External Fuel Tank
The external tank is the only non-reusable element of space shuttle. It is also the largest part of the space shuttle and provides structural backbone of the entire system. The chief purpose of external tank is to carry the fuels necessary to provide power for the orbiters main engines.
It mainly consists of three tanks –
1) Liquid oxygen tank located at the top
2) Liquid hydrogen tank located at the bottom
3) intertank connecting the liquid oxygen and liquid hydrogen tank
The intertank, connecting hydrogen and oxygen tank, is 22 feet, 6 inches long by 27 feet, 7 inches wide and its purpose is to distribute all the thrust loads that the Solid rocket boosters produce during launch and flight.
Since, the fuels stored in tank should be at low temperature to prevent explosion, hence these tank requires thermal protection from sunrays and friction due to atmosphere of earth. This is done by a one-inch layer of spray-on foam insulation applied over the forward portion of the liquid oxygen tank, the intertank and the sides and bottoms of the liquid hydrogen tank.
The foam insulation not only provides insulation from aerodynamic heating and friction heating but also reduces ice formation on the tank, which could increase the weight of the external tank and that can become hazardous to the space shuttle during launch. The ET also contains systems that are necessary for its operation like system to regulate tank pressure, environmental conditioning system, electrical system to provide and distribute power etc.
At launch, ET is attached to orbiter and SRBs. After launch, ET empties about 8.5 minutes after which it gets detached from the orbiter, breaks up and falls on the earth.