Radiation Exposure Estimates for Deep Space Missions Revisited

Various studies of potential exposures to the space radiation environment for astronauts on missions beyond low-Earth orbit (LEO) have been carried out and the results published in conferences and journals. These studies involved estimating radiation exposures from galactic cosmic rays and/or solar energetic particle events for missions to the moon, Mars and beyond. Estimating potential risks usually involved comparing the calculated doses and effective doses to NASA limits published in NASA Standard 3001. These radiation limits consist of: (1) short-term limits imposed to prevent early effects such as nausea, vomiting and lethality; (2) non-cancer lifetime limits are imposed to prevent late term degenerative effects in the lens of the eye, central nervous system, cardiovascular system; and (3) career effective dose limits to prevent a 3% excess risk of exposure induced death (REID) from cancer at the 95% confidence limit. Specific effective dose values for the career effective dose limits depend on the particulars of the specific mission, including the gender of the crew member, the expected environments, and the length of the mission. Many previous studies compared the estimates of effective doses for mission crew members to a table in NASA Standard 3001 that listed values for the 3% excess cancer risk. These values did not include the 95% confidence limits, which would have reduced those effective doses by an approximate factor of 3. Hence, some studies suggested that the estimated effective doses would be below the career limits, when in fact they would exceed those limits. In this work, we revisit some of these deep space mission analyses and compare the estimated doses and effective doses to the correct limits which include the 95% confidence limits.