cosmonaut

A person who is trained to travel in space, but may not necessarily be a professional astronaut.

"The cosmonaut training program was designed to prepare individuals for space travel."

A person who is interested in or studies space and space travel.

"The cosmonaut enthusiast attended the space conference to learn more about the latest developments."

A person who travels in space, especially one who is a professional astronaut.

"The cosmonaut spent several months on the International Space Station."