快猫短视频

IF YOU thought the threat of nuclear conflict ended with the cold war, developments over the past few months should have changed your mind.

In February, a leaked document from the Pentagon revealed details of a meeting planned for August at which the US military will discuss the construction of a new generation of tactical nuclear weapons. These weapons include a new range of mini-nukes specially designed to destroy deep bunkers.

It is a revelation that has unsettled many. In particular, observers believe that the threat posed by these weapons would encourage nuclear proliferation, and if the US dares to test them during development it could finish off the Comprehensive Test Ban Treaty.

Present USlaws forbid the development of new tactical nuclear weapons with an explosive yield of less than 5 kilotons. The proposed bunker busters will fall into this category, yet they would remain legal since they will be modifications of existing nuclear bombs rather than completely new designs.

But if the US already possesses mini-nukes, why the sudden need for new weapons? The only nuclear option for busting bunkers is the B61-11, a 3.65-metre, 500-kilogram nuclear bomb that can penetrate 6 metres of earth before detonating its warhead. The yield can be set to anything between 0.3 and 340 kilotons, but even its biggest possible explosion may not be enough to destroy deep bunkers.

So, in November, US Secretary of Defense Donald Rumsfeld began to seek permission from Congress to develop a new weapon: the Robust Nuclear Earth Penetrator. RNEP should be able to carve through at least 30 metres of soil and, because it is only a modification of an existing bomb, it would not violate the non-proliferation treaty that bans the development and testing of new nuclear weapons. If used, it would be used untested. Two of the US鈥檚 national labs are ready to start work on this new nuclear bunker buster, aiming to produce a bomb that could be as much as 80 times as powerful as the one dropped on Hiroshima (see 鈥淏igger bangs鈥�).

The National Defense Authorization Act for 2003 prohibits Congress from providing the money to develop such a weapon unless it is convinced the weapon is necessary. Put simply, Rumsfeld has had to lay out the precise military objectives of this nuclear weapon, and explain why it is the only thing that can do the job (快猫短视频, 23 November 2002, p 9). He has succeeded: the Senate and the House of Representatives approved the idea, and on 20 February the president gave the go-ahead for the development of a new nuclear weapon.

In terms of raw power, RNEP is indeed the best option for attacking deep bunkers. The advantage of a nuclear strike is the extremely powerful shock wave and high temperature it produces. Chemical agents can be neutralised by exposure to temperatures over 1000 掳C for a minute or more. That would also take out biological agents, which are relatively fragile 鈥� anthrax spores can be killed by a brief exposure to 200 掳C.

The nuclear option can achieve this, but not without enormous consequences. Rob Nelson of Princeton University鈥檚 Science and Global Security Program has carried out a detailed study of the effects of low-yield earth-penetrating nuclear weapons. Anyone within a 35-square-kilometre area would be killed by a 10-kiloton weapon. If used near third world urban populations, such a bomb could cause tens of thousands of civilian casualties and render a large area uninhabitable for years.

But there are alternatives to employing the nuclear option. Lockheed Martin and the Naval Surface Warfare Center, for instance, are building a warhead that ejects pellets of finely powdered titanium and boron, producing titanium diboride in a high-temperature incendiary reaction. As the temperature climbs past 300 掳C, the warhead fires out metal projectiles in all directions to rupture any chemical storage vessels and release their contents. It also scatters wicking material that draws up any pooled chemicals so they ignite and burn more easily. In the final stage the warhead releases lithium perchlorate, which reacts to generate hydrochloric acid and monatomic chlorine, so the target area is first burnt clean and then disinfected.

Of course, this is no good unless you can get the warhead in there in the first place. The most obvious way to do that is to design a bomb that does not detonate on impact, but instead pierces the ground and penetrates the bunker before it goes off. Such a penetrating bomb needs a narrow profile 鈥� the more needle-like the better 鈥� with a thick, hard casing to withstand the shock of impact, and a detonator that will ensure it does not explode until it has broken into the bunker itself.

The top-of-the-range bunker buster is the BLU-113 made by Lockheed Martin. It was hurriedly developed during the 1991 Gulf war to destroy deep Iraqi bunkers that had proved resistant to other attacks. Measuring 6 metres long and only 36 centimetres in diameter, it weighs in at over 2 tonnes. Most of this mass is in the 5-centimetre-thick casing, with the explosives accounting for only 290 kilograms. Dropped from high altitude, above 20,000 feet, this bomb can penetrate about 8 metres of concrete or rock, or more than 30 metres of earth.

These days, though, that鈥檚 not enough: bunkers such as those in Iraq are likely to be much better protected. One way to improve on the bunker-buster design would be to replace the steel casing, and perhaps some of the explosive payload, with something heavier, such as depleted uranium (DU). This increases the weapon鈥檚 weight per unit area upon impact, and hence its penetration.

But this is a far from perfect answer. For a start, the DU would leave radioactive contamination wherever the bomb strikes. Vala Ragnarsdottir, professor of environmental geochemistry at the University of Bristol in Britain, has studied DU contamination in Kosovo for UNEP and warns that the uranium in ground-penetrating weapons would disperse widely. 鈥淭he uranium will soon oxidise in contact with moisture, water and air,鈥� she says. 鈥淭his will cause huge problems for the local groundwater.鈥�

In any case, increasing the density by a factor of 2 鈥� which is the most that DU would achieve 鈥� isn鈥檛 enough. The only way to get much deeper penetration with kinetic weapons is to hit the target faster, but even this only works up to a point.

A bomb dropped from more than 20,000 feet hits the ground at about Mach 1, about 330 metres a second. To reach greater speeds, the US Defense Advanced Research Projects Agency is planning to use decommissioned Trident ballistic missiles. The missile would travel in a high arc and hit the ground at Mach 3, carrying a special penetrating warhead rather than a nuclear bomb. Meanwhile Boeing is working on HyFly, an air-launched missile capable of Mach 6 or more.

Even more ambitious alternatives are under development, including rapid-fire cannons and plasma-jet bullets (see 鈥淒igging deeper鈥�). But most of these weapons are not yet ready to roll. Could Rumsfeld be right: is nuclear the best option?

Not according to Michael Levi of the Federation of American 快猫短视频s. The key to dealing with such targets is not greater physical force but greater intelligence. 鈥淲eapons of mass destruction present no threat if they are stuck in an underground facility,鈥� he says.

Once identified, a facility can be constantly monitored by unmanned surveillance planes and ground sensors. With unmanned strike aircraft circling overhead, anything attempting to enter or leave the facility could be promptly destroyed. Precision bombing could collapse all the entrances and air shafts and then blanket the facility with foam sealant. Any occupants would suffocate, and any chemical or biological agents would be sealed in. Special Forces could even drop in to take over the installation. There already exists a portable cannon for breaking through blast doors, as well as an array of other new hardware, including remote-controlled robots adapted for underground combat.

Cleverness, Levi argues, is the best way to find relatively low-impact solutions to rendering bunkers harmless. And he is in good company. Physicist Stephen Younger is director of the Defense Threat Reduction Agency at the US Department of Defense, the agency charged with developing strategies to combat weapons of mass destruction. He has admitted that the best options may be the low-tech ones. In an interview for Physics Today, the magazine of the American Institute of Physics, he notes that all the hardware programmes may be promising, but they have yet to prove their worth. 鈥淭he best we may be able to do is immobilise the agent until ground forces have arrived,鈥� he says.

In other words, make sure the stuff stays underground. For all the millions of dollars of R&D, the scientific opinion appears to be rather an old-fashioned one: watch and wait. It鈥檚 less spectacular, but the fallout, in every sense, could be a lot less harmful.