X-15 Flight 91
X-15 Flight 91 was an August 22 , 1963 American crewed mission , and the second and final flight in the program to achieve sub-orbital spaceflight—a flight over 100 km in altitude—which was previously achieved during Flight 90 a month earlier by the same pilot , Joseph A . Walker . 
<triplet> X-15 Flight 91 <subj> Joseph A. Walker <obj> crew member <triplet> Flight 90 <subj> Joseph A. Walker <obj> crew member <triplet> Joseph A. Walker <subj> X-15 Flight 91 <obj> astronaut mission <subj> Flight 90 <obj> astronaut mission