There was a talk at the University of Maryland today by Daniel Kleppner, one of the co-chairs of the American Physical Society’s Boost Phase Missile Defence Study Group. The report is summarized here, and the whole thing is available here.

Anyway, the talk was very well presented, and it’s clear that if you accept the initial assumptions the conclusions follow logically. It’s the input assumptions that are somewhat problematic. I’ve seen people complain that the choice of initial assumptions is due to liberal bias, but Kleppner defended them quite well on the basis of the National Intelligence Estimate and the systems actually under consideration. Some of the parameters considered, such as the burn time, were skewed in favor of the defender, and they considered zero decision time cases, which also favor the defender. The minimum kill vehicle mass considered (90 lbs, including sensors, thrusters and fuel) seemed to me a little large, but I don’t have a basis to dispute it. This is a critically important parameter, since it scales all the other masses in the system.

Kleppner stated at a number of points that there is room for reasonable people to disagree on the assumptions, and that judgement calls needed to be made in order to choose concrete numbers to put into the models. Given the credentials of the people on the study team it’s unlikely that the numbers are off by much, though. It is clear, however, that under only slightly more optimistic assumptions (or under the assumption of an aggressive research program), the system can be made to work, at least against limited attack by relatively unsophisticated opponents. The technology horizon for consideration in the study was only ten years, and there was no consideration of potential breakthrough technologies.

The study also comes down firmly in support of the effectiveness of boost phase intercept against missiles launched from ships close to the borders of the US. This is significant for two reasons. First of all, this is the scenario considered most likely by the National Intelligence Estimate (which makes sense – it’s an easier attack, and it makes tracking the attacker harder). The second reason is that high tech systems tend to be most effective when developed incrementally. By starting with short range boost phase interceptors the system can be debugged before extending capabilities to intermediate range and finally to ICBM ranges.

Kleppner dismissed Brilliant Pebbles as not credible, despite considering much larger space based systems. The conclusions on the large space based systems were negative due to the need for greatly increased launch capacity. Launch is the long pole in the tent – all the other technological components needed were considered viable. Yet another reason to work to increase launch rates. The increase needed was cited as being 5-10 times current rates, which ought to be well within reach. If Uncle Sam was to decide to just go ahead and deploy space based BPIs it would be a massive boon for the launch industry, but I think that’s a faint hope at best. The dismissal of Brilliant Pebbles is a little more puzzling to me, and I can’t help wondering if maybe the study group simply didn’t look hard enough at the possibility of dramatically reducing sensor size, which would also help on the kill vehicle mass.

Overall it was a good talk. If you get a chance to see Kleppner talk, take it. He’s very clear, gives complete answers to questions and admits the limits of the study and his own knowledge. The study obviously has considerable limitations, but it’s a good starting point for policy discussions, which is pretty much the point. It’s a start, not an attempt to have the final word. A lot of the reporting on this topic in the press has suggested that the study’s conclusions are much firmer than they in fact are. It’s a nuanced study, as appropriate for a problem of this complexity. Trying to shoehorn it into either the pro or anti missile defense camp does a disservice to the study group and to the seriousness of the issue.