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NARRATOR: A space shuttle ready to launch has numerous connections to the launch pad

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that require careful attention to assure a safe liftoff.

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The ground umbilical carrier plate, called the GUCP, is one of those connections.

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The GUCP is at the end of the gaseous hydrogen vent arm on the fixed service structure.

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It attaches to the shuttle's orange external tank.

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The plate holds a large-diameter pipe that collects excess hydrogen gas from the tank as it's being filled with liquid hydrogen.

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The venting system funnels it to a larger pipe that takes it down the fixed service structure

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and out to a flare stack that burns the excess hydrogen off safely.

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At liftoff, the GUCP retracts away from the tank, cutting off the connection.

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The vent arm pulls back to the tower, safely away from the shuttle as it climbs straight up.

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Because the GUCP's connection to the tank is so important, it has sensors in place to watch for hydrogen leaking.

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Launch controllers track the readings from those sensors closely and when readings are outside the limits, the countdown is halted.