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A Demographic Analysis of Greenspace Exposure Requirements in Self-Sustaining Space Settlements

Benjamin W. Calloway¹, Parimala Krishnamurthy^1
1 Department of Human Factors and Culture, International Space Education and Research Guild (ISERG)

Published: Aug 2026

Type: Working paper

Citation
Calloway, B. W., and Krishnamurthy P., "A Demographic Analysis of Greenspace Exposure Requirements in Self-Sustaining Space Settlements," International Space Education and Research Guild, 2026.

DOI: https://doi.org/10.5281/zenodo.22071774

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A Demographic Analysis of Greenspace Exposure Requirements in Self-Sustaining Space Settlements Benjamin W. Calloway1, Parimala Krishnamurthy1 1 Department of Human Factors and Culture, International Space Education and Research Guild (ISERG), Walton, Kentucky, United States Abstract The design of space settlements presents unprecedented challenges to human factors, particularly regarding the ex-posure of inhabitants to “green” natural elements and environments. Prolonged absence from nature induces signifi-cant psychological and physiological degradation, and targeted exposure to nature results in stress reduction, cognitive restoration, immune system support, and decreased risk of mood disorders for some individuals. Through an integrative review of relevant literature, this paper evaluates the specific wellbeing requirements of key demographic groups – in-cluding children, students, working adults, and elders – within hypothetical space habitats. The analysis indicates that exposure requirements vary across life stages, with hands-on interaction, passive viewing, and immersion in green-space environments offering benefits such as mitigating solipsism syndrome, relieving work-induced mental fatigue, and restoring attention. To optimize the health, productivity, and operational resilience of space inhabitants, future set-tlement designs must strategically incorporate real physical greenspaces and plant-interaction opportunities tailored to demographic routines. 1 Introduction Early space settlers will have fewer amenities than we do on Earth. Specifically, they will have severely restricted access to nature. Most people on Earth can go outside and immediately be immersed in biodiversity currently known to be unique to our planet. For the initial genera-tion of space settlers, their emigration will come with a sense of loss and longing for what they may have taken for granted. Even on Earth, where nature surrounds us, we can get into situations where we are away from natural environments for weeks, months, or longer. During these periods, hu-mans are deprived of the multifaceted benefits of nature exposure. Psychologically, nature can reduce stress and anxiety and improve mood, cognitive function, attention, and more. Physiologically, it can lower blood pressure and reduce mortality from cancer and cardiovascular and respiratory issues. In current in-space habitats, these benefits are largely lost due to the low intensity and diver-sity of the natural elements found there. Using integrative methods [1], this paper will review the state of theory and study about how human health de-pends on exposure to nature and what these needs will be in a self-sustaining space settlement. To reduce selec-tion bias, two researchers (Calloway and Krishnamurthy) will screen the results of literature discovery. The re-search question to be answered is: In a first-generation Calloway and Krishnamurthy ISERG Page 2 of 8 space settlement, what are the psychological and physi-ological needs of prominent demographic categories for “green” nature exposure to maintain personal wellbeing? The findings will inform the future design of such space settlements so they may better accommodate inhabitant wellness. 2 How Nature Exposure Affects Human Psychology and Physiology There is much evidence, and many theories, connecting human health and physical nature exposure. Studies have demonstrated the benefits of natural elements and environments on our psychology and physiology. These studies inform the exposure requirements for the optimal performance and wellbeing of prominent demographic categories. 2.1 Benefits from Nature Exposure The psychological benefits from nature exposure will be discussed first. Across demographics, short-term expo-sure to greenspaces and other natural environments has positive effects on mood, self esteem, and emotions, and reductions in the negative effects of depression, stress, and attention fatigue [2–7]. Certain demographics are shown to benefit differently. Because the brains of children and adolescents are im-pressionable and developing, it is especially critical to maintain their psychological health. In children, contact with nature may improve their mood and cognitive func-tioning, increase their social interactions, and improve ADHD symptoms [8]. Also, in children and adolescents, high levels of “green time” (engagement