Liquid oxygen, as the name suggests, is the liquefied form of oxygen. It is chemically represented as LOx or Lox in the fields of aerospace, submarine, and gas, since this is one element, rather the form, which is very specific in its usage. Its color is pale blue and is paramagnetic in nature. It is also known as 'industrial gas', and as stated earlier, has specific uses in industrial and medical fields. It is obtained by fractional distillation of atmospheric air. Its density is somewhere around 1.141 g/cc, its boiling point is 90.188 K at 101.325 kPa of atmospheric pressure. The ratio of expansion is very low, and that is the reason it is used so widely in commercial and military airplanes.
Since it is cryogenic in nature, it causes substances in touch with it to become extremely brittle. Being a powerful oxidizing agent, organic materials burn rapidly and vigorously in liquid oxygen. It also causes substances to become super reactive and unpredictably explode at times. Asphalt also shows some kind of this behavior, and it is categorized as a petrochemical. It is a used as a propellant for spacecraft rocket applications, in combination with liquid hydrogen or kerosene. V2 missile, Redstone, R-7 Semyorka or Atlas were the initial rocket applications in which liquid oxygen was used. The main reason behind using it as a propeller, is that it creates a high specific impulse.
Use in Space Shuttles
A combination of liquid oxygen and liquid hydrogen is used in the main engine of a space shuttle. This combination is used for propulsion during its ascent, though the solid rocket boosters and orbital maneuvering system also work simultaneously. The overall weight of a space shuttle is approximately 3.2 tons, and to give it the ascent, a huge energy base is required. A space shuttle's rocket engines can function in extreme temperatures. Liquid hydrogen is stored at -253 degrees Celsius, but when combined with oxygen, the temperature is somewhere around 3,300 degrees Celsius.
Liquid oxygen is mainly used in the pre-burners and the thrust control systems. The fuel and the oxidizers are mixed, so that combustion can occur efficiently. There is a spark igniter chamber at the center of the injector of each pre-burner. In the engine start sequence, the dual redundant spark igniters are activated by the engine controllers. The whole system runs for approximately ten seconds, and then it can sustain itself. The fuel-rich hot gas that is produced by the pre-burners is passed through the turbines to generate power. The main oxidizer valve and the main fuel valve check the flow of liquid oxygen and liquid hydrogen to the engine, which is controlled by the engine controller. When one of the engines is operating, the main valves are fully open. The space shuttle's external tank contains the liquid hydrogen, that is the fuel and liquid oxygen, which is the oxidizer. When the time comes for ascent, the external tank supplies the fuel as well as the oxidizer under pressure to the three main engines in the orbiter.
The length of a liquid oxygen tank is approximately 55 feet, diameter is 27.6 feet, volume is 19,700 cubic feet, LOx mass is 1,387,457 lb, and the operation pressure is 20-22 psig. It is located at the top of the external tank of the space shuttle, and has a nose-cone-type shape to decrease aerodynamic drag and the heat produced as a result. The LOX tank also has an internal slosh and a vortex baffle to wet the fluid slosh. The latter is on top of the LOX feed outlet, so that the fluid swirl can be decreased, which results from the slosh, and also to avoid gases from getting entrapped.