They are evaluated on their performance of these tasks as well as on other phases of training. The evaluations determine whether or not the candidates will be accepted as astronauts. Becoming an astronaut does not guarantee immediate assignment to a mission. Some pilot astronauts have waited as long as 12 years before flying in space. While waiting, astronauts continue to work on various engineering assignments.
Some astronauts become experts in several support or operational areas.
Such special knowledge helps astronauts get assigned to flights on which their specialty is necessary. Once assigned to a crew, astronauts spend most of their time training in simulators. Simulators are devices that reproduce the conditions of space flight. Crew members spend as many as eight hours a day in simulators rehearsing every part of their mission. Instructors continually give the crew problems to solve and correct to prepare them for all possible emergency situations.