[smithian]

The tank holds liquid oxygen, which is the oxidizer for the engine. Since oxygen is a gas at the ambient Florida temperature, it boils off all the time. A it boils off, the gas is released into the atmosphere, and the tank is replenished.

[excuse-me]

Strictly speaking the white `gas` is water from the delightfully humid Florida climate condensing in the presence of the extremely cold Oxygen boil off.