Space Agriculture: A Comprehensive Systems-Level Review of Challenges and Opportunities

Abstract

As humanity prepares for prolonged space missions and future extraterrestrial settlements, developing reliable and resilient food-production systems is becoming a critical priority. Space agriculture, the cultivation of plants beyond Earth (particularly on the Moon and Mars), faces a constellation of interdependent environmental, biological, and engineering challenges. These include limited solar radiation, elevated ionizing radiation, large thermal variability, non-Earth atmospheric pressures, reduced gravity, regolith substrates with low nutrient-holding capacity, high-CO₂/low-O₂ atmospheres, pervasive dust, constrained water and nutrient availability, altered plant physiology, and the overarching need for closed-loop, resource-efficient systems. These stressors create an exceptionally challenging environment for plant growth and require tightly engineered agricultural systems. This review examines these constraints by organizing them across environmental differences, resource limitations, biological adaptation, and operational demands, emphasizing their systemic interdependence and the cascading effects that arise when one subsystem changes. By integrating findings from planetary science, plant biology, space systems engineering, biotechnology, robotics, and controlled-environment agriculture (CEA), the review outlines current limitations and highlights emerging strategies such as regolith utilization, advanced hydroponics, crop selection and genetic engineering, and the use of robotics, sensors, and artificial intelligence (AI) for monitoring and automation. Finally, the article underscores the broader relevance of space–agriculture research for terrestrial food security in extreme or resource-limited environments, providing a structured foundation for designing resilient and sustainable agricultural systems for space exploration and beyond.

1. Introduction

The aspiration to sustain human life beyond Earth has transitioned from science fiction to an engineering imperative. As space agencies and private ventures envision long-duration missions to the Moon, Mars, and potentially beyond, developing self-sufficient systems for life support becomes indispensable [1,2,3]. Among these, space-based agriculture is central, not only for providing fresh food, oxygen, and water recycling, but also for supporting crew psychological well-being and autonomy from Earth resupply [4,5]. In extraterrestrial environments where mass and volume are strictly constrained, traditional Earth-bound agricultural practices cannot be simply transferred [6]. Instead, they should be reimagined through the lens of space systems engineering, plant physiology under stress, and environmental control technologies.

As exploration timelines accelerate, particularly through the Artemis and Chang’e programs, the Moon and Mars have emerged as the primary near-term targets for sustained human presence due to their relative accessibility, available water ice, and favorable environmental cycles [7,8]. These developments heighten the need for agricultural systems that can operate reliably under reduced gravity, elevated radiation, and constrained resources.

Yet, the path to viable space agriculture is riddled with multifaceted challenges. Extraterrestrial conditions such as extreme radiation, low gravity, limited solar irradiance, and the absence of breathable atmospheres present unprecedented obstacles to plant growth [7,8]. Critical resources like water, nutrients, and arable substrate are either scarce or chemically unsuitable for direct use [9,10,11]. Physiological stressors disrupt plant–microbe interactions, and restricted genetic diversity further complicates crop development in off-Earth settings [12,13,14]. These challenges are further compounded by operational constraints, such as limited habitat volume, high crew time demands, and the necessity for automation to maintain system functionality and crew safety within closed-loop ecological systems [15,16,17].

Despite advances in closed-environment agriculture and plant experiments in space, several foundational questions remain unresolved. Key uncertainties include the long-term influence of partial gravity on plant reproduction and epigenetic regulation [18,19], the optimization of resource recovery and nutrient cycling [20], and the resilience of bio-regenerative systems under unanticipated stress or failure scenarios [21,22]. Additionally, the trade-offs between leveraging advanced biotechnological tools and maintaining operational simplicity continue to pose design challenges [23]. These knowledge gaps underscore the urgency of an integrated and cohesive interdisciplinary synthesis to clarify current understanding and guide future research [24].

This review provides a structured synthesis of the major challenges to sustainable agriculture in space. It covers environmental differences (e.g., solar energy, atmosphere, and gravity), resource constraints (e.g., water, soil, and nutrient availability), biological complexities (e.g., crop selection and plant health), and operational factors (e.g., space utilization, psychological impacts, and system resilience). To illustrate the system-level interactions in space agriculture, Figure 1 integrates the core plant-production module with the enabling subsystems and environmental constraints that shape system design. The inner ring depicts the engineered architectures required for stable crop production, while the outer ring summarizes the dominant extraterrestrial stressors that govern subsystem performance. This visualization highlights why space agriculture must be approached as a tightly coupled, multi-layer engineering–biological system rather than a collection of isolated components.

Moreover, the innovations and lessons from space agriculture have direct relevance to Earth’s own grand challenges. Designing systems that withstand extreme constraints—radiation, isolation, and severe resource limits—provides insights directly applicable to terrestrial food insecurity, climate variability, and environmental degradation. Space agriculture thus not only prepares us for extraterrestrial life but also inspires resilient solutions for fragile ecosystems and highly degraded or contaminated landscapes on our home planet [25].

By consolidating recent research and identifying persistent uncertainties, this review aims to inform both the scientific community and system designers about the essential elements required for building robust, scalable, and regenerative agricultural systems in space. Specifically, our objectives are to:

• Critically examine the key challenges and barriers to sustainable space agriculture across environmental, resource, biological, and operational dimensions.
• Highlight the interconnections among these factors and their implications for integrated system design.
• Synthesize current strategies and innovations, including controlled environment agriculture, regolith remediation, hydroponics, genetic engineering, robotics, and Artificial Intelligence (AI), and assess their potential for extraterrestrial application.
• Draw parallels with terrestrial challenges, emphasizing how lessons from space agriculture can inform food security, climate adaptation, and degraded-land restoration on Earth.
• Identify persistent uncertainties and future directions, providing a structured foundation to guide cross-disciplinary innovation in support of long-duration human missions.

Scope and Literature Collection

This article is intended as a narrative, problem-driven review rather than a formal systematic review or meta-analysis. We primarily drew on peer-reviewed journal articles and conference papers, complemented by selected space-agency and space-industry technical reports when they provided unique system-level data. Relevant literature was identified iteratively through scholarly search engines and reference lists of key publications, using combinations of terms related to space agriculture, bioregenerative life support, microgravity or partial-gravity plant experiments, regolith and in situ substrates, controlled-environment agriculture, and automation or AI-enabled control. For each topic, we prioritized studies that reported spaceflight experiments, ground-based analogs, quantitative environmental parameters, or explicit implications for BLSS design. As a result, coverage is intentionally denser in mature research domains such as regolith utilization and microgravity plant physiology and more selective in emerging areas such as psychosocial benefits of plants and AI-based control, which we explicitly flag as new but rapidly evolving fields.

2. Challenges in Space Agriculture

2.1. Biological and Agricultural Challenges

2.1.1. Crop Selection

Crop selection is one of the most critical biological decisions in designing space agriculture systems. Because space agriculture must operate with minimal space, energy, water, and crew time, crops must be chosen for both nutritional value and compatibility with controlled-environment systems such as controlled environment agriculture (CEA) chambers and closed-loop life support systems [4,26]. Key desirable traits include short growth cycles, compact architecture, high edible biomass, tolerance to environmental fluctuations, and consistent performance under artificial lighting [6]. Rather than maximizing species diversity, current spaceflight programs prioritize predictable, low-maintenance crops that reliably integrate into automated CEA routines. Low labor and processing requirements are also important for reducing crew workload [27].

Psychological benefits are also important: fresh colors, aromas, and textures help reduce menu fatigue during long missions [28,29]. Flight experience on the International Space Station (ISS) using the Veggie and Advanced Plant Habitat (APH) systems consistently shows that leafy greens, herbs, small root crops, and select fruiting plants can be grown reliably and accepted well by the crew [30,31]. To avoid unnecessary detail, representative examples are summarized in Table 1 rather than described extensively in text.

However, integrating calorie-dense staples (e.g., cereals, pulses) remains challenging because these species require more space, processing, and resources, making them more suitable for longer planetary missions than short orbital missions [4,32]. This gap reflects a broader trade-off: crops that maximize caloric return often increase system complexity, indicating that staple integration will depend on infrastructure maturity rather than biological feasibility alone.

Space-crop selection increasingly integrates mission architecture and recent advances in data-driven evaluation. Short-duration missions such as ISS or Gateway benefit from fast-turnover leafy greens, while lunar and Martian surface missions can incorporate more calorie-dense staples as infrastructure expands [19,30]. Modern crop-ranking frameworks (including EDEN ISS scoring criteria and NASA multi-criteria evaluation) combine productivity, reliability, resource efficiency, microbial safety, and psychological value to guide transparent species selection [33,34,35]. These tools reflect a shift from qualitative preference toward reproducible, system-level decision-making rather than expanding crop lists. Machine-learning models adapted for spaceflight datasets further support portfolio optimization under partial gravity and controlled-environment constraints [18,36].

Table 1. Candidate crops for space agriculture tested in spaceflight and analog systems, with reported outcomes and benefits, adapted from [30].

Crop Type	Example Crop (Cultivar)	Test Environment	Outcome/Benefits
Leafy greens	Lettuce (‘Outredgeous’, ‘Waldmann’s Green’)	ISS * Veggie	Safe crew consumption
	Mustards (Mizuna, ‘Wasabi’, ‘Amara’)	ISS * Veggie	Reliable growth; added menu diversity
	Pak choi (‘Extra Dwarf’)	ISS * Veggie	Efficient biomass per volume
	Kale (‘Red Russian’)	ISS * Veggie	Nutrient-dense
	Chinese cabbage (‘Tokyo Bekana’)	ISS * Veggie	Failed due to elevated CO2
	Lettuce (‘Dragoon’)	ISS * Veggie	Failed due to watering and seed storage issues; needs retest
	Lettuce (‘Paris Island’)		Commercial candidate
Root crops	Radish (‘Cherry Belle’)	ISS * APH	Crisp texture, psychological appeal
Cereal crop	Wheat (‘Apogee’ dwarf)	ISS * APH	Not consumed
Fruiting crops	Pepper (‘Española Improved’)	ISS * APH	First fruiting crop validated; strong crew acceptance
	Tomato (‘Red Robin’)	ISS * Veggie	Unsuccessful (watering issues); retest needed
	Tomato (‘Mohamed’)		Candidate ready for CRL6 * test
Small fruit	Strawberry (‘Delizz’)		Grows well from seed
Legumes	Pea (‘Feisty’, ‘Yellow Snap’)		Candidate crop; ready for CRL4 * test

* ISS: (international space station); APH: (advanced plant habitat); CRL: (crop readiness level) [37].

Table 1. Candidate crops for space agriculture tested in spaceflight and analog systems, with reported outcomes and benefits, adapted from [30].

