System and Sustainability Determinants of Life in Space: A Determinants-Based Conceptual Framework for Human Health Beyond Earth

Social Determinants of Health and Mental Health Models

Both the SDOH and SDOMH frameworks are rooted in systems and ecological theories that conceptualize health as the emergent property of nested social and environmental systems. The SDOH model draws from the social–ecological framework of Bronfenbrenner, ¹⁶ which posits that interactions among micro, meso, and macro-level systems shape individual well-being. It also aligns with systems theory in public health, which treats health outcomes as nonlinear and co-determined by interdependent social structures. ¹⁷ The SDOMH framework builds on these foundations by incorporating social justice theory, stress process theory, and structural vulnerability models, emphasizing that power, discrimination, and inequality are embedded determinants of psychological outcomes.^14,15

By integrating these perspectives, the determinant approach establishes a multi-level systems logic: individual, interpersonal, community, and structural domains interact dynamically to produce health outcomes. This theoretical lineage provides the conceptual scaffolding for extending determinant-based logic into extraterrestrial environments through SSDLiS, where the nested systems are technological, ecological, and psychosocial rather than purely social or environmental.

Over the past two decades, the SDOH model has reshaped the understanding of population health by emphasizing how social, economic, and environmental factors exert greater influence on health outcomes than medical care alone.^18,19 Core determinants such as education, housing, income, and community support highlight the systemic context within which individual health is produced. More recently, the SDOMH framework has extended this logic to psychological well-being, noting that structural conditions such as discrimination, inequality, and social isolation play central roles in shaping mental health outcomes. ²⁰ Both models emphasize that resilience and vulnerability are distributed across populations not only by biological predisposition, but by social systems, policies, and environments.

These frameworks provide a conceptual foundation for examining human life in space. Just as terrestrial health cannot be understood solely through biomedical interventions, astronaut well-being depends on a broader constellation of social, cultural, and environmental conditions.

Social Determinants of Health

The SDOH framework is grounded in the recognition that health outcomes are shaped more by social and environmental conditions than by medical care alone. The World Health Organization identifies five primary domains: (1) economic stability (employment, income, and financial security), (2) education access and quality, (3) health care access and quality, (4) neighborhood and built environment (housing, transportation, safety, environmental conditions), and (5) social and community context (support networks, discrimination, civic participation). ¹⁹ These determinants interact to shape health equity, underscoring that access to resources, opportunities, and supportive environments is foundational to population well-being. ¹⁸

Social Determinants of Mental Health

Building on this foundation, the SDOMH framework focuses specifically on psychological well-being. Core domains include (1) economic and work conditions, such as job security and workplace stress; (2) social support and inclusion, including freedom from discrimination and stigma; (3) early life conditions, particularly exposure to trauma or deprivation; (4) access to health care and mental health services; and (5) broader structural factors, including cultural norms, inequality, and social policy. ²⁰ The SDOMH model emphasizes that mental health is not simply an individual trait or disorder but is produced through interactions between individuals and their social environments.

Together, SDOH and SDOMH establish a critical logic that health and well-being are socially situated outcomes, shaped by overlapping systems rather than isolated variables. This insight provides a conceptual precedent for applying a determinants-based lens to space habitation, where health, psychosocial adaptation, and sustainability are similarly embedded in interdependent systems.

Determinants Considered in Spaceflight Research

In space contexts, research has focused mainly on technical and biomedical systems. NASA’s Human System Standards (NASA-STD-3001) outline acceptable exposure levels, health care capability requirements, and habitability guidelines to protect astronauts during missions. ²¹ Complementing this, the Human Research Program (HRP) Risk Catalog identifies categories of risk, including altered gravity, radiation, isolation, behavioral health, and medical capability, that must be mitigated for long-duration exploration. ⁶ These resources provide mission planners with rigorous biomedical thresholds and operational countermeasures, but they are less attentive to systemic social and sustainability dynamics.

