NASA requires its mission specialists and its commander and pilot astronauts to have bachelor's degrees in biological science, physical science, mathematics or engineering; most people take four years to earn these degrees. The administration prefers candidates for the above positions who have graduate or doctoral degrees. NASA tends to notice applications from candidates who have distinguished themselves academically, even as early as grade school.
The chances of a particular applicant being chosen as an astronaut are remote. The number of people entering the average NASA astronaut application round ranges from 4,000 to 8,000 people. Of these, NASA only chooses between eight and 35. The administration brings on trainees every four or five years. One of the primary factors considered is an applicant's education.
For years, NASA showed preference to candidates who had a background in military flight, particularly if they had more than 1,000 hours commanding a jet. However, in the late 1970s, the administration began giving equal weight to those with professional backgrounds in science and engineering, which vastly increased the number of astronauts who held advanced degrees.
Today, nearly all United States astronauts hold master's degrees, while many have doctorate degrees. Popular astronaut academic specialties include chemistry, medicine and even veterinary science.