with nature), as opposed to “screen time” (engagement with screen-based technologies), were associated with more favora-ble psychological outcomes [9]. College and university students are a demographic known to be especially encumbered by chronic psycho-logical effects including stress and depression. For peo-ple of college age, studies show that sitting or walking in natural settings may significantly and positively impact psychological wellbeing, including a reduction of stress symptoms [10,11]. Working adults are a much more numerous demographic than children, adolescents, or college students. Day-to-day employment activities vary in intensity and psycho-logical effect, and much of the workforce faces negative psychological effects from their employment at some point in their career. Outdoor nature contact during the workday was shown to correlate with higher task perfor-mance and prosocial behavior [12]. Adults who spend time in greenspace shortly after their workday may show improvements to positive emotion, subjective vitality, and restoration [13]. While exposure to natural environments is shown to have several benefits, absence from such environments for ex-tended periods is shown to reduce psychological wellbe-ing. On Earth, urban environments expose inhabitants to noise, pollution, commuter traffic, high task frequency, and other stressors. Entering a natural environment re-duces access to digital screens, distancing people from digital media relating to global crises like climate change and war, which if consumed excessively may negatively affect the viewer’s health. Even the view of greenspace through windows of a residence or confined space is as-sociated with a lower risk of psychological illnesses like anxiety and depression [14,15]. In children, a lack of interaction with nature in early life has been associated with multiple emotional and cogni-tive difficulties, termed “nature deficit disorder” (NDD) [16 (citing Louv, 2005)]. At post-secondary academic in-stitutions, it was found that counseling directors fre-quently must reduce the number of visits for non-crisis patients to handle an overall increase in their number of clients [17]. This implies that alternative modes of psy-chological amelioration should be accessible to students of such institutions. In working adults, confinement to na-ture-bare urban environments over extensive labor peri-ods can lead to stress accumulation, reduced task per-formance, reduced socialization, and other modes of psychological depletion [12,13]. People are affected not just psychologically by nature ex-posure, but physiologically as well. Natural environments Calloway and Krishnamurthy ISERG Page 3 of 8 are shown to reduce mortality related to cancer and res-piratory and cardiovascular issues, and the “greenness” of mothers’ neighborhoods was positively associated with higher infant birth weight [16]. Walking in a forest, or even sitting in a room with a natural view, was shown to cause a decline in blood pressure compared to walking or sitting in an urban environment [18]. Physical exposure to biodiverse plants and microbiota has been associated with better immune-system performance [2,16,19]. Chil-dren with higher access to greenery were shown to have lower blood pressure [20]. Exposure to sunlight is well known to correlate with the body’s creation of vitamin D3. It should be pointed out that studies on the effects of in-door plants on wellbeing have been reviewed to have mixed results, but a strong relation has been made be-tween the presence of plants and pain management [21]. Thus far, the discussion has been on exposure to real nat-ural environments. However, there have been several studies on the effects of simulated natural environments on psychological health. Immersion of individuals in a simulated natural environment through a virtual-reality (VR) headset was conducted to test the effects on stress, respite, and other psychological characteristics in highly fatigued frontline workers, hospital patients under critical active treatment, and people with limited access to na-ture (such as people with reduced physical mobility) [22–24]. Because of the differences in reality and perception between simulated and real natural environments, this study will focus on the latter while recognizing that future research should be done on the former. 