Starting in the middle or latter part of 2004, the United States should gain the capability of destroying ballistic missiles launched at US targets from Korea or China. According to US President Bush in 2002, until non-nuclear weapons are developed and found reliable, the anti-ballistic missiles will carry nuclear warheads. (Many think that non-nuclear warheads will take at least another half dozen and more likely another dozen years to develop and deploy.)
This action will complement the recent deployment of a US naval ship to the sea beside the Korean peninsula. This ship carries weapons that can shoot down shorter range ballistic missiles. (At the moment, the US has a very few such ships, which are modified Aegis destroyers. I have no idea whether the ships' weapons would work.)
Since this deployment is understood by US leaders as part of a negotiating process, the question is not perceived by them as whether the weapons work in reality, but whether they will be perceived as being sufficiently likely to work by other countries' governments as to improve the US negotiating position.
The reason for the ship deployment is to protect, or pretend to protect, a US ally, Japan. This is intended to remind the Japanese that they are dependent on the US government, just as the US government is dependent on the Japanese government.
Currently, the Japanese government is purchasing vast quantities of US government debt. Funding the US government debt is important to the current administration. The purchases are overtly intended to keep down the value of Japanese currency, thereby helping Japanese exports. (There is no doubt in my mind that this is a part, perhaps even the major part, of the Japanese government's motivation. Also, presumably, these purchases will provide some funding for future Japanese pensions, at virtually no cost to the Japanese.)
The reason for the anti-ballistic missile deployment is equally straight-forward:
North Korea has launched a long range missile, which it said was for a satellite. This miss Le, or a successor, might be able to carry a warhead to the US. Moreover, the US government believes the North Korean government when it says it is working on nuclear weapons. (In addition, of course, the development, construction, and deployment of this weapon system enables people in the US government to give large contracts to the most suitable bidders.)
The North Korean government can threaten the US in two ways:
The currently under-construction anti-ballistic missile site in Alaska counters the first threat. Everyone believes that you can stop a ballistic missile by detonating a nuclear bomb near it.
Moreover, many believe that President Bush would be willing to detonate a nuclear bomb, or several, over the North Pacific Ocean. (Not so many believed that President Carter would have been willing to detonate nuclear bombs at a low altitude over the Dakotas or the nearby part of Canada. President Carter's nuclear anti-ballistic missile system has been shut down.)
There are several reasons to believe that President Bush would be willing to order a launch against incoming missiles: Most of the EMP effect would be over water. Those parts of North America that would be hurt by the electromagnetic pulse (EMP) of a nuclear detonation are Alaska which does not have many voters, Canada, which does not vote in US elections, and parts of the US north-west that voted against Bush last time. Moreover, US commercial satellites are believed to be pretty well protected against EMP, but foreign satellites might be harmed.
The way around this kind of US defense is to orbit a satellite and then say it contains a nuclear warhead that can be de-orbited anywhere. This makes for a believable threat, since the Alaskan ABM site cannot destroy satellites that come over the US from the south-west.
The way to counter this new threat is to create an anti-satellite capability and advertise it. The airborne laser system, which might do the job, is late and over budget. It may be canceled. On the other hand, an older system consists of a small rocket launched from an F-15. The airplane can fly and then launch from anywhere. It can, therefore, intercept a satellite in any orbit. This weapon was developed more than a decade ago and, as far as I know, never deployed. It could be deployed.
As a practical matter, the US government probably does not fear that China would put a nuclear warhead in a satellite, since the US figures that China will be deterred by the threat of a US counter.
(However, it is easy enough to think up a scenario in which the Chinese launch a perfectly harmless rocket that comes down in Peoria, Ill. `purely by accident'. The Chinese government apologizes profusely and pays for damages. They say how lucky everyone is that the rocket did not carry a nuclear weapon. At this point, the US public decides it is not so keen on supporting Taiwan against a blockade, like the one several years ago. In that instance, the mainland Chinese simply tested non-nuclear missiles in such a way as to hinder ship traffic to and from the island. The US countered by sending an aircraft carrier group to the area. The goal of dropping something harmless on US soil would be to scare enough Americans that they would give up their promise to defend Taiwan.)
The prime stated purpose of an anti-missile capability is to prevent the North Korean government from successfully threatening the US.
While many do believe that the Chinese government can be deterred, few believe that North Korea can be deterred easily. The North Korean government has succeeded over the past decade by adopting and using the `brinkmanship' techniques that were developed and written up by Americans and Soviets in the 1950s and 1960s. Many in the US government believe that the members of the North Korean government who make the decisions may well be willing to accept what they might consider a 20% or 40% chance of being killed in order to gain large amounts of money and a guarantee by the US of their personal safety.