European efforts such as ESA’s Micro-Ecological Life Support System Alternative (MELiSSA) project address sustainability by developing bioregenerative closed-loop systems that recycle air, water, and nutrients to reduce dependence on resupply. ²² Analog studies such as Hawaii Space Exploration Analog and Simulation (HI-SEAS) and Scientific International Research in Unique Terrestrial Station (SIRIUS) simulations highlight the importance of crew composition, multicultural interactions, and shared food production for cohesion and adaptation.^3,8 Habitability research has also documented the influence of environmental factors such as volume, lighting, noise, and privacy on well-being and performance in confined habitats. ¹ Together, these studies highlight the value of integrating ecological resilience, psychological adaptation, and habitat design into space life-support strategies.

Gaps in Current Approaches

Despite significant advances in space life sciences and human systems research, there remains no unified framework that integrates biomedical, social, and sustainability determinants of life in space. Research remains largely siloed across disciplines such as engineering, psychology, and policy. The absence of an integrated determinants model may hinder efforts to systematically capture the interdependence of ecological, social, and cultural systems in extraterrestrial environments.^9,10 As recent reviews emphasize, most findings are either theoretical or analog-based, with limited empirical validation from long-duration missions beyond low-Earth orbit.

Critical gaps also remain regarding how fundamental biological processes in reproductive health and human development might function in extraterrestrial gravity environments. A foundational question remains inadequately addressed: can normal human growth and development occur in the absence of Earth-level gravity? While conception and fetal development in microgravity may be theoretically possible, evidence regarding whether infants can develop normally, achieve appropriate bone mineralization, and establish proper vestibular and musculoskeletal function in reduced or zero gravity is limited [38]. This represents a fundamental constraint on long-term human settlement scenarios that must be more thoroughly integrated into sustainability models.

Gaps remain in risk management and hazard mitigation across multiple domains. Beyond standard biomedical countermeasures, the framework must address comprehensive risk profiles including: isolation-induced psychological effects and mental health crises; ethical dilemmas in resource allocation, medical decision-making, and crew autonomy; death protocols and procedures in orbit or on extraplanetary surfaces; planetary protection measures to prevent biological and chemical contamination; crew safety during emergency scenarios; and principles for equitable risk distribution among crew members and across missions. These considerations represent existential factors for long-duration missions but remain underrepresented in current sustainability models.

Additionally, the question of which governance and settlement models will guide off-Earth human expansion remains largely unspecified. Will emerging settlements follow models derived from Antarctic research bases, which operate under international treaties and multi-institutional governance? Or will space settlements more closely resemble military or corporate command structures, with implications for autonomy, decision-making, and resource control? These governance questions shape not only operational procedures but also the psychological and social determinants of crew well-being and sustainability.

Space agencies and international organizations have explicitly called for frameworks that address this gap. NASA’s HRP Evidence Book ²³ and Human Exploration Strategy ²⁴ emphasize the need for integrated human systems risk modeling but acknowledge the lack of unifying frameworks that connect health, psychosocial, and operational sustainability. The European Space Agency’s SciSpacE 2030 Roadmap similarly calls for cross-disciplinary frameworks for human adaptation and sustainability extending beyond traditional life support research. The United Nations Office for Outer Space Affairs ²⁵ and the Organization for Economic Co-operation and Development ²⁶ have also highlighted the importance of ethical and human-centered approaches to space sustainability.

This fragmentation contrasts sharply with the terrestrial health sciences, where determinants frameworks have unified diverse domains into actionable policy and research agendas. Developing the SSDLiS framework offers a way forward by integrating health, social, ecological, and governance perspectives to guide the design of sustainable human systems in space.

Conceptual Framework

SSDLiS is introduced as a conceptual framework that proposes nine interdependent domains defining the conditions required for sustaining human health, performance, and psychosocial well-being beyond Earth. Rooted in the theoretical logic of the SDOH and the SDOMH frameworks. SSDLiS adapts these models conceptually to the engineered, closed, and fragile ecosystems that characterize extraterrestrial environments.^12–15 Whereas SDOH and SDOMH emphasize how environmental, social, and structural factors shape human outcomes on Earth, SSDLiS extends these principles to contexts in which such factors are designed, maintained, and continuously mediated through technology, governance, and human adaptation.

