Electrical wiring for space-vehicle applications has the same demands as for aircraft - reliable performance in a harsh environment for many years. Service life extensions are under consideration that would have the remaining fleet of space shuttles operating for 40 years. The ISS in orbit also will age over...
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Electrical wiring for space-vehicle applications has the same demands as for aircraft - reliable performance in a harsh environment for many years. Service life extensions are under consideration that would have the remaining fleet of space shuttles operating for 40 years. The ISS in orbit also will age over time. Accordingly, the shuttle Columbia Accident Investigation Board (CAIB) recommended a thorough assessment of aging wiring risks and needed actions to mitigate them. In the closing weeks of 2003, the National Aeronautics and Space Administration (NASA) issued a report on the ISS program's response to the CAIB report. What the report had to say about ISS wiring has obvious parallels for the durability and maintainability of aircraft wiring. The NASA report also underscores the importance of training people to inspect wiring, an important point developed in ATSRAC's (Aging Transport Systems Rulemaking Advisory Committee) efforts to develop training and inspection protocols for transport category aircraft:
"The nature of the ISS system dictates that physical wiring inspections be performed on orbit ... Internal wiring is susceptible to damage when it, or hardware nearby, is manipulated through normal daily activity ... Plans are in place to perform routine wiring 'inspections of opportunity' in high traffic areas as part of the normal ISS systems maintenance. External wiring was designed to operate in the micrometeoroid and orbital debris environment in low Earth orbit.
"Even though the ISS elements on orbit have only been in place for up to 5 years, the ISS Program will evaluate whether additional routine wiring inspections should be implemented in response to aging effects.
"While the crew has not been provided with standard criteria by which to evaluate wiring conditions, nor are there requirements for routine wiring inspection outside of maintenance activities, other means are used to control this risk ... When the crew is working in an area that has exposed wires, they report ... fraying or chafing of wires ... For example, the Service Module food warmer displayed signs of degradation of the protective covering of some wiring. Because crewmembers were trained to look for this type of anomalous situation, they reported the degradation to the ground and corrective action was taken. (ASW note: this illustration is analogous to the many galley wiring problems reported in this publication.)
"The ISS Program will also assess the risks of wiring aging through the whole vehicle life." (ASW note: The CAIB report called for a state-of-the-art means to inspect all Orbiter wiring, including that which is inaccessible. [Emphasis added] The ISS report did not address the challenge of inspecting space station wiring in inaccessible spaces.)
>> The ISS extract is from page 1-17 of the NASA report. The full report may be accessed at www.nasa.gov/pdf/53067main_station_imp_plan.pdf<<
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