This was unexpected. I saw him at the beginning of the month in Orlando at the NSS Space Settlement Summit. I quoted and referenced him in my Reason Foundation study, for his work in showing that multiple launches were actually lower mission risk than a single one. Lori Guisewhite (who I also saw there) remembers him as well.
RIP and Ad Astra.
So sorry to see this. I worked with Dave in the ’90s on ISS maintainability. He was gracious and wise and he helped us immensely.