W71
![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Spartanwarhd.jpg/220px-Spartanwarhd.jpg)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/fc/1971-CANNIKIN-2.jpg/220px-1971-CANNIKIN-2.jpg)
TheW71nuclear warhead was a USthermonuclear warheaddeveloped atLawrence Livermore National Laboratoryin California and deployed on theLIM-49A Spartanmissile, a component of theSafeguard Program,ananti-ballistic missile(ABM) defense system briefly deployed by the US in the 1970s.
The W71 warhead was designed to intercept incoming enemywarheadsat long range, as far as 450 miles (720 km) from the launch point. The interception took place at such high altitudes, comparable tolow Earth orbit,where there is practically no air. At these altitudes,x-raysresulting from the nuclear explosion can destroy incomingreentry vehiclesat distances on the order of 10 miles (16 km), which made the problem of guiding the missile to the required accuracies much simpler than earlier designs that had lethal ranges of less than 1,000 feet (300 m).[1]
The W71 warhead had a yield of around 5 megatons of TNT (21 PJ). The warhead package was roughly a cylinder, 42 inches (1.1 m) in diameter and 101 inches (2.6 m) long. The complete warhead weighed around 2,850 pounds (1,290 kg).[2]
The W71 produced great amounts of x-rays, and needed to minimize fission output and debris to reduce theradar blackouteffect thatfission productsand debris produce on anti-ballistic missile radar systems.[1][3]
Design
[edit]The W71 design emerged in the mid-1960s as the result of studies of earlier high-altitude nuclear tests carried out before thePartial Nuclear Test Ban Treatyof 1963. A number of tests, especially those ofOperation Fishbowlin 1962, demonstrated a number of previously poorly understood or underestimated effects. Among these was the behaviour of x-rays created during the explosion. These tended to react with the atmosphere within a few tens of meters at low altitudes (seerope trick effect). At high altitudes, lacking an atmosphere to interact with, themean free pathof the x-rays could be on the order of tens of kilometers.[4]
This presented a new method of attacking enemy nuclear reentry vehicles (RVs) while still at long range from their targets. X-rays hitting the warhead's outermost layer will react by heating a thin layer of the material so rapidly thatshock wavesdevelop that can cause theheat shieldmaterial on the outside of the RV to separate or flake off. The RV would then break up during reentry.[5]The major advantage of this attack is that it takes place over long distances, as great as 30 kilometres (19 mi), which covers the majority of thethreat tubecontaining the warhead and the various radar decoys and clutter material that accompanies it. Previously the ABM had to approach within less than 800 feet (240 m) of the warhead to damage it through neutron heating, which presented a serious problem attempting to locate the warhead within a threat tube that was typically at least a kilometer across and about ten long.[4]
Bell received a contract to begin conversion of the earlierLIM-49 Nike Zeusmissile for the extended range role in March 1965. The result was the Zeus EX, or DM-15X2, which used the original Zeus' first stage as the second stage along with a new first stage to offer much greater range. The design was renamed Spartan in January 1967, keeping the original LIM-49 designation. Tests of the new missile started in April 1970 from Meck Island, part of theKwajalein Test Rangethat had been set up to test the earlier Nike Zeus system. Because of a perceived need to rapidly deploy the system, the team took a "do it once, do it right" approach in which the original test items were designed to be the production models.[4]
The warhead for Spartan was designed byLawrence Livermore National Laboratory(LLNL), drawing on previous experience fromOperation Plowshare.A nuclear explosion at high altitude has the disadvantage of creating a significant amount of electronic noise and an effect known asnuclear blackoutthat blinds radars over a large area. Some of these effects are due to the fission fragments being released by the explosion, so care was taken to design the bomb to be "clean" to reduce these effects. Project Plowshares had previously explored the design of such clean bombs as part of an effort to use nuclear explosives for civilian uses where the production of long-livedradionuclideshad to be minimized.
To maximize the production of x-rays, the W71 is reported to have used a gold tamper,[citation needed]rather than the usualdepleted uraniumorlead.The lining normally serves the primary purpose of capturing x-ray energy within the bomb casing while the primary is exploding and triggering the secondary. For this purpose, almost anyhigh-Zmetal will work, and depleted uranium is often used because the neutrons released by the secondary will cause fission in this material and add a significant amount of energy to the total explosive release. In this case the increase in blast energy would have no effect as there is little or no atmosphere to carry that energy, so this reaction is of little value. The use of gold may have been to tailor its transparency to x-rays.[6]In Congressional testimony on potential dismantling of the W71, a DOE official described the warhead as "a gold mine".[7]
In 2008, theUnited States Department of Energydeclassified the fact that the radiation case of the W71 containedthoriummetal.[8]
Lethality
[edit]Under good conditions, the W71 warhead had a lethal exo-atmospheric radius as much as 30 miles (48 km),[9]although it was later stated to be 12 miles (19 km) against "soft" targets, and as little as 4 miles (6.4 km) against hardened warheads.[10]
Production & service history
[edit]There were 30 to 39[11]units produced between 1974 and 1975. The weapons went into service in 1975, but were retired that same year, and the warheads stored until 1992 when they were dismantled. The shortservice lifeof the W71, Spartan andSafeguard Programin general, is believed to have been partly tied to it largely becomingobsoletewith the development of Soviet offensiveMIRV(Multiple independentre-entryvehicles) warheads, that unlikeMRVs(multiple re-entry vehicles), can create a substantial spacing distance between each warhead once they arrive in space, hence would require at least approximately oneSpartan missilelaunch to intercept eachMIRVwarhead. As the cost of the Spartan and an enemyICBMwere roughly the same, an adversary could afford to overwhelm theABMsystem by adding ICBMs with MIRV warheads to itsnuclear arsenal.