The SSDLiS framework draws on multiple theoretical traditions that collectively ground each domain in established bodies of scientific and social thought. These theories extend the model beyond descriptive classification toward a coherent systems-based foundation that links human, environmental, and technological sustainability.

As a conceptual model, SSDLiS is not intended to prescribe empirical variables or measurement tools directly but to offer a theoretical structure that organizes thinking about how human life can be sustained in space as an interdependent system of determinants. The framework provides a basis for future operationalization through research, design, and policy development, while its current purpose is to define the conceptual relationships among key ecological, technological, and psychosocial systems that make life beyond Earth possible.

Physical and Environmental Habitat

The first domain, Physical and Environmental Habitat, addresses the physical and environmental conditions that constitute the foundation of human survival in space. This includes exposure to radiation, microgravity, atmospheric regulation, thermal control, and lighting. On Earth, the built environment functions as a determinant of health through factors such as housing quality, environmental pollution, and safety; in space, these variables become direct determinants of both physiological and psychological functioning. ⁷ Habitat integrity and environmental stability determine not only survival but also circadian alignment, cognitive performance, and mood regulation. ⁵

This domain is informed by ecological systems theory and environmental psychology, which together explain how environmental design influences health, cognition, and emotional regulation. Ulrich’s ²⁸ research on stress recovery and restorative environments and Evans’s ²⁹ analysis of how the built environment affects mental health both demonstrate that environmental quality, including lighting, spatial configuration, and noise, functions as a determinant of psychological well-being. In extraterrestrial habitats, where the environment is entirely engineered, these principles become central to designing spaces that minimize stress and support adaptive functioning.

Life Support and Resource Sustainability

The second domain, Life Support and Resource Sustainability, encompasses the systems that sustain biological life through the recycling of air, water, and food. In terrestrial settings, infrastructure and resource access correspond to determinants such as water quality, nutrition, and sanitation. In space, however, these are achieved through closed-loop ecological systems, where even minor failures can result in cascading, life-threatening consequences. ²² Conceptually, sustainability within this domain is characterized by redundancy, efficiency, and psychological security, referring to the human sense of safety that arises from confidence in life support systems.

This domain aligns with resilience theory and complex adaptive systems theory. Holling ³⁰ defined resilience as the capacity of a system to absorb disturbance and reorganize while maintaining core function, a concept later expanded by Folke ³¹ to emphasize dynamic adaptation across scales. Applied to closed-loop space systems, this theoretical lens reframes sustainability not as static redundancy but as an ongoing process of feedback, adaptation, and regeneration between technological and biological subsystems.

Technological Infrastructure and Operational Reliability

The third domain, Technological Infrastructure and Operational Reliability, reflects the central role of technology and information flow in mediating human existence in space. Cognitive and communication systems function as cross-domain determinants within this domain, linking technological reliability with psychosocial adaptation. On Earth, access to health care and digital infrastructure are key components of the SDOH framework; in extraterrestrial environments, the reliability and integration of these systems become direct determinants of both physical and psychological well-being. This domain includes the performance and redundancy of life-support technologies, robotics, propulsion, and automation, as well as the cognitive and communicative systems that enable situational awareness, decision-making, and coordination. Communication latency, data overload, and evolving dynamics of human–Artificial Intelligence (AI) interaction shape how crews perceive, process, and act on information, influencing trust, cohesion, and adaptive capacity.^4,5 Within the conceptual logic of SSDLiS, this domain illustrates how technology functions not only as an operational tool but as a determinant of psychosocial and systemic sustainability.

This domain is grounded in human-systems integration and sociotechnical systems theory, both of which view technology and human operators as interdependent components of complex systems. Carayon ³² describes sociotechnical systems as configurations where human, technological, and organizational factors interact to determine safety and performance, while Baxter and Sommerville ³³ emphasize the need for co-design processes that integrate human capabilities into system engineering. Within SSDLiS, this perspective positions technology as an adaptive partner in sustaining human function rather than as a neutral tool.

