Radiation Measurements at the International Space Station Orbits

Construction of the International Space Station is now a reality with the start of permanent human presence. Radiation presents a serious risk to the health and safety of the astronauts with the clear requirement for estimating their exposures prior to and after the flight. Over the last few years, a tissue equivalent proportional counter (TEPC) has been flown at a fixed mid-deck location onboard Shuttle flights in 51.65° inclination flights. These flights have provided data that covers the expected changes in the radiation exposure due to changes in altitude, and solar activity from the solar minimum to the solar maximum of the current 23^rd solar cycle. Comparison with data acquired by a TEPC flown on the Mir has been made and shows excellent agreement. Based on this data a simple function of the solar deceleration potential has been developed to predict 90 days ahead of time of observations, the internal galactic cosmic radiation dose rate to ± 10% throughout the solar cycle. Asymmetry of trapped dose rates due to Shuttle orientation, consistent with earlier observations, is confirmed. The dose rate due to trapped particles is found to be a power law function of the atmospheric density, and within 10% of normalized trapped belt model predicted function. This relationship can be used to predict trapped dose rates to ±10% four to twelve months prior to the time of observation, depending upon the time in the solar cycle. Combined GCR plus trapped prediction capabilities are thus ±15%. The model has been used to predict the dose rates in the ISS Node 1 and R-16 ion chamber locations.