2.2 Nature-Exposure Requirements for Human Satisfaction These benefits imply that natural elements should be in-tegrated into urban environments and that natural envi-ronments (distinct from urban environments) should be accessible to everyone per common humanitarian eth-ics. On Earth, there are relatively few instances where it is prohibitive to enable such access. However, in addition to physical accessibility, there are other considerations to maximize the effectiveness of greenspace: opportunity of CategoryDemographicType of ExposureIntensity (Period or Frequency)Experiment ResultsSourceMiddle-school pupilsAccess to a renovated schoolyard with greenery, water features, and wooden furnitureRegular daily access during school breaksProven: a greener schoolyard related to reduced physiological stress, as well as improved psychological wellbeing and perceived restorativenessKelz et al. (2013)Preschool pupilsOutdoor playtime in natural environmentsVariable (averages of outdoor hours throughout the year)Proven: more daily outdoor hours related to reduced inattention and hyperactivity in the following yearsUlset et al. (2017)University studentsSelf-chosen natural environment20 minutes once a week, for three weeksProven: restorative natural environments related to wellbeing and reduced stress and burnoutPayne et al. (2020)Full-time office employeesPhysical contact with nature outside the office during the workdayVariableProven: exposure to nature at work related to improved task performance and prosocial behaviorTang et al. (2023)Healthy working adultsUrban natural environments (a park and a woodland)15 minutes of viewing while sitting, followed by a 30-minute self-paced walkProven: increased perceived restorativeness, subjective vitality, mood, and creativity, while decreasing negative mood (compared to city-center control)Tyrväinen et al. (2014)Adults with restricted mobilityMale prisoners under pandemic-related isolationViewing greenspace through cell windowsVariableProven: visibility of nature related to life satisfaction, wellbeing, distress tolernance, and reduced loneliness, depression, and anxiety symptomsLi et al. (2021, "Prisoners")Table 1. Categorization of demographics and associated type, intensity, and effects of nature exposureStudying or working adultsChildren Calloway and Krishnamurthy ISERG Page 4 of 8 use (e.g. having the time to use it), personal motivation and reasons for use (e.g. having multiple outlets of value extraction, such as walking the dog, birdwatching, and using it as a shortcut), and ease of use (e.g. appropriate weather conditions and lighting) [25]. Biodiversity is an-other factor being explored [16]. It has also been shown that different demographics ben-efit differently from nature exposure varied by magnitude, period, frequency, and type. Data exemplifying this were collected from a scoping sample of literature and sum-marized in Table 1. 3 Characterization of Space Settlements and Inhabitants For this study, we define a space settlement as a self-sus-taining settlement of people outside the biosphere of Earth. The settlement is assumed to be operating in a steady state, thus fully constructed, operational, and with appropriate population and demographic ratios. In The High Frontier, one of the foundational works on space settlement, O’Neill proposes several types of space settlement [26], with one such being a long-term roving research community. The population of such would be thousands, about 25% of whom would be school- or college-aged individuals and about 50% would be an active workforce. Prominent categories in such a workforce would be composed of community service workers, equipment servicers and technicians, and re-searchers. The large student population implies that schools, universities, and/or training programs would be present to educate upcoming members of the workforce. Earlier embodiments of settlements would require inten-sive workload, so there may be little to no unemployment. In later, more optimized settlements, on-site retirement of elderly populations would be possible. A “starship” capable of a successful 5-generation inter-stellar migration is estimated to require about 40,000 people [27]; about 13,600 would be “subadults” (children and adolescents); 23,400 adults; and 3,000 elders. Across the generations, it is obvious that the children would need to learn, and the adults would need to main-tain the spacecraft and operations. Another settlement, smaller in scale, is proposed of about 491 people, most of which would come from large cities to source the technical expertise necessary to op-erate such a complex space structure [28]. If a catastrophic event were to occur on Earth prompting an emergency extraterrestrial settlement operation, Mars is a proposed location [29]. Such a settlement would be composed of individuals selected for their value to the continuation of the race: “astronauts, science engineers, space policy experts, and, most importantly, average cit-izens with general or specific skills”. Depending on the purpose of the settlement, other specific roles may be re-quired, such as doctors, medics, miners, and soldiers. SourceO'Neill (1976)Smith (2014)Covey and Faber (2017)Szocik et al. (2020)Settlement CharacterizationLong-term roving research communityA "starship" capable of a successful 5-generation interstellar migration A small-scale, first-generation space settlement (4 rotations per minute)An early, high-risk Martian outpostDemographic Children and adolescentsSchool-aged children"Subadults"ChildrenChildrenStudying or working adultsCollege-aged adults; active workforce (community services, equipment servicers, researchers)"Adults"Adults with technical expertiseAdults with general and specific skillsetsEldersWorking elders; compensated retirees"Elders"Not reportedNot reportedTable 2. Demographic categorization of space settlement modelsProminent Roles Calloway and Krishnamurthy ISERG Page 5 of 8 The demographic distributions per cited model are sum-marized in Table 2. These case-based demographics are categorized into children, studying or working adults, and elders, which relate to the categories of study cited in Section 2. 