 The Saturn V rocket used by Apollo 8 was designated SA @-@ 503 , or the " 03rd " model of the Saturn V ( " 5 " ) Rocket to be used in the Saturn @-@ Apollo ( " SA " ) program . When it was erected in the Vertical Assembly Building on December 20 , 1967 , it was thought that the rocket would be used for an unmanned Earth @-@ orbit test flight carrying a boilerplate Command / Service Module . Apollo 6 had suffered several major problems during its April 1968 flight , including severe pogo oscillation during its first stage , two second stage engine failures , and a third stage that failed to reignite in orbit . Without assurances that these problems had been rectified , NASA administrators could not justify risking a manned mission until additional unmanned test flights proved that the Saturn V was ready . 