Health and Biological Systems Maintenance

The fourth domain, Health and Biological Systems Maintenance, represents the ongoing biomedical and physiological processes required to maintain human function under non-terrestrial conditions. Countermeasures against bone and muscle loss, immune dysregulation, and circadian disruption serve as daily determinants of well-being. ⁵ In contrast to Earth, where environmental stability supports health passively, astronauts must engage in continuous, structured, and monitored practices to preserve physiological homeostasis. Within the conceptual structure of SSDLiS, preventive care, self-management, and real-time health monitoring are viewed as determinants embedded within closed, self-regulating systems rather than as separate medical interventions.

This domain is rooted in Engel’s ²⁷ biopsychosocial model, which proposed that health outcomes emerge from the interplay of biological, psychological, and social factors. This integrative approach has since guided aerospace medicine and human performance research, recognizing that physiological maintenance in space, such as countermeasures for bone loss or circadian disruption, cannot be separated from psychological adaptation or social cohesion.

Psychosocial and Behavioral Adaptation

The fifth domain, Psychosocial and Behavioral Adaptation, addresses the mental and interpersonal determinants of functioning under isolation, confinement, and distance from Earth. Where SDOMH frameworks emphasize social cohesion, stigma reduction, and access to support, the space context reframes these determinants as autonomous psychosocial resilience and group-level adaptation to environmental stress. ¹⁴ Determinants in this domain include coping strategies, emotional regulation, interpersonal communication, and conflict management. Conceptually, SSDLiS situates these determinants as central to system stability, highlighting how self-regulation and intra-crew cohesion contribute directly to mission sustainability.

This domain draws from stress and coping theory, ³⁴ which conceptualizes adaptation as a dynamic process of cognitive appraisal and behavioral response to stressors. In confined, isolated, or high-risk environments, effective coping and group cohesion are essential determinants of mission success. Group dynamics theory further reinforces this domain, underscoring how communication, leadership, and shared norms shape collective resilience in extreme settings.

Cultural and Ethical Determinants

The sixth domain, Cultural and Ethical Determinants, reflects the influence of cultural norms, moral reasoning, and social justice on individual and collective well-being. Multinational crews bring diverse languages, values, and ethical frameworks into confined and high-stakes environments, shaping decision-making, leadership, and team interaction. ¹⁵ Ethical challenges such as prioritizing limited resources, distributing risk, or defining mission success can generate moral stress and impact performance, cohesion, and psychological health. This domain also extends to environmental ethics and planetary stewardship, recognizing that human sustainability in space is inseparable from responsible engagement with extraterrestrial environments. Conceptually, SSDLiS positions this domain as a bridge between psychosocial and governance determinants, emphasizing that sustainability depends on fairness, respect, and moral responsibility toward both human and non-human environments.

This domain incorporates perspectives from moral philosophy and cross-cultural ethics. Cockell ³⁵ argues that space exploration has intrinsic moral value linked to humanity’s broader ethical development, highlighting the need for moral reflection in extraterrestrial activity. This theoretical grounding situates cultural and ethical determinants not as peripheral to sustainability but as constitutive systems of meaning and decision-making that affect interpersonal trust, justice, and planetary stewardship.

Governance and Policy Structures

The seventh domain, Governance and Policy Structures, captures the macro-level determinants that define authority, regulation, and accountability in space missions. Similar to public policy and institutional structures in SDOH, governance determines how decisions are made, how risks are distributed, and how crew autonomy is balanced with institutional oversight. Transparent governance fosters trust, while rigid hierarchies or ambiguous authority can undermine cohesion and psychological safety. ⁵ Conceptually, this domain highlights that sustainability in space requires clear governance mechanisms as determinants of stability and ethical practice, particularly as missions become increasingly international and commercial.

This domain draws from institutional and organizational systems theory, which explains how formal and informal structures shape behavior, authority, and accountability. Institutional theory emphasizes that governance systems create the norms and incentives that guide collective action, suggesting that equitable and transparent governance is a determinant of both mission integrity and psychological safety.

