Life Sciences in the S/wtr Program 



Table 1. Sources of Radiation 



(1) LET: linear energy transfer— a measure of the amount of energy deposited as radiation interacts with matter; tor ,1 ^iven radiation dose biological effects 

 are strongly dependent on the LET of the radiation 

 ■ i Earth radius, equal to 6,000 km 



(3) GEO Geosynchronous Earth orbit 



(4) LEO: Low-Earth orbit 



The purpose of this section is to define the principal radiation hazards as part of 

 the prelude to outlining what needs to be known concerning these environments. 



Loiv-Earih Orbit 



One of the principal missions designed for low-Earth orbit is the Space Station. At 

 the projected orbit parameters (450 kilometers, 28 degrees inclination), the main 

 source of radiation will be the trapped protons in Ihe South Atlantic Anomaly, 

 with a much smaller fraction coming from GCR. Data measured with thermo- 

 luminescent dosimeters from the Skylab missions (flown at approximately the 

 same altitude but at larger inclination, 50 degrees) indicate that the average daily 

 lose rate is in the range of 60-70 millirads per day (1). At the greater orbital 

 clination, the dose due to the South Atlantic Anomaly decreases somewhat, and 

 CR dose increases due to less geomagnetic shielding. Calculations by SB 

 al., for the proposed mission parameters yield doses of 97 millirem per 

 he blood-forming organs behind shielding of 1 g/cm**2 Al (2). At these 

 ■s, lung missions (180 days and more) would require careful personal 

 3 maintain accepted radiation health limits. As the inclination of the 

 l's, geomagnetic shielding decreases and exposure to solar particle 

 radiation and ( .CR increases. 



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