Gemini 8

This became the prime crew on Gemini 11.

• Walter Cunningham (Cape CAPCOM)
• James A. Lovell (Houston CAPCOM)

March 16, 1966

• Docked: 23:14 UTC
• Undocked: ~23:45 UTC

The Agena Target Vehicle is launched into space on an Atlas rocket in preparation for Gemini 8

Five months earlier, NASA had launched an Agena Target Vehicle for Gemini 6, but the Atlas-Agena launch failed when the Agena's engine exploded during orbital injection and the mission had to be rescheduled. The next attempt succeeded. Everything worked perfectly; the Agena put itself into a 161-nautical-mile (298 km) circular orbit and oriented itself to the correct attitude for the docking.

A Gemini-Titan launch vehicle lifts Gemini 8 into orbit, March 16, 1966.

The Gemini spacecraft was launched into an 86-by-147-nautical-mile (159 by 272 km) orbit by a modified Titan II on March 16, 1966 (coincidentally the 40th anniversary of the launch of the world's first liquid-fuelled rocket by Dr. Robert H. Goddard), at 10:41:02 a.m. EST. Gemini 8's launch was nominal and no significant anomalies occurred with either the Titan II or the spacecraft.

The Agena Target Vehicle as seen from Gemini 8 during rendezvous.

Their first course adjustment was made at one hour and 34 minutes into the mission, when the astronauts lowered their apogee slightly with a five-second Orbit Attitude and Maneuvering System (OAMS) thruster burn. The second adjustment was made near apogee of the second orbit, and raised both the apogee and perigee by adding 49 feet per second (15 m/s) to their speed. The third adjustment was made over the Pacific Ocean, a southward orbital plane change, made with a 59 feet per second (18 m/s) sideways thruster burn. When they were over Mexico, Jim Lovell, the Houston capsule communicator, told them they needed one last correction, a 2.6 feet per second (0.79 m/s) speed addition.

The rendezvous radar acquired the Agena Target Vehicle at a distance of 179 nautical miles (332 km). At 3 hours, 48 minutes and 10 seconds into the mission they performed another burn that put them in a circular orbit 15 nautical miles (28 km) below the Agena. They first sighted it when they were 76 nautical miles (141 km) away, and at 55 nautical miles (102 km) they gave the computer automatic control.

After several small burns they were 151 feet (46 m) away and with no relative velocity. After 30 minutes of visually inspecting the Agena to make sure that it had not been damaged by the launch, they were given the go for docking. Armstrong started to move towards the Agena at 3.15 inches (8 centimeters) per second. In a matter of minutes, the Agena's docking latches clicked and a green light indicated that the docking had been successfully completed. "Flight, we are docked! Yes, it's really a smoothie," Scott radioed to the ground.

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.

Location of Gemini OAMS and Reentry (mislabeled "Reaction") Control System thrusters

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. From start to finish the incident lasted nearly 30 minutes.[9]

NASA turned off the squawk box at Armstrong's home, alarming his wife. 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."[10] 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,[11] 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.

Scott (L) and Armstrong (R) await USS Leonard F. Mason

It was decided to let the spacecraft reenter one orbit later so that it could land in a place that could be reached by secondary recovery forces. The original plan was for Gemini 8 to land in the Atlantic, but that was supposed to be three days later. USS Leonard F. Mason started to steam towards the new landing site 800 kilometers (430 nmi; 500 mi) east of Okinawa and 1,000 kilometers (540 nmi; 620 mi) south of Yokosuka, Japan.

Reentry took place over China, out of range of NASA tracking stations.

Planes were also dispatched, and U.S. Air Force pilot Les Schneider spotted the spacecraft as it descended precisely on time and on target. Three pararescuers jumped from their C-54 and attached a flotation collar to the capsule.[12]

All of the pararescuers and astronauts suffered from seasickness. Three hours after splashdown, the Leonard F. Mason had both men and the spacecraft on board. The astronauts were exhausted, but had otherwise survived the flight and their time on the water in good condition. They were briefly checked and slept for nine hours.

The next morning, the ship docked at the port of Naha. Fellow astronaut Walter Schirra and other NASA officials flew in to greet them before the astronauts were summoned back to the ship for medical tests and debriefing. After release, they were brought by limousine to waiting helicopters where they flew to Kadena Air Base and then on to Florida on a C-135.[13]

Upon the return, the spacecraft was covered with a tarp. As part of the investigation into the mishap, ground controllers tested the Agena stage for the next several days by ordering it to perform various in-orbit maneuvers until exhausting its propellant and electrical power.

Four months later, the crew of Gemini 10 rendezvoused with the inert Agena and astronaut Michael Collins retrieved its micrometeorite collector.

• Gatland, Kenneth (1976). Manned Spacecraft (Second ed.). New York: Macmillan.
• Hacker, Barton C.; Grimwood, James M. (1977). On the Shoulders of Titans: A History of Project Gemini. NASA SP-4203. Washington, D.C.: National Aeronautics and Space Administration. Archived from the original on 2010-01-13. Retrieved 2015-01-02.
• NASA (March 11, 1966). "Gemini 8 press kit" (PDF) (Press release). NASA. Archived from the original (PDF) on February 27, 2012. Retrieved February 27, 2015.

 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.