Learning and Systems Adaptability

The eighth domain, Learning and Systems Adaptability, emphasizes education, training, and feedback as conceptual determinants of resilience and growth. On Earth, access to education and health literacy influence health outcomes; in space, the capacity for continuous learning, problem-solving, and systems-level adaptability determines resilience. ⁷ Adaptability operates at both individual and organizational levels: astronauts must integrate new information quickly, while mission systems must evolve based on real-time data. Within the conceptual framework, adaptability is posited as a determinant linking cognitive flexibility to systemic resilience, thereby enabling recovery and innovation under unpredictable conditions.

This domain builds on Senge’s ³⁶ organizational learning theory, which defines adaptive organizations as those capable of continuous feedback, self-correction, and collective learning. In long-duration space missions, adaptability functions as a survival determinant: the ability of crews and systems to learn from errors and integrate new information directly affects resilience and sustainability. This domain includes continuous training, skill refreshment, and crew education, which are critical components for long-term mission success in dynamic and unpredictable environments.

Intergenerational and Reproductive Health

Finally, Intergenerational and Reproductive Health extends the SSDLiS model into future settlement contexts. While current missions involve small, adult crews, the long-term sustainability of human presence beyond Earth will depend on reproductive health, developmental environments, and transgenerational well-being.^37,38 This domain parallels lifespan determinants in SDOH, including maternal and child health and early development, but reframes them conceptually for extraterrestrial conditions such as radiation exposure, microgravity, and confined ecological systems. A foundational question that must guide research in this domain is whether normal human development and growth can occur in reduced or zero gravity. This encompasses questions of fetal development in microgravity, infant skeletal and muscular development, vestibular system maturation, and the physiological prerequisites for viable, thriving human life across generations. As human habitation evolves, this domain represents the ultimate conceptual measure of sustainability.

This domain draws from lifespan developmental theory and Bronfenbrenner’s bioecological model of human development, ¹⁶ which conceptualizes development as an outcome of interactions between individuals and their environmental systems over time. Applying this perspective to extraterrestrial contexts emphasizes that sustainable human presence must account for reproductive health, developmental processes, and transgenerational well-being as integral components of space settlement.

Risk Mitigation Considerations

Risk mitigation within the SSDLiS framework requires attention to a set of cross-cutting hazards that extend beyond traditional biomedical countermeasures and intersect multiple domains. Isolation and psychological effects, for example, emerge most directly within Psychosocial and Behavioral Adaptation (Domain 5), where extended confinement and distance from Earth can precipitate depression, anxiety, and deteriorating mental health, demanding psychosocial monitoring, peer support structures, and access to mental health resources.

Ethical and moral decision-making challenges are rooted in Cultural and Ethical Determinants (Domain 6) and Governance and Policy Structures (Domain 7), as crews and institutions confront dilemmas related to resource allocation under scarcity, distribution of risk among crew members, medical prioritization, and end-of-life care in extreme environments, all of which require ethical frameworks and training in moral reasoning. Death in orbit and off-world similarly represents a convergence of Health and Biological Systems Maintenance (Domain 4), Psychosocial and Behavioral Adaptation (Domain 5), and Cultural and Ethical Determinants (Domain 6), since procedures for managing remains, multiple-casualty scenarios, and long-term psychological processing must be developed in ways that honor cultural norms while supporting crew functioning over time.

Planetary protection concerns sit at the intersection of Cultural and Ethical Determinants (Domain 6) and Governance and Policy Structures (Domain 7), reflecting the scientific and moral imperative to prevent harmful contamination between terrestrial and extraterrestrial environments through quarantine protocols, sterilization standards, and containment of hazardous materials. Crew safety during emergencies highlights the importance of Technological Infrastructure and Operational Reliability (Domain 3) and Health and Biological Systems Maintenance (Domain 4), as effective emergency response procedures, evacuation and rescue capabilities, and medical care during system failures depend on reliable hardware, clear protocols, and rehearsed coordination.

