Its main drawback is that it is moderately cryogenic, and therefore not suitable for military uses where storage of the fuelled missile and quick launch are required. High purity liquid oxygen has a light blue colour and is transparent. It has no characteristic odour. Liquid oxygen does not burn, but will support combustion vigorously. Gaseous oxygen can form mixtures with fuel vapours that can be exploded by static electricity, electric spark, or flame.
Liquid oxygen is obtained from air by fractional distillation.
The 1959 United. States production of high-purity oxygen was estimated at nearly 2 million tonnes. In January 1953 Rocketdyne commenced the REAP program to develop a number of improvements to the engines being developed for the Navaho and Atlas missiles. Among these was development of a special grade of kerosene suitable for rocket engines. Prior to that any number of rocket propellants derived from petroleum had been used.