Mercury-Atlas 5 (MA-5) was the final qualification flight of the Mercury-Atlas system before NASA would commit to sending an astronaut into orbit. Launched on November 29, 1961 from Cape Canaveral Launch Complex 14, the mission carried Enos, a 5-year-old chimpanzee who had been trained to perform lever-pulling tasks in response to flashing lights — a way to prove that a living occupant could work effectively in the orbital environment.

Enos had been trained at Holloman Air Force Base in New Mexico over a period of more than a year. During the flight, he was required to pull specific levers within a set time window when prompted by symbols on a display. If he chose correctly, he received a banana pellet; if he chose wrong or failed to respond, he received a mild electric shock to the soles of his feet. However, a malfunction in the reward/punishment mechanism caused Enos to receive shocks even when he responded correctly — yet he continued to perform his tasks accurately, demonstrating remarkable composure under stress.

The mission was planned for three orbits but was cut short to two when a thruster malfunctioned, causing the spacecraft to drift out of its proper attitude. Combined with an overheating issue in the cabin, Mission Control decided to bring the spacecraft home early. Enos splashed down in the Atlantic Ocean approximately 200 miles south of Bermuda after 3 hours, 20 minutes, and 59 seconds. The destroyer USS Stormes recovered the capsule, and Enos was found to be in excellent condition.

Despite being shortened, MA-5 was considered a success. It proved the Mercury-Atlas system was ready for crewed orbital flight and paved the way directly for John Glenn’s historic Friendship 7 mission less than three months later. Sadly, Enos died of a shigella-related illness on November 4, 1962 — unrelated to his spaceflight.