The differentiation is that they are titles granted by various space organizations. The two of them mean essentially something very similar, and the two of them originate from Greek. The Russian Space Agency utilizes cosmonaut. The space explorer is utilized by NASA, ESA, CSA, and JAXA. A space explorer or cosmonaut (Russian) is an individual prepared by a human spaceflight program to order, pilot, or fill in as a group individual from a rocket.