Crop Type	Example Crop (Cultivar)	Test Environment	Outcome/Benefits
Leafy greens	Lettuce (‘Outredgeous’, ‘Waldmann’s Green’)	ISS * Veggie	Safe crew consumption
	Mustards (Mizuna, ‘Wasabi’, ‘Amara’)	ISS * Veggie	Reliable growth; added menu diversity
	Pak choi (‘Extra Dwarf’)	ISS * Veggie	Efficient biomass per volume
	Kale (‘Red Russian’)	ISS * Veggie	Nutrient-dense
	Chinese cabbage (‘Tokyo Bekana’)	ISS * Veggie	Failed due to elevated CO2
	Lettuce (‘Dragoon’)	ISS * Veggie	Failed due to watering and seed storage issues; needs retest
	Lettuce (‘Paris Island’)		Commercial candidate
Root crops	Radish (‘Cherry Belle’)	ISS * APH	Crisp texture, psychological appeal
Cereal crop	Wheat (‘Apogee’ dwarf)	ISS * APH	Not consumed
Fruiting crops	Pepper (‘Española Improved’)	ISS * APH	First fruiting crop validated; strong crew acceptance
	Tomato (‘Red Robin’)	ISS * Veggie	Unsuccessful (watering issues); retest needed
	Tomato (‘Mohamed’)		Candidate ready for CRL6 * test
Small fruit	Strawberry (‘Delizz’)		Grows well from seed
Legumes	Pea (‘Feisty’, ‘Yellow Snap’)		Candidate crop; ready for CRL4 * test

* ISS: (international space station); APH: (advanced plant habitat); CRL: (crop readiness level) [37].

Crop selection is not merely a biological decision but a systems-engineering problem. Crops differ in their interactions with nutrient cycling, atmospheric balance, water use, and waste recovery, so crop portfolios must be evaluated at the system level [38,39]. Tools such as crop-ranking models and multi-criteria evaluation (e.g., those used in the EDEN ISS project) aid species selection and help match crops to resource constraints [33,34]. However, these frameworks remain limited by sparse long-duration performance data, meaning selection criteria will continue to evolve as more operational evidence accumulates. Maintaining genetic diversity and ensuring seed viability across generations remain long-term priorities, especially under variable light, humidity, and partial gravity conditions [18,19].

In summary, optimal space crops share short growth cycles, compact form, high edible yield, and reliable performance under controlled conditions. For longer missions, reproductive stability and compatibility with closed-loop resource use have become essential.

2.1.2. Plant Health and Disease Management

Ensuring plant health in extraterrestrial agriculture is a critical challenge because crops grown in sealed habitats are highly vulnerable to microbial, physiological, and environmental stressors [19]. In the absence of diverse microbial communities that support nutrient cycling and suppress pathogens on Earth, plants become more sensitive to environmental fluctuations and opportunistic microbes [40,41]. Risk profiles also differ by mission duration, with repeated hardware reuse in long-duration missions increasing contamination persistence [42]. Short-duration ISS missions allow periodic hardware replacement and resupply, whereas lunar and Martian surface operations must maintain plant health across repeated reuse cycles without external support. From an operational standpoint, this shifts plant health from a biological concern to a reliability constraint within BLSS operation.

Microgravity alters plant–microbe interactions and plant physiology, affecting root development, fluid transport, and defense signaling pathways [12,43,44]. Although these mechanisms are increasingly characterized, their combined operational significance for crop performance remains unclear. Some microbial species also exhibit altered virulence or stress responses in microgravity [45,46], suggesting multiple converging factors rather than a single pathway. However, the long-term stability of plant immune function under partial gravity is still unknown. This uncertainty limits the ability to predict whether crops can maintain consistent health status across repeated growth cycles.

Closed cultivation systems lack ecological competitors, allowing low-level contaminants to proliferate rapidly [47]. Human-associated microorganisms can persist within growth modules [48], and moist root zones combined with recirculating irrigation support their survival [49,50]. Available evidence indicates that contamination accumulates gradually within shared water- and air-loops rather than arising from discrete events, and existing sanitation strategies have not been validated for multi-year operation. As a result, prevention-focused approaches may be more effective than reactive containment in sealed habitats. To provide a concise overview of key risks,

Table 2. Key pathogen sources in closed plant systems and corresponding controls.

Pathogen Source	Mechanism in Closed Systems	Primary Controls
Human-associated microbes	Introduced through crew activity; persists on surfaces and in shared air loops	Sanitation, air filtration, restricted crew–plant contact
Waterborne/root-zone contaminants	Amplify in recirculating irrigation lines	UV/thermal water treatment, filtration, periodic line flushing
Biofilm-forming opportunists	Thrive in moist, low-competition environments	Moisture control, material choice, scheduled module cleaning
Seedborne pathogens	Introduced at system startup	Seed sterilization, certified clean seed, quarantine protocols

summarizes the primary pathogen sources in closed cultivation systems and the corresponding mitigation strategies relevant to long-duration extraterrestrial agriculture.

Introducing beneficial microbes remains difficult because microgravity and radiation influence microbial survival and function [51], complicating efforts to establish stable engineered microbiomes. Related challenges in regolith-based and nutrient-recycling substrates are discussed in Section 2.2.2 and Section 2.2.3. At present, microbial augmentation cannot be considered a dependable mitigation strategy for long-duration missions.

Early detection is essential in sealed environments. Imaging platforms, spectral sensors, biosensors, and AI-based diagnostics show promise but require adaptation for autonomous, resource-limited conditions [34,52,53]. Most tools remain untested under failure scenarios, and no studies have linked sensor outputs to actionable management responses in space-relevant contexts. This represents a critical gap between detection capability and operational decision-making.

Plant-disease outbreaks can also degrade air and water quality through volatile organic compounds and microbial metabolites [42,54]. Effective plant-health management therefore requires coordinated control of environmental conditions, sanitation, microbial risk, early detection, and crop/inoculant selection for long-duration missions. A major knowledge gap remains the long-term stability of plant immune function and microbial communities across repeated growth cycles in partial gravity, which directly affects confidence in BLSS reliability.

2.1.3. Genetic Stability and Reproductive Viability

Maintaining genetic stability across generations is essential for long-duration space missions, where crops must reproduce reliably without resupply from Earth [4,55]. In contrast to short ISS missions, lunar and Martian operations require repeated seed-to-seed cycles, meaning reproductive reliability becomes a functional requirement rather than a logistical preference. Transit missions introduce additional constraints because generations must progress without environmental buffering or emergency intervention, making propagation reliability a mission-critical parameter rather than a biological outcome.

Radiation exposure can induce heritable genetic changes, including DNA damage and chromosomal alterations [56,57]. Fractional-gravity studies further suggest that altered cytoskeletal organization and amyloplast behavior may influence genome stability across generations [18,58]. Current evidence suggests that radiation and reduced gravity function as cumulative stressors, with effects likely to emerge over multiple reproductive cycles rather than within a single generation. For BLSS planning, this increases the importance of evaluating multi-cycle performance rather than single-generation viability.

Microgravity also affects reproductive processes by reducing pollen viability, fertilization success, and embryo development [59,60], which may impair propagation reliability under partial gravity [18]. However, the persistence of these effects across repeated cycles remains untested, and thresholds required for dependable seed-to-seed completion have not been defined. This gap prevents determining whether space-grown crops can achieve autonomous regeneration without intermittent resupply.

Chronic exposure to galactic cosmic rays and solar particle events may also trigger persistent epigenetic modifications, including shifts in DNA methylation and chromatin structure, that can influence gene regulation, developmental stability, and stress tolerance across generations [61,62,63]. Spaceflight experiments in Arabidopsis and wheat have reported radiation-linked methylation drift and transcriptional instability, indicating that epigenetic mechanisms may be as vulnerable as DNA integrity during long-duration missions. These findings link genetic stability to broader crop-selection and plant-health considerations, emphasizing the need to evaluate epigenetic resilience alongside genomic stability for long-term BLSS agriculture.

Seeds stored during spaceflight exhibit accelerated aging and reduced vigor [64]. Closed storage conditions and radiation can decrease longevity and increase trait variability in subsequent generations [65,66], highlighting the need to evaluate storage stability alongside reproductive performance. These storage-related risks compound reproductive uncertainties, reinforcing the need for multi-cycle assessment.

Environmental stresses also influence epigenetic regulation, altering DNA methylation and gene-expression patterns [67]. Recent omics-based studies report transcriptomic, proteomic, and epigenomic shifts under space-relevant conditions [18,68,69], suggesting that heritable changes may involve both genetic and epigenetic components rather than single pathways.

Overall, key unknowns include multigenerational stability under partial gravity, thresholds for radiation-induced heritable change, and the persistence of epigenetic modifications across repeated growth cycles, indicating that resolving these uncertainties is essential to determine whether BLSS can sustain closed-loop crop production without external seed inputs.

These biological constraints point directly to the need for technologies that extend plant tolerance limits, including genetic optimization, microbiome engineering, and autonomous sensing systems that can support sustained crop performance in space.

2.2. Resource Availability and Sustainability Challenges

2.2.1. Water Availability and Recycling

Water is fundamental to space agriculture, supporting transpiration, nutrient transport, and thermal regulation. However, its limited availability, high logistical cost, and altered fluid behavior in reduced gravity make reliable management a central constraint for bioregenerative life support systems [70]. Sustainable plant production therefore depends on closed-loop water sourcing and recycling rather than resupply, especially for lunar and Martian missions, which require high water autonomy [71,72]. Mission needs vary by architecture: short ISS missions rely on resupply, whereas lunar and Martian surface missions must achieve nearly closed-loop water use [19]. For lunar and Martian surface systems, water storage and recovery must support multi-year operation, while transit missions face stricter mass and failure-tolerance constraints due to the absence of emergency redundancy. In practical terms, this shifts water from a consumable resource to a core determinant of BLSS feasibility.

Transporting water from Earth remains prohibitively expensive, necessitating in situ resource utilization [73]. Remote-sensing and mission data confirm the presence of frozen or hydrated water on the Moon and Mars [74,75], but shallow ice deposits are highly site-dependent, and extraction consistency has not been demonstrated at an operational scale [76,77]. As a result, ISRU water sources cannot yet serve as a primary supply without substantial buffering or storage capacity.

Recovered or recycled water must also meet strict chemical and microbial standards to protect both crops and crew [78]. Treatment approaches range from multistage filtration to hybrid biological–physicochemical systems [79], with continuous monitoring of pH, EC, nutrient composition, and microbial load required for long-term reliability [80,81]. Insights from Antarctic analog facilities such as EDEN ISS demonstrate that modular treatment and automation can reduce crew workload [34,82], although most demonstrations remain short-duration and have not validated autonomous, fault-tolerant operation. This highlights a key readiness gap, as BLSS water systems must function without routine human intervention.

Water dynamics differ fundamentally in microgravity, where adhesion and surface tension dominate fluid movement. Instead of draining, water can accumulate around roots, causing hypoxia or localized dehydration [83,84]. Partial gravity may lessen these effects but does not eliminate the need for redesigned substrates and irrigation strategies suited to altered capillary behavior [85]. These conditions require irrigation systems that prevent stagnation and maintain stable aeration without relying on gravity-driven drainage, making stability and aeration the primary design priorities.

Closed-loop recovery is therefore essential to minimize water loss. ISS-class systems reclaim approximately 90% of wastewater [86], while plant-based systems contribute through transpiration capture and recirculating hydroponic solutions [87]. However, redundancy remains critical because failures in pumps, filters, or microbial control can compromise both crop productivity and habitat safety [88]. Ground-based and flight experiments, including early Lunar Palace 1 and Tiangong plant-growth studies, show the feasibility of integrated recycling, but long-term durability and autonomous control remain incompletely characterized [89,90]. More recent results from China’s Lunar Palace 1/2 extended BLSS trials provide multi-cycle, long-duration datasets on system stability, reliability modeling, atmospheric regulation, nutrient-loop closure, and crew–plant integration [91,92]. Complementing these ground-based trials, CNSA’s Tiangong Space Station has demonstrated in-orbit seed-to-seed plant cultivation and validated controlled-environment growth modules for long-duration missions [93]. For mission planning, this means that reliability rather than efficiency is the limiting factor for deployment.

