into orbit on april twelfth one thousand nine hundred sixty one. yuri gagarin circled the earth for two hours just four years later both russian and american astronauts were already leaving their protective capsules to carry out spacewalks and perform repairers nowadays life in orbit has become almost routine missions on the international space station can last twelve months but a stay in space is hazardous astronauts are exposed to high levels of cosmic rays which may cause cancer bones and muscles weaken under conditions of weightlessness although crews on the spent hours exercising every day the world record for the longest space flight was actually set twenty three years ago. russian cosmonaut valery poliakoff spend four hundred thirty seven days on the mir space station apparently with no ill effects on his health. the next destination for human