 Sixteen months later , Lovell would once again have to perform a similar manual re @-@ alignment , under more critical conditions , during the Apollo 13 mission , after that module 's IMU had to be turned off to conserve energy . In his 1994 book , Lost Moon : The Perilous Voyage of Apollo 13 , Lovell wrote , " My training [ on Apollo 8 ] came in handy ! " In that book he dismissed the incident as a " planned experiment " , requested by the ground crew . In subsequent interviews Lovell has acknowledged that the incident was an accident , caused by his mistake . 
