Changing Safety Requirements – Benefits, Challenges, Risks

After several years of operating the International Space Station, a growing tendency for usage of commercially available hardware items can be noticed. The challenge for certifying the safe operation on-board the ISS leads to the need for changing also some safety requirements.

This paper analyzes the historic basis for the safety requirements that were used for the development of the Station, its systems and payloads, e.g. due to the limited information on environmental effects over extended durations. It evaluates the current situation of safety requirement changes or safety requirement interpretation changes in the international environment based on factors like onboard experience and better understanding of the environment which can lead to relaxation of safety requirements. But also the challenges are highlighted, as any system is as strong as the weakest leg. Special attention should be taken to not stop to worry, especially if it is not traceable why the original requirement has been defined in the first place.

Some elements for improved safety requirement - definition, - background traceability and - changes for future programs for complex and long operated on-board systems are proposed to reduce reactive adoptions via safety NCRs, waivers or operational workarounds.