Future astronauts sent on long duration flights to Mars or beyond will have to worry about more risks than merely launching into space and reentering planetary atmospheres safely. Space radiation, prolonged exposure to weightlessness and the psychological impact of extended confinement inside a space ship are just some of the challenges detailed in Naked Science: Spacemen (9 p.m. EDT, National Geographic Channel). While much of the material covered in Spacemen may seem old hat to dedicated followers of NASA’s space exploration efforts, the program provides a basic primer of the fundamental obstacles facing astronauts in Earth orbit today and in...