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.
Solid propellants have the fuel and oxidiser embedded in a rubbery matrix.
They were developed to a high degree of perfection in the United States in the 1950's and 1960's. In Russia, development was slower, due to a lack of technical leadership in the area and rail handling problems. Once ignited, they cannot be easily shut down or throttled. Thereafter they have to be pre-cast or milled out for a specific mission. Last update 22 December 2000.