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During the Space Shuttle STS-80 mission, the two planned Extravehicular Activities (EVA) were scrubbed when the astronauts discovered that the outer airlock hatch would not open. This impacted the plan to evaluate the EVA tools that would be used for the construction and maintenance of the International Space Station.

Upon return from the mission, troubleshooting revealed that the airlock actuator that is used for latching and unlatching the hatch was defective. This actuator was removed and replaced. Troubleshooting on the removed actuator revealed that a small screw had come loose from an internal assembly and lodged in the planetary gears of the actuator. Space Shuttle Program Corrective Action Record Number AE0959-010 documented this problem. The Failure/Problem Report Number NSLAD-RE-97-044 documented the actuator findings. Both of these reports are attached to this Lesson Learned input.