The immediate aftermath of a launch, Jack Albert said later, was normally something of an anticlimax. Except, that is, on 4 December 1965, when spirits remained high. Another Gemini would be despatched in just a few days’ time, and, judging from the minimal damage sustained by Pad 19, one major obstacle standing in the way of the joint mission had dissolved. The next day, the two stages of GLV-VI had been erected and by sundown the Gemini VI-A spacecraft was added. A computer problem quashed hopes to launch on 11 December, but the installation of a replacement part brightened prospects for Schirra and Stafford to fly a day later.

On the morning of the 12th, the astronauts awoke, showered, breakfasted and suited-up just as they had seven weeks earlier, albeit on this occasion Schirra dispensed with smoking a cigarette. Launch was scheduled for six seconds past 9:54 am and the countdown clock ticked perfectly toward an on-time liftoff. Precisely on cue, the Titan’s first-stage engines ignited with a familiar whine. Then, after less than 1.2 seconds, they shut down. Instantly, Schirra, his hand clasping the D-handle which would have fired his and Stafford’s ejection seats and boosted them to safety, faced a life-or-death decision. The mission clock on the instrument panel had started running, as it would in response to the vehicle lifting off, but Schirra could feel no movement in the rocket. If the Titan had climbed just a few centimetres from the pad at the instant of shutdown, there was a very real risk that its 150,000 kg of volatile propellants could explode in a holocaust, known, darkly, among the astronauts, as a Big Fucking Red Cloud (BFRC).

In his autobiography, Stafford remembered vividly the moment that the behemoth came alive and, just as vividly, the instant at which its roar ceased. ‘‘The sound of the engines died even though the clock started and the computer light came on, both indications that we had lifted off,’’ he wrote. ‘‘But I could feel that we hadn’t moved. More important, there was no word from [Capcom] Al Bean, confirming liftoff, which was critical.’’ In fact, it was the feeling of stillness in the

Titan that convinced Schirra not to risk ejecting. Kenneth Hecht, head of the Gemini escape and recovery office, was surprised that he did not eject, but in reality, neither Schirra nor Stafford had much confidence in the seats and, as test pilots, instinctively desired to remain with their ‘bird’ for as long as possible. Stafford felt that the 20 G acceleration of an ejection would have left him with, at best, a cricked neck for months. Moreover, there was a very real risk of death. ‘‘Given that we’d been soaking in pure oxygen for two hours,’’ Stafford wrote, ‘‘any spark, especially the ignition of an ejection seat rocket, would have set us on fire. We’d have been two Roman candles shooting off into the sand and palmetto trees.’’ Yet Schirra would not have put them in undue danger. ‘‘If that booster was about to blow,’’ he said, ‘‘if we really had a liftoff and settled back on the pad, there was no choice. It’s death or the ejection seat.’’

In emotionless tones, the unflappable Schirra reported that propellant pressures in the Titan were lowering and Martin’s test conductor, Frank Carey, responded in a similarly calm manner with ‘‘Hold kill’’, a missile-testing term denoting a shutdown. Although Schirra knew that the rocket had not left the pad and that the mission clock – which should have started at the instant the Titan began to climb – was wrong, his ‘gutsiness’ that morning would win him deserved praise from his fellow astronauts. Had he and Stafford ejected, the entire rendezvous would have been over. There would have been no way that Gemini VI-A could have been readied for another launch attempt in less than the six remaining days of Borman and Lovell’s mission. Moreover, with the increasing likelihood that another Agena-D would not be ready until the spring of 1966, the crucial step of proving rendezvous as a means of getting to the Moon would have been seriously jeopardised.

When the smoke had cleared, and after receiving assurances that the ejection seat pyrotechnics had been safed, Guenter Wendt and his team returned to the capsule to begin extracting the two disappointed astronauts. ‘‘It took 90 minutes to raise the erector and get us out, a lot longer than it should have,’’ wrote Stafford. ‘‘Although he had kind words for Guenter and the pad crew, Wally was furious.’’ The families of the two men were also understandably anxious and, from then onwards, it would become standard practice to have another astronaut present with them during a launch attempt. The day itself was already a bad one: a Cape Kennedy rescue helicopter had crashed in the nearby Banana River and Randy Lovelace – bane of the astronauts’ lives during their selection – and his wife had been killed in a private aircraft crash in Aspen, Colorado.

Later that same afternoon, President Johnson told Jim Webb that he was ‘‘greatly disturbed’’ by the abort, although he was assured that enough time remained to identify the Titan glitch, fix it and get Gemini VI-A into orbit before the end of Borman and Lovell’s mission. That glitch did not take long to find: an electrical tail plug had dropped prematurely from the base of the rocket and activated an airborne programmer – a clock in Gemini VI-A’s cockpit which should not have started until liftoff. The plug was supposed to require 18 kg of ‘pull’ in order to separate, but had rattled loose from its housing. Although it had been installed properly, tests revealed that some plugs did not fit as snugly as others and pulled out more easily.

Then, as engineers pored over engine trace data, it became clear to Ben Hohmann of the Aerospace Corporation that the Titan’s oxidiser pressure and overall thrust had begun to decline before the plug fell out. Subsequent analysis of oscilloscope wiggles identified a blockage in the gas generator and, eventually, an Aerojet technician found the answer: a thimble-sized dust cover had been accidentally left on its fuel inlet port during processing. Months earlier, when the engine was still at Martin’s plant in Baltimore, the gas generator had been removed for routine cleaning and when the check valve at its oxidiser inlet was detached, a plastic cover was installed to keep dirt out. As checkout of the engine proceeded, the dust cap was overlooked and forgotten. To be fair, its location would have been almost impossible to find. However, had the initial tail plug dropout not stopped the launch, the gas generator blockage certainly would have done. “It was serendipitous that we shut down,’’ said Joe Wambolt, then a Gemini propulsion engineer, in an interview published years later in Quest magazine, “because the other engine was not going to thrust.’’ In his autobiography, Wally Schirra wrote that, had he known of this ‘second’ brewing problem at the time, he probably would have chosen to fire the ejection seats.

By 13 December, the gas generator had been cleaned and replaced and the launch was provisionally targeted for the 16th, just two days before Borman and Lovell were due to return to Earth. However, Elliot See radioed the Gemini VII crew with the news that, barring any further problems, the 15th seemed a more likely launch date.

In addition to demonstrating the steely nerves of the Gemini VI-A crew – one of Schirra’s first messages had been ‘‘We’re just sittin’ here breathing’’ – the abort also verified, in the most dramatic manner possible, that the Titan’s malfunction detection system worked. Sensing no upward movement, it had correctly and automatically closed the valves to prevent more fuel entering the combustion chambers and had duly shut down the engines. Catastrophe had been averted. In the Soviet Union, Nikolai Kamanin, fuming over his nation’s failure to catch up with the Americans, admitted in his diary that, despite the abort, a successful Gemini rendezvous was only a matter of days away. Indeed it was.