| NASA is very interested in improving its ability to monitor and forecast the radiation levels that pose a health risk to space-walking astronauts as they construct the International Space Station and astronauts that will participate in long-term and deep-space missions. Human exploratory missions to the moon and Mars, within the next quarter century, will expose crews to transient radiation from solar particle events which include high-energy galactic cosmic rays and high-energy protons. The primary risk for radiation exposure is the dose-equivalence to blood-forming organs (BFO) and the propensity for radiation-induced cancer. The issue is assessing the risk—determining the dose and dose-equivalence at the organ sites.; Models of the radiation environment are required to estimate the radiation dose to the astronauts. Confidence in the estimates of incurred dose for space missions is directly related to the accuracy and development of the current space radiation environmental models. Such a model is the Space Environment Information Systems (SPENVIS) modeling program, developed by the Belgian Institute for Space Aeronautics.; Calculations for the absorbed dose and dose-equivalent under varying shielding conditions were done to determine the dose distribution to the blood-forming organs (brain, heart, thyroid, colon, and stomach). Relative comparisons of the calculated results with measured data (from the active and passive dosimeters) indicate a very good agreement between the sets of data (0 to 10% variance) with the exception being the absorbed dose for the stomach with a variance of 77%. The calculated absorbed dose, dose equivalent, and quality factor (Q), as predicted by SPENVIS, compare favorably to the values obtained by the active dosimeters and the TLDs and are less than the predicted values, as identified in the NCRP Report-98, for a space mission in low earth orbit. |
