Fifty years later, Apollo 9 stands as a pioneering flight that proved the competence of the entire Apollo hardware, including the uniquely designed lunar lander and updated Apollo spacesuit that would become the life support system sustaining astronauts on the surface of the Moon.

McDivitt’s first spaceflight took place in the cramped seat of a two-man Gemini capsule. “The Gemini was very, very tight. It was extremely tight — you couldn’t stretch all the way out. You were in the seat, and that’s where you stayed,” he says. His was the second manned Gemini flight, following Gemini III, which had lasted just under five hours. Gemini IV drastically upped the ante, keeping McDivitt and White circling Earth for four days.

Apollo 9 lasted more than twice as long as Gemini IV, and the three-man crew enjoyed a relatively roomier home away from home. “In Apollo, we’d get up and float around, so it was much more comfortable. It was a much bigger spacecraft,” McDivitt says. The spacecraft was also “quite a lot more complicated,” he adds, as was the mission to test it.

“Gemini IV was a medical experiment. [No American] had been up in space for more than a day, and we were going up there for four days, and there was a lot of medical monitoring that happened with us. Apollo 9 was an engineering test flight, so we operated all the systems, checked everything out, and it was much more complicated.”