Project Gemini

Gemini was the bridge. Mercury proved you could survive space. Apollo required that you could navigate it, live in it for two weeks, and perform precise maneuvers around another celestial body. Gemini built those skills flight by flight, frequently nearly killing someone in the process. Gemini 3 proved the capsule could maneuver on orbit. Gemini 4 gave Ed White the first American EVA — 23 minutes outside the vehicle, tethered by an umbilical, during which he reported that returning to the capsule was the saddest thing he had ever done. Gemini 8 achieved the first orbital docking, immediately followed by a thruster malfunction that sent the joined vehicles into a roll approaching one revolution per second; Neil Armstrong killed the main thruster system and brought the spacecraft home. Gemini 12 had Buzz Aldrin complete three EVAs totaling five and a half hours, demonstrating that suited work in vacuum was possible if the tools and handholds were designed correctly. Gemini 7 stayed up for fourteen days — longer than a Moon mission would require — to answer the question of whether the human body could tolerate it. Frank Borman and Jim Lovell came back functional. The bridge was built.