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International Space Station Operational Experience and Its Impacts on Future Mission SupportabilityOperational experience gained on the International Space Station (ISS) has enabled significant improvements in failure rate estimates for various Orbital Replacement Units (ORUs). These improved estimates, in turn, allow more efficient and accurate spare parts allocations for future missions, enabling significant reductions in both logistics mass and risk. This paper examines the value of ISS experience to date in terms of its impact on supportability for future missions. A supportability model is presented that assesses the spares required as a function of mission endurance and risk, taking into account uncertainty in failure rate estimates. Changes in ISS Environmental Control and Life Support (ECLSS) ORU failure rate estimates are described and discussed, both in terms of the overall population of ORUs and the evolution of failure rate estimates over time for a particular item. The value of those updated failure rate estimates is assessed by calculating the estimated spares mass requirements for two cases, using the initial, pre-ISS estimates and using the estimates informed by on-orbit experience. Hidden risk resulting from underestimated failure rates is also assessed. These results indicate that, for a 1,200-day Mars mission, ISS experience has enabled a 3.9 t to 6.0 t reduction in ECLSS spares mass required and uncovered failure rate underestimates that would have resulted in an order of magnitude increase in risk had they not been discovered and corrected. The implications of these results for system development and mission planning are discussed, including approaches to accelerate the rate of failure rate refinement and the risks associated with making changes or introducing new systems. Overall, test time is a critical factor that must be carefully considered in system development, and new systems must budget appropriate time for testing in a relevant environment or accept higher risk and logistics requirements on future missions.




Document ID
20200002558
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Owens, Andrew C.
(Massachusetts Institute of Technology (MIT) Cambridge, MA, United States)
de Weck, Olivier L
(Massachusetts Institute of Technology (MIT) Cambridge, MA, United States)
Date Acquired
April 17, 2020
Publication Date
July 8, 2018
Subject Category
Systems Analysis And Operations Research
Report/Patent Number
NF1676L-29461
ICES-2018-198
Report Number: NF1676L-29461
Report Number: ICES-2018-198
Meeting Information
Meeting: International Conference on Environmental Systems
Location: Albuquerque, NM
Country: United States
Start Date: July 8, 2018
End Date: July 12, 2018
Sponsors: International Conference On Environmental Systems, Inc.
Funding Number(s)
WBS: 089407.09.23
CONTRACT_GRANT: NNX14AM42H
Distribution Limits
Public
Copyright
Public Use Permitted.
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