Total Ionizing Dose from Ground Level Enhanced Solar Proton Events and ISS Radiation Effects Experience

In addition to minimizing the space radiation exposures to humans for deep-space exploration missions, it is also imperative that onboard radio-sensitive systems be protected, especially electronic components that are vulnerable to space environment effects (SEE). A parametric space radiation effects study was performed to investigate the total ionizing dose (TID) to electronics components from extremely large (GLE – Ground Level Events) solar proton events for several shielding configurations. Typically, electronics packages are housed in aluminum “boxes” having wall thicknesses on the order of 50-100 mils. As the source term, seven (7) historically-large GLEs were selected where the proton energy spectra ranged from 10 MeV to 5 GeV based on earlier studies using the Band function fitting method. Electronic box configurations were chosen that included a 50, 80, and 100 mil aluminum wall thicknesses. A second shielding configuration consisted of aluminum boxes “lined” with varying thicknesses of polyethylene. A third case consisted of boxes with varying thicknesses of tungsten (85%)-copper (15%) alloy. In addition, galactic cosmic radiation (GCR) exposures for both solar minimum and solar maximum were calculated for these various shielding configurations using the Badhwar-O’Neill GCR model. Finally, the ISS radiation effects experience is discussed in detail.