After being selected to the astronaut office , crewmembers go through an initial two year training flow , astronaut candidacy , where they learn the basic skills necessary for spaceflight . While the bulk of astronaut candidate training currently centers on the multiple subjects required for ISS operations ( EVA skills , Russian language , ISS systems , etc . ) , training also includes geoscience training designed to train crewmembers in Earth observations , teach astronauts about other planetary systems , and provide field training designed to investigate field operations and boost team skills . This training goes back to Apollo training and has evolved to support ISS operations and future exploration missions .