page_title: Gemini 8
section_title: Emergency
hierarchical_section_title: Gemini 8 / Flight / Emergency
caption_attribution_description: Deutsch: Prinzipskizze des RCS der Gemini-Kapsel, Juni 1962English: The general arrangement of liquid rocket systems (OAMS and RCS) in the Gemini spacecraft. The insert displays a typical thrust chamber assembly.)
context_page_description: Gemini 8 was the sixth crewed spaceflight in NASA's Gemini program, launched March 16, 1966. It was the twelfth crewed American flight and the twenty-second crewed spaceflight of all time. The mission conducted the first docking of two spacecraft in orbit, but suffered the first critical in-space system failure of a U.S. spacecraft which threatened the lives of the astronauts and required an immediate abort of the mission. The crew was returned to Earth safely.
  Command pilot Neil Armstrong's flight marked the second time a U.S. civilian flew into space, and the first time a U.S. civilian flew into orbit. Armstrong had resigned his commission in the United States Naval Reserve in 1960. The Soviet Union had launched the first civilian, Valentina Tereshkova, aboard Vostok 6 on June 16, 1963.
context_section_description: There was some suspicion on the ground that the Agena's attitude control system was malfunctioning and might not have the correct program stored in it. This suspicion was found to be incorrect. Shortly before radio blackout, Mission Control cautioned the astronauts to immediately abort the docking if any abnormalities occurred with the Agena.
  After the Agena began execution of its stored command program, which instructed the Agena to turn the combined spacecraft 90° to the right, Scott noticed that they were rolling. Armstrong used the Gemini's OAMS thrusters to stop the roll, but after it stopped, it immediately started again. Gemini 8 was out of range of ground communications at this time.
  Armstrong reported that the OAMS fuel had dropped to 30%, indicating that the problem could be on their own spacecraft. With concern that the high rate of rotation might damage one or both spacecraft or even cause the propellant-heavy Agena to rupture or explode, the crew decided to undock from the Agena so they could analyze the situation. Scott switched the Agena control back to ground command, while Armstrong struggled to stabilize the combined vehicle enough to permit undocking. Scott then hit the undock button, and Armstrong fired a long burst of translation thrusters to back away from the Agena. Without the added mass of the Agena, Gemini started rotating more rapidly.
  The astronauts realized that the problem was on the Gemini. By now the tumble rate had reached 296 degrees per second and Armstrong decided to shut down the OAMS and use the Reentry Control System (RCS) thrusters, located on the Gemini's nose, to stop the tumble.  Scott later praised Armstrong's actions as their spacecraft spun: "The guy was brilliant. He knew the system so well. He found the solution, he activated the solution, under extreme circumstances ... it was my lucky day to be flying with him." The spacecraft came in range of the ground communications ship Coastal Sentry Quebec. After steadying the spacecraft, the crew tested each OAMS thruster in turn and found that Number 8 had stuck on. Almost 75% of the reentry maneuvering fuel had been used to stop the tumble, and mission rules dictated that the flight be aborted once the Reentry Control System was fired for any reason. Gemini 8 immediately prepared for an emergency landing.
caption: Location of Gemini OAMS and Reentry (mislabeled "Reaction") Control System thrusters
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