§ 4.2.2 Thermal Extraction of Volatiles
Asteroids are rich in volatile elements such as water, hydrogen, carbon, sulfur, and other elements. Extracting these is easy.
The material is channelled into a solar oven where the volatiles are cooked out. In zero gravity and windless space, the oven mirrors can be huge and made of aluminum foil. The gas stream is piped to tanks located in a cold shadow of space. The tanks are put in series so that the furthest one away is coldest. This way, water condenses more in the first one, whereas carbon dioxide and other vapors tend to migrate and condense in the tanks downstream.
Notably, rocket fuel for the delivery trip to Earth orbit can be produced by separating oxygen and hydrogen gases from the mix, or by electrolysis of water. Alternatively, the hydrogen could be chemically bonded with carbon to produce methane fuel.
Tanks for storing frozen volatiles for sending to Earth orbit can be manufactured by some of the free nickel iron metal, by use of a solar oven for melting the nickel iron metal. For example, a cast can be made from sand or glass-ceramic material from melted leftover ore. The tank doesn't need to be a highly pressurized tank, as the volatiles will be frozen to a very cold temperature in space. Alternatively, thin tanks could be sent, remanufactured from spent fuel tanks used to get to orbit from Earth. Or the spent fuel tanks could be sent as-is. The re-use of spent fuel tanks in space is discussed in the chapter on products and services.