https://orcid.org/0000-0001-5220-4206
ABSTRACT
This editorial initiates a dialogue on transport planning within permanent space settlements. It introduces a conceptual model outlining key elements and contextual factors integral to the development and operation of transport systems in space communities. The unique constraints of space environments (e.g. cosmic radiation, gravity, atmosphere, temperature, dust and soil) require systems prioritising efficiency, safety, resilience, accessibility, and well-being beyond Earth’s requirements. Collective and active modes along vertical and horizontal axes within compact settlements may be optimal due to resource constraints. Innovative energy storage and sharing systems, enhanced materials, and new maintenance protocols will likely be required for modular, adaptable pressurised tunnel or tube-based transport systems. To ensure safety and operational integrity, a rigorously managed traffic environment is anticipated, requiring a balance between demand, capacities, and service frequencies. Comfortable and joyful travel environments would be needed to alleviate stressors associated with tunnel-based travel. Governance and policies would be expected to prioritise aspects such as well-being and social equity in response to harsh space conditions and resource constraints. Future research could involve system-level, interdisciplinary and participatory futures and simulation methods to address the complexity and uncertainties inherent to transport planning in space settlements.
1. Introduction
Humanity plans long-term space settlements driven by curiosity, science, environmental and economic reasons. The International Space Exploration Coordination Group (ISECG; 14 Space Agencies) outlines a three-phase roadmap for expanding human presence from low Earth orbit to the Moon and Mars (ISECG, Citation2018, Citation2022). Phase 1 (Boots to the moon) involves manned and robotic missions to the Moon, supporting future phases. Phase 2 (Lunar exploration – expanding and building) comprises the identification of optimal sites for human landing and exploring the lunar surface for extended habitation and resource utilisation. Phase 3 (Sustained lunar opportunities) plans for a sustained lunar presence and the initiation of Mars explorations. Phase 1 is currently being developed by lunar missions like Artemis (NASA, US) and Chang’E (CNSA, China), and it is anticipated to be completed in 2027.
Despite detailed plans for phases 1 and 2, phase 3 (regarding permanent lunar communities) remains largely unexplored, with minimal discussion on the organisation and operation of other extraterrestrial settlements. Current research has predominantly centred on the “known unknowns” of phase 1 and 2, including technology, habitat and mobility aspects. Habitat studies have explored the architectural and structural design, materials, energy supply, and life-support systems (see e.g. Farries et al., Citation2021; Hartwick et al., Citation2023; Higgins & Benaroya, Citation2020; Paul et al., Citation2022). Mobility studies have focused on the development of rover concepts, designs and technologies (e.g. general architecture (wheels, suspensions, brakes, powertrain): Baratta et al., Citation2019; traverse path planning: Heldmann et al., Citation2016; autonomous decision making and obstacle avoidance: Candela & Wettergreen, Citation2022; teleoperation: Coloma et al., Citation2022; wheel performance in reduced gravity: Daca et al., Citation2022; high speed mobility: Rodríguez-Martínez et al., Citation2019) as well as on the energetics of human locomotion (e.g. stability, posture, movement: Newman & Alexander, Citation1993; and the dynamics of extra-vehicular activities in low-gravity surface environments: Spencer & Gast, Citation2013). However, thorough studies addressing transport systems tailored for space settlements are lacking, signifying an important area for future research. Exploring these concepts could be pertinent in adapting terrestrial transport systems given environmental challenges and the ongoing climate emergency.
This editorial argues for opening the discussion for transport planning in permanent space settlements shedding, for the first time, light on a fundamental dimension of phase 3 space exploration. What would be the travel needs and preferences of people and companies in extraterrestrial space settlements? By which travel modes and transport infrastructures could these needs be served? How a transport system in extraterrestrial space settlements could operate and under which restrictions? What types of freight transport are suitable for various activities on extraterrestrial planets? What would be the implications of the transport system development for safety, environment, health, well-being and social equity of the space settlement inhabitants? These are among the essential questions that transport planning in permanent space settlements would need to explore. It is important to underline that this editorial does not advocate for diverting attention from the pressing and immediate need to protect Earth, especially during this period of climate emergency. Rather, this work suggests that developing space settlements on the Moon and Mars should be seen as thoughtful stepping stones towards humanity’s broader goal of multi-planetary expansion, essential for evolutionary adaptation and resilience.
