With this flight, the US finally took the manned spaceflight endurance record from Russia, while demonstrating that the crew could survive in zero gravity for the length of time required for a lunar mission. However the mission was incredibly boring, the spacecraft just drifting to conserve fuel most of the time, and was 'just about the hardest thing I've ever done' according to a hyperactive Pete Conrad. An accident with freeze dried shrimp resulted in the cabin being filled with little pink subsatellites.
Gemini 6 was to have been the first flight involving docking with an Agena target/propulsion stage. However the Agena blew up on the way to orbit, and the spacecraft was replaced by Gemini 7 in the launch order.
For lack of a target, NASA decided to have Gemini 6 rendezvous with Gemini 7. This would require a quick one week turnaround of the pad after launch, no problem with Russian equipment but a big accomplishment for the Americans. The first launch attempt was aborted; the Titan II ignited for a moment, then shut down and settled back down on its launch attachments. Schirra waited it out, did not pull the abort handles that would send the man catapulting out of the capsule on their notoriously unreliable ejection seats. The booster was safed; Schirra had saved the mission and the launch three days later went perfectly. The flight went on to achieve the first manned space rendezvous controlled entirely by the self-contained, on-board guidance, control, and navigation system. This system provided the crew of Gemini 6 with attitude, thrusting, and time information needed for them to control the spacecraft during the rendezvous. Under Schirra's typically precise command, the operation was so successful that the rendezvous was complete with fuel consumption only 5% above the planned value to reach 16 m separation from Gemini 7.
Major objectives of the mission were to rendezvous and dock and to evaluate extravehicular activities (EVA). Among the secondary objectives were tethered vehicle evaluation, experiments, third revolution rendezvous and docking, automatic reentry demonstration, docked maneuvering for a high-apogee excursion, docking practice, systems tests, and Gemini Agena target vehicle (GATV) parking. The high-apogee excursion was not attempted because an anomaly was noted in the GATV primary propulsion system during insertion, and parking was not attempted because the GATV's attitude control gas was depleted. All other objectives were achieved. Nine spacecraft maneuvers effected rendezvous with the GATV. The onboard radar malfunctioned before the terminal phase initiate maneuver, but the crew used onboard backup procedures to calculate the maneuvers. Rendezvous was achieved at 3 hours 46 minutes ground elapsed time, docking 28 minutes later. Two phasing maneuvers, using the GATV secondary propulsion system, were accomplished, but the primary propulsion system was not used. The first of two periods of standup EVA began at 19 hours 29 minutes into the flight and lasted for 2 hours 29 minutes. During a more than two-hour umbilical EVA which began at 42 hours 48 minutes, Aldrin attached a 100-foot tether from the GATV to the spacecraft docking bar. He spent part of the period at the spacecraft adapter, evaluating various restraint systems and performing various basic tasks. The second standup EVA lasted 55 minutes, ending at 67 hours 1 minute ground elapsed time. The tether evaluation began at 47 hours 23 minutes after liftoff, with the crew undocking from the GATV. The tether tended to remain slack, although the crew believed that the two vehicles did slowly attain gravity-gradient stabilization. The crew jettisoned the docking bar and released the tether at 51 hours 51 minutes. Several spacecraft systems suffered problems during the flight. Two fuel cell stacks failed and had to be shut down, while two others experienced significant loss of power. At 39 hours 30 minutes ground elapsed time, the crew reported that little or no thrust was available from two orbit attitude and maneuver thrusters.