Gemini XII was the 10th and final crewed Gemini flight, commanded by NASA veteran James A. Lovell and rookie Edwin "Buzz" Aldrin. Gemini XII also achieved the fourth docking and fifth rendezvous with an Agena target vehicle. Gemini XII marked a successful conclusion to the Gemini program, seeing as it achieved the program's last goal of having astronauts effectively work outside the spacecraft. This achievement was instrumental in paving the way for the Apollo program.
The Gemini XII spacecraft was launched on November 11, 1966, and all launch vehicle systems performed nominally during powered flight. However, the first stage oxidizer tank ruptured during staging, similar to what happened during Gemini X's launch.
After the previous Gemini flight, the program still had not demonstrated that an astronaut could work easily and efficiently outside the spacecraft. Previous to Gemini XII, astronauts had attempted EVAs, but their successes were limited due to insufficient techniques and a lack of proper restraints. However, new, improved restraints were added to the outside of the capsule for Gemini XII, and an underwater training technique was introduced. The main goal of the Gemini XII mission was to develop and test new methods of working outside the spacecraft safely and effectively. Aldrin's two-hour, 20-minute tethered spacewalk demonstrated the feasibility of extravehicular activity as he retrieved a micrometeorite collector, photographed star fields, and did other tasks. Two other EVAs carried out by Aldrin went smoothly, as did the routine rendezvous and docking with the Agena target vehicle, which was done using the onboard computer and charts when a rendezvous radar failed. However, the climb to a higher orbit was canceled because of a problem with the Agena booster.
The Agena Target Vehicle engine experienced a drop in turbopump speed during orbital injection, which lasted around 2.5 seconds and then returned to normal. Telemetry data showed erratic pump speeds, but the engine performance did not reflect this. The anomaly, a brief 30 psi drop in the thrust chamber of the rocket, was found later. The pressure drop raised concerns about a planned orbital maneuver that would have pushed Gemini XII into a higher orbit, and ground controllers decided not to follow through, considering the reason for the pressure drop was unclear.
A computer controlled the re-entry, and the capsule splashed down 4.8 km from its target and was recovered by the USS Wasp. Neither astronaut showed unusual conditions in their postflight medical examination. Both were dehydrated due to problems with the spacecraft's water supply system, slightly exhausted, and Lovell had a mild case of pinkeye. Gemini XII's success paved the way for the future success of the Apollo missions and the eventual Moon landing less than 3 years later.