Dynamic/Anisotropic Low Earth Orbit Environmental Models

The first level of space infrastructure is represented by the International Space Station (ISS), which is now permanently occupied by space career astronauts. It is imperative that we understand the ISS exposures dynamically for career planning and insure that the regulatory requirement of keeping exposures as low as reasonably achievable (ALARA) is adequately implemented. This is especially true as ISS matures with increasing complexity resulting in a larger drag coefficient requiring operation at higher altitudes with increased exposure rates. In applying ALARA, it is desirable to augment the shielding in areas where the crew spends significant amounts of time. One such area is the crew quarter that has the added problem of being generally located against the pressure vessel wall where shielding is minimal and exposure rates tend to be high. A significant portion of the exposure results from trapped protons and is highly directional. In addition, some directions of approach of galactic cosmic rays are shielded below the Earth’s horizon and greater numbers of low energy particles enter from the west than the east. Clearly, the augmentation requires an understanding of this directionality to block major radiation components. We describe herein a new model of trapped and galactic cosmic radiation as seen in ISS operations in preparation for the design of an augmentation of the ISS crew quarter.