Training was more intense for him than for Ham, who had become the first great ape in space in January 1961, because Enos was exposed to weightlessness and higher gs for longer periods of time.

[3] Enos was scheduled to complete three orbits, but the mission was aborted after two, due to two issues: capsule overheating and a malfunctioning "avoidance conditioning" test subjecting the primate to 76 electrical shocks.

According to one history of primatology, "The chimpanzee, about five years old, behaved like a true hero: despite the malfunctions of the electronic system, he conscientiously performed all the tasks he had learned during the entire flight of over three hours...Enos demonstrated that he was careful to successfully complete his mission and that he perfectly understood what was expected of him.

"[4] After his space capsule made an ocean landing, Enos "had become angry and frustrated at the three-hour wait" before being retrieved by U.S. Navy seamen.

[8] Enos's flight was a full dress rehearsal for the next Mercury launch on February 20, 1962, which would make John Glenn the first American to orbit Earth.