Cernan was originally selected with Thomas Stafford as backup pilot for Gemini 9 . When the prime crew of Elliot See and Charles Bassett was killed in the crash of NASA T-38A " 901 " ( USAF serial 63-8181 ) at Lambert Field on February 28 , 1966 , the backup crew became the prime crew — the first time in NASA history this happened . Gemini 9A encountered a number of problems ; the original target vehicle exploded during launch and the planned docking with a substitute target vehicle was made impossible by the failure of a protective shroud to separate after launch . The crew , however , performed a rendezvous that simulated procedures that would be used in the Apollo 10 mission ; the first optical rendezvous and a lunar-orbit-abort rendezvous . Cernan performed the second American EVA — the third-ever spacewalk — but overexertion caused by a lack of limb restraints prevented testing of the Astronaut Maneuvering Unit and forced the early termination of the spacewalk . Cernan was also a backup pilot for the Gemini 12 mission
crash
1966 NASA T-38 crash
Gene Cernan