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Space radiation exposure limits for astronauts are based on recommendations of the National Council on Radiation Protection and Measurements. These limits now include the age at exposure and sex of the astronaut. A recently-developed computerized anatomical female (CAF) model is discussed in detail. Computer-generated, cross-sectional data are presented to illustrate the completeness of the CAF model. By applying ray-tracing techniques, shield distribution functions have been computed to calculate absorbed dose and dose equivalent values for a variety of critical body organs (e.g., breasts, lungs, thyroid gland, etc) and mission scenarios. Specific risk assessments, i.e., cancer induction and mortality, are reviewed.

Major improvements have recently been completed in the approach to spacecraft shielding analysis. A Computer-Aided Design (CAD)-based system has been developed for determining the shielding provided to any point within or external to the spacecraft. Shielding analysis is performed using a commercially available stand-alone CAD system and a customized ray-tracing subroutine contained within a standard engineering modeling software package. This improved shielding analysis technique has been used in several vehicle design projects such as a Mars transfer habitat, pressurized lunar rover, and the redesigned Space Station. Results of these analyses are provided to demonstrate the applicability and versatility of the system.

One of the risks associated with long-term space flights is cancer incidence resulting from chronic exposure to space radiation. Assessment of incurred risk from radiation exposure requires quantifying the dose throughout the body. The space radiation exposure received by Space Shuttle astronauts is measured by thermoluminescent dosimeters (TLDs) worn during every mission. These dosimeters measure the absorbed dose to the skin, but the dose to internal organs is required for estimating the cancer risk induced by space radiation. A method to extrapolate these skin dose measurements to realistic organ specific dose estimates, using the Computerized Anatomical Man (CAM) and Computerized Anatomical Female (CAF) models, is discussed in detail. A transport code, which propagates high energy nucleon and charged particles, is combined with the CAM/CAF-generated shielding areal distributions to evaluate the absorbed dose at selected organ sites.

Passive dosimeters have been extensively used to measure space radiation exposures to crewmembers for over three decades. Although a significant evolution in materials, processes, readout, and analysis techniques for these sensors has been witnessed during this period, these simple devices remain the backbone of the current operational dosimetry program for the Space Shuttle. Indeed, the utilization of passive dosimeters is also planned for the space station as well as advanced manned exploration programs, i.e., Lunar Base and Mars missions. Sensor materials and types have included thermoluminescent dosimeters, radiation-sensitive films and emulsions, and plastic nuclear track detectors. Early, transitional, and current passive dosimeter materials, systems, and techniques to measure space radiation are described and discussed, with major emphasis on the development of thermoluminescent dosimetry (TLD) techniques.

During EVAs astronauts can receive significant additional radiation exposure to the skin and eyes due to the minimal shielding provided by the EMU. Occupational health and safety standards for astronaut radiation exposure exist, but there are no unique EVA rules nor requirements for the shielding provided by the EMU. The ALARA concept requires “reasonable” actions be taken to minimize additional exposure. This is most effectively accomplished by avoiding EVAs in orbital regions where additional exposure occurs. Measurements during the Shuttle program do not properly reflect actual EVA exposures because of the poor location of the dosimeter inside the EMU. A measurement program is underway to determine the shielding provided by the EMU, as well as the optimal location for accurate dosimetric measurements.