There is a peculiar symmetry to Washington's decision last week to activate its ground-based missile-defense system and North Korea's threat to launch a long-range missile. While research, development, and even limited deployment of the U.S. system make sense, it will be years before it is dependable. Fortunately, it will also be years before North Korea will be able to nuke the United States.
There are four ways this crisis can end. If North Korea launches a missile, the United States can shoot it down, hold fire, or try to shoot it down and miss. Pyongyang can also back down and not test its missile. The first outcome would be a mixed blessing; the second would be embarrassing; the third would be a disaster. Whatever happens now, though, given the lack of an immediate threat to American cities, Washington's decision to activate the ground-based missile defense was probably a mistake.
If North Korea launches a missile, and the United States shoots its down, it will be a great advertisement for missile defense and will reduce the appeal to North Korea and others of developing ICBMs.
But that will not come without costs. If North Korea sticks to past form, it will launch a satellite, not a warhead, allowing it to claim that its test was for "peaceful purposes." It will also show the world that it is capable of launching a real warhead, since any missile that can launch a satellite can also fire a warhead thousands of miles. When it works, the missile-defense system destroys the missile's payload—either a warhead or a satellite—after the missile itself has done its job. Think of the missile as a pitcher, and the payload as a baseball. Missile defense doesn't destroy the pitcher; it blows up the baseball on its way to home plate.
The United States has never shot down an enemy satellite *—anti-satellite weapons, or ASATs, are a contentious point of international debate, with China the most vociferous proponent of a treaty that would outlaw them. Opposition to ASATs is long-standing and draws on a mix of ideological motives (it's closely associated with Cold War anti-nuclear activism) and strategic concerns (China would rather not have its satellites shot down). Were the United States to shoot down a satellite, it would, ironically, antagonize its most important partner in dealing with North Korea. It would also hurt its chances of concluding a treaty to ban production of nuclear material for weapons, something the Bush administration has recently promoted but that China has intermittently held hostage to its long-sought-after ASAT ban. On balance, then, it's unclear whether a successful intercept would help or hurt U.S. nuclear security in the long run.
We'll probably never know, though, because the odds of shooting down a North Korean missile are small. The ground-based missile-defense system the United States has activated has succeeded in four of its last eight tests, but as David Wright and Lisbeth Gronlund of the Union of Concerned Scientists have documented, this hardly suggests even a 50-50 chance of success in real-world conditions. As the ground-based defense has been developed, each test has introduced new challenges but included important artificialities. The idea is to isolate parts of the system and perfect them before the defense is integrated as a whole. So, for example, in each test, the target warhead has carried a "GPS transmitter and/or a C-band beacon" to help guide the missile-defense interceptor to its target. That's fine for a testing program, but North Korea probably won't be quite so cooperative.
That hasn't stopped Missile Defense Agency chief Henry "Trey" Obering from claiming that he is "very confident" that the U.S. system would shoot down a North Korean missile. That's consistent with his agency's past estimate of 80 percent effectiveness, but decisively at odds with the Pentagon's chief weapons evaluator, who "has calculated that the system may be capable of hitting its targets only about 20% of the time." It's also worth recalling that when, in 2003, Undersecretary of Defense Edward "Pete" Aldridge told the Senate Armed Services Committee that the system would have a 90 percent chance of success, Sen. Carl Levin rebuked him, declaring, "I know the classified number."
It also hasn't stopped naive observers from making extraordinary claims about the system. Speaking on a TV talk show last Friday, Charles Krauthammer claimed a "seven out of eight" success rate for the system. Unfortunately, he was confusing the ground-based system with something else, the "Aegis Ballistic Missile Defense," which cannot shoot down ICBMs. (It's easy to get confused—the ground-based system can use Aegis radars, but otherwise is completely different from the Aegis Ballistic Missile Defense.)
If the United States attempts to intercept a North Korean missile, it's likely to miss. Whatever deterrent value the U.S. defense now has will be gutted by such a public failure. That might lead the United States to hold fire—but even that decision, coming after a public announcement that the missile defense has been activated, would be interpreted as a lack of confidence in the system.
So, we should hope that North Korea decides not to launch a missile. In that case, some will claim that the decision to activate the defense was responsible for the North Korean decision not to fire. But they'll be wrong. The point of a North Korean launch is to test its missile, to showcase its wares to would-be missile buyers like Iran, and to show the world that Pyongyang is willing to take provocative steps. Activating the ground-based missile defense affects none of these motivations.