The physical is similar to a military or civilian Class II flight physical. Mission specialist applicants must be 58.5 to 76 inches tall, and pilot applicants must be 64 to 76 inches tall. NASA continually accepts applications for mission specialist and pilot astronauts from both civilians and military personnel. The applications are reviewed, and new astronauts are selected every two years as needed. Some NASA missions include payload specialists, but these positions are filled by people who are nominated by a payload sponsor or customer group.
Competition is tough.
NASA receives approximately 4,000 applicantions per selection period. On average, only 118 of these applicants are asked to participate in a week-long interview, medical evaluation and orientation program. During the program, applicants are judged on their experience and potential, motivation, ability to work with a team, communication skills and adaptability. Mission Specialist Candidate Leroy Chiao some of the instruments in the T-38 jet at Ellington Field. The group is cut down to 20 people, who then enter the astronaut candidate training program.