2. Conceptual model of transport system in permanent space settlements
This editorial draws theoretically from the conceptualisation of the Earth’s transport system by Van Wee (Citation2023) to develop a model outlining the key components of a transport system in a permanent space settlement. This concept divides the system into core, travel, and impact elements (see ). The core element comprises the needs, preferences and choice options (travel modes and infrastructures) of people and companies in space settlements, the location of activities (living, working, leisuring, shopping) and the transport resistance (time, cost, other factors). The travel element involves the travel behaviour (travel mode choices, travel frequencies, travel distances), and the volume, composition and spatiotemporal distribution of traffic. The impact element regards the implications for safety, environment, health, well-being, accessibility, and social equity. Two important factors introducing high uncertainty are space contextual factors (e.g. cosmic radiation, gravity, atmoshere, temperature, dust and soil) and governance (structure, goals and policies). These factors are expected to substantially shape the transport system’s development and operation in extraterrestrial environments, with the space context also affecting governance in permanent space settlements.
Figure 1. Conceptual model outlining the key elements and contextual factors of a transport system in a permanent space settlement. Adapted from Van Wee (Citation2023).
2.1. Core element
The core element aspects (i.e. needs, infrastructure, location activities, transport resistance) are expected to be significantly influenced by space environments. For instance, transport modes and infrastructure may largely depend on technologies adhering to the extraterrestrial location’s physical properties. Different gravity levels could change the energy requirements and feasibilities of various transport systems. In a Mars settlement with roughly one-third of Earth’s gravity, traditional rovers will have less traction, increasing travel times or requiring alternative modes like tunnel-based systems or low-altitude flight modes. Extreme conditions like temperature fluctuations, long day/night cycle, and dust (e.g. lunar regolith) could affect the operation and durability of transport modes, needing protective materials and maintenance procedures (e.g. solar-powered vehicles would likely need to stay parked during long lunar nights or have onboard energy storage for up to 2 weeks). Moreover, the allocation of activities within the settlement could be heavily influenced by spatial constraints, resource consumption minimisation, protection from radiation and potentially the need to contain certain processes for the viability of the settlement within controlled environments. For instance, a Mars settlement might adopt a vertical, rather than horizontal, development pattern to minimise surface exposure to harmful cosmic radiation and maximise the use of available resources. Activities such as agriculture, habitation, or leisure might be layered vertically, or even developed underground, requiring transport systems that can operate effectively on the vertical axis, such as elevators or vertical rail systems. Transport resistance might include not just time and cost, but also safety and psychological factors associated with travel in confined or hazardous settings. Hence, a transport system prioritising radiation protection, reliability, comfort and travel enjoyment could ease the stressors of space settlement life.
2.2. Travel element
The travel element aspects (i.e. travel mode choice, travel frequency, travel distances, traffic) will likely differ in space settlements compared to Earth due to spatial and resource constraints. For example, travel mode choice might be heavily influenced by the requirements for safety and efficiency, with energy being sourced most likely from solar and nuclear power. Thus, collective and active modes might be more viable and preferable over individual motorised mobility, due to their inherent efficiency benefits. Active modes like cycling or adapted forms of walking could be promoted in environmentally controlled areas for health and energy-saving benefits. Regenerative braking systems, advanced energy storage solutions like supercapacitors, and energy sharing among transport systems and settlements would also contribute to an energy efficient system. Travel distances might be limited due to settlements’ compact design. For instance, in Mars settlements, facilities might be closely clustered to maintain a controlled atmosphere, reducing the need for long travels. Long distance travel in a multi-nuclei spatial pattern or to distant resource extraction sites would likely be fast and exlusively via collective modes to reduce radiation exposure. These modes would likely be modular, adaptable, with redudant critical systems to ensure continuous operation even when certain modules fail. Furthermore, travel schedules and vehicle capacities would be determined by rigorous resource and energy management, requiring precise calibration of demand, capacity, and frequency. The volume and distribution of traffic, both horizontal and vertical, would need tight control to ensure safety and operational integrity. A well-regulated scheduling system might be essential to avoid traffic conflicts and maintain efficiency, considering that freight transport shares the infrastructure.