Finally, equitable risk distribution underscores the role of Governance and Policy Structures (Domain 7), Cultural and Ethical Determinants (Domain 6), and Psychosocial and Behavioral Adaptation (Domain 5), since fair allocation of occupational risks across missions, assignments, and roles is fundamental to psychological safety, trust, and long-term commitment to space exploration. Taken together, these interrelated hazards illustrate how SSDLiS not only classifies determinants but also provides a structure for understanding and addressing the complex risk landscape of human life in space.

Governance and Settlement Model Considerations

A fundamental question for long-term space sustainability concerns which governance models will guide off-Earth human expansion. One potential precedent is an international governance framework, such as that in Antarctica, based on scientific cooperation, environmental protection, and shared responsibility, with an explicit prohibition on military activities. Antarctic research bases operate under multi-institutional governance, with decision-making distributed among international partners and local authority structures negotiated among participating nations.

In contrast, early space settlements may adopt governance models more similar to military or corporate command structures, where authority is hierarchical, decision-making centralized, and operational priorities shaped by commercial or strategic objectives. Such structures may enhance operational efficiency but could compromise crew autonomy, transparency, and equitable resource allocation, which are factors documented as important for psychological health and cohesion.

The SSDLiS framework does not prescribe a specific settlement model but highlights that governance choices directly affect multiple sustainability domains such as psychological well-being, cultural integration, ethical decision-making, and learning capacity. Future space policy and settlement design may explicitly address these choices and their implications for human sustainability.

Comparison of SSDLiS with Established Determinant Frameworks

The conceptual foundation of the SSDLiS framework aligns closely with established models of the SDOH and the SDOMH. These Earth-based frameworks emphasize that health outcomes are shaped by broad social, environmental, and structural factors rather than individual choices alone.^12,13 In developing SSDLiS, similar principles are adapted conceptually to extraterrestrial contexts, where determinants are reframed around the distinctive conditions of space habitats, which are entirely engineered, highly interdependent, and inherently fragile.

The SDOH domains identified by WHO, including economic stability, education, health care access and quality, neighborhood and built environment, and social and community context, provide a starting point for understanding the structural components of well-being. SDOMH frameworks highlight how social inequities, stigma, trauma exposure, and access to support shape mental health outcomes.^14,15 The SSDLiS framework extends and reconfigures these models at a conceptual level to address the unique ecological and psychosocial realities of space habitation.

The Physical and Environmental Habitat domain parallels the built environment in SDOH, but shifts focus to fully engineered habitats, where environmental parameters such as radiation exposure, gravity, atmospheric composition, and lighting become active determinants of survival. ⁷ Life Support and Resource Sustainability reinterprets the role of infrastructure and basic resources, emphasizing closed-loop systems for water, air, and food, as well as the necessity of redundancy and resilience to maintain equilibrium. ²²

The domains of Technological Infrastructure and Operational Reliability and Health and Biological Systems Maintenance further expand SDOH’s concern with health care systems and preventive services. In space, these determinants include the reliability of mission operations, robotics, artificial intelligence, and monitoring technologies, as well as the biomedical countermeasures essential to maintaining physical health under microgravity and radiation stressors. ⁵

Social and psychological determinants are represented through the domains of Psychosocial and Behavioral Adaptation and Cultural and Ethical Determinants, which extend SDOMH concepts of community support, cultural context, and stigma. These domains address the challenges of isolation, communication delay, multicultural team dynamics, and ethical decision-making in confined and high-risk environments. Here, mental health is conceptualized as being sustained not only through external support but also through autonomous psychosocial resilience and intercultural competence.^4,15

At a structural level, Governance and Policy Structures function as the analog of legal and institutional determinants in SDOH, determining how authority, autonomy, and resource allocation are distributed within mission contexts. This domain acknowledges that space governance operates beyond traditional national systems, requiring new policy frameworks for safety, equity, and sustainability. Learning and Systems Adaptability reframes the SDOH domain of education, emphasizing continuous learning, adaptive capacity, and feedback mechanisms as essential determinants of resilience in uncertain environments.

