In Les Navigateurs de l'infini (1925) by J.-H. Rosny aîné, the word astronautique (astronautics) was used.
ɪn lˈɛs nˌævɪɡɐtˈʊɹz də ˈɛlɪnfˈiːni nˈaɪntiːnhˈʌndɹɪd twˈɛnti fˈaɪv baɪ dʒˈeɪ.ˈeɪtʃ. ɹˈɑːsni eɪnˈeɪ, ðə wˈɜːd ˌæstɹənətˈiːk ˌæstɹənˈɔːɾɪks wʌz jˈuːzd.