The Space Shuttle external tank (ET) is the largest single element and the only major non-reusable component of the Shuttle system. The ET is 154 feet (47 meters) long and 27.6 feet (8.4 meters) in diameter and carries more than 528,600 gallons (2 million liters) of cryogenic propellants that are fed to the orbiter's three main engines during powered flight.The ET is the structural backbone of the Shuttle system and absorbs the total 6,610,000-pound thrust loads generated by the orbiter's three main engines and two solid rocket boosters. The tank is non-reusable, and must be produced economically in quantities needed to meet the frequency of Shuttle flight.
The ET is actually three components in one: a liquid oxygen tank located in the forward position; a liquid hydrogen tank located aft; and an intertank assembly that connects the two propellant tanks and houses the forward solid rocket booster attachment points. The ET weighs approximately 1,655,600 pounds (751,000 kilograms) when filled with propellants and 66,000 pounds (29,900 kilograms) when empty.
The ET is covered with a multilayered thermal protective coating approximately 1 inch (2.5 centimeters) thick. The insulation allows the tank to withstand the extreme internal and external temperatures generated during prelaunch, launch, and flight. The exact materials, thicknesses, and methods of application vary at different locations on the tank.
The tank's design has been modified to reduce its weight and thus increase the shuttle's payload capability. The first lightweight ET flew on the sixth shuttle mission in April 1983, and weighed over 10,000 pounds (4,500 kilograms) less than the ET used o n the first shuttle flight.
At launch, propellants are pressure fed at a combined rate of 1,035 gallons (3,900 liters) per second through 17-inch (43.2 centimeter) diameter feedlines to the orbiter's three main engines. Eight and one-half minutes into flight, the orbiter and ET have reached an altitude of about 71 miles (114 kilometers), the main engines are cut off and the tank is jettisoned. Residual gaseous oxygen is used to initiate a slow tumble away from the orbiter, prevent the ET from skipping off the Atmosphere, and assist in its break-up and descent into a remote ocean area.<
The external fuel tank falls toward Earth following its jettisoning from the Space Shuttle Endeavour during the first ten minutes of the six-day Earth-orbital STS-54 flight. On board the spacecraft were astronauts John H. Casper, Donald R. McMonagle, Gregory J. Harbaugh, Mario Runco Jr. and Susan was taken with a 35mm camera.
NASA Photo. STS054-27-024 13 Janaury 1993
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