Early on Sunday morning, December 12, 1965, I sat in front of my family’s black-and-white TV in Calgary, Alberta, waiting for the next two-astronaut Gemini spacecraft to launch. My brother Gordon was there and probably other family members. Only eight days earlier I had watched the successful ascent of Gemini VII, which carried Frank Borman and Jim Lovell on a record-setting fourteen-day endurance flight. Piloted by Wally Schirra and Tom Stafford, Gemini VI-A was to carry out the world’s first space rendezvous with VII, six hours (four orbits) after launch.

Schirra and Stafford’s mission had acquired the “A” because it was not the mission they were supposed to fly. On October 25, an Atlas-Agena took off from Launch Complex 14 at Cape Canaveral Air Force Station, Florida, the same complex Schirra had launched from on Mercury-Atlas 6 in October 1962. The Agena second stage was the target vehicle for the first attempt to rendezvous and dock in space, but shortly after separating from the Atlas booster, the uncrewed Agena blew up; Schirra and Stafford were waiting for launch in their spacecraft on LC 19 a couple of miles away. Dejectedly, the two astronauts exited, facing the possibility of months of delay. However, a couple of engineers from the Gemini spacecraft’s builder, McDonnell Aircraft of St. Louis, pitched a seemingly crazy idea—why not launch Gemini VII on its scheduled long-duration mission in December, then repair the pad and re-erect Gemini VI and its Titan II booster in a rush operation? Two more astronauts could then be launched, and the two crews could rendezvous. NASA officials at first were very skeptical, but soon concluded that the daring plan could work.

The plan was to get Gemini-Titan 6 (as the combination was called) ready in nine days after the GT-7 launch. Yet, the pad crews did it in only eight. The countdown on December 12 went perfectly. As I watched, the clock reached zero, the first-stage engines on the Titan II ignited, just as on four earlier crewed Gemini flights, and then just as suddenly they cut off. It was completely unexpected, but watching it unfold on live TV, I had no idea how tense and dangerous the situation was. Schirra and Stafford were sitting on top of a rocket fueled, armed, and ready to go, and their cockpit’s mission elapsed time clock began running as if it was a real launch. According to mission rules, command pilot Schirra was supposed to pull the D-ring between his legs to fire the ejection seats. If the Titan II had risen only a few inches and then fallen back on the pad, the vehicle would crumple and collapse, setting off a tremendous explosion. But, in an act of ultimate test-pilot cool, Schirra felt no lift and did nothing. Ejection, especially off the pad, was known to be very dangerous. The acceleration of the seats would subject them to 20 Gs—twenty times the force of gravity—and rocket them to a few hundred feet in altitude so that their parachutes would open in time, if they worked. Assuming the two survived, serious injury seemed likely. As Schirra later put it succinctly, if he had sensed motion, “it was death or the ejection seat.”

Sitting in the cockpit, Schirra and Stafford waited tensely as the launch team figured out how to back out of the dangerous situation. At one point, Schirra remarked: “We’re just sitting here breathing.” Eventually, the pad crew returned and got them out of the spacecraft. One of the Titan’s umbilical plugs, which carried electrical signals to the launch equipment, had prematurely fallen out, triggering a shutdown. During the subsequent evaluation, technicians noted that the thrust was already dying in one of the two engine chambers of the first stage. Eventually, someone found a dust plug mistakenly left in one of the lines of the gas generator that burned propellants to power the turbopumps on the main engines. If the plug hadn’t fallen out, the failing thrust would have triggered a shutdown—before liftoff, if they were lucky.

There was just enough time left in Gemini VII’s record-setting mission to make another attempt. The pad crew executed a four-day turnaround in three. On December 15, Wally Schirra and Tom Stafford finally got to fly. Later that day they met Frank Borman and Jim Lovell in orbit, carrying out what was indeed the first space rendezvous in history. Having achieved all objectives, Schirra and Stafford splashed down in the Atlantic the next day. Borman and Lovell had to endure two more tedious days in their tiny, crammed, smelly cockpit, landing near the same aircraft carrier, the USS Wasp, on December 18.

There was a coda to the close call on the twelfth. Thirteen-and-a-half months later, three of their colleagues, Gus Grissom, Ed White, and Roger Chaffee, would die in a launch-pad fire inside the Apollo 1 spacecraft on LC 34. To save weight, Mercury, Gemini, and Apollo spacecraft were designed to operate at a cabin pressure of 5.5 lbs. per square inch of pure oxygen in space. When the spacecraft were pressurized on the launch pad, however, they had to be a couple of pounds over atmospheric pressure, 14.7 lbs. per square inch, to keep the cabin in pure oxygen. As the fire demonstrated, one small spark in that high pressure could set off a raging inferno. Tom Stafford’s hindsight observation was that, after soaking in pure oxygen for a couple of hours, if they were to eject, they would have come rocketing out of the Gemini as two “Roman candles” with their spacesuits on fire. Whether that would have been true, we’ll never know. Instead, they carried out one of the most important feats in the space history.

Michael J. Neufeld is a senior curator in the Museum’s Space History Department and is responsible for Mercury and Gemini spacecraft, among other collections.