4 Nature Exposure for Space Inhabitants There has been prior research evaluating the nature-ex-posure needs of space dwellers, and there are numerous anecdotes of astronauts and cosmonauts expressing af-fection for plants while on space missions. These re-sources in addition to those collected in the previous sec-tions will be synthesized to suggest recommended na-ture-exposure conditions for prominent demographic categories expected to be found in self-sustaining space settlements. 4.1 Existing Research and Discussion Some evaluation has been done to predict the needs of future space inhabitants for nature exposure and interac-tion. NASA released a report titled Space Settlements: A Design Study, which includes an appendix on the “Psy-chological and Cultural Considerations” of “Human Needs in Space” [30]. The appendix mentions “solipsism syndrome”, “the state of mind in which a person feels that everything is a dream and is not real”. The NASA research-ers suggest the highly controlled and organized environ-ment of a space settlement would be conducive to this state. They also suggest the risk can be alleviated by in-troducing unpredictable elements, such as plants and animals with some independence from “human plan-ning”. In contrast to the nature-bare urban environments and deserts on Earth, O’Neill envisioned free-flying space set-tlements with diverse natural environments composed of grass, trees, flowers, and animal species [26]. He also mentioned that the first humans living in space will expe-rience a “future shock” that should be quelled in part by familiar and natural environments. He noted that sunlight is quite accessible but suggested a day/night cycle should be implemented to align with natural human circadian rhythms. He also suggested that his proposed communities would be well populated with greenery for the purpose of inhabitant wellness: “Within, I suspect that the traveling laboratory would be landscaped in a manner expressive of the inhabitants' need for the psy-chological solace of lush vegetation.” [26, p. 244]. He also suggested that the elderly or infirm population, which on Earth would normally be confined to beds or other limited-mobility situations, would have opportuni-ties to mobilize freely at higher “elevations” in the space-craft (closer to the rotational center). This implies that such demographics would be more freely able to explore the greenspace of the settlement compared to people in similar situations on Earth. However, greenspace imple-mentations at such elevations may be limited, for exam-ple, to hydroponic growth and vertically climbing species. In addition to ambient nature exposure, hands-on inter-actions with plants are shown to have benefits, and sev-eral anecdotes exist of astronauts and cosmonauts showing affection to handling plants. It is suggested that gardening or caring for plants can restore “directed atten-tion” used for complex cognitive processes [31] such as those common to the daily research activities of astro-nauts on long-duration space missions [32] and which will surely be prominent in space settlements, especially in early embodiments. An early indication of the positive psychological effects of growing plants in space is given by the spaceflight diary of cosmonaut Valentin Lebedev: “we feel sad and uncomfortable without our garden and without our dear plants. It was such a pleasure to take care of them. Man probably has a need to take care of things and without those things feels empty.” [33]. Peggy Whitson, Don Pettit, Scott Kelly, and other astronauts have also quoted sympathies for plants they cared for in space [32]. 4.2 Exposure Suggestions for Inhabitants The models cited in Section 3 for future space settle-ments support the assumption that a majority percent-age of the population of such a settlement would be working or learning. Due to the complex and underdevel-oped nature of early space settlements, the workload of such would likely be especially intense. An intense Calloway and Krishnamurthy ISERG Page 6 of 8 workload implies mental and physical stress, the effects of which are negative in chronic amounts. Stress may lead to further psychological or physiological issues. Even for inhabitants not exposed to intense workloads, it’s assumed that there will be some with chronic mental or physical illnesses that affect similar people on Earth today. Zeroth-generation settlers (i.e. those who formerly lived on Earth) may have more intense needs for nature expo-sure due to homesickness. Sufficient