Shot Grommet Cannikin
[edit]Prior to the W71 test, a calibration test known asMilrow of Operation Mandrelwas conducted in 1969. Despite political andpressure groupopposition to both tests, and in particular the full yield W71, coming from then US SenatorMike Gravel[12][13][14]and the nascentGreenpeace,[15]a Supreme Court decision led to the test shot getting the go-ahead,[16]and a W71 prototype was successfully tested on 6 November 1971 in Project Cannikin ofOperation Grommet[17]in the world's largest underground nuclear test, onAmchitka Islandin theAleutian IslandsoffAlaska.The second highest-yield underground test known occurred in1973, when the USSR tested a 4 Mt device392
The W71 was lowered 6,150 feet (1,870 m) down a 90-inch-diameter (2.3 m) borehole into a man-made cavern 52 feet (16 m) in diameter. A 264-foot-long (80 m) instrumentation system monitored the detonation. The full yield test was conducted at 11:00 am local time November 6, 1971 and resulted in a verticalground motionof more than 15 feet (4.6 m) at a distance of 2,000 feet (610 m) from the borehole, equivalent to an earthquake of magnitude 7.0 on theRichter scale.A 1-mile-wide (1.6 km) and 40-foot-deep (12 m) crater formed two days later.
See also
[edit]References
[edit]- ^ab"W71".Globalsecurity.org.Archivedfrom the original on 2021-08-25.Retrieved2006-03-29.
…the design of the warhead for Spartan, the interceptor used in the upper tier of the U.S. Safeguard Anti-Ballistic Missile (ABM) system. Spartan missiles were to engage clouds of reentry vehicles and decoys above the atmosphere and destroy incoming warheads with a burst of high- energy x rays.… The Spartan warhead had high yield, produced copious amounts of x rays, and minimized fission output and debris to prevent blackout of ABM radar systems. Livermore also developed and first tested the warhead technology for the second-tier interceptor, the Sprint missile.
- ^"Complete List of All U.S. Nuclear Weapons".nuclearweaponarchive.org.14 October 2006.RetrievedJune 6,2007.
- ^"Accomplishments in the 1970s: Lawrence Livermore National Laboratory".Archived fromthe originalon 2005-02-17.Retrieved2006-10-09.
- ^abcABM Research and Development at Bell Laboratories, Project History(PDF)(Report). Bell Labs. October 1975.Archived(PDF)from the original on 2016-03-03.Retrieved2015-05-19.
- ^Garwin, Richard; Bethe, Hans (March 1968)."Anti-Ballistic-Missile Systems"(PDF).Scientific American.Vol. 218, no. 3. pp. 21–31.Bibcode:1968SciAm.218c..21G.doi:10.1038/scientificamerican0368-21.Archived(PDF)from the original on 23 June 2021.Retrieved13 December2014.
- ^Sublette, Carey."4.4 Elements of Thermonuclear Weapon Design – 4.4.5.4.1" Clean "Non-Fissile Tampers".Nuclear Weapons Frequently Asked Questions– via Nuclear Weapons Archive.
- ^Schwartz, Stephen (2011).Atomic Audit: The Costs and Consequences of U.S. Nuclear Weapons Since 1940.Brookings Institution. p. 332.ISBN9780815722946.
- ^"Classification Bulletin WNP-118"(PDF).U.S. Department of Energy. March 12, 2008.Archived(PDF)from the original on February 3, 2017.RetrievedSeptember 13,2019.
- ^Bennett, M. Todd, ed. (2011).National Security Policy, 1969–1972(PDF).Foreign Relations of the United States. Vol. XXXIV. p. 41.Archived(PDF)from the original on 2021-11-18.Retrieved2014-10-21.
- ^Bennett 2011,p. 54.
- ^Wm. Robert Johnston,"Multimegaton Weapons"Archived2012-06-04 at theWayback Machine,6 April 2009.
- ^Gravel, Mike (1969-07-31)."Risks in Alaska Tests"(fee required).The New York Times.Letters to the Editor.Retrieved2007-12-30.
- ^Richard D. Lyons (1971-08-23)."Underground A-Test Is Still Set For Aleutians but Is Not Final"(fee required).The New York Times.Retrieved2007-12-30.
- ^"Witnesses Oppose Aleutian H-Blast"(fee required).The New York Times.1971-05-30.Retrieved2007-12-30.
- ^"The Amchitka Bomb Goes Off".Time.1971-11-15. Archived fromthe originalon September 30, 2007.Retrieved2006-10-09.
- ^"W71".Globalsecurity.org.Archivedfrom the original on August 25, 2021.RetrievedMarch 29,2006.
…the Supreme Court ruled by a 4–3 margin that the test could take place. On November 6, 1971, at 6:30 a.m. in Amchitka, the go-ahead came from the White House on a telephone hotline.
- ^"Declassification of fact that Cannikin event was a proof test of the W71 warhead"(PDF).Archived(PDF)from the original on 2017-03-28.Retrieved2019-06-08.