Emerging research indicates that predictive monitoring may support system stability. Machine-learning approaches and soft-sensor models can identify fouling, contamination, and performance drift [94,95], suggesting pathways toward autonomous control for closed water loops. Overall, significant progress has been made in ISRU concepts, microgravity-compatible irrigation, and closed-loop purification, yet major uncertainties remain regarding fouling behavior under partial gravity, multi-year stability, and the robustness of autonomous diagnostics in sealed environments.

2.2.2. Soil and Regolith Utilization

Space-based crop production has primarily relied on hydroponic and aeroponic systems because they provide efficient resource control in microgravity [96,97]. Extraterrestrial soils, particularly lunar and Martian regolith, remain attractive for in situ resource use, offering mechanical support and reduced dependence on Earth-supplied substrates. Unlike ISS cultivation, regolith-based substrates apply only to lunar and Martian surface missions; transit habitats and microgravity platforms will continue to rely on hydroponic or aeroponic systems due to mass and particulate-containment limitations. However, raw regolith is chemically and physically unsuitable due to perchlorates, high pH, and extremely limited nutrient availability [98,99,100]. Therefore, regolith cannot function as a direct soil substitute and requires staged processing before supporting sustained cultivation. In operational terms, this makes substrate preparation a prerequisite rather than an optional enhancement.

Water-retaining amendments such as hydrogels can improve moisture distribution and reduce desiccation stress in regolith simulants, with some studies reporting increased biomass and germination [101,102]. Yet these approaches do not address underlying chemical limitations, and additional amendments such as biochar, organic matter, or microbial inocula remain necessary [103,104,105]. These results show that moisture management alone is insufficient and must be integrated with chemical and biological remediation strategies.

Recent experiments illustrate how targeted amendments can improve crop performance in regolith simulants. Hydrogel addition to a Martian soil analog increased radish germination to ~27% compared with near-zero emergence in untreated controls [106]. Biochar supplementation of lunar simulant also enhanced nutrient availability and improved lettuce seedling growth under controlled conditions [107]. These results demonstrate that physical and biochemical amendments can partially offset the poor water retention and nutrient deficiencies of raw regolith, although validation under space-relevant conditions remains necessary.

Both lunar and Martian regoliths exhibit very low cation-exchange capacity and lack clay minerals and organic matter, limiting nutrient retention and buffering capacity [11,99,108]. Structurally, regolith consists of angular particles with limited pore diversity, and under reduced gravity, capillary forces dominate water movement, creating localized saturation and drought zones that weaken root anchorage [83,109,110]. These combined physical constraints indicate that substrate modification must be integrated with environmental control rather than applied in isolation.

Chemically, regolith contains essential nutrients such as Mg, Ca, and K but with poor bioavailability due to the absence of organic chelators and microbial cycling [104]. Martian regolith presents additional risks from perchlorates and, in some cases, elevated heavy metals [10,111,112,113]. As a result, chemical detoxification is a prerequisite for food production, and its long-term stability under closed-habitat conditions remains unverified. From a systems perspective, these chemical and physical limitations reinforce one another and require coordinated rather than incremental remediation.

Biologically, regolith is sterile and lacks microbial communities required for nutrient cycling, nitrogen fixation, and pathogen suppression [114]. Inoculation strategies using selected bacteria and actinomycetes show promise but remain difficult to stabilize in sealed environments [115]. Regolith can also attenuate radiation, which may support subsurface microbial survival [116,117], although its agricultural relevance is uncertain. Overall, functional microbiomes may be achievable in regolith, but predictable long-term performance has not yet been demonstrated under spaceflight resource constraints. Key physical and chemical properties of lunar and Martian regolith compared to Earth soils are summarized in

Table 3. Physical and chemical properties of lunar and Martian regolith compared to Earth soils, with implications for plant growth.

Property/Feature	Earth Soils	Lunar Regolith/Simulants	Martian Regolith/Simulants	References
Cation Exchange Capacity	2–34 cmol(+)/kg	Very low (<1 cmol(+)/kg (LHS-1 simulant)	~7.9 cmol(+)/kg (MMS-1 simulant)	[118,119]
Organic matter/microbiota	Present; supports nutrient cycling and buffering	Absent; biologically sterile	Absent; biologically sterile	[11]
pH and buffering	Buffered by clays and organic matter	High pH, poor buffering	High pH, low buffering; unstable nutrient balance	[99,120]
Toxic compounds	Typically within safe limits	Cd at ng/g levels (Apollo samples)	Perchlorates 0.5–0.6% (~5000–6000 mg/kg); Cd 1–5 mg/kg; Pb up to 20 mg/kg	[111,121,122,123]
Nutrient content	Macronutrients (Ca, Mg, K) bioavailable	Ca, Mg, Fe present but poorly available	Ca, Mg, Fe, K present but poorly available	[11,104]
Soil structure	Aggregated; diverse pore sizes	Fine, angular, electrostatically charged; compact and abrasive	Loose, poorly cemented; variable pore sizes	[11,124,125,126]
Water retention	Stable retention; micro/macro pore balance	Localized saturation and desiccation; poor retention	Unstable retention; rapid leaching; heterogeneity	[11,105,109,125]

, illustrating the limitations in nutrient retention, buffering, and water dynamics.

Despite these limitations, regolith cultivation remains strategically important. Some crops, particularly those with extensive or long-cycle root systems, perform better in solid substrates than in a purely hydroponic system [15,127]. Regolith-based approaches may therefore complement hydroponics by expanding production capacity and reducing dependence on Earth-supplied media, with terrestrial soil-reclamation practices offering relevant precedents [103,128]. However, because physical, chemical, and biological constraints interact, validation must occur through integrated rather than single-factor testing, and early in situ trials during future Mars missions will be required to confirm both feasibility and stability [129].

Current knowledge of regolith-based cultivation remains limited because most plant studies still rely on simulants, which cannot fully reproduce the nanophase iron, agglutinates, and surface reactivity observed in real lunar soils [130,131]. Recent analyses of Chang’e-5 samples highlight these differences and are now enabling higher-fidelity simulant development calibrated to true regolith properties [132,133]. Future BLSS experiments will require targeted testing with actual returned materials from Chang’e and Artemis missions to validate assumptions about water flow, nutrient dynamics, and root-substrate interactions.

2.2.3. Nutrient Limitations

In the closed systems of space agriculture, maintaining a consistent and balanced nutrient supply is one of the most complex and essential challenges [20]. Unlike on Earth, where nutrient cycling is driven by diverse biological and geological processes, space habitats lack natural sources for replenishment [104]. Nutrient strategy also depends on mission architecture: ISS missions rely on stored solutions and periodic resupply, whereas lunar and Martian habitats must achieve near-complete nutrient recycling. Instead, nutrients are required to be either brought from Earth, extracted from in situ materials, or regenerated within artificial biogeochemical loops, all under the constraints of limited mass, volume, and energy availability [20,70,104].

The lack of a soil microbiome removes critical symbiotic processes such as nitrogen fixation and phosphate solubilization [134]. Microbial inoculation strategies are being explored, but long-term stability and functional reliability under extraterrestrial conditions remain uncertain [135,136].

Essential nutrients (nitrogen, phosphorus, potassium, calcium, magnesium, and trace elements) should be supplied synthetically or via recycling [4,137]. Because these inputs lack microbial buffering and transformation, nutrient availability depends entirely on external control, making the system more vulnerable to imbalances or interruptions [27]. Critically, nutrient uptake by plants varies dynamically with species, developmental stage, light environment, and temperature, often resulting in imbalanced nutrient concentrations and uptake ratios in the growth medium and within plant tissues over time [138]. Different crop groups impose distinct nutrient demands—for example, leafy greens require higher nitrogen, whereas fruiting crops demand more potassium and calcium [139]. Without continuous monitoring and adjustment, these plant-driven shifts become more problematic in closed space systems, where limited sensing capacity and restricted resupply options hinder rapid correction. This can lead to deficiencies or toxicities, reducing crop productivity and quality [18]. These factors indicate that nutrient supply in space depends on continuous external control rather than biological buffering, increasing system vulnerability to even short-term operational disturbances.

Recovering nutrients from onboard waste streams is essential for long-duration missions. Nutrients must be reclaimed from plant residues, inedible biomass, human waste, and food leftovers. Bioregenerative systems aim to close these loops, with emphasis on nitrogen recovery through decomposition, nitrification, and filtration processes that must operate reliably under microgravity and sterile conditions [140,141]. The composition of human waste fluctuates with diet and hydration, introducing variability in recovery efficiency, and contaminants such as pharmaceuticals or heavy metals require selective removal [142]. Projects such as ESA’s MELiSSA aim to convert organic waste into plant-available nutrients while addressing challenges such as sodium removal from urine and overall nutrient balancing [20]. Recent work demonstrates progress in stabilizing MELiSSA nitrogen-processing bioreactors and improving overall nutrient-loop robustness [20]. Recent systems-level analyses demonstrate improved modeling and control of nutrient loops in fully closed BLSS architectures [20,136].

Physicochemical and biological nutrient-recovery approaches exhibit distinct efficiency profiles relevant to different mission durations. Reverse osmosis systems can remove >90% of dissolved inorganic nitrogen under controlled terrestrial wastewater conditions [143], offering operational robustness suited to short missions. Biological recovery pathways developed for BLSS, such as MELiSSA’s urine-nitrifying reactors, show promise but currently display variable recovery efficiencies influenced by feed composition and reactor stability [141]. In contrast, high-performing algal and algal–bacterial systems in terrestrial studies frequently exceed 85–95% removal of dissolved inorganic nitrogen and phosphorus under optimized conditions [144,145], illustrating their long-term potential once microbial reliability is ensured. These findings suggest that membrane-based treatments offer robustness and operational simplicity suited to short-duration or transit missions, whereas biological loops provide higher nutrient closure and reduced resupply burden for long-term lunar or Martian habitats.

To visualize how these waste streams re-enter the bioregenerative cycle, Figure 2 presents a simplified nutrient-loop schematic for closed plant production systems.

Water and nutrient delivery systems in microgravity add additional complexity. Without gravity, water and dissolved nutrients behave unpredictably, leading to nutrient stratification, localized salt accumulation, or impaired root oxygenation [146,147,148]. Delivery systems must rely on capillarity, diffusion, or controlled misting, all of which are strongly influenced by humidity and transpiration rates. Without precise control, nutrient gradients can form in the root zone, affecting uptake and overall crop performance [96,109]. Recent hydroponic-design assessments highlight long-term risks of nutrient-solution drift under altered gravity, requiring new control strategies for stable BLSS operation [96]. These findings suggest that delivery constraints are not simply engineering challenges but directly shape nutrient availability, meaning physical transport and biochemical supply must be managed as a coupled process.

Long-term nutrient storage is also constrained by stability, compactness, and purity requirements. Stock solutions may degrade, precipitate, or become contaminated under fluctuating environmental conditions. Chemical formulations must ensure compatibility and resistance to microbial growth [149,150,151]. Microbial or algal bioreactors offer an alternative by capturing and recycling nutrients but introduce challenges of biological stability and contamination control [136,152]. Engineering analyses of spacecraft wastewater systems emphasize the importance of brine management, contaminant removal, and operational reliability in nutrient-recycling modules [153].

