system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the white stuff (I assume it's ice) that I always see falling off of space shuttles at take off and what does it do?
gpt
It's ice.  It forms on the fuel tanks becauce the fuel is very cold.  What does it do?  It falls off.  




Edit:  Our benevolent overlords have required more details about the fuel and tank.  Very well, but no peeking in this section if you are under five.  The fuel consists of liquid hydrogen, along with a liquid oxygen oxidiser, both of which have very low boiling points at pressures typically encountered on earth.  In order to be liquid at the pressures inside the fuel tank, the fuel and oxidiser are kept at an extremely low temperature.  This, combined with relatively thin fuel tank walls (gotta save weight on rockets), means the outer surface of the fuel tank will be very cold, bringing the temperature of the water vapor in the air around it low enough that ice forms on the tank and then falls off as the whole contraption shakes mightily as it takes off.  There's no purpose to the ice, it's just a byproduct of the fuel used.