Expanded life-cycle analysis to optimize spacecraft life support system design.

摘要

The life-cycle of a human space mission begins with the conceptual design and ends with the return or disposal of the spacecraft. A major component of the spacecraft is the environmental control and life support system (ECLSS) that supports the crew. Historically, conceptual designs of ECLSS focused on launch costs; however, current missions with longer timelines have meaningful life cycle costs beyond launch costs. To reduce these costs, the author proposed an expanded life cycle analysis to optimize designs while meeting the somewhat contradictory goals for success and safety. Expanding the life cycle analysis of ECLSS, is particularly important, because space-habitat-maintenance has been anecdotally reported as taking time away from science activities on the International Space Station (ISS). To understand this potential issue, the author examined ISS crew time use and different approaches to ECLSS design.; An analysis of ISS crew time use determined that each crew member spent at least 1.8 hours per day performing ISS maintenance tasks. Regardless of the confounding causal mechanisms, crew time spent on habitat maintenance on Skylab and ISS exceeded that estimated by design, thus reducing crew time allotted to perform other tasks, although not necessarily science. Upon further examination, analysis of ECLSS maintenance revealed that operational crew time estimates for the ISS mission design were low by an order of magnitude. A review of the literature indicates this work is the first time that design estimates were compared quantitatively to operational time and shown to be less for ECLSS.; Based on these findings, Skylab and ISS missions were oversubscribed due to a mismatch between maintenance and operational time requirements. This mismatch most likely occurred, because only part of operational crew time was considered. Even with the inclusion of operational crew time, the ECLSS design for ISS may not have changed, but the ISS-equivalent case study indicated that launch mass and operational crew time constraints were equally controlling. Therefore, ECLSS design approaches should expand to include operational crew time, and the expanded life cycle analysis with historical data used to justify refocusing mission objectives or the development of specific, new technologies as necessary.