@Sam Dietrich In my previous professional life I co-authored an ESA handbook on radiation hardened design techniques:
http://microelectronics.esa.int/asic/ECSS-Q-HB-60-02A1September2016.pdf
This gives an overview of a lot of techniques for radiation hardened design. It goes too far to go in detail here but for example for digital design using DICE based flipflops but not hardening your IO cells or clock tree will still make your final design radiation sensitive.