Introduction

A new era of lunar exploration is defined by a shift from brief sorties to establishing a permanent, sustainable human habitat on the Moon. Current lunar exploration programs, such as China’s Chang’e Program and the United States’ Artemis Program, have evolved beyond the strategic objective of short-term exploration missions toward the shared goal of establishing permanent lunar bases capable of supporting sustained scientific and economic activities1,2.

The fundamental challenge to lunar habitation is the Moon’s extreme physical environment. The absence of a substantial atmosphere and the low thermal conductivity of the regolith result in surface temperatures plummeting to approximately 95 K during the 14-day lunar night3,4,5,6. The near-vacuum enables continuous radiative heat loss to cold deep space7, while microgravity suppresses natural convection8, together posing a significant challenge to nighttime survival.

To address this challenge, current research is exploring diverse options for supplying thermal energy to lunar bases at night. Established approaches include the use of mature, high-reliability systems such as small radioisotope heater units (RHUs) and advanced multi-layer insulation (MLI) for baseline thermal control9. In parallel, researchers are leveraging in situ resource utilization (ISRU), especially large-scale thermal energy storage (TES) systems that would capture and retain solar heat in lunar regolith10,11. In parallel, to meet anticipated future demands for high-power, long-endurance energy, the development of megawatt-class space nuclear fission reactors is also a primary area of investigation12.

Existing research often examines these technologies in isolation, focusing on the optimization of a single solution without a holistic context. In this review, we provide a systematic and forward-looking assessment of the key technologies for ensuring lunar base surviving at night. We map these technologies onto a phased construction framework, aligning energy and thermal management strategies with the distinct needs of “short-term survival”, “mid-term operations”, and “long-term development”. Through a developmental lens, we propose a sustainable pathway for the lunar base founded on multi-source energy complementarity—one that enables the transition from passive environmental adaptation to active, sustainable development.

Nighttime survival technologies for lunar base

Short-time lunar base

The primary objective for lunar base survival during the short lunar night is to maintain safe operational conditions for equipment over several weeks. For short missions, the priority is to ensure stable detector operation with minimal energy consumption.

Early lunar exploration adopted relatively simple strategies for night survival: passive insulation and active heating. The surveyor landers entered hibernation during the lunar night13,14, while the Apollo program combined MLI with radioisotope thermoelectric generators (RTGs) to achieve a hybrid of passive insulation and active heating for the Apollo lunar surface experiment package15,16 (Fig. 1a). Modern thermal-control architectures for lunar exploration equipment are more integrated and intelligent. For instance, Chang’e and Yutu spacecraft combine MLIs, RHUs, and phase-change materials (PCMs) for efficient nighttime thermal management17,18. MLIs are used to isolate thermal radiation from cold space (Fig. 1b)19, RHUs/RTGs provide essential baseline heat (Fig. 1c)20, PCMs store and release energy to stabilize temperature.

Fig. 1: Short-time lunar base night survival technologies.
Fig. 1: Short-time lunar base night survival technologies.
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a Apollo 11 Lunar module Eagle at Tranquillity Base, Image courtesy of NASA (public domain). b Thermal energy model of the multilayer insulation, reproduced from Mesforoush et al.19 with permission from Elsevier (license number: 6164041008480). c Exploding diagram of the model in the simulation, reproduced from Tailin et al.20 with permission from Elsevier (license number: 6166521110886).

As planning for permanent lunar bases advances, researchers are exploring the use of in situ resources to address engineering challenges. A prominent example is the “thermal wadis” concept21,22. Thermal wadis involve using large areas of nature lunar regolith to absorb and store solar energy during the lunar day. The stored thermal energy is then gradually released during the lunar night, providing a relatively warm environment for rovers and other base facilities. Climent et al.23 demonstrated that thermal wadis can provide sufficient heat to maintain the temperature of lunar equipment above 243 K. The strategy for lunar night survival is evolving from early reliance on insulation and supplementary heating to the exploration of ISRU-based approaches. This transition lays a critical foundation for establishing sustainable, long-term lunar bases in the future.

Long-time lunar base

Compared with short-time missions, long-time lunar bases face substantially higher engineering complexity in nighttime thermal environment management. As the base size increases, the residence time is extended, and functional zones, such as habitation, scientific research and industrial processing are gradually expanded, the night-time heat load is expected to rise from hundreds of watts for short-term missions to several hundred kilowatts or even the megawatt level24,25. Similar to short-time missions, the survival of long-term bases during the lunar night cannot rely on a single solution; instead, a composite thermal control architecture should be established, in which passive thermal protection and active heat sources are synergistically combined. In this framework, passive thermal protection focuses on reducing the baseline heat loss of the infrastructure, while active heat sources provide the continuous heat input required to maintain a stable environment under prolonged periods without solar illumination.

