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The Propellant Storage Facilities are located at
both pads. A 900,000-gallon (3,406,860-liter) tank situated at the northwest
corner of each launch pad stores the liquid oxygen, which is used as an oxidizer
by the orbiter's main engines. These ball-shaped vessels are actually huge
vacuum bottles. They maintain the supercold liquid oxygen at temperatures of
minus 297 degrees Fahrenheit (minus 183 degrees Celsius). Two pumps which supply
1,200 gallons (4,540 liters) of oxidizer per minute each transfer the liquid
oxygen from the storage tank to the orbiter's external tank.
Similar 850,000-gallon (3,217,590-liter) vacuum
bottles at the northeast corner of the pads store the liquid hydrogen for the
orbiter's main engines. Pumps are not required to move the liquid hydrogen from
the storage tank to the orbiter's external tank during fueling operations.
First, a small amount of liquid hydrogen vaporizes. This action creates a gas
pressure in the top of the tank that moves the extremely light fuel through the
transfer lines.
The vacuum-jacketed transfer lines carry the
supercold propellants to the Mobile Launcher Platform, where they feed through
the orbiter into the external tank through the Tail Service Masts.
Hypergolic propellants used by the orbiter's
Orbital Maneuvering Engines and Attitude Control Thrusters are also stored at
the pad in well-separated areas. A facility located on the southeast corner of
each pad holds the fuel, monomethyl hydrazine. A facility on the southwest
corner stores the oxidizer, nitrogen tetroxide. These propellants feed by
transfer lines to the Fixed Service Structure and continue to the Rotating
Service Structure's Hypergolic Umbilical System, with its three pairs of
umbilicals attached to the orbiter.
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