So during the time at Orion I did a lot of calculations of fallout and we studied the literature and how many people would be killed per kiloton of fall out and... and we took it very seriously, and our estimate was that it would be a public health hazard, but very small compared with other things that you might compare it with, like coal mining... the... not to mention traffic accidents and other causes of death. So we considered it at that time acceptable, but it was fairly clear then that this would be the major obstacle it would have to overcome; that... that in order to use this way of getting into space the public would have to be convinced that it was worth the price. And I became convinced myself that it wasn't going to work, largely because of the fall out question. I remember, in the summer of... '58 I guess it was, I'm not sure - no, it was '60... later on, it was toward the end of the Orion time. Orion finally finished in 1965, I was at the Disarmament Agency for the summer in 1962 and again in 1963, and so it was during the Kennedy presidency - I spent two summers at the Disarmament Agency, and there of course I was deeply involved with the test ban negotiations, and so I had to make up my mind then, at the Disarmament Agency, was I for the test ban or against it? And obviously the conclusion was, I was for it, that was what the Disarmament Agency was about. And what convinced me was that I plotted a little curve of the total number of tests per year that were being done, right from 1945 until 1963; and the total number of tests per year was simply a rising exponential curve with a doubling time of about three years, and it was obvious at that point that this thing couldn't go on, that we just were not going to continue testing exponentially for ever, that fairly soon one would have to put an end to it, and the only way one could put an end to it was to have a test ban. So that to me was the convincing argument. And the reason why the doubling time was three years was fairly obvious, because it takes three years to prepare a test, so every time you do a test you have two unanswered questions which require two new tests to answer, so it's a natural process of exponential growth. So there has to be a stop somewhere, otherwise the thing is... just becomes... unacceptable. And so I fought then at the Disarmament Agency to get the test ban adopted. That meant saying goodbye to Orion, and so that was my final point of decision, that if it was a choice between a test ban and Orion I clearly chose the test ban.