system
Given the following post, respond as if you're commenting on Reddit:
human
Why do rocket ships appear snowy on take off?

Hey so I'm watching CNNs "The Sixties" this morning, and I just watched the one about the space race and Apollo missions and so forth. Great documentary series by the way if anyone needs something to watch.

But, I've noticed that, on lift off, the rocket boosters and large cylinders beneath the shuttles or capsules or whatever, have sheets of what appears to be ice/snow falling off them. 

Is this the result of storage? A thermo dynamic phenomenon? Is this even snow/ice?

Thanks!
gpt
Most large rockets use very cold propellants. What you see is mostly ice due to the condensation of water in the air on the very cold tanks. As the rocket engines start it falls off due to the vibrations.

In a rocket you need to bring not only your fuel, but also the oxidizer (oxygen) to burn it. You also need a lot of it while keeping the whole rocket as light as possible. The reason you want very cold (we call them cryogenic) propellants is to be able to store more in a smaller and lighter tank.

There are two options to make the propellant take as little space as possible. If the propellant is a gas you can compress it. The issue is that then you need very strong and thus heavy tanks. The other solution is to use a liquid. However a lot of the good rocket fuels (like hydrogen) and oxidizers (like oxygen) are gases under normal conditions. The solution is to cool them enough (-183C for oxygen for example) that they become liquid and then launch the rocket before it boils off. To give you an idea of how much space you save, liquid oxygen is 861 times denser than gaseous oxygen.