▁as ▁expos ure ▁to ▁higher ▁g - for ces , ▁as ▁well ▁as ▁e jection ▁seat ▁experience ; ▁also ▁the ▁Americans ▁had ▁chosen ▁the ▁Mercur y ▁Seven ▁in ▁April ▁ 1 9 5 9 , ▁all ▁of ▁whom ▁had ▁av iation ▁background s . ▁The ▁candidates ▁had ▁to ▁be ▁intellig ent , ▁comfortable ▁in ▁high - str ess ▁situations , ▁and ▁phys ically ▁fit . ▁ ▁Chief ▁designer ▁of ▁the ▁Soviet ▁space ▁program , ▁Serge i ▁Kor ole v , ▁decided ▁that ▁the ▁cos mon aut s ▁must ▁be ▁male , ▁between ▁ 2 5 ▁and ▁ 3 0 ▁years ▁old , ▁no ▁t aller ▁than ▁ 1 . 7 5 ▁meters , ▁and ▁we igh ▁no ▁more ▁than ▁ 7 2 ▁kil og rams . ▁The ▁final ▁specific ations ▁for ▁cos mon aut s ▁were ▁approved ▁in ▁June ▁ 1 9 5 9 . ▁By ▁September ▁inter views ▁with ▁potential ▁cos mon aut s ▁had ▁begun . ▁Although ▁the ▁pil ots ▁were ▁not ▁told ▁they ▁might ▁be ▁flying ▁into ▁space , ▁one ▁of ▁the ▁phys icians ▁in ▁charge ▁of ▁the ▁selection ▁process ▁believed ▁that ▁some ▁pil ots ▁had ▁dedu ced ▁this . ▁Just ▁over ▁ 2 0 0 ▁candidates ▁made ▁it ▁through ▁the ▁interview ▁process , ▁and ▁by ▁October ▁a ▁series ▁of ▁demand ing ▁physical ▁tests ▁were ▁conducted ▁on ▁those ▁remaining , ▁such ▁as ▁expos ure ▁to ▁low ▁press ures , ▁and ▁a ▁cent rif uge ▁test . ▁By ▁the ▁end ▁of ▁ 1 9 5 9 , ▁ 2 0 ▁men