Gemini 5 tested whether astronauts and spacecraft systems could endure the roughly eight-day duration needed for a future lunar mission, using fuel cells for power for the first time. The mission suffered pressure problems that curtailed some experiments, but it proved NASA could sustain long-duration flight, a critical milestone en route to Apollo.
Cooper and Conrad carried a small sign into orbit reading "Eight Days or Bust," a nod to the mission's grueling endurance test and a joke on the Western pioneer spirit. The flight came close to being cut short when a fuel cell oxygen pressure problem forced mission control to power down non-essential systems for nearly two days.
The cramped Gemini capsule, barely larger than the front seat of a small car, left both men aching and stiff by splashdown in the Atlantic. Their endurance answered a fundamental question hanging over Apollo planning: could human bodies and machines really survive over a week in space without catastrophic breakdown?
The mission also quietly returned to Earth 100 miles off target after a computer error, landing the crew in rough seas well short of their recovery ship, a minor embarrassment that nonetheless didn't diminish the mission's technical triumph.
Key people: Gordon Cooper, Charles Conrad