Finally, Intergenerational and Reproductive Health extends the SSDLiS framework toward long-term habitation and settlement contexts, paralleling lifespan health determinants in SDOH. It anticipates future considerations such as reproduction, child development, and the intergenerational transmission of health and well-being in off-Earth environments.

Overall, SSDLiS conceptually mirrors the logic of SDOH and SDOMH but reorients it for the engineered, closed, and interdependent systems of space life. Whereas Earth-based models address disparities in access, resources, and opportunity, SSDLiS addresses fragility, autonomy, and adaptation as determinants of sustainability. By integrating physiological, psychosocial, technological, and governance dimensions, the framework proposes a comprehensive conceptual approach for understanding and promoting human well-being beyond Earth.

Potential New Space Applications

The SSDLiS framework offers a foundation for conceptually exploring systems-based approaches to human sustainability across scientific, policy, design, and psychosocial domains. Within the New Space context, the framework highlights how human-centered sustainability can inform emerging sectors such as commercial habitats, private orbital stations, and space tourism. It provides a prospective lens for considering how private-sector actors developing human-rated systems might integrate determinants of human sustainability into their business models and design criteria to reduce risk and improve mission outcomes.

As an early-stage conceptual model, SSDLiS is not yet empirically validated, but it may offer an adaptable structure for future operationalization, measurement, and intervention as human presence in space evolves. The framework could serve as a bridge between human research and enterprise strategy, promoting interdisciplinary dialogue and conceptual alignment across sectors in the emerging space economy. The following applications illustrate possible areas where SSDLiS may inform theory development and practice.

Research and Measurement

SSDLiS provides a conceptual basis for developing future quantitative and qualitative metrics to capture the interdependence of environmental, technological, physiological, and psychosocial systems. Each domain can serve as a category for designing assessment tools or mission health indices that extend beyond individual performance outcomes. Existing instruments, such as the Integrated Space Habitability Observation Recording Tool and the Space Habitability Assessment Questionnaire, illustrate how environmental and psychosocial factors are currently evaluated. ¹ NASA’s Behavioral Health and Performance tools monitor mood, stress, and cohesion across mission phases, ³ and ESA’s MELiSSA program uses closure metrics for air and water cycles to assess environmental sustainability. ²²

These instruments demonstrate how the logic of SSDLiS could be applied to measurement development, supporting future evidence-based mission planning and systems integration. Subsequent research may test hypotheses regarding how changes in one determinant influence others. The framework thus encourages conceptual movement toward multidomain data architectures capable of examining human sustainability as an emergent property rather than an isolated variable. ⁵

Policy and Governance

The SSDLiS framework can conceptually inform future policy and governance efforts in space exploration. Existing initiatives such as the Space Sustainability Rating and planetary protection protocols^2,10 reflect a trend toward ethical stewardship. Embedding SSDLiS within these governance frameworks could broaden their focus to include psychosocial health, equity, and intergenerational justice, reframing human sustainability as central rather than peripheral.

At the policy level, SSDLiS offers a conceptual lens for integrating human well-being into sustainability rating systems and international collaboration frameworks. Drawing on guidance from the National Academies of Sciences, Engineering, and Medicine, ⁷ the model underscores the value of cross-disciplinary integration of life sciences, behavioral health, and systems design. SSDLiS domains such as Governance and Policy Structures and Cultural and Ethical Determinants may serve as theoretical foundations for future human-centered sustainability standards. Such integration remains aspirational but highlights a conceptual shift from reactive safety management to proactive sustainability planning.

Habitat and Mission Design

For architects and engineers, SSDLiS provides a conceptual roadmap for embedding human factors into the physical and organizational structure of space habitats. Current design research already emphasizes modular layouts, lighting for circadian health, and acoustic management. ¹ The SSDLiS framework aligns with and extends these considerations by proposing that psychosocial and cultural determinants should also inform early-stage design.

