Question

when is an astronaut typically assigned to a mission?
after graduating college
after obtaining a phd
after finishing postdoc research
after completing a two - year training

Explanation:

Astronauts typically undergo a two - year training program after being selected. Only after successfully completing this training are they usually assigned to a mission. College graduation, obtaining a PhD, or finishing postdoc research are part of the educational background requirements for astronaut candidates but do not directly lead to mission assignment.

Answer:

after completing a two - year training