Spacecraft built-in radiation shielding for selected orbits and attitudes

Current availability of numerical tools to evaluate the radiation environment, including directional characteristics of the impinging fluxes, allows to perform realistic simulations since the first steps of a mission design. Once the orbit and the attitude have been selected, it is possible to evaluate in a quantitative manner the protection needed by the on-board electronics, taking into account the contribution of the other subsystems (structures, batteries) typical of the spacecraft. Of course, this approach is inherently limited to TID-related problems. However, timely consideration of the shielding needed should enable to save mass by identifying the best possible placement of the devices with respect to the impinging flux. This paper proposes a shielding evaluation technique, taking into account both orbital and attitude characteristics, which combines the features of SPENVIS simulation tool (by ESA/BIRA) with an in-house developed software. The introduction of a "complementary shielding function" allows comparison among several possible configurations, enabling also an easy graphical presentation of the results. Differences in shields' mass, and therefore mass savings, can be in the order of 10%.