This article was originally published in 2013.
In NASA's early years, the agency learned by doing; developing tests and procedures as programs wore on. One test developed and used in the Mercury program was the "plugs-out test," a prelaunch test of the spacecrafts systems through a simulated countdown on launch. It was never considered a dangerous test, but on Jan. 27, 1967, Apollo 1′s plugs-out test claimed the lives of the crew.
Typical for the first flight of a new program, the plan for Apollo 1 was a simple shakedown cruise. The crew – Mercury astronaut Gus Grissom, Gemini veteran Ed White, and rookie Roger Chaffee – would take just the Command and Service Module (CSM) into Earth orbit.
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The plugs-out test started out routinely with the flight-ready spacecraft mounted on its unfueled Saturn IB rocket. The umbilical power cords that supplied power were removed - the plugs were out - putting the spacecraft on its internal batteries and the crew cabin was pressurized with 16.7 pounds per square inch of pure oxygen. As the crew entered the spacecraft around 1pm that afternoon, a full launch-day staff of engineers in mission control took their positions for the test. There was also a staff of men in the White Room; the room that gave the astronauts passage to the spacecraft remained attached to the vehicle.