Nuclear bunker buster
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Bunker-busting nuclear weapons, also known as earth-penetrating weapons (EPW), are a type of nuclear weapon designed to penetrate into soil, rock, or concrete to deliver a nuclear warhead to a target. These weapons would be used to destroy hardened, underground military bunkers buried deep in the ground. In theory, the amount of radioactive nuclear fallout would be reduced from that of a standard, air-burst nuclear detonation because they would have relatively low explosive yield. However because such weapons necessarily come into contact with large amounts of earth-based debris, they may, under certain circumstances, still generate fallout. Warhead yield and weapon design have changed periodically throughout the history of the design of such weapons.
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[edit] Methods of operation
[edit] Penetration by explosive force
Concrete design remains little changed since 60 years ago. The majority of protected concrete structures in the US military are derived from standards set forth in Fundamentals of Protective Design, published in 1946 (US Army Corps of Engineers). Various augmentations, such as glass, fibers, and rebar, have made concrete less vulnerable, but far from impenetrable. Raymond T. Moore [1] was able to create a "human sized hole" in 18 inch (45 cm) thick reinforced concrete in less than 48 seconds with a mere 20 lb (9 kg) of explosive and a bolt cutter.
When explosive force is applied to concrete, three major fracture regions are usually formed: the initial crater, a crushed aggregate surrounding the crater, and "scabbing" on the opposite side of the crater. Scabbing, also known as "spalling," is the violent separation of a mass of material from the opposite face of a plate or slab subjected to an impact or impulsive loading (this does not necessarily mean that the barrier itself must have been penetrated at this point).
The crater volume varies approximately inversely with the square root of the concrete's compressive strength. Therefore, increasing the compressive strength of the concrete by 50% will yield an approximately 25% smaller crater.
As the compressive wave propagates to the opposite side of the concrete and is reflected, the concrete fractures, and scabbing occurs on the interior wall. As such, an asymptotic relationship exists between the strength of the concrete and the damage that will be done between the crater, aggregate, and scabbing.
While soil is a less dense material, it also does not transmit shock waves as well as concrete. So while a penetrator may actually travel further through soil, its effect may be lessened due to its inability to transmit shock to the target.
[edit] Penetration with a hardened penetrator
Further thinking on the subject envisions a penetrator, dropped from service height of a bomber aircraft, using kinetic energy to penetrate the shielding, and subsequently deliver a nuclear explosive to the buried target.
The problems with such a penetrator is the tremendous heat applied to the penetrator unit when striking the shielding (surface) at hundreds of meters per second. This has partially been solved by using metals such as tungsten (with a much higher melting point than steel), and altering the shape of the projectile (such as an ogive).
Additionally, altering the shape of the projectile, to incorporate an ogive shape has yielded substantial results. Rocket sled testing at Eglin Air Force Base has demonstrated penetrations of 100 to 150 feet in concrete when traveling at 4,000 ft/s. The reason for this is liquefaction of the concrete in the target, which tends to flow over the projectile. Variation in the speed of the penetrator can either cause it to be vaporized on impact (in the case of traveling too fast), or to not penetrate far enough (in the case of traveling too slow). An approximation for the penetration depth is obtained with an impact depth formula derived by Sir Issac Newton.
[edit] Combination penetrator-explosive munitions
Another school of thought on nuclear bunker busters is using a light penetrator to travel 15 to 30 meters through shielding, and detonate a nuclear charge there. Such an explosion would generate powerful shock waves, which would be transmitted very effectively through the solid material comprising the shielding (see "scabbing" above).
[edit] Criticism and controversy
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The main criticism of Nuclear bunker busters is nuclear fallout. The purpose of an earth-penetrating nuclear "bunker buster" is to reduce the required yield needed to ensure the destruction of the target by coupling the explosion to the ground, yielding a shock wave similar to an earthquake. For example, the United States retired the B-53 warhead, with a yield of 9 megatons, because the B-61 Mod 11 could attack similar targets with much lower yield (400 kilotons) because the latter can penetrate into the ground. Thus the fallout of a B-61 Mod 11 would likely be less than that of a B-53. Supporters note that this is one of the reasons Nuclear bunker busters should be developed.
Fallout from any nuclear detonation is increased with proximity to the ground. While a megaton class yield will inevitably throw up many tons of (newly) radioactive debris, which falls back to the earth as fallout, critics contend that despite their relatively miniscule explosive yield, Nuclear bunker busters create more fallout per kiloton yield.
The partisan scientific group, Union of Concerned Scientists, points out that at the Nevada Test Site, the depth required to contain fallout from an average yield nuclear test was over 100 meters, depending upon the weapon's yield. They contend that it is improbable that penetrators could be made to burrow so deeply. With yields between 0.3 and 340 kt of TNT, they contend, it is unlikely the blast would be completely contained.
