**Warning: Contains audio of three people trapped inside a capsule on fire**
NASA calls the Apollo 1 mission 'one of the worst tragedies in the history of spaceflight'.
On 27 January, 1967, a group of astronauts boarded the Apollo 1 spacecraft. They were undertaking a pre-flight test, ahead of what was set to be the first low Earth orbital test using the using the Apollo 1 spacecraft.
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The spacecraft was set to take off from Cape Kennedy, Florida on February 21 - but things didn't go to plan during the test.
A devastating fire broke out while three crew members were inside, and audio has been released of their final moments.
Gus Grissom, Ed White, and Roger Chaffee were taking part in the test, with NASA saying: 'They were taking part in a "plugs-out" test, in which the Command Module was mounted on the Saturn 1B on the launch pad just as it would be for the actual launch, but the Saturn 1B was not fueled. The plan was to go through an entire countdown sequence.'
The test was initially delayed due to 'a number of minor problems', and then a power surge was recorded, with NASA saying that was 'possibly indicating a short circuit'.
NASA continues: 'The cockpit recording is difficult to interpret in places but a few seconds later one of the astronauts (probably Chaffee) is heard to say what sounds like "Flames!". Two seconds after that White was heard to say, "We've got a fire in the cockpit".'
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The recording is from a microphone worn by one of the astronauts and you can hear the astronauts realizing there's a fire.
A clip of the audio has been posted to X (formerly known as Twitter), by @Morbidful.
The astronauts can be heard shouting, before the audio cuts out - NASA said crew communication ended 17 seconds after the first indication of fire.
The cabin was filled with pure oxygen, meaning fire spread incredibly quickly - in a matter of seconds. The three astronauts lost their lives in the blaze, as it reportedly would have taken at least 90 seconds to open the hatch, which was closed by a number of latches and can only be opened from the outside. Eventually, it was opened around five minutes after the fire started.
The Apollo program was paused while the accident was investigated. It was found that the fire was likely caused by a short circuit from a bundle of wires.
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Many changes were subsequently made in the Apollo program - including using a nitrogen-oxygen mixture instead of pure oxygen, and installing a hatch that could also be opened from the inside.
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