memory in home PCs around the year 2000.
The disk storage was considered completely immune to radiation from nearby nuclear explosions, making it an ideal storage medium, if a bit slow. To overcome speed problems, the contractor (the Autonetics Division of North American Aviation, which produced small commercial computers that used a disk for memory) had developed special software that optimized the placement of the instructions on the disk to give the system a speed boost (a technique employed on earlier magnetic drum computers).
The Minuteman II program was economically crucial to the development of integrated circuits. It was the first mass-produced system to use a computer constructed from integrated circuits, and used most of the production of such circuits from 1962 through 1967. The other major customer of these circuits was the Apollo Guidance Computer, which had similar weight and ruggedness constraints.
The Minuteman II flight computer continued to use rotating magnetic disk for primary storage.
The Minuteman III Honeywell HDC-701 flight computer used NDRO (non-destructive read out) plated wire memory instead of rotating magnetic disk for primary storage.
The author Thomas Pynchon worked as a technical writer for the field support unit for the Minuteman missile, something that is probably reflected in the narrative of his novels The Crying of Lot 49 and Gravity's Rainbow.
The Minuteman Missile National Historic Site in South Dakota has recently been created. It preserves a Launch Control Facility and a missile silo complex under the control of the National Park Service.
Satellite launching role
The U.S. Air Force has considered using some decommissioned Minuteman missiles in a satellite launching role. These missiles would be stored in silos, for launch upon short notice. The payload would be variable, and would have the ability to be replaced quickly. This would allow a surge capability in times of emergency.
- Strategic-Air-Command.com Minuteman Missile History
- Minuteman ICBM History site
- 1408KB MPEG Video of Minuteman III launch at Vandenberg Air Force Base in California.
- Minuteman Missile National Historic Site
- U. S. Air Force Fact Sheet - LGM-30
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