Without gravity, people’s muscles atrophy and their bones weaken. Astronauts develop eye problems and anemia, get blood clots and have to exercise a few hours each day to overcome weight­less­ness’s effects on the body. Many experience space-motion sickness. Animals living at very low or zero gravity develop osteoporosis, problems with their eyes and kidneys, and reproductive issues. In 1962, NASA had viable designs for rotating wheel space stations that could have given astronauts artificial gr...