Authors Kleppner, Lamb, and Mosher report on an excellent APS study that provides a wealth of data and analysis. Especially new are the array of possible maneuvers during the boost phase of intercontinental ballistic missiles (ICBMs) and the problems those maneuvers pose for a boost-phase intercept (BPI) system. My judgment from the report itself of the utility of BPI against North Korean ICBMs, however, is more positive than are the executive summary and press reports of the APS study.

For instance, according to an earlier Physics Today story ( Physics Today 0031-9228 56

200326September 2003, page 26 ), “Boost-phase missile defense … is virtually impossible in all but a few limited circumstances.” But among those few is the most likely circumstance for ICBM attack: a liquid-fueled ICBM launched from North Korea against the continental US. I have long proposed using 14-ton interceptors based on ships or land near North Korea to defend against such an attack. 1 And I assumed the boost phase of such an ICBM to be 250 seconds, little different from the 240 s assumed by the APS study, and not the “300 s or more, as some earlier studies had [assumed],” as stated in the January 2004 Physics Today article. The study’s first conclusion, that the “interceptor rockets would have to be substantially faster (and therefore necessarily larger) than those usually proposed,” refers to some people who have advocated much smaller interceptors than my 14-ton proposal.

If the US Department of Defense decided to deploy within four years a system using large surface-based interceptors against North Korean ICBMs, the US could likely expect at least several years of protection.

Necessary? Maybe not. Feasible? Yes. And that is not the end of the line for boost-phase intercept. Simple geometry shows that airborne radar at altitudes typical of modern airline jets (12 km) will see to the ground at a range of 400 km, adding important tens of seconds to the time available for intercept by a ground-or sea-based BPI system.