Any engine needs air for the fuel to burn. It’s the burning fuel that causes an explosive reaction, and when that reaction is directed through an engine bell it turns into the thrust a rocket needs to get off the ground. But because a rocket passes through the atmosphere so quickly, it can’t use atmospheric oxygen for this reaction. That’s why rockets carry their own oxidizer, but in a liquid rather than a gaseous form. Liquid oxygen, or LOX, is super-cooled oxygen that remains in a liquid state at temperatures below -298 degrees Fahrenheit (which is about -183 degrees Celsius).
The GIF shows the inside of a LOX tank, likely on the Falcon 9’s second stage.
The footage starts with the LOX resting at the base of its tank. That’s because the rocket’s second stage is firing. According to the launch video, the first shot of the LOX tank appears when the rocket is traveling at around 2.4 miles per second (or 4 km/s). With the rocket moving so fast and accelerating, it’s pulling enough g-forces to push the fuel against the bottom of the tank. It’s like standing in an elevator that suddenly shoots up really quickly — the g-forces would knock you to the floor. If you had a bottle of water in your hand, the water would also be forced to the base of the bottle.
Then we see a change in the fuel tank when the second stage shuts down. At this point in the flight, the remaining pieces of the rocket are in orbit, so the g-forces of launch have dropped off to nothing. With no g-forces keeping the fuel against the bottom of the tank, it starts to float. If the elevator you were in started suddenly falling, you and the water in your bottle would float upwards thanks to the sudden loss of g-forces. Of course, It probably wouldn’t look this dang cool, or spontaneously produce a Kurt Russel.
You can watch the whole video of SpaceX’s most recent Falcon 9 launch online, which includes shots from inside the LOX tank, here.
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