What do you call a person trained to travel in spacecraft?

A person trained to travel in spacecraft is referred to as an astronaut. The term originated from the Greek words "astro," meaning star, and "naut," meaning sailor, which collectively signifies a "sailor among the stars." Astronauts undergo extensive training to prepare for various aspects of space missions, including science experiments, spacecraft operation, and physical fitness for the challenging conditions of space travel.

While "cosmonaut" is a valid term used primarily in Russia to describe space travelers, the more universal term in English-speaking contexts is astronaut. "Astrobotanist," on the other hand, refers to a specialist who studies plant life in space, and "aerospace engineer" pertains to the design and development of aircraft and spacecraft rather than someone who travels in them. Hence, astronaut is the most appropriate answer for someone specifically trained to embark on missions into space.