Subject

Abstract

Driving Event

Three sections of a telescoping tube assembly at Pad B rotating service structure (RSS) fell while being extended to incorporate a planned modification (MOD). The MOD intended to eliminate binding that had been experienced during testing and verification. The falling tubes impacted and severely damaged the RSS and orbital maneuvering system pod covers. The contributing factor to this failure is that the fillet welds on tube "D" provided an outward ramp effect that caused excessive wear on the keepers and the eventual bowing of tube "C" which allowed less surface contact area between the welded stops and the keepers.

Lesson(s) Learned

1. Excessive wear of the load bearing surfaces on the keepers of tube "C" was the result of impact during approximately 30 retraction cycles.
2. To stow the tubes, normal operations required bypassing the "up" limit switch and using observers to determine when to stop the upward travel.

Recommendation(s)

1. Design tube hoist assemblies that do not incorporate fillet welds on the inside of the tubes and opposite the tubes stops. This will reduce/eliminate wearing down of the tube stops.
2. Add "up" limit switches exclusively dedicated to tube stowage operations.

Evidence of Recurrence Control Effectiveness

Program Relation

Program/Project Phase