ET Project - Tank Information I. External Tank Description The External Tank of the STS is designed to fill two primary needs. These are to safely carry sufficient cryogenics to deliver the orbiter into Low Earth Orbit (LEO) and to serve as the structural heart - the strongback - of the STS during the launch phase. The basic empty weights, volumes, and dimensions are detailed in the first figure. The tank is constructed in three primary segments which are the hydrogen tank, the intertank, and the oxygen tank. The oxygen tank rests on top of the stack. It is constructed of aluminium in four sections and includes internal slosh baffles. It is bolted to the intertank section which carries its’ loads in compression during flight. The intertank is the primary strength member of the tank. It is unpressurized and constructed using a skin stringer and ringframe arrangement. It also carries a beam which carries the thrust loads of both solid rocket boosters (SRBs) during flight. The intertank is bolted to the top of the hydrogen tank, the largest section of the external tank. The hydrogen tank is designed to carry the required liquid hydrogen during launch. It also carries the loads imposed on the stack by the orbiter engines (SSME) during launch. The entire tank is covered with Spray-On Foam Insulation (SOFI) which serves primarily to prevent ice buildup on the tank before launch and to prevent excessive boiloff of the cryogenics. Typical depth of the insulation is between one and one and one half inches (1-1 1/2"). There are also additional items attached including range safety hardware, feedlines, sensors, electrical lines, tumble valve, and venting systems (63). II. Current ET Operations After construction and testing, the ET, with low pressure in both the hydrogen and oxygen tanks, is shipped by barge to the launch site. The hydrogen tank is pressure tested to over 36 psi. The oxygen is pressure tested by filling it with water at the factory. Neither can tolerate an outside pressure differential greater than .2 psi. (48) Shipping it
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