Spinning Out of Control: Gemini VIII’s Near-Disaster

Fifty-five years ago, on March 16, 1966, the Gemini VIII astronauts made the world’s first space docking, quickly followed by the first life-threatening, in-flight emergency in the short history of the U.S. human spaceflight program. Gemini VIII, joined to its Agena target vehicle, began spinning and gyrating; when the astronauts undocked, Gemini’s rotation accelerated to the point where the crew could black out and die.

Neil Armstrong led the mission, which was to demonstrate space docking, a technique essential to the Apollo lunar landing program. Forty months later, he would become the first human to set foot on the Moon as commander of Apollo 11. His Gemini crewmate was David Scott, who would be the command module pilot of Apollo 9 and the commander of Apollo 15, the first lunar landing to carry a roving vehicle. Their cool handling of the Gemini VIII crisis ensured their leading roles in the Apollo program.

I recently wrote about the scary pad shutdown of Gemini VI-A on December 12, 1965, followed by the successful launch and rendezvous with Gemini VII three days later. Gemini VIII’s primary objective was to accomplish what Gemini VI-A could not do: dock with an Agena, a rocket stage boosted by an Atlas Intercontinental Ballistic Missile (ICBM). The uncrewed Atlas-Agena Wally Schirra and Tom Stafford were to dock with had blown up during launch on its Atlas booster the preceding October 25, necessitating the alternate plan for their mission. On Gemini VIII, Armstrong and Scott’s secondary objective was to gain more experience with “extravehicular activity” (EVA), another technique crucial to Apollo. Scott was to make the second spacewalk in the U.S. program, after Ed White’s on Gemini IV in June 1965, during a flight lasting three days.

At 10:00 am on March 16, the mission’s Atlas-Agena lifted off from Pad 14 at Cape Canaveral Air Force Station in Florida and successfully orbited the Agena. An hour and forty-one minutes later, after it had made one circuit and passed over Florida, Armstrong and Scott’s Gemini-Titan II rocket ascended from Pad 19 to give chase. Five minutes later, after experiencing the high G-forces of riding America’s second-generation ICBM, the Titan II, the two were in orbit. In Gemini terminology, they were to make an “M=4 rendezvous”—catch-up to the Agena in four orbits, about six hours. Everything went smoothly and at 6:33 mission elapsed time, Armstrong and Scott docked.

Twenty-seven minutes later, as the Agena was executing a planned maneuver to turn the combined spacecraft 90 degrees, Scott noticed that they were also rolling. Armstrong used the Gemini’s thrusters to stop the roll, but it immediately started again and began to get worse, a combined roll and tumble. Out of touch with Houston controllers on the far side of the world, far from any tracking stations, Armstrong struggled to gain control, to no avail. Soon they began to gyrate at rates that made seeing the instrument panel difficult. The two were afraid the Agena might break apart and blow up. Believing that an attitude-control failure on the docking target was likely, they decided to undock. Scott had a small panel that allowed him to control the Agena; he reset it to ground control and hit the undock button. Away from the target vehicle, Gemini VIII began to roll even more violently. It became obvious that the problem was a stuck thruster in the Orbital Attitude and Maneuvering System (OAMS) on the white adapter module of the Armstrong and Scott’s spacecraft. Unable to turn off individual thrusters, and in danger of losing consciousness from the ever-accelerating rotation, Armstrong turned off the OAMS and activated the Reentry Control System (RCS), two rings of thruster rockets around the nose. After using three-quarters of their RCS propellants, he stopped the spin. The RCS thrusters were needed after the retrorockets were fired and the adapter separated, so mission rules dictated an immediate return to Earth. Armstrong knew what that decision implied, but had no choice. Scott later said: "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." (See the Smithsonian Channel video about the crisis; it is also depicted in the Neil Armstrong biopic First Man.)

By the time they got back in touch with Mission Control via a tracking ship in the Pacific, the crisis was over. Houston allowed them to stay up for one more orbit so Armstrong and Scott could get to a contingency splashdown zone. An hour –and –a half later, they reentered over Communist China, which made them nervous, and landed right in the middle of the target area 600 miles east of Okinawa island, south of Japan. The mission lasted 10 hours and 41 minutes. An Air Force Rescue C-54 aircraft saw them parachuting to the ocean and dropped three pararescue divers to install a flotation collar around the spacecraft. Then they waited three hours for the Navy destroyer USS Leonard F. Mason to arrive. It had been steaming at full speed to get to the landing zone.

Subsequent investigation showed that OAMS thruster number 8 had short-circuited, opening the valves to the two liquid propellants, which ignited on contact, as intended. Since the adapter module had been jettisoned before reentry, the errant engine could not be recovered and studied, so the investigators depended on instrumentation recordings. From Gemini IX onward, the astronauts had circuit breakers to turn off individual groups of thrusters, allowing them to isolate a potential problem, although thanks to modifications to the thrusters, the problem never happened again. One lesson NASA could not learn from the mission was the challenge of doing any work during EVA, because Scott lost his chance to go outside. The next spacewalk, by Eugene Cernan on Gemini IX, was even more ambitious in the goals and would prove to be quite dangerous, in part because of the missing experience on Gemini VIII. But Armstrong and Scott’s mission should be remembered for what they did accomplish: the first space docking in history.

Michael J. Neufeld is a senior curator in the Museum’s Space History Department and is responsible for Mercury and Gemini spacecraft, among other collections.