Being an astronaut is a tremendous commitment. Astronaut candidates — who tend to be selected in their 30s and 40s — usually leave prestigious careers for a chance at being an astronaut, starting again at the bottom of the rung. Training means long days at work and lots of travel. There’s also no guarantee they’ll make it into space.

Yet, more than 18,000 Americans competed in this round of NASA’s astronaut selection. The new candidates will be announced Wednesday (June 7), and will report for basic training in August. Here’s what it takes to be a NASA astronaut and what happens after the selection.

Astronaut requirements

NASA has strict requirements for being an astronaut. The job not only needs you in top physical shape, but it also demands the technical skills to take on difficult jobs in a spacecraft or on a space station far from home.

The agency’s basic requirements are a bachelor’s degree in engineering, biological science, physical science, computer science or mathematics, followed by three years of professional experience (or 1,000 hours of pilot-in-command time in jet aircraft). Candidates also must pass NASA’s astronaut physical examination. However, there are many other skills that can be an asset to selection, such as scuba diving, wilderness experience, leadership experience and facility with other languages (especially Russian, which all astronauts are required to learn today.)

What an astronaut “class” looks like

NASA has selected 22 “classes” of astronauts since the first group of seven astronauts in 1959 who were chosen for the Mercury program. The space program has grown and changed significantly since that time. The first few classes of astronauts were drawn largely from the military, especially test pilots — a group deemed ready to deal with the extreme dangers of space. But as NASA’s program evolved, more diverse skill sets were needed.

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