Buzz Aldrin on July 20, Aldrin and Armstrong entered "Eagle", and began the final preparations for lunar descent. At 17:44:00 "Eagle" separated from the "Columbia". Collins, alone aboard "Columbia", inspected "Eagle" as it pirouetted before him to ensure the craft was not damaged, and that the landing gear was correctly deployed. Throughout the descent, Aldrin called out navigation data to Armstrong, who was busy piloting the "Eagle". Five minutes into the descent burn, and above the surface of the Moon, the LM guidance computer (LGC) distracted the crew with the first of several unexpected alarms that indicated that it could not complete
Buzz Aldrin used a sextant and rendezvous charts he helped create to give Lovell the right information to put the spacecraft in position to dock with the target vehicle. Gemini 12 achieved the fourth docking with an Agena target vehicle. The next task was to practice undocking and docking again. On undocking, one of the three latches caught, and Lovell had to use the Gemini's thrusters to free the spacecraft. Aldrin then docked again successfully a few minutes later. The flight plan then called for the Agena main engine to be fired to take the docked spacecraft into a higher orbit, but