2.3. Impact element
The impact element aspects (i.e. safety, environment, health, well-being, social equity) are expected to be critical in space settlement transport systems. Given the human vulnerability in extraterrestrial environments, rigorous safety standards would be necessary. Environmentally, there would be a need to limit resource consumption and waste, possibly by designing transport vehicles for longevity and maintenance ease using recyclable modular components. Health and well-being would also be critical, addressing psychological effects of confined space travel through interior design (e.g. ample lighting, ergonomic seating) and the physiological issues arising from prolonged exposure to reduced gravity with solutions like artificial gravity stations. Enhanced accessibility and social equity would be essential to counter potential social isolation, requiring inclusive transport systems accessible to all settlement residents irrespective of their abilities or roles. Transport routes and schedules would need to ensure equal access to essential facilities, while a flat-rate or free transport service could ensure cost is not a barrier to mobility.
2.4. Governance
In addition to contextual factors, governance is expected to play an important role in determining the transport system in space settlements. Early literature identified deficiencies in the current international legal framework concerning governance structures in extraterrestrial settlements, including national jurisdiction, resource utilisation, conflict resolution, and environmental protection (Dapremont, Citation2021). Discussions focus on establishing a central authority for space settlements to manage resources (Bruhns & Haqq-Misra, Citation2016) or following a shared-governance model similar to the Antarctic Treaty System. Regardless of the specific governance structure in a space settlement, agreements on sharing and managing transport resources, like energy and infrastructure, would be essential. Policies might prioritise energy-efficient collective transport modes to conserve energy and minimise infrastructure wear. Moreover, they could promote vertical and compact development, paired with corresponding collective transport systems and active modes. Enhancement of human well-being and social equity in response to the social, psychological and physiological effects of space habitats as well as the necessary shared effort for survival could translate into equitable access to all sectors of the settlement (habitation, research, recreation, resources), affordability (e.g. minimun amount of travel credits), and physical and digital accessibility for all to the transport system. Due to the unique nature and unpredictability of space settlements, flexible and adaptive governance would be required, potentially incorporating adaptive management approaches for continual learning and adjustment.
3. Future research
Future research on transport planning in permanent space settlements is indeed surrounded by deep uncertainty because there is (a) lack of knowledge or data about the mechanism or functional relationships being studied, (b) the possibility of unpredictable, surprising, events (Marchau et al., Citation2023). Given this context, it appears that futures techniques, such as speculative design, design fiction, and participatory scenario analysis, may serve as suitable starting points for exploring this field. The initial explorations need to adopt a systems approach, focusing on the holistic interaction of the different elements of the transport system considering their strong interdependencies (much stronger than transport systems on Earth). Interdisciplinary teams would be required given the complexity of the analysis involving, for example, transport planners, urban planners, human geographers, science and technology experts, policy scientists, psychologists, sociologists, philosophers, and space engineers. At a later stage, modelling and computer simulations could provide useful insights on the infrastructure layout, transport modes, travel behaviour and associated implications. Moreover, qualitative methods like participant observation in live or virtually (human-in-the-loop) simulated space transport system environments could provide firsthand understanding of the potential challenges of travelling in a transport system of a space settlement. Historical analysis of the development and evolution of transport systems on Earth, and the factors that influenced them, could also provide useful guidance. While space is a vastly different environment, human mobility needs and the design principles such as efficiency, safety, reliability, and resiliance remain relevant, regardless of the context.
Disclosure statement
No potential conflict of interest was reported by the author(s).
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