Abstract:
Qualification testing at extreme cold temperatures found that noise could be generated from the minute differential expansion between semi-rigid aluminum coaxial cables and their attached stainless steel shells. Beware of the intermodulation product phenomenon, and test for it during antenna subsystem pre- and post-environmental tests, after antenna installation on the spacecraft, and prelaunch.
Description of Driving Event:
(Relevant Historical Lesson(s) Learned) During qualification testing of coaxial cables at cold temperature (-200C for TA) it was found that intermodulation product signal levels were generated. These levels only occurred at the extreme cold temperature. On Viking it had been found that broadband noise could be generated in the mating surfaces of the aluminum four channel track connector. To eliminate that problem the Voyager connector mating parts were made of stainless steel. It was found in testing that there was minute differential expansion between the semi-rigid aluminum coaxial cables and the stainless steel shells that attach to the cables. The problem was eliminated by increasing the fabrication torque from 20 in-lbs to 45 in-lbs to prevent the loosening at extreme temperatures. Additional Keyword(s): Connector Fabrication Techniques, RF Intermodulation, Thermal Expansion Reference(s): Voyager PFR 38668
Lesson(s) Learned:
Maintain a rigorous test program for detecting intermodulation products all the way up to launch. This would involve the use of a two-signal intermodulation test-set to assure that coaxial connectors or other components with contacting metal surfaces do not generate intermodulation products.
Recommendation(s):
- Testing to verify the absence of such products should be performed during the pre- and post-environmental tests at the antenna subsystem level, and also after installation of the antenna on the spacecraft in tests at the Spacecraft Assembly Facility (SAF) and as part of prelaunch preparations.
- The Hardware Design Engineer must be continuously cognizant of the intermodulation product phenomenon and implement design practices for its avoidance.
- Install the stainless steel mating shells on the semi-rigid aluminum cables with a torque from at least 45 in-lbs.
Evidence of Recurrence Control Effectiveness:
N/A
Documents Related to Lesson:
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Mission Directorate(s):
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Additional Key Phrase(s):
- Hardware
- Test & Verification
Additional Info:
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