far as counting techniques are concerned. I think that a lot can be done. As a matter of fact in the early days, at least with some of the work done with Junge's samples, we have been able to suggest things and see a lot of improvement in some of their results. I think that there is some hope that, whatever we talk about as a limit, whether it is a 1~micron particle, or whatever, if it were proven valuable and worth while, microprobe analyses could be greatly improved by applying some of the knowledge gained in low-level counting. Floor: There was a statement about re-entry vehicles burning up at certain altitudes. Can you restate that? Dr. Friend: I said that, as far as I have been able to determine, the mesophere is where the peak burnup occurs, Floor: I don't think you would find general agreement on that. Dr. Friend: This is where they would like to plan to have it burn up. Floor: How are you defining the mesophere? Dr. Friend: Fifty to eighty kilometers. Floor: This is far above any place where any normal re-entry vehicle would burn up. Dr. Friend: The burnup is actually lower than 50 kilometers? Floor: Yes, 30 kilometers or less, Dr. Friend: For things like SNAP we are talking about a 1-degree entry angle at 25,000 feet per second. Floor: This is fine, but you have to do something pretty drastic to make something burn up at 80 kilometers. 94