First launch attempt
The launch abort of Gemini 6A, attempted December 12, 1965.
The first attempt to launch the 6A mission (second attempt for Gemini spacecraft No. 6) was on December 12, 1965 at 9:54 a.m. EST.[3] All went well right up to ignition—in fact the engines did ignite, but then a plug fell out of the bottom of the rocket, starting the onboard computer. This was not meant to happen until the rocket had actually lifted off, and the onboard computer detected that there was no upwards motion, causing it to abort the launch. At this point mission rules dictated that the crew should eject from the spacecraft, as the rocket would explode on impact with the pad if it had lifted off by even an inch (2.54 cm).
Schirra elected not to eject as neither he nor Stafford had detected any upwards motion, and the ejection seats were seen as a last resort. In an early test of the system involving a dummy, the hatch had failed to blow off and the dummy's head was rammed into the side of the spacecraft. Also all ejection seats cause a dangerous compression of the spine as these were designed to carry the astronauts as quickly as possible (with the goal of evacuating the astronauts a couple of hundred meters away from an exploding rocket).
The Martin and Air Force teams who erected and tested the rocket found that some plugs on the rocket were able to pull out more easily than others. They replaced them with the ones that were harder to pull out on future missions, and a safety wire was added to make sure that the rocket had lifted off.
However, another problem was found as the engineers examined the thrust versus time graph. They found that the thrust rose nominally but started to decrease before the plug had fallen out. Through the night, engineers examined the rocket engine piece by piece until they found that a plastic cover had been left in the gas generator port. With this problem solved the rocket and spacecraft were rescheduled for a launch three days after the first attempt.