Brought on by weightlessness in protracted space flight, besides the obvious hazards of meteors, rocky debris, and radiation, astronauts also have to deal with muscle atrophy.
Choices A, B, and C misplace the modifier in protracted space flight, which should follow astronauts, and A also misplaces brought on by weightlessness, which should follow atrophy. Choice C also makes an error in the idiom brought on by. Choice D is wordy.