scope:

Description of Driving Event:

On June 4, 1990, in High Bay 1 of the Orbiter Processing Facility (OPF) at the Kennedy Space Center (KSC), the aft bridge of the Payload Bay Bridge and Hoist System was moved approximately 78 inches aft of its set position for Payload Bay Door (PLBD) operations. The right-hand PLBD Zero-G System was configured to support a scheduled PLBD closing operation on first shift, June 4, 1990, except the Zero-G weight baskets were left pinned to their weight cages. The right Payload Bay Door (PLBD) was supported by the Zero-G cabling (not pinned to the platform). Movement of the bridge put the Zero-G cabling into tension and at an angle sufficient to shear a portion of the weight basket pulley "V," fray the Zero-G cabling, move the weight basket off its track, and deflect the C-hook approximately 2 to 3 inches. Since the weight basket was pinned, the aft movement of the bridge also caused the right PLBD aft portion to rise approximately 31 to 33 inches (calculated).