Having the old NACA/NASA guys die off is unfortunate. However death is part of that package deal we call "life". What's tragic is the old guys are dying or retiring and taking their knowledge with them. NASA (or at least NASA Ames) has no mentor/apprentice program for the old guys to transfer their knowledge to the next generation. Only a tiny fraction of their knowledge is actually written down. Much of aerospace engineering is based upon "rules of thumb" that is passed on through oral tradition. For example: Ask almost anyone in my business "Why does the Mars Viking and Mars Pathfinder have a 70 degree half angle aeroshell?" and you'll get a blank expression. Until recently I could find no one who knew why. People normally guessed that shape was selected for packaging reasons (wrong!). In truth we used the 70 deg. shape because that's what people used in the past and it was considered "safe". On day I was talking to an "old timer" who knew about the design process surround Viking. Here's his answer: It is desirable to make the half angle as large as possible to increase drag. More drag reduces the amount of heat shield material required. However if the half angle is increased too much then shockwave detachment from the nose tip occurs and stability is lost. If one does the Newtonian theory for carbon dioxide then 70 degrees turns out to be the magic number. This basic design concept was not written down anywhere to my knowledge (except here for the first time). I guess the old guys figured it was so obvious that no one needed to write it down.

Gary.