nature exposure is also important to prevent the recession of human-nature interactions across generations [34], which could be det-rimental to the population and prohibitively difficult to re-cover from. In addition, for the long-term health of the im-mune system and microbiome of humans living in space, a sufficiently biodiverse environment may be necessary [35]. This may reduce health risks in the settlement pop-ulation and in any individual returning to the biodiversity of Earth (refer to David Vetter, the “bubble boy”). Virtual-reality (VR) simulations of nature exposure have been studied as a compromise for demographics without feasible access or opportunity to use real natural environ-ments. However, simulated exposure is assumed to not be as effective at mitigating solipsism syndrome as expo-sure to real nature in part because simulation code is ul-timately human-controlled. However, simulated natural environments are still an active area of study, and the benefits and applications of such in space settlements should also be a topic of future study. Useful cases for a simulated natural environment such as via VR headset in-clude situations of intense work in constrained environ-ments (e.g. missions on a confined spacecraft or isolated section of the habitat) or for analogous purposes as are currently proposed on Earth (e.g. during intense extended medical procedures). As on Earth, nature exposure needs in a self-sustaining space settlement will differ across demographics. How-ever, the most obvious general implementation is to in-sert natural elements and environments into the routines of individual people. For working people, it would be ben-eficial for natural environments to be accessible or in view during the work period [12,14]. For workers commut-ing between their residence and their workplace, it would be beneficial for them to be able to pass through a natural environment for an extended period (at least 15 minutes) [13], though this may be infeasible for space-constrained settlements. People with a shorter commute or an ab-sence of one should have access to easily usable green-space for at least 20 minutes a week [11]. There should also be opportunities to handle plants (e.g. via gardening or light care) and to have them indoors [21,32]. For children, prolonged access to natural envi-ronments during the school day should be possible and encouraged [20,36], but the effective embodiments of such (e.g. green schoolyards) should be studied further. The implementation of all such embodiments of nature exposure would allow the most inhabitants the greatest ease to obtain the benefits relevant to their demographic. It is currently unclear whether each of these embodi-ments would be feasible and to what extent they would be redundant relative to each other, so further research is called for. 5 Conclusions Research on the benefits of “green” nature exposure on human health was collected and categorized by demo-graphic category, showing the variation of exposure type, intensity, and effects. Typical space settlement models were collected and compared, highlighting historical mentions of nature-exposure benefits and needs to the hypothetical inhabitants. Finally, a demographic catego-rization of a typical self-sustaining space settlement was performed, the need for nature exposure in such a settle-ment was validated by prior research and anecdotes, and suggestions were made for the exposure requirements of future space inhabitants, with special needs suggested for early settler generations and on early settlement em-bodiments. It is suggested that, if feasible, all correlating beneficial natural elements and environments should be designed for and implemented in future space settlements to yield maximum positive effects on the psychological and phys-iological wellbeing for the greatest number of inhabitants. Since such an ideal is unlikely, more research is needed to determine the most feasible and effective embodi-ments of natural elements and environments. Calloway and Krishnamurthy ISERG Page 7 of 8 Nature-exposure needs of the initial settlers (i.e. the ze-roth generation, coming from Earth) should be predicted and compared to the predicted needs of later generations (i.e. those born in the settlement). Of the exposure types found to benefit various demographics on Earth (green-space access, passive elements, viewing, handling, digi-tal simulation, etc.), those relevant in space settlements should be ranked – by factors like effects on wellness, ef-fects on productivity, difficulty of design, cost of imple-mentation, and sustainability – to determine priority and feasibility, which would in turn inform future space-set-tlement mission designs. In addition, since leisure and choice are expected to be more restricted in space settle-ments than generally on Earth, the characterization and effects of these restrictions should be applied to the de-sign of realistic nature access in such settlements. 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