"space-traveler," 1929 in scientific speculation, popularized from 1961 by U.S. space program, a compound from Greek elements, from astro- "star" + Greek nautes "sailor," from PIE root *nau- "boat." French astronautique (adj.) had been coined 1927 by "J.H. Rosny," pen name of Belgian-born science fiction writer Joseph Henri Honoré Boex, on model of aéronautique, and Astronaut was used in 1880 as the name of a fictional spaceship by English writer Percy Greg in "Across the Zodiac."
in the names of sciences or disciplines (acoustics, aerobics, economics, etc.), a 16c. revival of the classical custom of using the neuter plural of adjectives with Greek -ikos "pertaining to" (see -ic) to mean "matters relevant to" and also as the titles of treatises about them. Subject matters that acquired their English names before c. 1500, however, tend to be singular in form (arithmetic, logic, magic, music, rhetoric). The grammatical number of words in -ics (mathematics is/mathematics are) is a confused question.
<a href="https://www.etymonline.com/word/astronautics">Etymology of astronautics by etymonline</a>
Harper, D. (n.d.). Etymology of astronautics. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/astronautics