Radiation 



prospective experiments, and the lack of experience with the quality of radiation 

 and low dose rates encountered in space. 



Research is conducted on a variety of levels: biomolecular, cellular, tissue systems, 

 animal models, and humans. The impetus for this research lies in the need to 

 understand basic interactions between living beings and radiation, to exploit 

 radiation effects for medical ends, and to understand the risks associated with 

 medical, industrial, and military uses of radiation. Hence, a wide range of 

 organizations is involved in radiation research. 



The biological effects of low LET radiations are much better understood than those 

 of high LET radiations. Many data exist on radiation effects on the suborganism 

 level and animal models, but it is not always easy to extrapolate those results to 

 humans. One of the major effects of low-level radiation is carcinogenesis. Much 

 work has been done in this area, but results are often difficult to interpret because 

 of the high natural incidence of cancer and the presence of numerous confound- 

 ing factors. Recent work indicates that the effects of exposure to low dose rates of 

 high LET radiation are quite different from the effects of low LET radiation. This 

 may have a profound impact on space missions, and extensive research needs to 

 be done. 



The establishment of RBE's for different radiations and different tissues is currently 

 the subject of a number of experiments, but the task is far from complete. The 

 importance of microlesions induced by high LET radiation is another subject that 

 needs to be understood more fully. 



Findings and Recommendations 



Solar Particle Events 



Findings 



• For all of the proposed missions, except the Space Station in LEO, the possi- 

 bility exists of the mission crew being exposed to debilitating or lethal doses of 

 radiation as a result of solar particle events. 



• The degree of our ignorance of these events, coupled with the potentially 

 disastrous consequences to both the crew and the mission, establish SPE's as 

 the most pressing challenge for the humans in space program. 



• Much work needs to be done to characterize fully the flux, spectral 

 distribution, and time evolution of SPE's. In addition, support should be 

 available for astrophysical studies and solar modeling work relevant to 

 establishing an early warning and prediction system. 



Recommendation 



• NASA should vigorously pursue basic research in solar physics in order to 

 model and predict catastrophic radiation events and to investigate short-time 

 warning systems that will provide time for the crew to seek protection. 



63 



