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James Ionson is far from reassuring

To the Editor:

I have grave doubts about the feasibility of a Strategic Defense System (SDS), and about the merits and influences of the Strategic Defense Initiative as a funding vehicle for academic research. I therefore eagerly attended Dr. Ionson's speech last week to hear what reassurances he might provide. To my dismay, I found Dr. Ionson unable or unwilling to address the policy issues surrounding the possible uses of the results of research conducted with the aid of his office. My disappointment with Dr. Ionson stems from lack of substance -- not from any disagreement with the one insignificant technical claim about an SDS he made. I have no argument with Dr. Ionson's statements regarding the actual feasibility of an SDS, because, as far as I could detect, he made none!

I think Dr. Ionson is badly misrepresented in Steve Pao's article ["Ionson defends SDI program," Oct. 29]. In his speech, Dr. Ionson did consider the possible effectiveness of a layered SDS, but he repeatedly emphasized that the figures he was using for his example calculation were purely hypothetical. He actually said he was just "throwing these figures out." Pao's article clearly indicates that:

O+ "Ionson claimed this [the first] layer is 90 percent effective."

O+ "The second layer...can be covered with 80 percent efficiency."

O+ "In the midcourse phase ... Ionson claimed that SDI's 70 percent effectiveness would allow..."

O+ "Dr. James Ionson predicted last Monday that there will be an 85 percent chance SDI systems can stop all but one Soviet missile from reaching the United States."

despite the fact that Dr. Ionson quite carefully (and explicitly) refrained from doing just that. According to Pao, Dr. Ionson almost made it sound like some kind of operational SDS was in place! All Dr. Ionson claimed that his numerical example showed was that a layered SDS would be more effective than its individual stages. As it happens, this is a consequence of the way we multiply numbers less than one, which lead me (upon reading Pao's article) to consider Dr. Ionson's (and consequently Pao's) abilities in this particular area of elementary mathematics.

Dr. Ionson stated that if the final stage of an SDS had a 95 percent chance of destroying individual warheads, and was presented with 17 such warheads, then there would be an 85 percent chance that "only one" warhead would reach its target. How this figure of 85 percent was obtained is a mystery to me. It seems to me that the change of destroying all 17 warheads is exactly (0.95)17 and the chance that exactly one warhead is not destroyed is 17x0.05x(0.95)16. Those chances being 0.418 and 0.374 respectively, the chance that "only one" (at most one) warhead strikes is 79.2 percent, not 85 percent. An interesting discrepancy, to say the least.

Another way to interpret these numbers is that even with an SDS composed of multiple layers (each of 80-95 percent effectiveness) there is a 58.2 percent chance that at least one warhead will strike if an enemy fires "only" 1400 missiles. Reassuring, isn't it?

James O'Toole G->