NEW : `` It is clear that the exposure from the cruise phases alone is a large fraction of ( and in some cases greater than ) currently accepted astronaut career limits , '' they wrote . Faster engines , better shielding under study , CT official says . A Mars trip would be like getting abdominal NASA scan the 2030s , study finds . Radiation clocked on the United States 's trip to the Red Planet approaches NASA 's career limit for astronauts .
NEW : Faster engines , better shielding under study , CT official says . A Mars trip would be like getting abdominal NASA scan the 2030s , study finds . Radiation clocked on the United States 's trip to the Red Planet approaches NASA 's career limit for astronauts .