Radiation 



10 2 



jO 10° 



10 1 



Neutron (rem) 



C.R. (rad) 



100 



200 300 400 



Depth (g/cm 2 ) 



500 



600 



Figure 2. A comparison of the annual dose equivalent due to secondary neutrons 

 and cosmic-ray nuclei, as a function of shielding; also the absorbed dose 

 rate due to cosmic-ray nuclei 



Mars Mission 



The radiation space environment for a mission to Mars is essentially the same as 

 that for a lunar colony, with the exception that during the long space flight, there 

 is no massive shielding readily available in case of a giant SPE. Thus, one must 

 consider the radiation sources as galactic cosmic rays and solar particle events. 

 During the flight, one is limited to spacecraft shielding, and the radiation is 

 isotropic (i.e., there is no shielding of half the solid angle by the planet or Moon). 

 A baseline dose for the Mars trip is 43 rem per year in essentially free space, 36 

 rem per year behind 4 g/cm**2 Al, and 24 rem per year at the center of a 30 cm 

 diameter sphere of water (8). On its surface, Mars shields half the GCR and the 

 carbon dioxide atmosphere provides some shielding, so estimates of the dose at 

 the surface are approximately 10 rem per year. 



As with the other missions beyond the Earth's magnetosphere, the possibility of 

 catastrophic SPE's must be taken into account. More than the other missions, the 

 trip to Mars is especially vulnerable. The trip itself will take on the order of a year 

 to complete, and during that time, there will be no possibility of moving to a 



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