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[i]At depressurization, just prior to the third lunar extravehicular activity, the Lunar Module Pilot noted that his chronograph crystal was gone. The chronograph hands and face were not hit. However, about 12 minutes later the movement stopped. Most likely, warpage caused by thermal cycling allowed the differential pressure across the acrylic crystal to pop it out of the case. The exposure to and penetration of lunar dust contamination about the Lunar Module Pilot's sleeves probably caused the failure of the chronograph movement.
These chronographs are certified to a maximun temperature of 160° F. Testing has demonstrated that in the range of 190° F, the crystal is weakened to the point where internal pressure can push the crystal off. For the chronograph to reach a temperature of 190° F, direct continuous exposure to incident solar radiation normal to its surface is required for approximately 12 minutes.
These chronographs are tested at the Manned Spacecraft Center when received, again before shipment to the Kennedy Space Center and again just prior to flight. The Apollo chronograph is a secondary timing device and is not critical to mission success or crew safety. There are no plans for corrective action.
This anomaly is closed.[/i][/B][/QUOTE]
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