Gemini 10

Gemini 10, also known as Gemini X, was a crewed NASA mission that launched in 1966. It marked the eighth crewed flight of the Gemini program, the sixteenth crewed American spaceflight, and the twenty-fourth spaceflight overall. Command pilot John Young and pilot Michael Collins flew the mission, and Collins performed one spacewalk.

The mission had several key goals: rendezvous and dock with an Agena Target Vehicle, perform extravehicular activity, and also dock with the Agena left behind by the earlier Gemini 8 mission. Since that Agena’s battery had failed months prior, approaching it would test the ability to rendezvous with a passive, unpowered object. Gemini 10 was not the first mission to fire an Agena’s own rocket—Gemini 8 and Gemini 9 had done so before—but the crew did use their Agena's engine to reach higher orbits. The flight confirmed that radiation at high altitude was not a problem. After docking with their own Agena in low orbit, Young and Collins used its engine to climb to 412.4 nautical miles (763.8 km). They then left that Agena and performed the program’s first double rendezvous, meeting the derelict Gemini 8 Agena without radar, using only visual cues.

During the subsequent spacewalk, Collins tethered himself to the Gemini and moved over to the dormant Agena, becoming the first person to meet another spacecraft in orbit. He retrieved a cosmic dust-collecting panel from its side. While focusing on keeping his tether clear, his Hasselblad camera slipped away, so he could not take photos during the EVA.

The launch went smoothly for the Agena, and Gemini 10 lifted off 100 minutes later, entering an initial orbit of 86.3 by 145.2 nautical miles, about 970 nautical miles behind the target. Two anomalies occurred during launch: a propellant fill umbilical snagged and remained attached to the second stage, and the first stage oxidizer tank dome ruptured after staging, releasing a cloud of nitrogen tetroxide. Review of other Titan II launches found at least seven similar ruptures, likely from debris or exhaust, but NASA concluded it posed no safety risk and took no action.

For the first rendezvous, Collins struggled with the sextant, mistaking airglow for the horizon. He switched to another instrument, but its small field of view made it impractical. Ground computers provided backup. A series of burns put them into a 143-by-147-nautical-mile o