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The external tank contains the liquid hydrogen fuel and liquid oxygen oxidizer and supplies them under pressure to the three space shuttle main engines in the orbiter during lift-off and ascent. When the SSMEs are shut down, the ET is jettisoned, enters the Earth's atmosphere, breaks up, and impacts in a remote ocean area. It is not recovered.
The ET is attached to the orbiter at one forward attachment point and two aft points. In the aft attachment area, there are also umbilicals that carry fluids, gases, electrical signals and electrical power between the tank and the orbiter. Electrical signals and controls between the orbiter and the two solid rocket boosters also are routed through those umbilicals.
The largest and heaviest (when loaded) element of the space shuttle, the ET has three major components: the forward liquid oxygen tank, an unpressurized intertank that contains most of the electrical components, and the aft liquid hydrogen tank.
The ET is 153.8 feet long and has a diameter of 27.6 feet. Beginning with the STS-6 mission, a lightweight ET was introduced. Each weighs approximately 66,000 pounds inert. The last heavyweight tank weighed approximately 77,000 pounds inert. For each pound of weight reduced from the ET, the cargo-carrying capability of the space shuttle spacecraft was increased almost one pound.
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