Falcon 9· guided tour

Liquid Oxygen Tank

the cold half

This tank is full of liquid oxygen — that is the same oxygen you breathe, made so cold it turns into a pale blue liquid. Fire needs oxygen, and there is none in space, so the rocket carries its own.

Temperature
about −207 °C
Loading starts
T−35 min
Why so cold
Denser = more fuel
How it works

SpaceX chills it even colder than it has to be. Colder liquid is denser, which means more of it squeezes into the same tank — and more fuel means the rocket can go further. That is why loading only starts 35 minutes before launch: any earlier and it would warm up.

For the grown-up

Falcon 9 uses sub-cooled LOX at roughly 66 K, below the 90 K boiling point, for a density gain of about 8%. This late densified load is the reason the vehicle cannot hold at T−0 for long and why crewed missions use load-and-go fuelling.

Falcon 9 countdown timeline