RESILIENCE POTENTIAL: METRIC DEVELOPMENT AND APPLICATION TO LUNAR HABITATS

Designing safe and resilient extraterrestrial habitats is challenging. They will be exposed to harsh conditions—low gravity, extreme temperature, radiation, and a lack of breathable atmosphere. Habitats will incorporate closed-loop, tightly coupled systems where faults can cascade rapidly to catastrophe with little margin for error. The absence of real-time Earth-based intervention due to communication delays and logistical constraints further exacerbates the risks. Given the safety-critical nature of these habitats, coupled with severe resource constraints and budget limitations, safety measures must be selected parsimoniously and effectively—we cannot simply add redundancy or ‘just in case’ features.

While some hazards can be addressed by clever system design that avoids or mitigates hazards in an integrated manner, most hazards must be addressed directly, through safety controls. The methods and metrics engineers use to evaluate these safety controls have two limitations: (1) they are based on heuristics or assess controls indirectly through their effect on the system’s risk, and (2) none of them cover designing for unforeseen hazards. These limitations prevent engineers from selecting the best set of safety designs, which is crucial for cost-effective and performance-driven design that achieves the desired level of safety. In previous work, we developed a control effectiveness metric that evaluates the effectiveness of a safety control implementation strategy in mitigating known hazards. There is no similar metric for unforeseen hazards. Literature on unforeseen hazards recommends incorporating system attributes such as flexibility, adaptability, agility, versatility, and robustness to enhance a system’s ability to respond to unanticipated hazards. These recommendations are often discipline-specific and not quantifiable. This limitation prevents engineers from generalizing their use to other systems.

To bridge this gap, we propose a new metric for resilience potential. We defined the Resilience Potential as a measure of the effectiveness of a safety control implementation strategy (SCIS) in addressing multiple hazards, including those for which it was not explicitly designed. An SCIS that can target multiple hazards, including those for which it was not explicitly designed, can do so by providing multiple functions. These functions can be leveraged to address unforeseen hazards. We define a numerical measure of resilience potential for active safety control implementation strategies that evaluates safety controls based on the functions they can provide. Our measure captures the enabling capabilities defined by a safety control’s perception, decision-making, mobility, manipulation, and communication abilities, as well as the implementation strategy and a resource capability score. The resource capability score determines the use cases of a safety control to mitigate a hazard. The resilience potential metric helps identify safety controls that enhance a habitat’s flexibility and adaptability, thereby mitigating both foreseen and unforeseen hazards and increasing its safety and resilience.

To validate and test the resilience potential metric, we developed a notional lunar habitat model on the Control-Oriented Dynamic Computational Modeling platform, as well as a detailed test plan. The habitat model enabled us to simulate various disruptions and hazards and test how implementing safety controls affected the habitat’s resilience. The habitat model encompasses functional relationships between modeled systems, including structure, power, interior environment, and others as needed by the simulation. The test plan comprises two complementary approaches to determine whether selecting a high-resilience potential safety control implementation strategy yields high resilience. In the first study, we evaluate six safety controls with varying resilience potential. We find that high-resilience potential safety controls mitigate multiple hazards in solar power generation and enhance the system’s resilience. Our results also show that the criticality of targeted hazards and the effectiveness of safety controls impact resilience improvement. In the second study, we evaluate six different general-purpose safety controls with varying resilience potential on two disruption scenarios (cooling system cascade and disruption dilemma). We find that high-resilience safety controls can effectively mitigate hazards that they were not initially designed for—unforeseen hazards.

Our research shows that selecting high-resilience potential safety controls enhances a system’s safety and resilience by enabling the system to mitigate multiple hazards, including unforeseen ones. Safety and resilience for foreseen hazards are also enhanced by selecting safety controls that have high effectiveness and target critical hazards. Therefore, for a safe and resilient habitat against both foreseen and unforeseen hazards, engineers must select safety controls that have high resilience potential, effective control, and target critical hazards.