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It was while Gemini 8 was docked with the Agena that the joined vehicles suddenly began to tumble as if some attitude-control thrusters had gone amuck. Since the Gemini's thrusters were turned off and the Agena's could be seen firing, Armstrong assumed that it was the Agena controls that were at fault. After cutting off the Agena thrusters, he struggled for 10 minutes to bring the joined ships under control. Then he undocked, still unaware that the real trouble was a short circuit in Gemini's electronic control system that had caused its No. 8 thruster to begin firing intermittently. The Agena's thrusters—weaker than Gemini's—had been firing automatically in a futile attempt to stabilize the two orbiting spacecraft. Once cut loose from the Agena's stabilizing thrusters, the Gemini immediately increased its roll rate under the continuing push of No. 8, which now had even more effect because it was no longer turning the combined mass of the two ships, only the Gemini itself.
Re-Entry Endangered. As the roll rate increased to a terrifying one revolution per second, Armstrong realized that Gemini was at fault; he quickly threw circuit breakers that cut off the flow of fuel and oxidizer to all of the attitude thrusters, including No. 8. The roll—with no friction or counterfiring thruster to stop it—continued undiminished. It was at this point that Armstrong resorted to the independent reentry rocket system to bring Gemini back under control. Once the vital re entry control fuel had been tapped, however, Gemini's ability to make a successful re-entry was endangered and it was necessary to return to earth as quickly as possible.
Had Gemini been within range of a tracking station when trouble began, ground controllers could have immediately diagnosed the problem and told Armstrong how to solve it. But the spaceship was in a dead zone between stations, and in all its maze of instruments, none was designed to report when thrusters were firing. Though the short circuit might have required early termination of the mission anyway, such on-board instrumentation would have enabled Armstrong to bring Gemini under control much more quickly.
Coriolis & Nystagmus. As it was, according to NASA's Dr. Charles Berry, both Armstrong and Scott began to experience two conditions brought on by their rapid rotation: 1) the coriolis effect, a complete loss of orientation caused by the effects of rotation on the inner ear, and 2) nystagmus, an involuntary rhythmic motion of the eyes. Had either or both those effects be come severe enough, the two astronauts would have been unable to see or operate their controls. They might well have perished.
The malfunction might have been even more serious had it occurred when Scott was taking his scheduled walk in space. Some experts believe that outside the spacecraft Scott would have quickly spotted the firing thruster and warned Armstrong in time for him to shut off its propellant. Others are convinced that the rolling Gemini would have whirled Scott around in space at the end of his 75-ft. tether, eventually slamming him against the spacecraft and probably causing fatal injuries.