Efforts to optimize nutrient management are further limited by monitoring capability. Key parameters such as electrical conductivity (EC), pH, and ion concentrations must be tracked continuously, yet sensors that function reliably in low-gravity, humid, confined environments are still under development. Delays in detecting nutrient fluctuations can trigger crop stress or failure, a critical issue in space where resupply is limited and food production directly sustains crew survival. Because microbial absence, delivery constraints, recycling performance, storage stability, and sensing limitations interact, nutrient management cannot be optimized through isolated interventions and instead requires coordinated system-level control.

Current research trends suggest that nutrient management in BLSS has advanced significantly, particularly through waste-recovery bioreactors and improved nutrient-delivery technologies, but major uncertainties remain, including long-term microbial stability, nutrient-solution drift under reduced gravity, and the robustness of recycling loops for multi-year missions.

These resource limitations indicate the importance of closed-loop water and nutrient recovery, efficient fluid-handling architectures, and alternative substrate strategies capable of maintaining productivity under strict mass and resupply constraints.

2.3. Environmental Challenges

2.3.1. Solar Energy and Radiation

Solar radiation is a central environmental constraint for plant growth in space because extraterrestrial light environments differ fundamentally from Earth in intensity, spectral quality, and temporal stability. The Moon receives unfiltered, high-energy solar flux due to the absence of an atmosphere, exposing plants and hardware to intense ultraviolet (UV) and ionizing radiation [154,155]. In contrast, Mars receives ~43% of Earth’s solar irradiance because of its greater heliocentric distance, and its frequent planet-wide dust storms further diminish and redden incident light, reducing the photosynthetically active radiation (PAR) available to crops [156,157]. At Earth’s orbit, top-of-atmosphere solar irradiance averages ~1361 W m⁻², while Mars receives only ~40–45% of that (~590 W m⁻²) at 1.52 AU before additional dust attenuation [158,159]. For comparison, controlled-environment crop systems typically deliver ~150–250 µmol m⁻² s⁻¹ PPFD for leafy greens and ~400–800 µmol m⁻² s⁻¹ for higher-light species [160,161]. These differences influence both total photon flux and spectral balance, which are critical for photosynthesis. These differences mean that extraterrestrial light environments cannot be treated as scaled-down versions of Earth conditions, and lighting requirements must be defined by mission location rather than generalized design assumptions.

Plants acclimate to fluctuating or stressful light environments through mechanisms such as non-photochemical quenching, yet their productivity still depends on maintaining PAR above species-specific compensation and saturation thresholds [162,163,164]. The extreme 28-day lunar day–night cycle creates prolonged heat-load and deep-freeze periods, demanding substantial thermal buffering and energy-storage capacity for any biological system [165]. As a result, extraterrestrial cultivation requires carefully engineered lighting systems, both for photobiological needs and thermal–operational stability. Therefore, acclimation mechanisms are insufficient to offset extreme photothermal variability, meaning biological performance ultimately depends on engineered buffering rather than plant plasticity alone.

Radiation is an additional limiting factor. Without Earth’s magnetosphere, lunar and Martian environments expose plants to chronic galactic cosmic rays (GCRs) and episodic solar particle events (SPEs). Modeled unshielded doses reach ~0.57 Gy yr⁻¹ on the Moon and ~0.77 Gy yr⁻¹ on Mars [166,167], far exceeding Earth’s natural background (~0.0024 Gy yr⁻¹). Large SPEs can deliver acute doses >1 Gy, posing risks of DNA damage, oxidative stress, reduced growth, and impaired reproduction [168,169,170]. Experimental GCR simulations indicate that standard crops (lettuce, tomato, Arabidopsis) show developmental impairment at doses of 0.4–0.8 Gy, especially with high-Linear Energy Transfer (LET) heavy ions [57,171], although germination may remain relatively tolerant. However, crop performance under combined chronic GCR exposure and realistic shielding has not yet been demonstrated, leaving operational thresholds and long-term reproductive stability unresolved.

Thermal and radiative stresses interact: absence of atmospheric convection on the Moon forces reliance on radiative heat transfer alone, which complicates greenhouse temperature control under high infrared loads [172]. For these reasons, effective solar filtering, supplemental lighting, habitat shielding, and robust energy-storage strategies form essential components of extraterrestrial agricultural design. Consequently, radiation and light management jointly determine shielding mass, energy demand, and crop feasibility, making them primary drivers of mission-level system design.

2.3.2. Atmosphere Differences

Atmospheric conditions on the Moon and Mars present significant barriers to agricultural sustainability, primarily due to stark contrasts with Earth’s atmospheric environment. Earth’s atmosphere, dominated by nitrogen (78.1%) and oxygen (20.9%), not only provides stable pressure and robust radiation protection (~1000 g/cm² protective mass) but also maintains plant-essential gases, including ~400 ppm of CO₂ for photosynthesis and 1–5% water vapor for regulating transpiration and preventing excessive water loss [173,174]. Conversely, the Moon completely lacks an atmosphere, while Mars possesses an extremely thin atmosphere composed predominantly of carbon dioxide (95%), with minor constituents including nitrogen (2.7%), argon (1.6%), and negligible oxygen (0.13%) [175,176]. Mars’ extremely low total pressure (~0.6 kPa) prevents open-air plant growth, making pressurized cultivation environments essential [177]. These atmospheric differences mean that extraterrestrial plant-growth systems cannot rely on passive environmental buffering and instead require fully engineered control of pressure, composition, and humidity to maintain basic physiological function.

The absence of a protective atmosphere on Mars and the Moon significantly amplifies harmful UV exposure. Mars receives substantially higher UV fluxes than Earth because its thin atmosphere provides limited attenuation, while the Moon’s lack of atmospheric filtering results in direct exposure to UVC–UVB wavelengths [155,178]. Experiments consistently show that UV-B levels exceeding terrestrial norms suppress photosynthesis and cause tissue damage, underscoring the need for shielding or spectral filtering in extraterrestrial plant habitats [179].

Atmospheric pressure differences further complicate agriculture. Earth’s standard atmospheric pressure (~101 kPa) ensures optimal gas exchange, transpiration, and humidity control [180,181]. Mars, with an average surface pressure of merely ~0.6 kPa, is near the triple-point threshold of water, making stable liquid phases difficult to maintain and promoting rapid evaporation or sublimation [182]. The Moon’s near-vacuum environment exacerbates these challenges by instantly vaporizing any exposed water [183,184]. Studies have shown that even modest pressure reductions can significantly impair transpiration, delay development, and alter gas exchange in plants [185,186]. As a result, closed plant-growth systems on the Moon or Mars must maintain carefully regulated internal pressures and humidity to sustain transpiration, nutrient uptake, and CO₂ assimilation. However, the optimal pressure ranges that balance plant performance with habitat energy cost remain uncertain, and few studies have tested multi-crop responses under sustained sub-Earth atmospheres relevant to lunar or Martian operations.

When considered together, atmospheric composition, pressure, and UV exposure impose stringent requirements for sealed, pressurized, and shielded plant-growth environments on the Moon and Mars, making atmospheric control a central design priority for extraterrestrial agriculture.

2.3.3. Plant Physiology (Temperature, Humidity, Gravity), and Cultivation Systems

Plant growth and development in extraterrestrial environments are strongly influenced by key abiotic factors that directly alter physiological processes. Temperature, humidity, and gravity interact to shape photosynthesis, transpiration, nutrient transport, and plant architecture and together determine the environmental controls required for reliable BLSS crop production in space.

Temperature regulation is essential because extraterrestrial surfaces exhibit extreme and highly variable thermal environments. CEA systems must buffer these fluctuations and maintain biologically permissive temperatures, as poor thermal control can impair enzyme activity, slow development, and increase physiological stress [187]. Growth chambers, therefore, need robust thermal management capable of handling large external gradients.

Humidity management is similarly critical. In sealed habitats, humidity influences transpiration, disease pressure, and water status. High RH promotes microbial proliferation, whereas low RH accelerates water loss and reduces photosynthesis [188,189]. Low-pressure environments such as Mars further increase evaporative losses, requiring precise humidity control, airflow management, and dehumidification to prevent condensation hotspots [190]. These findings indicate that humidity control is not simply a comfort parameter but a primary determinant of plant water status and disease risk, and optimal RH ranges for long-duration, low-pressure habitats remain undefined.

Altered gravity exerts broad influence over plant structure and function. Microgravity and partial gravity modify orientation responses, cellular organization, resource transport, and whole-plant architecture, requiring adapted cultivation strategies for space agriculture [13,191]. Microgravity disrupts statolith sedimentation and auxin redistribution, leading to disoriented root and shoot growth and increased reliance on light and tactile cues for orientation [192,193]. Spaceflight studies also report changes in cell-wall thickness, cytoskeletal structure, and microtubule alignment, which together reduce mechanical stability [194,195]. Recent work indicates that altered amyloplast sedimentation and cytoskeletal reorganization underpin gravity sensing under reduced-gravity conditions [18,58], refining current models of statolith-mediated signaling and confirming earlier ESA-supported observations of cytoskeletal responsiveness [24]. From an operational perspective, these structural sensitivities make compact cultivars and mechanical stabilization preferable for BLSS cultivation, and crop performance may depend more on architectural traits than on restoring Earth-like gravity, an outcome not yet demonstrated at lunar or Martian levels.

Resource transport also shifts under reduced gravity. With hydrostatic gradients diminished, BLSS rely on capillarity and controlled pressurization to deliver water and nutrients while avoiding waterlogging or localized hypoxia [109,196]. Reproductive development is also gravity-sensitive. Spaceflight and partial-gravity studies show reduced pollen viability, altered seed composition, and lower fruit set, with implications for long-duration seed-to-seed agriculture [65,197]. Recent CNSA experiments aboard the Chinese Space Station have demonstrated successful seed-to-seed development under microgravity [93], providing the most current benchmark for multi-generational cultivation in orbit. Whether seed-to-seed reproduction can be sustained under lunar or Martian partial gravity remains unknown, making generational stability under fractional-g a critical open question for surface-based BLSS. It is also unclear whether reduced reproductive performance would persist across multiple cycles, leaving long-duration crop continuity unresolved for future missions.

Partial gravity provides only limited physiological restoration. At 0.17–0.38 g, plants continue to show altered tissue differentiation and root anchorage, indicating that Moon- or Mars-equivalent gravity may not fully re-establish Earth-like development [13,198]. Recent omics studies, including results from JAXA’s Kibo-based Advanced Plant Experiments (APEX), also report stress-responsive transcriptional shifts under fractional-gravity conditions [18,69]. Ground-based partial-gravity experiments using ESA’s Large Diameter Centrifuge similarly demonstrate that Moon- and Mars-level gravity only partially restores developmental organization [58,199]. Complementary clinostat-based simulations, including NASA-supported multi-axis platforms, further reveal altered early growth responses under sustained fractional-g [200,201], indicating that reduced gravity induces distinct physiological programs rather than a linear transition between microgravity and 1 g. Although transcriptomic data are expanding, metabolomic profiles under space-relevant radiation and epigenomic analyses of multi-generation plants remain largely absent, representing important knowledge gaps. Recent multi-omics frameworks also highlight the need to integrate transcriptomic, proteomic, metabolomic, and epigenomic datasets to guide space-agriculture development [202]. Overall, threshold values required for stable development under partial gravity remain undefined for most crop species.

