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The report does not give specifics on the number of experts who are retiring or the numbers needed to replace them, but it says about 20,000 research and development scientists and engineers work in the aerospace industry as a whole, down from more than 140,000 in the mid-1980s.
When peace broke out, downsizing decimated the missile defense industry. I know of one R&D group who went from a headcount of ~630 down to 84 - Many others just closed up shop. As a general rule, only those with 15 or more years of experience survived. Now most of that experience core is heading into retirement.