In March 1966, Neil Armstrong completed the first docking in space, then a stuck thruster sent Gemini 8 spinning once every second — fast enough to blur the astronauts’ vision and threaten unconsciousness — forcing Armstrong to shut down the main control system and save both men with the re-entry thrusters three years before he flew to the Moon

On 16 March 1966, Neil Armstrong did something no one had done before: he flew one spacecraft up to another and joined them together, the first docking in the history of spaceflight. Within half an hour that success had turned into the most dangerous few minutes any American crew had yet faced in orbit, with the capsule spinning fast enough to blur the two astronauts’ vision and push them towards blacking out. How Armstrong got out of it is part of why he was later trusted with the first landing on the Moon.

The docking that had to work

Gemini VIII carried Armstrong as command pilot and David Scott as pilot. Their central task was the docking, a manoeuvre that had never been attempted and that the later Apollo missions would depend on completely, since going to the Moon would require joining and separating spacecraft far from home.

They flew up to an uncrewed target vehicle called the Agena, closed the last distance carefully, and locked the two craft together. It worked cleanly. For a short while the mission was a straightforward triumph, the hardest new task on the flight plan already behind them.

When it started to go wrong

About 27 minutes after docking, the joined vehicles began to roll and yaw on their own. Armstrong used the Gemini’s thrusters to stop the motion, and it steadied, but as soon as he let go it began again and grew worse.

With no way yet to see the cause, the crew reasonably suspected the Agena, the unfamiliar vehicle they had just attached themselves to. So they undocked and backed away from it. That decision was sound on the information they had, and it made things worse, because the fault was not in the Agena at all. It was in their own spacecraft.

The spin

One of the Gemini’s small manoeuvring thrusters, number 8, had short-circuited and stuck open, firing continuously whether the crew commanded it or not. While the heavy Agena was still attached it had partly masked the problem. Freed of that mass, the lighter Gemini capsule spun up quickly, and the rate climbed until the craft was turning at close to one full revolution every second.

At that speed the situation was no longer just a control problem, it was a medical one. As the spin approached a rotation a second, the astronauts’ vision began to blur, and the next stage, if it continued, was disorientation and loss of consciousness. A crew that blacked out would have no way to recover the spacecraft at all. Armstrong had a shrinking window in which to act while he could still see and think clearly.

The decision that saved them

Armstrong’s move was to give up on finding which thruster had failed and instead shut the whole system down. He switched off the entire Orbit Attitude and Manoeuvring System, the main set of thrusters used for moving and steering in orbit, killing power to the stuck thruster along with all the others.

Then, with that system dead, he brought in the one that was never meant for this job. The Re-entry Control System was a separate set of thrusters in the nose of the capsule, kept in reserve for guiding the craft home through the atmosphere. Armstrong used it to fight the spin, and slowly brought the tumbling under control until the Gemini was steady again. Stopping the spin cost him nearly three quarters of the re-entry system’s propellant.

The price of the fix

Saving the spacecraft meant ending the mission. The rules were firm: once the re-entry control system had been fired, the flight had to come down at the next opportunity, because there was no longer enough of that propellant left to risk staying in orbit. Ground controllers ordered an emergency return, and Gemini VIII splashed down in the western Pacific during its seventh orbit, only about ten and a half hours after launch. A flight planned to last three days was over in less than half of one, but both men were alive and unhurt.

Why it is remembered

Gemini VIII still counts as the mission that achieved the first docking, the step the whole Apollo programme was built on. But it is remembered at least as much for the emergency that followed, and for how it was handled. Faced with a spacecraft spinning towards the edge of what its crew could physically withstand, Armstrong diagnosed enough of the problem to act, chose a drastic fix, and carried it out in the time he had.

It was three years before he commanded Apollo 11 and stepped onto the Moon. The steadiness that made him the obvious choice for that flight was not a matter of reputation. Some of it had already been demonstrated, in orbit, in the few minutes when Gemini VIII was turning once a second and running out of time.