Oxidizers include nitric acid, nitrogen tetroxide, liquid oxygen, and liquid fluorine. Most fuels, with the exception of hydrogen, are liquids at ordinary temperatures. Others require an igniter to start them burning, although they will continue to burn when injected into the flame of the combustion chamber. In general, the liquid propellants in common use yield specific impulses superior to those of available solids. No. 1460, may 1958.
Liquid oxygen is the standard oxidizer used in the largest United States rocket engines.
It is chemically stable and noncorrosive, but its extremely low temperature makes pumping, valving, and storage difficult. If placed in contact with organic materials, it may cause fire or an explosion. Nitric acid and nitrogen tetroxide are common industrial chemicals. Although they are corrosive to some substances, materials are available which will safely contain these fluids. Nitrogen tetroxide, since it boils at fairly low temperatures, must be protected to some degree.