Gravity also shapes cultivation system design. Soil-like substrates drain poorly under reduced gravity, making hydroponic and aeroponic systems, which rely on controlled fluid delivery and capillary management, more suitable for space agriculture [5,15].

Together, temperature, humidity, and gravity impose integrated physiological constraints on plant growth in space, requiring tightly regulated CEA systems with engineered thermal buffering, humidity control, and gravity-independent fluid delivery. A comparative summary of environmental parameters relevant to plant cultivation on Earth, the Moon, and Mars is presented in

Table 4. Comparative environmental parameters of Earth, the Moon, and Mars relevant to space agriculture.

Parameter	Earth	Moon	Mars	References
Atmospheric composition	78.1% N2, 20.9% O2, ~400 ppm CO2	None	95% CO2, 2.7% N2, 1.6% Ar, 0.13% O2	[173,174,175,176,203]
Atmospheric pressure	~101 kPa	Near vacuum	~0.6 kPa	[180,182,184]
Gravity	1 g	0.17 g	0.38 g	[191]
Temperature extremes	Buffered by atmosphere	–153 °C (night) to +138 °C (day)	–100 °C (night) to +20 °C (day)	[204,205]
Day–night cycle	24 h	27.3 Earth days (≈14 light, 14 dark)	24 h 37 min	[204,205]
Magnetosphere	Well-developed global field	Absent	Weak, patchy	[206,207,208]
Water availability	Abundant liquid water	Polar ice deposits	Subsurface ice, possible brines	[75,209]
Dust	Not a major hazard	Sharp, abrasive, electrostatically charged	Pervasive dust storms, perchlorate-laden dust	[156,210]
Solar irradiance	100% baseline	Direct, unfiltered solar flux	~43% of Earth	[155,156,157]
Ultraviolet radiation (200–400 nm)	0.88–50 kJ/m2/day	UVC + UVB ≈ 26.8 W/m2	27.0–42.4 W/m2	[155,178,211]
Background radiation	~2.4 mSv/yr (~0.0024 Gy/yr)	~0.57 Gy/yr (unshielded)	~0.77 Gy/yr (unshielded)	[166]
Radiation environment	Shielded by magnetosphere	Exposed to GCR * and SPEs *	Exposed to GCR * and SPEs *	[166]

* GCR (galactic cosmic ray); SPE (solar particle events).

.

These environmental stressors make clear the necessity of engineered countermeasures, such as shielding, precise climate control, and gravity-independent fluid systems, to maintain stable and biologically viable growth conditions.

2.4. Operational Challenges

2.4.1. Space Constraints and Efficiency

In extraterrestrial agriculture, physical space is among the most limiting factors due to the high cost of launch mass and volume. Every cubic meter aboard spacecraft or within surface habitats is essential to justify its functional utility, requiring agricultural systems to achieve high productivity within minimal spatial footprints [15]. Space for plant cultivation must compete with other BLSS elements, including oxygen generation, waste recycling, habitation, and scientific payloads, within tightly constrained habitat volumes [212,213].

Traditional plant cultivation methods are not scalable for space missions. Instead, food production systems require being configured to operate vertically or in compact modular formats [214]. Increasing planting density can compromise airflow, light distribution, and horticultural access, producing microclimatic heterogeneity that reduces uniformity and system reliability [96,215]. These findings indicate that increasing density is not a simple scaling strategy, because spatial compression introduces emergent microclimate risks that cannot be mitigated solely through lighting or airflow adjustments.

Volume efficiency is also intricately linked to resource input and waste output. Higher yield per unit volume can increase water, nutrient, and energy demands unless carefully managed, and highly miniaturized systems may become more prone to mechanical failure or biofouling [216]. Compactness must therefore be balanced with maintainability and system robustness.

Another significant constraint in space agriculture is the limited surface area available for effective lighting infrastructure. Uniform exposure to photosynthetically active radiation (PAR) is essential for plant development, yet achieving this in densely packed environments often requires increased light output, optimized fixture placement, or optical redistribution [217,218]. Maintaining PAR uniformity becomes increasingly energy-intensive as canopy layers shade one another. Uneven light distribution can cause photoinhibition in upper leaves or insufficient light in lower canopy layers, reducing overall productivity [219]. Balancing light penetration with heat load and power consumption remains a persistent design challenge [220]. As a result, lighting efficiency and volume minimization are tightly coupled, and no current system has demonstrated stable PAR uniformity at high canopy densities under mission-scale power limits.

In addition to spatial layout, the physical mass and footprint of the entire plant growth unit, including nutrient reservoirs, root support media, sensors, actuators, and control electronics, need to be minimized [221]. Materials should balance durability, sterility, low mass, and modularity [222]. Non-modular systems hinder maintenance, upgrades, and mission adaptability [223].

Environmental shielding and compartmentalization also compete for internal habitat volume. Agricultural modules require containment to prevent cross-contamination with other BLSS systems and to maintain controlled humidity and gas-exchange environments [224]. These isolation measures consume valuable volume and can complicate heat dissipation and airflow management [225,226,227].

In combination, these spatial limitations define a design environment in which every cubic centimeter must be optimized to support reliability, adaptability, and long-term mission stability [228,229].

2.4.2. Energy Constraints and Power Management

Space agricultural systems face severe energy constraints owing to limited onboard power generation capacity and the high energy demands of controlled-environment operations [4]. Photosynthesis efficiency at the canopy/system level is intrinsically low, converting only ~1–2% of incident solar energy into biomass (with edible yield a subset governed by harvest index) [230,231,232]. Martian insolation is roughly 43% of Earth’s due to increased heliocentric distance, and dust storms can further reduce solar input for days to weeks [156,157]. As a result, plant-based food production in space requires substantial electrical input, conceptually exceeding 10 kW per crew member to support meaningful crop yields in BLSS concepts [213,232]. These estimates indicate that plant-based food production is not power-neutral and remains fundamentally limited by lighting and thermal loads rather than biological productivity alone.

CEA systems consume power for lighting, heating/cooling, air circulation, humidity control, pumping, and automation. On Earth, greenhouse heating and cooling account for 65–85% of total energy use [233]. Even with strong insulation, habitats on the Moon and Mars must buffer large external temperature swings, increasing thermal-control loads [234]. Supplemental artificial lighting further increases energy intensity, at times accounting for >30% of system demand [235].

BLSS frameworks introduce further power requirements for air revitalization, water purification, and environmental control. Concept designs for Martian greenhouses estimate peak loads above 50 kW, driven largely by LED lighting and thermal regulation [236,237]. These estimates highlight the need for high-efficiency lighting, waste-heat management, and integrated resource-recycling strategies. However, the ability to sustain continuous crop production within mission-scale power budgets remains uncertain, underscoring the need for improved lighting efficiency and waste-heat recovery.

Power supply reliability on Mars and the Moon is further challenged by variable environmental conditions. Dust accumulation progressively reduces photovoltaic output, and panel efficiency declines at extremely low temperatures or when insolation drops during dust storms or lunar night [238,239]. Because these fluctuations can extend for days, energy systems require sufficient buffering capacity, hybridization, or alternative power sources such as a small nuclear system [240,241]. Small fission reactors such as NASA’s Kilopower designs offer stable, dust-independent power for lunar or Martian agriculture, but their integration is limited by shielding mass and waste-heat rejection requirements [242]. These constraints make nuclear power most suitable for long-duration surface habitats where continuous power output outweighs added mass and safety considerations.

Energy constraints also increase system vulnerability: loss of power rapidly disrupts lighting, temperature stability, gas exchange, and fluid circulation. Without active control, tightly packed growth chambers can quickly accumulate heat, CO₂, and ethylene, stressing plants and reducing yield [15,243]. Energy-storage systems add mass, have finite cycle lifetimes, and may require periodic replacement, complicating long-duration mission planning [244].

Viewed holistically, energy remains a central limiting factor for extraterrestrial agriculture, driving the need for highly efficient lighting, thermal management, power storage, and hybrid energy architectures capable of supporting continuous plant growth in isolated environments.

2.4.3. Crew Interaction and Human Factors

Human involvement in space agriculture introduces substantial operational challenges, particularly concerning crew time, ergonomics, psychological balance, contamination risks, and procedural consistency [16,245]. Agricultural tasks, such as seeding, watering, pruning, harvesting, and troubleshooting, traditionally require sustained manual input [246]. ISS plant-growth trials and recent analog studies report that plant care can require several hours of crew time per week, creating competition with scientific, maintenance, and health-related duties [16,243]. Emerging automation frameworks aim to reduce this burden by shifting routine irrigation, sensing, and environmental adjustments to autonomous control [247].

Space habitats further constrain crew interactions due to limited available volume and altered ergonomic contexts. In microgravity or partial gravity, traditional postures and movements used in agricultural work do not apply [248,249]. Tools and systems not designed for these environments can cause inefficient motions, musculoskeletal strain, and task fatigue. Modules that lack adjustable interfaces or standardized access points can hinder operational accuracy and increase strain risk [250]. Recent design studies emphasize modular work envelopes and glove-friendly interfaces to enhance ergonomics in constrained habitats [251]. These findings indicate that ergonomics in space agriculture is not a direct translation of terrestrial workflows, and optimal task design remains undefined for partial-gravity environments.

The psychological dimension adds another layer of complexity. Caring for plants can offer sensory stimulation and psychological comfort, particularly important in long-duration missions where monotony and isolation are known stressors [243,252]. However, integrating this benefit without compromising operational efficiency remains a design challenge, and recent mission-simulation work suggests that structured, low-frequency plant-care sessions may optimize both morale and workflow [253]. Recent behavioral studies further show that biophilic, plant-rich interiors enhance cognitive performance during confinement [254], while spectrum-tunable lighting improves circadian stability in isolated habitats [255]. Engagement with plants in analog missions also reduces stress and supports emotional resilience [256].

Contamination risk is another significant concern. Plant systems introduce additional moisture, particulates, and microbial load into the closed habitat environment. Without proper containment, crops can become vectors for mold spores, bacteria, or other bioaerosols that compromise crew health and system integrity [257,258]. Surveillance of substrates and high-humidity zones is essential to prevent microbial blooms, consistent with contamination-control protocols for BLSS habitats [49]. Recent studies also highlight the need for UV-C or surface-sanitization strategies compatible with plant modules [259]. However, the long-term effectiveness of these countermeasures under continuous operation remains uncertain, and contamination dynamics across multiple crew rotations have not yet been evaluated.

Finally, differences in crew training, prior agricultural experience, and operational discipline present further barriers. Crew rotations create variability in interaction patterns and protocol adherence [260,261]. Without standardized procedures and user-friendly interfaces, even small deviations can escalate into system failures or crop loss. Recent BLSS-operations research emphasizes structured task sequences, error-proof interfaces, and real-time decision support to improve consistency across crew cycles [262,263].

In combination, these human-factor challenges underscore the need for ergonomically accessible, contamination-resilient, and increasingly automated plant-growth systems that minimize crew workload while preserving psychological benefits and operational reliability.

