Becoming an astronaut is a highly competitive process that requires a combination of education, experience, and physical fitness. Here are some special requirements to be an astronaut:
1. Education: NASA requires its astronaut candidates to have at least a bachelor's degree in engineering, biological science, physical science, computer science or mathematics. Many astronauts also have advanced degrees such as a master's or doctorate.
2. Experience: Candidates must have at least three years of related professional experience obtained after degree completion OR at least 1,000 hours pilot-in-command time on jet aircraft. The professional experience could be teaching, research or other roles that require problem-solving skills.
3. Physical Fitness: Astronaut candidates must pass the NASA long-duration spaceflight physical, which includes vision and blood pressure tests. They must have distant visual acuity: 20/100 or better uncorrected, correctable to 20/20 each eye and blood pressure not to exceed 140/90 measured in a sitting position.
4. Age: There is no age requirement for the astronaut program. However, the rigorous physical requirements and the long duration of training typically favor younger candidates.
5. Citizenship: To apply for NASA's astronaut program, you must be a U.S citizen.
6. Skills: Astronauts need to have skills in leadership, teamwork and communications as they often work in small teams for long periods under high stress conditions.
7. Language Skills: English is mandatory as it is the working language of the International Space Station (ISS). Knowledge of Russian can also be beneficial since Russian Soyuz spacecraft are currently used for crew transportation to and from the ISS.
8. Swimming Skills: Astronauts should be comfortable in water and should know swimming because much of their training for spacewalks takes place underwater.
9. Psychological Stability: Astronauts need to demonstrate psychological stability and the ability to cope with the mental demands of space travel such as isolation from family and friends for extended periods.
These requirements may vary slightly depending on the space agency (NASA, ESA, Roscosmos etc.) but generally follow similar guidelines.