Pronunciation Key – Show Spelled Pronunciation[koz-muh-nawt, -not]

–noun a Russian or Soviet astronaut.

[Origin: 1955–60; cosmo- + (aero)naut, repr. Russ kosmonávt]

—Related forms

cos·mo·nau·tic, adjective

cos·mo·nau·ti·cal·ly, adverb

http://www.infoplease.com/dictionary/cosmonautics

astronautics, esp. as applied to space flight.

http://dictionary.reference.com/search?q=cosmonautics&r=66

–noun (used with a singular verb)

astronautics, esp. as applied to space flight.

The English word that is used normally is astronautics-the theory and practice of navigation through air or space.

The rest of the world has astronauts.

In the beginning of the space race, Russia called its astronauts cosmonauts. So the origin of this usage is Russian-from1959, Anglicization of Rus. kosmonavt.

I don’t know if “cosmonautics” is a word, but if it is, it would be relating to the subject or practice of space travel.