2.4.4. Psychological and Ethical Challenges

Long-duration space missions impose profound psychological stress due to isolation, confinement, monotony, and disconnection from Earth. Space agriculture, while primarily intended for food and life support, also serves as a psychological countermeasure, though its benefits must be balanced against operational constraints [16,264]. Evidence from analog missions reinforces these risks: analyses from the Mars500 project documented stress elevations, mood fluctuations, and the need for structured psychological countermeasures during prolonged confinement [265].

A key limitation is the variable psychological response of crew members to plant cultivation. While many studies show therapeutic benefits such as reduced anxiety and improved mood, responses differ across individuals, cultural backgrounds, and stress profiles [266]. Given limited volume and crew time, psychological benefits must be weighed against operational priorities [16].

Plants can provide sensory stimulation within artificial spacecraft interiors, but restricted volume and lighting often limit visibility and interaction opportunities [35,267]. Designing accessible, low-maintenance placement of plant modules can enhance psychological utility without imposing excessive workload. Crop choice can also influence morale, though psychological considerations must be balanced with yield, resource efficiency, and system complexity [268].

On the ethical front, space agriculture raises difficult questions about biotechnology and resource allocation. Genetically modified crops may be a necessity for space conditions, but their use needs to be weighed against biosafety risks and crew acceptance [269,270]. Enclosed habitats heighten biosafety stakes due to limited redundancy, and planetary-protection frameworks limit any deployment beyond controlled modules [271].

Ethical tensions also arise from resource prioritization: allocating water, light, and volume to psychologically beneficial or culturally meaningful crops must be justified relative to core life support demands [272]. Decision-making authority around crop selection and agricultural workload intersects with autonomy, mission discipline, and equitable use of shared resources [273,274].

Finally, investment in space agriculture occurs alongside global challenges such as food insecurity and environmental degradation on Earth, raising recurrent debates on the balance between space exploration and terrestrial responsibility [275]. Viewed together, these psychological and ethical challenges highlight the need for plant systems that support well-being, respect biosafety constraints, and allocate scarce resources responsibly within long-duration missions.

These operational constraints highlight the need for automation, fault-tolerant scheduling, and adaptive control systems capable of maintaining agricultural tasks under restricted labor, time, and crew workload conditions.

2.5. System Reliability and Risk Management

2.5.1. Backup Systems and Redundancy

Reliable space-agriculture systems require robust backup architectures and redundancy strategies, particularly because failures cannot be corrected through rapid resupply or external servicing. Operational constraints such as crew time, maintenance demand, and system redundancy are central to system reliability, since agricultural modules must continue functioning even when crew availability is limited or maintenance intervals are long. In isolated environments such as lunar bases or Mars habitats, any component failure in growth chambers, such as lighting arrays, pumps, sensors, or CO₂ management, can halt food production within hours, potentially compromising mission safety [276,277]. Hence, system reliability depends less on individual component robustness and more on architectural resilience that prevents single-point failures from propagating through the BLSS.

Critical system redundancies are essential. Photovoltaic (PV) modules degrade over time, with median rates of 0.5–0.6% and mean rates up to 0.9% per year for crystalline silicon technologies [278,279]. In hot-dry climates, rates can reach 1.1% annually [280]. Common failure modes include delamination, browning, and solder fatigue [281]. These degradation patterns demonstrate the importance of redundant or hybrid power systems capable of maintaining agricultural operations during periods of reduced PV output. Life support and plant chamber components onboard the ISS are often duplicated or triplicated in an N + 1 (where N is the minimum number of components required for operation, and the additional +1 provides spares to maintain function in case of failure) or triple redundancy configuration, significantly reducing the probability of complete system failure. Tripling critical components with a single-unit failure probability of 0.1 can lower overall failure probability to 0.001, offering reliability gains far beyond what is achievable through incremental component hardening [282]. However, mission-scale redundancy remains logistically constrained for lunar and Martian habitats, meaning future systems must balance redundancy with mass, power, and maintenance limitations rather than simply replicating ISS approaches.

Long-duration missions also demand predictable failure rates and structured maintenance planning. Agricultural subsystems, such as LED arrays, irrigation pumps, valves, nutrient-delivery lines, airflow fans, and sensors, remain vulnerable to internal degradation even in controlled environments. LEDs experience spectral drift and diode burnout; pumps and seals wear or clog from biofilm; sensors drift and require periodic recalibration [283,284,285]. Shields mitigate external threats such as radiation and micrometeoroids, but internal stressors such as thermal cycling, humidity, and continuous mechanical operation drive time-dependent failures. Unlike on Earth or the ISS, where replacements can be shipped or swapped, Mars missions face long resupply times and limited in situ repair capacity. This makes redundancy, modular design, and fault-tolerant architectures indispensable for safeguarding food production and mission continuity. These constraints indicate that redundancy alone is insufficient without modular components designed for rapid isolation, replacement, or bypass when failures occur.

As a result, these factors highlight that redundancy is not only a technical safeguard but also an operational necessity: systems must remain functional despite limited crew time, infrequent maintenance, variable power availability, and component degradation over long missions. Overall, the literature agrees on the necessity of fault tolerance, but the optimal balance between redundancy, modularity, and automation for multi-year missions remains unresolved.

2.5.2. Unknown Unknowns

Agricultural systems designed for extraterrestrial habitats contend not only with identified hazards but also with emergent challenges that arise from unfamiliar, complex environments. What is known is that equipment failures, microbial shifts, and environmental instability are major risk drivers in closed systems. What remains unknown are the long-term biological and mechanical interactions that may emerge under fractional gravity, high radiation, or tightly coupled BLSS operation [286,287].

Risk models for space missions show that decision-making often fails when relying solely on Earth-based historical data or probabilistic forecasts [288]. Deep uncertainties persist because micro-environmental fluctuations, planetary dust behavior, and plant responses to radiation or mechanical stress remain insufficiently characterized [43,289]. For example, the interaction of Martian dust with filters, optics, or root-zone systems is still largely unquantified, creating potential blind spots during long-duration missions [290].

Compounding these gaps is the absence of true long-term analog missions for lunar or Martian surface agriculture. Unknowns include cumulative low-dose radiation effects, multi-generational microbial evolution, and fractional-gravity plant development, none of which can be modeled reliably without operational data [291,292].

Because of these uncertainties, static engineering designs are often inadequate. Adaptive, uncertainty-tolerant design frameworks, such as model-based adaptive planning and robust configuration-drift management, are increasingly recognized as essential for BLSS architectures [293]. Space agriculture remains constrained by “unknown unknowns,” where biological, environmental, and technical variables interact in ways that cannot yet be fully predicted or validated.

These reliability challenges underscore the importance of integrated sensing, predictive analytics, and resilient system architectures that can detect, isolate, and mitigate failures before they cascade across BLSS subsystems.

3. Engineering and Technological Solutions

Engineering solutions for space agriculture must operate under strict mass, power, volume, and reliability constraints, making subsystem design inseparable from mission architecture. This section outlines the major engineering components and their current maturity levels, along with mission-driven trade-offs that shape practical deployment.

Most agricultural subsystems currently fall within TRL 3–6, with lighting and environmental control more mature than bioregenerative nutrient or microbial processes.

3.1. Controlled Environment Agriculture (CEA)

CEA forms the core of extraterrestrial plant production by enabling precise regulation of environmental parameters such as temperature, humidity, CO₂ levels, and photoperiod [294]. As a key subsystem within BLSS, CEA supports stable yields in enclosed habitats while shielding crops from extreme lunar and Martian surface conditions [212]. Environmental instability and humidity fluctuations are actively managed through closed-loop control systems [295]. Advanced LED lighting tailored to plant-specific spectra, primarily red and blue for photosynthesis, with supplemental green for canopy penetration and psychological benefits, enhances energy efficiency and crop quality [296,297,298,299]. A persistent engineering trade-off is that tighter environmental stability generally increases energy demand, requiring careful optimization under limited mission power budgets. Optimization of light spectra also supports circadian regulation and reduces physiological stress [300].

3.2. Water Management and Recycling

Water, being both scarce and heavy to transport, demands high-efficiency recycling systems in space habitats [4]. Techniques such as innovative closed-loop hydroponics, condensate recovery, and porous tube irrigation enable precise delivery and conservation [301]. Porous tubes regulate moisture without gravitational drainage, a critical solution in microgravity or reduced gravity settings [302]. Sensor-based feedback systems continuously monitor root-zone moisture levels to prevent evaporation loss [303]. These systems complement spacecraft water recycling units by managing greywater sources while ensuring pathogen-free irrigation [304].

3.3. Gravity Mitigation Strategies

Gravity influences water transport, root development, and plant orientation [305,306]. Under reduced or microgravity conditions, plants exhibit complex morphological and physiological responses, including altered root growth direction, changes in vascular anatomy, and disrupted nutrient transport [306]. To simulate gravitational stimuli and mitigate these anomalies, experimental setups such as clinostats, rotating growth chambers, and centrifuge-based systems have been employed [307]. Horizontal clinorotation has been shown to affect amyloplast distribution and root orientation in lentils [308], while long-term simulated microgravity in tomato plants leads to thinner root epidermis and cortex, reduced germination, and irregular root growth [309]. Clinostat-grown Arabidopsis thaliana also displays distinct morphological traits compared to upright or centrifuge-grown controls [310], highlighting the need for more advanced ground-based simulation systems. Overall, ground-based simulations and centrifugation approaches provide valuable tools to study how gravity affects xylem development, root orientation, and resource transport, and to design countermeasures for spaceflight plant cultivation systems [311]. However, these platforms cannot fully replicate fractional-gravity conditions on the Moon or Mars, so their relevance for long-duration seed-to-seed production remains uncertain.

3.4. Radiation Shielding and Atmospheric Solutions

Space agriculture systems require addressing both radiation protection and atmospheric stability to ensure crew safety and plant productivity. Exposure to SPEs, GCRs, and unfiltered ultraviolet radiation in space habitats poses significant biological risks. Burying agricultural modules under lunar or Martian regolith remains a practical passive shielding strategy, offering strong protection against SPEs while adding minimal mass to habitat design [312,313]. Hydrogen-rich materials, such as water layers or polyethylene liners, further attenuate high-energy particles, though shielding remains far more effective for SPEs than for GCRs, whose high energies limit feasible attenuation in mass-constrained habitats [314,315]. Emergency shelter concepts for cislunar missions emphasize rapid-access, high-attenuation spaces for worst-case SPEs, applying ALARA-based threshold limits without adding unnecessary mass [316].

Atmospheric control is a critical component of space greenhouses, requiring precise regulation of pressure, gas composition, and humidity to support plant growth and system stability. Low-pressure operation (10–101 kPa) reduces structural mass and leakage but requires careful balancing of plant gas exchange and habitat safety margins [189]. CO₂ levels can be elevated to ~1500 ppm in plant zones to enhance photosynthesis [317]. CO₂ and O₂ concentrations are regulated through photosynthetic uptake, electrolysis, and chemical scrubbers. Active ventilation and precision-controlled pumps sustain appropriate gas distributions [318]. Continuous monitoring supports early detection of instability in mass-balance dynamics [319]. Humidity is controlled using sensors and dehumidification units, essential under reduced pressure where evaporation and transpiration behaviors differ from Earth. However, gas balance is maintained through a combination of plant uptake and engineered life support processes rather than detailed mechanistic pathways, ensuring atmospheric stability without unnecessary process-level explanation.

