Marty Hanna
Physics Today
College Park, Maryland

Dear Marty Hanna,

The PT article by Daniel Kleppner, et al, reports on an excellent study of the APS which provides a wealth of data and analysis. Especially new is the array of maneuvers possible by ICBMs in boost phase that stress the capabilities of a boost-phase intercept system (BPI). 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 PT (September, 2003, pp. 26-27), "Boost-phase missile defense ... is virtually impossible in all but a few limited circumstances..."

But the most likely circumstance for ICBM attack is among those few-- particularly a liquid-fueled ICBM launched from North Korea against the continental United States. I have long proposed using 14-ton interceptors based on ships or land near North Korea for this purpose (1). And I assumed the burn time of this ICBM to be 250 s, little different from the 240 s assumed by the APS study, and not the "300 s or more, as some earlier studies [assumed]" (from p. 35 of the January 2004 PT article).

The first conclusion of the Study, that the "interceptor rockets would have to be substantially faster (and therefore necessarily larger) than those usually proposed," refers not to my publications but to others who have advocated much smaller interceptors.

If the Defense Department made the design choices to deploy within four years a system using large surface-based interceptors against North Korean ICBMs, it would likely provide at least several years of protection.

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

Richard L. Garwin IBM Fellow Emeritus, Room 26-234 IBM Thomas J. Watson Research Center 1101 Kitchawan Road, Route 134 Yorktown Heights, NY 10598

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1. Please read (Nov. 17, 1999).