A service structure (supply tower or launch tower) is a structure constructed on a launch pad to facilitate fueling, loading cargo and crew into the spacecraft. A supply tower also usually includes an elevator which allows maintenance and crew access. Immediately before ignition of the rocket's motors all connections between the tower and the craft are severed and the bridges over which these connections pass often quickly swing away to prevent damage to the structure or vehicle. In contrast with launch towers, service structure towers do not guide rockets as they lift off.
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