pl oration ▁of ▁Cos mic ▁Space ▁by ▁Me ans ▁of ▁Re action ▁Dev ices ), ▁published ▁in ▁ 1 9 0 3 . ▁ ▁T si ol kov sky ' s ▁ro cket ry ▁work ▁was ▁not ▁fully ▁appreciated ▁in ▁his ▁lifetime , ▁but ▁he ▁influenced ▁Serge y ▁Kor ole v , ▁who ▁became ▁the ▁Soviet ▁Union ' s ▁chief ▁ro cket ▁designer ▁under ▁Joseph ▁St alin , ▁to ▁develop ▁inter cont inental ▁ball istic ▁miss iles ▁to ▁carry ▁nuclear ▁weapons ▁as ▁a ▁counter ▁measure ▁to ▁United ▁States ▁bom ber ▁plan es . ▁Der iv atives ▁of ▁Kor ole v ' s ▁R - 7 ▁S emy ork a ▁miss iles ▁were ▁used ▁to ▁launch ▁the ▁world ' s ▁first ▁artificial ▁Earth ▁satellite , ▁S put nik ▁ 1 , ▁on ▁October ▁ 4 , ▁ 1 9 5 7 , ▁and ▁later ▁the ▁first ▁human ▁to ▁orbit ▁the ▁Earth , ▁Y uri ▁G ag arin ▁in ▁V ost ok ▁ 1 , ▁on ▁April ▁ 1 2 , ▁ 1 9 6 1 . ▁ ▁Space fl ight ▁became ▁an ▁engineering ▁possibility ▁with ▁the ▁work ▁of ▁Robert ▁H . ▁God d ard ' s ▁publication ▁in ▁ 1 9 1 9 ▁of ▁his ▁paper ▁A ▁Method ▁of ▁Re aching ▁Ext reme ▁Alt itudes . ▁His ▁application ▁of ▁the ▁de ▁L aval ▁no zz le ▁to ▁liquid ▁fuel ▁rock ets ▁improved ▁efficiency ▁enough ▁for ▁inter plan et ary ▁travel ▁to ▁become ▁possible . ▁He ▁also ▁proved ▁in ▁the ▁labor atory ▁that ▁rock ets