Gemini 4 was America's first multi-day spaceflight

Gemini IV, launched from Cape Kennedy on June 3, 1965, was America’s first multi-day spaceflight: James McDivitt and Edward White stayed aloft 4 days, 1 hour and 56 minutes, circling Earth 62 times before splashing down in the Atlantic on June 7.

The flight is sometimes described as a space endurance record, but it was a US record, not a world record. Before June 1965 the longest American flight was Gordon Cooper’s 34 hours on Mercury 9 in May 1963. A month after Cooper, Soviet cosmonaut Valery Bykovsky spent five days in orbit aboard Vostok 5. Gemini IV’s roughly 98 hours left the Soviet mark standing; the United States overtook it only in August 1965, when the eight-day Gemini V doubled the record Gemini IV had just set.

Duration was the point. NASA’s main objective was to test how the crew and capsule, and their work schedules and flight plans, held up over an extended time in space, a prerequisite for a week-long trip to the Moon and back. The crew also ran 11 experiments, including star sightings with a sextant to test a navigation technique for Apollo.

Gemini IV was the first flight followed from the new Mission Control at the Manned Spacecraft Center in Houston; every earlier Mercury and Gemini mission had been controlled from the Cape.

Not every goal was met. The first task in orbit was to rendezvous with the rocket’s spent second stage, but with only two running lights on the stage and no radar to judge range, the chase proved harder than expected, and McDivitt dropped it to protect the spacewalk. White’s 23-minute excursion, which he called “just tremendous,” became the image everyone remembers. The four days of endurance mattered as much for Apollo.