Some advanced Mars greenhouse concepts integrate plant systems with habitat air-management modules to support pressure transitions and supplemental oxygen generation while maintaining crop stability [317]. However, these designs remain at the conceptual stage, and no demonstration has been validated with coupled atmospheric–plant systems under operational Martian conditions, highlighting the need for further verification before deployment.

These approaches highlight that shielding and atmospheric management are foundational requirements for stable extraterrestrial crop production, balancing radiation safety with efficient environmental control in mass-limited habitats.

3.5. Nutrient Availability and Recycling

Closed-loop nutrient management is essential for sustaining plant production in space, where resupply is limited and nutrient losses cannot be tolerated. Core elements such as nitrogen, phosphorus, and potassium can be recovered from crew waste, food residues, and inedible biomass through combined physicochemical and biological processes [20,140]. Struvite precipitation stabilizes ammonium and phosphate into a slow-release fertilizer, while microbial consortia used in urine nitrification and anaerobic digestion convert unstable compounds into plant-available nitrate or mineralized slurry suitable for hydroponic reuse [320,321,322]. Integrated bioreactors further support continuous organic-matter cycling and reduce dependence on external inputs [323,324].

Regolith-based substrates introduce additional challenges due to low cation-exchange capacity, requiring buffering strategies to mitigate salt accumulation and improve nutrient retention [9,98]. Supplemental micronutrient delivery may still be necessary during long-duration missions, particularly when relying on ISRU-derived materials. Advances in sensor-based monitoring and closed-loop feedback now enable real-time adjustment of nutrient composition, preventing deficiencies and toxicities while maximizing recovery efficiency [325,326,327].

3.6. Advanced Sensor Systems

Precision agriculture in space relies on integrated, miniaturized sensor systems that enable real-time monitoring of plant, environmental, and system health. Compact, low-power sensors continuously track critical parameters such as temperature, relative humidity, atmospheric gas composition (O₂, CO₂, ethylene), light intensity, pH, EC, dissolved oxygen, and chlorophyll fluorescence [328,329,330]. Spectral sensors, including multispectral and hyperspectral cameras, support early detection of physiological stress, nutrient imbalances, or disease symptoms through non-invasive imaging [331,332]. Volatile organic compounds (VOCs) and microbial signatures in the air and nutrient solution can be detected using biosensors and lab-on-chip diagnostic tools [333,334]. Wireless sensor networks, often using low-power communication protocols (e.g., Zigbee, LoRa), minimize wiring and energy use in closed habitats. These sensors integrate into automated control systems that regulate lighting, nutrient dosing, ventilation, and irrigation based on real-time data feedback [335,336,337].

For long-duration missions, sensors are critical to remain robust against radiation exposure, pressure fluctuations, and variable gravity, necessitating redundancy, fault tolerance, and reliable calibration. However, sensor calibration poses a persistent challenge, as drift in bias and scale factors can degrade data quality and limit autonomous operation if not periodically corrected [338]. To mitigate these risks, advanced solutions such as the AuRelia project (an initiative on FPGA-based smart sensor reliability) have introduced In-System-Failure-Detection (ISFD) techniques, offering real-time fault detection and enhanced resilience to radiation up to 70 krad (i.e., 70,000 rad, equivalent to 700 Gy), thereby improving data integrity in harsh space conditions [339].

3.7. Automation and Robotics

Automation and robotics are integral to sustainable space agriculture, reducing manual workload and stabilizing operations in confined and hazardous environments [340,341]. Autonomous systems support core functions such as seeding, nutrient delivery, canopy monitoring, pruning, and harvesting [341]. Advanced robotic arms with multi-degree-of-freedom manipulators and vision-guided end effectors enable precise plant interaction, while mobile robotic platforms can navigate constrained habitats for site-specific crop care [342,343]. In situ substrate preparation and perchlorate handling may also be automated, but these applications remain largely conceptual rather than operationally validated. Integration with AI and machine learning enhances adaptability under changing environmental and crop demands, enabling predictive maintenance and real-time decision-making [344,345]. Modular, reconfigurable platforms are increasingly emphasized to balance reliability and maintainability in long-duration missions, where repair capability is limited [346,347]. Taken together, automation is shifting from task-level mechanization toward integrated autonomy focused on crew-time reduction and operational stability rather than maximizing technological complexity. Recent follow-on developments from the EDEN ISS Antarctic testbed, particularly the EDEN LUNA redesign, explicitly target improved subsystem reliability and significant reductions in crew time through robotic plant handling, redesigned nutrient systems, and optimized maintainability [348]. Parallel efforts at NASA have advanced multilayered root-zone control through the Ohalo crop-production system, supported by the development and ground testing of zero-discharge root-zone modules designed for microgravity integration [349].

3.8. Artificial Intelligence and Data Management

AI and data management systems form the backbone of intelligent, adaptive control in extraterrestrial crop production. By continuously processing high-resolution data from environmental and plant health sensors, AI enables real-time optimization of growth conditions such as light intensity, nutrient dosing, temperature, and humidity. Machine learning algorithms support predictive modeling for crop growth, early detection of biotic and abiotic stresses, and anomaly identification in closed-loop systems [350,351,352]. The Vyoma-ADS system, designed for space agriculture, combines IoT technology with adaptive anomaly detection using machine learning models like DBSCAN to maintain optimal growing conditions in the unique environment of space [353]. AI-driven phenotype recognition and computer vision facilitate automated trait monitoring, enabling precision agriculture at the plant level [354]. Onboard edge computing architectures minimize latency and allow autonomous operation during communication blackouts or long signal delays, particularly for Mars missions [355]. Early-stage edge platforms (e.g., Versal-class adaptive processors) are being explored to support low-latency onboard AI, although their readiness for long-duration missions remains uncertain [356]. Meanwhile, ground-based systems support long-term data storage, model retraining, and cross-mission learning [357]. These systems facilitate data fusion strategies that integrate multisource inputs, including spectral imaging and environmental measurements, to improve decision support in dynamic extraterrestrial environments [358]. As space exploration advances, there is a growing need for strategies to increase science return from existing datasets, promote data sharing, and support community-focused environments for data assimilation and cross-mission learning [359]. However, challenges remain, including data scarcity and high equipment costs. Future research should focus on developing open-access datasets, optimizing lightweight models, and exploring the long-term impacts of AI and robotics on agricultural ecosystems [360].

3.9. Biotechnological and Genetic Approaches

Biotechnological innovations are crucial for developing crops suitable for space environments. Inoculating crops with extremophilic endophytes has improved performance under simulated space-relevant stress, although these results remain limited to early-stage experiments [361]. Advanced techniques like CRISPR/Cas9 gene editing and synthetic biology enable the development of stress-tolerant crops, demonstrating significant yield and resilience gains in adverse conditions [362]. Current efforts prioritize staple crops that maximize edible biomass per resource input [363].

Spaceflight-specific stressors, including microgravity and elevated radiation, may induce heritable changes, though their stability and agronomic relevance remain uncertain [364]. Synthetic biology also enables engineering of plants and microbes to produce essential nutrients, pharmaceuticals, and bio-based materials [365,366]. Photosynthetic microorganisms offer further advantages due to high light-to-biomass conversion efficiency and potential roles in oxygen generation during long-duration missions [367].

Integration of omics-based gene discovery with AI-driven trait prediction supports targeted development of candidate “space crops,” particularly for nutrient-use efficiency and stable plant–microbiome interactions within closed systems [366,368]. Together, current biotechnological approaches provide a promising toolkit, but their operational readiness for multi-year missions remains largely untested, highlighting the need for validation under authentic spaceflight constraints.

3.10. In Situ Resource Utilization (ISRU)

ISRU is essential for reducing dependency on Earth-supplied materials and supporting long-term agricultural viability [369]. By leveraging local planetary resources, such as regolith, subsurface ice, and atmospheric gases, ISRU reduces launch mass and supports more autonomous BLSS operation [369,370].

Lunar and Martian regolith can be repurposed as shielding and, after treatment, as a limited-use plant substrate. Beneficiation methods, including magnetic separation, thermal volatilization, and acid leaching, reduce toxic compounds and improve chemical suitability, though no approach has yet demonstrated stable performance under closed-habitat conditions [371,372,373]. Biological approaches may complement physical treatment, but their reliability in sealed environments remains unvalidated [104].

Accessible water ice deposits represent another critical ISRU target. On Mars, shallow mid-latitude subsurface ice has been confirmed beneath ~1–2 m of regolith, whereas deeper sources remain inaccessible [8,209,374]. On the Moon, spectroscopic observations reveal patchy, low-abundance ice in permanently shadowed regions [75,375]. Extraction concepts exist, but field-scale performance and energy cost remain uncertain [376].

The CO₂-rich Martian atmosphere supports oxygen production via solid-oxide electrolysis, demonstrated by the MOXIE experiment [377,378]. Pressurized cultivation systems may also use atmospheric CO₂ to support cyanobacterial growth, but nitrogen scarcity limits biological productivity without supplementation [379].

Looking ahead, ISRU may become a key enabler of autonomous agriculture, but realization will require empirical validation of extraction performance and BLSS integration beyond laboratory settings.

3.11. Redundancy and Backup Systems

Redundancy and fail-safe architectures are essential to ensure continuous operation of space-based agricultural systems, where maintenance opportunities are limited and system failure could jeopardize food supply and crew safety. Because systems must remain functional despite constrained crew time and long maintenance intervals, redundancy planning extends beyond power and life support to include irrigation, nutrient delivery, environmental control, and data acquisition subsystems. However, most redundancy concepts remain adapted from terrestrial engineering rather than validated in plant-production settings, leaving uncertainty around performance under reduced maintenance and high-risk mission profiles.

Redundancy in systems can be classified into passive and active approaches, each with distinct characteristics and applications. Passive redundancy includes mechanisms like thermal mass buffers and gravity-fed reservoirs, while active redundancy involves parallel modules that can be automatically activated upon fault detection [380]. In the context of BLSS, the relevance of these frameworks lies less in their mechanistic detail and more in demonstrating that redundancy must balance reliability with mass and energy cost, rather than maximizing duplication.

Space habitats commonly apply N + 1 or N + 2 redundancy, allowing continued operation if one or more components fail [381,382]. Critical control elements such as sensors, pumps, and actuators require duplication or integrated diagnostics to detect drift or malfunction, reducing the risk of cascading failures in closed environments. Recent space-greenhouse operations show that redundancy is most effective when paired with early-warning diagnostics rather than simple hardware duplication, shifting the emphasis from backup capacity to failure prevention. Biological redundancy provides an additional layer of resilience: staggered planting schedules and cultivar diversity help maintain food production even if individual batches fail [383]. This highlights that redundancy in agriculture is both mechanical and biological, a distinction not typically reflected in engineering-centric redundancy models.

Reliability-based design methods, including Failure Mode and Effects Analysis (FMEA) and Fault Tree Analysis (FTA), support early identification of weak points and guide mitigation strategies [384]. Emergency protocols such as manual overrides, isolation valves, and reversion to safe environmental baselines further minimize system vulnerability during unexpected disruptions [385]. Yet, few studies report how these approaches perform under fractional gravity, prolonged autonomy, or limited crew intervention, making operational readiness uncertain for multi-year missions. Ultimately, redundancy must be balanced against strict mass, volume, and energy constraints, requiring modular architectures that prioritize essential subsystems according to mission duration and crew size [386]. Overall, current evidence suggests that redundancy will need to evolve from hardware-based duplication toward modular, fault-tolerant, and diagnostically guided architectures tailored to constrained, autonomous extraterrestrial habitats.

