Gemini VII was a mission of endurance — a grueling 14-day marathon in a capsule the size of the front seat of a Volkswagen Beetle. The primary objective was to prove that humans could survive and function in space long enough for a round trip to the Moon, which NASA estimated would take about two weeks. Launched on December 4, 1965, astronauts Frank Borman and James Lovell spent nearly 14 days orbiting Earth, breaking the Soviet Union’s endurance record of nearly five days set by Vostok 5 in 1963.

The crew conducted 20 medical experiments during the mission, monitoring everything from cardiovascular health and bone density to calcium loss and visual acuity. To conserve fuel and consumables for such a long flight, the astronauts tested lightweight “soft suits” — a departure from the rigid pressure suits worn on earlier missions. They were allowed to remove their suits for portions of the flight, making the cramped cabin somewhat more bearable, though both men suffered from the confinement by mission’s end.

On Day 11, the mission took on an additional historic role when Gemini VI-A, carrying astronauts Wally Schirra and Tom Stafford, launched and performed the first rendezvous between two crewed spacecraft. The two Gemini capsules flew in formation for over five hours, closing to within one foot of each other. This station-keeping exercise proved the rendezvous techniques essential for Apollo lunar missions, where the Command Module would need to find and dock with the Lunar Module after ascending from the Moon’s surface.

Gemini VII splashed down in the Atlantic Ocean on December 18, 1965 and was recovered by the USS Wasp. The crew was tired and stiff but in good health, proving that the human body could endure the duration of a lunar mission. Both Borman and Lovell would go on to fly Apollo missions — Borman commanding Apollo 8, the first crewed flight to the Moon, and Lovell serving on Apollo 8 and commanding the ill-fated Apollo 13.