Space colonization.
D018533:Biomass; D018504:Ecological Systems, Closed; D005118:Extraterrestrial Environment; D006801:Humans; D008021:Life Support Systems; D018535:Mars; D012371:Robotics; D013026:Space Flight; D018531:Spacecraft; D014481:United States; D018557:United States National Aeronautics and Space Administration; D014893:Weightlessness