On January 27, 1967, a fire broke out inside the Apollo 1 spacecraft during a pre-launch test, killing astronauts Gus Grissom, Edward White, and Roger B. Chaffee. The fire, which was caused by an electrical spark in a pure oxygen environment, led to the cancellation of the Apollo 1 mission. The tragedy prompted significant changes in the design of the spacecraft and NASAs safety protocols. The event remains one of the most devastating losses in the history of space exploration.