Rather than prescribing specific standards, SSDLiS invites exploration of how the interplay between physical, technological, and psychosocial systems supports habitability, crew cohesion, and autonomy, which are factors associated with long-term mission success. ⁴ As mission architectures evolve toward lunar bases and Martian settlements, SSDLiS may serve as a conceptual design-check framework, ensuring that built systems support not only survival but also well-being and adaptability.

Behavioral Health, Counseling, and Training

The SSDLiS framework also provides a conceptual structure for linking counseling psychology, behavioral health, and astronaut training. Long-duration missions intensify psychosocial challenges such as isolation, cultural tension, and delayed communication. While interventions such as resilience training, cultural competence workshops, and premission counseling are well-documented,^3,39 SSDLiS offers a framework for organizing and contextualizing these efforts.

The psychosocial, ethical, and adaptability domains highlight areas for further research on psychological readiness and in-mission support. The model also aligns conceptually with emerging digital and AI-based behavioral health systems, ⁵ though their integration into long-duration missions remains hypothetical. Collectively, these examples illustrate how SSDLiS can guide future empirical exploration of psychosocial sustainability.

Long-Term Human Settlement and Sustainability

In anticipation of future permanent or semi-permanent habitation, SSDLiS suggests conceptual directions for studying intergenerational well-being, reproductive health, and social continuity. The Intergenerational and Reproductive Health domain emphasizes research needs related to prolonged exposure and development.^37,38 Similarly, the Governance and Learning domains underscore the importance of adaptive institutions for sustaining ethical and cultural integrity across generations.^2,25,26

In this sense, SSDLiS functions as a theoretical framework rather than a predictive model, guiding inquiry into how biological, social, and ethical systems might coevolve beyond Earth. ⁹

Limitations and Future Directions

As a conceptual model, the SSDLiS framework remains preliminary and theoretical. While it provides an integrative structure linking environmental, technological, and psychosocial determinants, it has not yet been operationalized or empirically validated. Several limitations should be noted.

First, the framework is derived largely from Earth-based logics that assume social and environmental stability. These assumptions may not fully translate to closed, high-risk space environments. Second, domain interdependence is conceptually strong but methodologically challenging, since measuring cross-domain feedback loops will require new analytic tools. Third, empirical data from long-duration missions beyond low Earth orbit remain scarce, which limits validation of the framework under sustained extraterrestrial conditions.

To address these limitations, future research should test and refine SSDLiS through analog environments such as HI-SEAS, SIRIUS, and Concordia Station. These settings simulate the isolation, confinement, and interdependence of extraterrestrial living systems, allowing exploration of determinants such as psychosocial adaptation, governance, and resource sustainability. Mixed-methods designs that combine physiological monitoring, behavioral analysis, and qualitative ethnography could help identify measurable indicators within each domain.

Cross-sector consortia could also coordinate data-sharing platforms for SSDLiS validation, linking engineers, behavioral scientists, and policy specialists. The creation of a Human Sustainability Observatory, which would be a distributed research network integrating analog mission data, AI-based simulations, and Earth-space comparison studies, could accelerate the framework’s transition from conceptual theory to applied model. Such initiatives would position SSDLiS as a foundation for developing human sustainability metrics that are comparable across missions, agencies, and commercial platforms.

Interdisciplinary collaboration will remain central to this agenda. Engineers, biologists, behavioral scientists, and ethicists should co-develop research protocols that view human sustainability as an emergent property of coupled human, technological, and environmental systems. SSDLiS may serve as a conceptual reference for structuring such collaborations and for establishing shared terminologies or metrics across organizations such as NASA, ESA, and private-sector partners. Its application should remain exploratory until empirical evidence supports broader operational use.

Over time, continued testing and refinement of SSDLiS could help anticipate the transition from mission-level to settlement-level sustainability. As research evolves to include intergenerational health, social continuity, and governance in extraterrestrial environments, the framework may inform early theoretical and policy development. By linking determinants conceptually rather than prescriptively, SSDLiS provides a foundation for the next generation of integrative human research, guiding the gradual emergence of evidence-based models for sustainable life beyond Earth.