Before becoming the first man to set foot on the moon, Neil Armstrong played another space race milestone 55 years ago: the first spacecraft engagement outside of Earth.

Armstrong and David Scott were launched in the Gemini 8 spacecraft aboard a Titan II rocket from Cape Canaveral on March 16, 1966, about three hours after their target, the unmanned Agena spacecraft, lifted off on an Atlas rocket.

The Gemini 8 mission was scheduled to last three days, during which Armstrong and Scott would rendezvous with the Agena-D target and conduct four docking tests. The flight was supposed to build on the success of the crews of the Gemini 6 and Gemini 7 spacecraft, which in December 1965 made the first approach between two manned spacecraft.

After six hours of flight, completing five orbits and nine approach maneuvers, Armstrong closed the gap between Gemini and Agena and proceeded to dock. Within minutes, the Agena connection latches closed and a green light indicated a successful connection.

Soon the problems started. As the Agena spacecraft began to execute its orientation control program, which maneuvered the attached ships to turn 90 degrees to the right, Scott realized that Gemini 8 was already spinning. Armstrong used his ship’s thrusters to stop the rotation, but once stopped, the process immediately started again.

Armstrong reported that the fuel in the propulsion plant had dropped to 30%, indicating that the problem may have originated in his own spacecraft. They decided to disconnect from Agena to analyze the situation. Scott handed over control of the Agena to ground command while Armstrong attempted to stabilize the combined vehicle enough for it to be undocked. Scott then pressed the disconnect button and Armstrong fired a long burst of transmitters to break away from the Agena.

Without Agena’s added mass, Gemini’s spin rate began to accelerate rapidly, reaching one revolution per second, causing the astronauts’ vision to blur and putting them in danger of losing consciousness. Armstrong decided to shut down the OAMS propulsion system and used the Re-entry Control System (RCS) engines to stop the spin.

After stabilizing the spacecraft, they checked each OAMS engine one by one and it was found that number 8 was stuck. Almost 75 percent of the reentry fuel was used to stop the spin, and mission rules required the flight to be aborted if RCS was used for any reason. Gemini 8 immediately prepared for an emergency landing.

It was decided to allow the ship to complete one more orbit so that it could land in a location that could be reached by the evacuation force. The original plan called for Gemini 8 to land in the Atlantic, but it ended up in the Pacific Ocean, 800 kilometers east of Okinawa and 1,000 kilometers south of Yokosuka, Japan. The astronauts were safely extracted.