To become an astronaut means to undergo the necessary training, education and selection process to become a professional space traveler, working for an organization such as NASA or a space agency in another country. Full definition
Do your kids have dreams of becoming an astronaut? (thespruce.com)
Marshburn was a flight surgeon with NASA before training to become an astronaut in 2004. (businessinsider.com)
In high school, Hernandez was inspired by astronaut Franklin Chang - Diaz, and set his course on becoming an astronaut himself. (scientificamerican.com)