Another criticism is that bunkers can be built more deeply to make them more difficult to reach. The target's vulnerability is then limited to openings like the ventilation system, which don't require nuclear warheads, it is contended. Proponents of Nuclear bunker busters respond that the more deeply buried, the more expensive to construct, limiting the potential enemies who can withstand Nuclear bunker busters.
Politically, as well, such nuclear bunker busters are unpopular in leftist circles. Most targets are near cities, they argue, and even minimal fallout will inflict unacceptable levels of collateral damage. Furthermore, they state, the testing of new nuclear weapons would be prohibited by the proposed Comprehensive Test Ban Treaty, although the United States has refused to agree to be bound by this treaty. Despite the fact that both Russia and China are spending billions of dollars to update and increase their nuclear stockpiles, while the United States is doing nothing, critics fear that developing such capabilities would lead to a new global nuclear arms race.
Finally, the need to use nuclear weapons in this role is questioned by critics. They argue that conventional ground penetration weapons are able to destroy enough buried or strengthened sites to lessen or even remove the need to use nuclear technology. Other conventional weapons such as thermobaric weapons have proven effective in defeating buried targets which have not been hardened.
[edit] Development of bunker-busting weapons
As early as 1944, the Wallis Tallboy bomb and subsequent Grand Slam weapons were designed to penetrate deeply fortified structures through sheer explosive power. These were not designed to directly penetrate defences, though they could do this (for example the Valentin submarine pens had ferrous concrete roofs 7 metres (23 feet) thick which were penetrated by two Grand Slams on 27 March 1945), but rather to penetrate under the target and explode leaving a camouflet (cavern) which would undermine foundations of structures above, causing it to collapse, thus negating any possible hardening. The destruction of targets such as the V3 guns at Mimoyecques or with the first operational use of the Tallboy, one bored through a hillside and exploded in the Saumur rail tunnel about 18m (60 ft) below, completely blocking it; show that these weapons could destroy any hardened or deeply excavated installation, and modern targeting techniques allied with multiple strikes could unquestionably perform a similar task.[1][2][3]
Development continued, with weapons such as the nuclear B61, and conventional thermobaric weapons and GBU-28. One of the more effective housings, the GBU-28 used its large mass (4,700 lb) and casing (constructed from barrels of surplus 203 mm howitzers) to penetrate 20 feet of concrete, and more than 100 feet of earth. The B61 Mod 11, which first entered military service in January 1997, was specifically developed to allow for bunker penetration, and is speculated to have the ability to destroy hardened targets a few hundred feet beneath the earth.[1]
While penetrations of 20–100 feet were sufficient for some shallow targets, both the Soviet Union and the United States were creating bunkers buried under huge volumes of soil or reinforced concrete in order to withstand the multi-megaton thermonuclear weapons developed in the 1950s and 1960s. Bunker penetration weapons were initially designed out of this Cold War context.
The weapon was revisited in the post-Cold War during the 2001 U.S. invasion of Afghanistan, and again during the 2003 invasion of Iraq. During the campaign in Tora Bora in particular, the United States believed that "vast underground complexes," deeply buried, were protecting opposing forces. While a nuclear penetrator (the "Robust Nuclear Earth Penetrator", or "RNEP") was never built, the DOE was allotted budget to develop it, and tests were conducted by the Air Force Research Laboratory. Such complexes were not found.
As well, it has been stated [2] that Iran may have such deeply buried bunkers to guard its nuclear program.
The Bush administration removed its request for funding of the weapon in October 2005. Additionally, US Senator Pete Domenici announced funding for the nuclear bunker-buster has been dropped from the Department of Energy's fiscal 2006 budget at the department's request.
While the project for the RNEP seems to be in fact cancelled, Jane's Information Group speculates work may continue under another name.
[edit] See also
[edit] References
- Barrier Penetration Tests, Moore, R. T. National Bureau of Standards, ASIN B0006CHZT6
- Penetration Resistance of Concrete: A Review, James R. Clifton, The Physical Security and Stockpile Directorate, Defense Nuclear Agency, ASIN B0006E76U2
- U.S. Nuclear Weapons: Changes In Policy And Force Structure, Woolf, Amy F., ISBN 1-59454-234-1
- Nuclear Weapon Initiatives: Low-yield R&D, Advanced Concepts, Earth Penetrators, Test Readiness, Ernest, Jonathan V., et al., ISBN 1-59454-203-1
[edit] External links
- Earth Penetrating Weapons by Lisbeth Gronlund, David Wright and Robert Nelson, Union of Concerned Scientists, May 2005
- Bunker-busters set to go nuclear by David Hambling, New Scientist, 07 November 2002
- Low-Yield Earth-Penetrating Nuclear Weapons by Robert W. Nelson, Federation of American Scientists, January/February 2001, Volume 54, Number 1
[edit] Footnotes
- ^ Grand Slam raids
- ^ RAF web site: RAF Bomber Command: July 1944 (See V-3 July 6 The photograph shows clearly the camouflet effect)
- ^ RAF web site: RAF Bomber Command: saumur