Table 5. Key challenges for extraterrestrial crop production and representative mitigation strategies.

Challenge	Representative Mitigation Strategies
High radiation exposure (GCR, SPE, UV) *	Regolith shielding or burial; hydrogen-rich shielding (water, polyethylene); SPE * storm shelters; minimizing exposure under ALARA *; crop selection and genetic engineering for antioxidant capacity and DNA repair; precision monitoring with AI * to manage exposure; redundant shielded growth modules to ensure food supply if one chamber is compromised
Extreme temperature fluctuations	Insulated and actively heated/cooled growth chambers; regolith berms or underground siting for thermal buffering; CEA * automation and AI * for predictive climate control; crop selection and genetic engineering for temperature tolerance; backup thermal systems for resilience
Low gravity and altered fluid dynamics	Capillarity-aware irrigation (porous tubes, wicking, root-zone designs); hydroponics/aeroponics with pumped circulation to overcome gravity dependence; clinostats/centrifuge modules for testing; airflow management to prevent hypoxia; AI *-driven precision irrigation to avoid localized drought or oversaturation; redundant irrigation methods to prevent single-point failure; crop selection/genetics for altered gravitropic responses
Absence of atmosphere/low pressure	Pressurized greenhouse structures (10–101 kPa); CO2 enrichment (~1500 ppm); O2 generation (electrolysis); chemical scrubbers (zeolites, LiOH); active ventilation and dehumidification; CEA * automation and AI * for stable atmospheric control; modular habitat design to provide backup chambers in case of leaks or system failure
Lighting constraints and energy reliability	Supplemental LED lighting; resilient energy storage/backup (nuclear, PV-battery hybrids, solar panels); energy-efficient CEA * design; AI * optimization of light use for high output/low input; crop selection for low-light tolerance; redundant power and lighting systems for safety
Water scarcity and recycling	Hydroponics and aeroponics; ISS *-class WRS * (>90% recovery); multi-stage filtration and catalytic oxidation; microbial/bioreactor urine processing; distillation/freezing; recovery of transpired water; fogponics and hydrogels; crop selection and breeding/genetics for water-use efficiency; AI *-based irrigation optimization for resource efficiency; redundant and modular water systems (soil + hydro + aero) to increase safety factor and hydrogels; crop selection and breeding/genetics for water-use efficiency;
Poor regolith CEC and soil structure	Organic amendments (compost, biochar); microbial consortia; controlled-release fertilizers; hydrogels to stabilize moisture; alternative substrates (hydroponics, synthetic soils, 3D-printed media); crop selection/genetics for tolerance to low fertility and drought; AI *-supported nutrient delivery; redundant substrate systems for reliability
Chemical toxicity (perchlorates, heavy metals)	Beneficiation/detox (acid leaching, thermal volatilization, magnetic separation); microbial remediation; pH buffering; infrastructure barriers to prevent crew contamination; robotic/automated regolith handling for crew safety; backup safe substrates to maintain food security if toxicity cannot be controlled
Absence of microbiome and plant–microbe interactions	Inoculation with beneficial microbes; engineered microbial consortia; carbon-rich carriers for inoculants; shallow burial for microbial protection; genetic engineering for microbe-independent nutrient uptake; AI * monitoring of plant–microbe interactions; redundancy in inoculant sources
Susceptibility to pathogens	Resistant cultivars; sterile controlled growth systems; genetic engineering for pathogen resistance; AI *-driven early pathogen detection and monitoring across the crop cycle; backup crop modules to safeguard against outbreaks
Monitoring and diagnostics	Integrated sensor networks (EC *, pH, ion concentrations, microbial load, VOCs *); continuous closed-loop monitoring; automation and AI * for end-to-end monitoring from seeding to harvest, growth rates, nutrient stress, and disease; redundant monitoring systems for safety
Psychological stress (menu fatigue, altered sensory perception)	Crop diversity; aromatic and spicy plants; rapid-cycle leafy greens and microgreens; crop selection for sensory appeal and functional phytochemicals; backup fresh-crop modules to ensure continuous availability of psychologically supportive foods

* GCR (galactic cosmic ray); SPE (solar particle events); UV (ultraviolet); ALARA (as low as reasonably achievable); AI (artificial intelligence); ISS (international space station); WRS (water recovery system); EC (electrical conductivity); VOCs (volatile organic compound).

synthesizes the major environmental, biological, and operational challenges for extraterrestrial crop production, together with representative mitigation strategies, ranging from shielding, detoxification, and recycling systems to cross-cutting approaches such as crop selection, genetic engineering, robotics, precision agriculture, and AI-enabled automation designed for high output with low input and modular redundancy.

4. Discussion

The development of sustainable agricultural systems for extraterrestrial environments represents a multifaceted engineering and biological challenge. As this review outlines, the environmental, physiological, and operational constraints imposed by space habitats, ranging from radiation and gravity to closed-loop nutrient cycles, require an integrated approach that merges biology, engineering, and data science. What is well established is that individual subsystems such as lighting, nutrient delivery, and atmospheric regulation can function effectively in isolation under controlled conditions. However, a critical uncertainty is their behavior when tightly coupled in long-duration, failure-prone missions, where interactions may produce emergent effects not yet captured by existing experimental evidence. These uncertainties reflect the limits identified across Section 2 and Section 3, particularly in radiation tolerance, fluid handling, microbiome stability, and nutrient-loop robustness, which remain only partially characterized experimentally.

The transition from isolated technologies to a unified life support ecosystem introduces substantial systems-level complexity. For example, water management needs to simultaneously consider gravity-induced fluid dynamics, evaporation control under low pressure, and resource regeneration from waste. Similarly, nutrient cycles require biological sufficiency coupled with computational management through sensor feedback and AI prediction to avoid toxicity, imbalance, or inefficiencies [4,20,301,304,326]. These cross-dependencies highlight that optimizing individual components is insufficient without accounting for system-level feedback and cascading effects. Accordingly, the focus is shifting from component-level optimization toward whole-system resilience and fault-tolerant design.

Because failures in water, nutrient, atmospheric, thermal, and microbial loops can propagate across shared system components, BLSS agriculture must be evaluated using integrated risk frameworks that capture cascading failures, cross-linked subsystem vulnerabilities, and overall system fault tolerance.

CEA functions as the backbone of space farming efforts, offering a modular and reconfigurable platform for integrating lighting, climate control, irrigation, and diagnostics [28]. Yet, its resource intensity, particularly in power demand and thermal management, poses serious constraints in off-Earth environments. Solutions such as LED spectrum optimization, solar-to-electric conversion efficiencies, and waste heat utilization offer partial relief, but trade-offs between precision and resource cost remain unresolved research challenges [296,297,300]. Recent CEA innovation therefore emphasizes stability and efficiency under constrained energy budgets rather than continual increases in environmental precision.

The deployment of genetically optimized crops and microbial consortia tailored for microgravity and radiation resistance is a promising frontier, yet also raises ethical and containment considerations [135,387]. Advanced monitoring through spectroscopy, hyperspectral imaging, and AI-driven diagnostics will be essential for both sustaining plant health and anticipating failures in ways not required in terrestrial agriculture [331,332]. Moreover, psychological and ethical dimensions, while secondary to life support, remain critical operational considerations, especially as mission duration increases [388,389,390]. Collectively, these developments expand operational capability but also broaden the decision space, requiring governance frameworks that balance scientific benefit, operational risk, and crew well-being.

A recurring theme across all domains is the tension between precision and resilience. Highly engineered systems offer control but increase failure risk through interdependency. Conversely, biologically inspired redundancy, such as soil-augmented hydroponics or polymicrobial inoculants, may enhance robustness but at the cost of predictability [391,392,393]. Future priorities will require identifying hybrid strategies that maintain stability without over-engineering, particularly in reduced-gravity and closed-loop configurations where corrective interventions are limited.

Recent exploration analyses and mission-planning studies anticipate that sustained lunar surface activities will intensify through the late 2020s–2030s [394,395,396], while emerging Mars exploration architectures generally converge on the earliest feasible crewed opportunities in the mid-2030s [397]. These timelines align with NASA’s Artemis campaign objectives and the planned Lunar Gateway biological payload opportunities [398], as well as China’s Chang’e-7/ILRS Phase I activities projected for the 2027–2028 time frame [394]. As humanity advances toward sustained lunar and Martian habitation, space agriculture will not remain a peripheral function but will become a central pillar of BLSS.

Despite the substantial technical, environmental, and biological challenges, investing in space-based food systems represents a vital step toward securing human presence beyond Earth. Moreover, the innovations developed for extraterrestrial agriculture have immediate relevance to terrestrial challenges (from closed-loop nutrient recovery to climate-resilient CEA), indicating meaningful bidirectional benefits. Concrete Earth applications already demonstrate this translation. Closed-loop water technologies developed for space, such as the ISS Water Recovery System with ~93–94% reclamation efficiency [399], have informed advanced CEA systems in arid regions, contributing to freshwater-use reductions of 20–30% in demonstration greenhouses [400]. Laboratory-scale hybrid biological–RO systems likewise achieve ~90% recovery from simulated humidity condensate [401], illustrating their suitability for terrestrial water-scarce regions. In parallel, AI-based crop-monitoring workflows derived from EDEN ISS spectral-imaging research have been applied in polar research stations, where they reduced manual inspection time by approximately 60% while improving early-stress detection [82].

Overall, while current knowledge establishes a strong technological foundation, the most critical unknowns (long-term system behavior, biological adaptation, and reliability under deep uncertainty) define the next phase of research and will require coordinated testing across ground analogs, ISS platforms, and upcoming lunar surface missions. Priority research areas emerging from this review include long-duration microbial and nutrient-loop stability studies, partial-gravity plant development across multiple generations, and subsystem-integration testing that combines lighting, water, nutrient, and environmental control architectures under mission-relevant constraints.

In summary, current evidence demonstrates that controlled-environment agriculture can support short-duration missions, but long-term reliability under partial gravity and closed-loop constraints remains unverified. Key unresolved challenges include system-level interactions between subsystems, biological adaptation across multiple crop generations, and maintaining stability under limited corrective capacity. Addressing these gaps will require coordinated multi-platform testing that links ground analogs, ISS experiments, and upcoming lunar surface deployments.

5. Conclusions

To advance the field, future research should prioritize a focused set of high-impact directions. First, long-duration biological experiments in partial gravity are essential to determine multigenerational stability, reproductive reliability, and potential epigenetic changes in space crops. Equally important is the need for fully integrated subsystem testing that combines lighting, water handling, nutrient loops, sensing, shielding, and autonomy under mission-relevant conditions rather than relying on isolated component trials. Progress also depends on higher-fidelity regolith and substrate studies, including experiments with returned lunar samples and improved simulants that more accurately reflect root-zone chemistry and physical behavior. Strengthening automation and fault-tolerance frameworks remains a critical engineering priority to reduce crew workload and maintain safe BLSS operation during incidents or sensor failures. Additionally, predictive models that couple environmental variability with crop performance will enable more reliable control strategies in constrained, sensor-limited habitats. Finally, emphasizing dual-use technology development such as closed-loop water systems, energy-efficient lighting, and AI-based crop monitoring will ensure that advances in space agriculture also contribute to terrestrial food security and climate resilience.