The core of passive thermal protection lies in site selection and envelope design. Due to the strong latitude dependence of illumination and thermal cycling, the thermal environment varies significantly across the lunar surface. Equatorial regions experience continuous darkness and extreme diurnal temperature swings, which impose stringent requirements on insulation capability26. In contrast, the peaks of eternal light (PELs) located at polar crater rims are characterized by shorter shadow periods and milder temperature fluctuations, therefore reducing the night-time heat load at the source27. However, the total area of polar PELs is limited, and the local terrain is often complex, which constrains the scalability of base expansion and reduces flexibility in infrastructure layout. From a structural point of view, lunar regolith, owing to its low thermal conductivity and high thermal inertia, is regarded as the most promising in situ insulation material28. The regolith overburden with a thickness of several meters can significantly attenuate the approximately 280 K surface diurnal thermal cycle, thus effectively reducing the demand for active heating. Nevertheless, even an optimized passive insulation strategy cannot fully offset the continuous heat losses associated with long-term habitation; active heat sources, therefore, remain indispensable for providing thermal compensation during the lunar night. At present, the main active technological routes include solar thermal storage and nuclear heat supply. The former stores solar energy during the lunar day by heating processed regolith and releases the stored heat during the lunar night via fluid loops or heat pipes, thereby achieving a relatively stable thermal output29,30. The nuclear heat supply relies on space nuclear reactors with high energy density to provide long-term, continuous heat that is independent of illumination conditions, and can be configured in cogeneration modes to simultaneously supply both electricity and heat31,32,33. These two classes of technologies, representing respectively a renewable energy-based thermal storage pathway and a high-power continuous heat source pathway, jointly form the key technological foundation for night-time thermal management of future long-duration lunar bases.

To address the high nighttime heat loads and complex operational requirements of long-term lunar bases, the thermal energy support system needs to evolve into a composite thermal control system in which passive envelopes and active heat supply are deeply coupled. Considering that different active heating technologies exhibit distinct capability limits, scalability and system complexity, the following discussion on “Architecting the lunar thermostat: integrated thermal systems for ISRU and sustained industrial operation” will provide a systematic review of their research progress and, based on their thermodynamic characteristics, will discuss their suitability and deployment pathways at different stages of lunar base development.

Architecting the lunar thermostat: integrated thermal systems for ISRU and sustained industrial operation

Engineering of lunar regolith

Large-scale TES through ISRU represents a key pathway to addressing the energy and thermal control challenges of the lunar night. As an in situ thermal storage material, lunar regolith is critical importance to the efficiency of thermal energy systems. The concept of using lunar regolith for TES dates back several decades. As early as the Apollo era, Barna et al.34 performed an initial feasibility study on storing solar heat in the lunar surface during the day for nighttime use. Similarly, Notsu et al.35 proposed placing heaters at predetermined depths within the regolith to enable heat storage in lunar daytime and heat release in lunar nighttime.

Because natural lunar regolith is loosely consolidated and has very low thermal conductivity, in situ modification is necessary to enhance thermal storage capabilities. In terms of methodology, current modification techniques primarily involve processing lunar regolith simulants within terrestrial laboratories under simulated lunar environmental conditions. Within in this framework, researchers have explored various approaches, which primarily include compaction36,37, doping38,39 (Fig. 2a), sintering40,41,42,43 (Fig. 2b, d), and melting44,45 (Fig. 2c). Compaction is the simplest method to increase the density of lunar regolith, Hu et al.36 numerically simulated the thermal storage properties of compacted lunar regolith, finding that its storage density could reach 0.25 kW h kg−1 over one lunar day. Overall heat transfer can also be improved by introducing high-conductivity additives. Tillotson et al.46 proposed enclosing the regolith in an airtight bag and filling it with lightweight, highly conductive helium to create a helium-regolith composite medium with macroscopic thermal conductivity. Sintering is currently regarded as one of the most effective modification methods, because it is simple and can be driven by concentrated solar energy. Balasubramaniam et al.47 found the thermal conductivity of solar sintered regolith increased to 2.1 W m−1 K−1 and the density reached 3000 kg m−3, while the specific heat capacity was 800 J kg−1 K−1. Han et al.48 found the specific heat capacity of the vacuum-sintered HUST-1 simulant reached 920 J kg−1 K−1 at 1323 K, and the thermal conductivity was approximately 0.9 W m−1 K−1. Schreiner et al.49 developed regression models linking lunar regolith thermophysical properties to temperature and composition. The models indicate that native regolith has a very low thermal conductivity (0.012 W m−1 K−1), whereas densified material approaches 1 W m−1 K−1 with a marked increase in density. In a systematic experimental study of different modification techniques, Fateri et al.50 found the specific heat capacity of the regolith remained stable at approximately 740 J kg−1 K−1, and the thermal conductivity of laser-sintered samples increased to 1.1 W m−1 K−1. Although the optimization outcomes vary, the reviewed studies consistently report improvements in key properties such as density and thermal conductivity (Table 1). However, the direct applicability of these terrestrial results is constrained by inherent compositional differences between simulants and native regolith, as well as by the fundamental environmental disparities between Earth and the Moon. Consequently, while the overall technological progress is evident, the reported performance metrics ultimately need to be validated through in situ lunar experiments.

Fig. 2: Lunar regolith modification technologies.
Fig. 2: Lunar regolith modification technologies.
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a Lunar regolith doping preparation process, reproduced from Liu et al.38 with permission from Elsevier (license number: 6164101385676). b Laser engineered net shaping/laser metal deposition, reproduced from Zhang et al.40 under the CC BY license. c Melt-extrusion device on lunar regolith composites reproduced from Zhao et al.41 with permission from Springer Nature (license number: 6164111036741). d Sketch and pictures of the solar oven, reproduced from Meurisse et al.44 with permission from Elsevier (license number: 6164191071095).

Table 1 Thermophysical properties of modified lunar regolith
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Active in situ solar thermal storage systems

Among the various proposed solutions for surviving the lunar night, ISRU-based solar-TES is one of the simplest and most valuable. A typical system consists of a solar concentrator, a heat exchanger, a lunar regolith heat storage tank, and a thermal energy utilization core component, which aims to provide a stable and continuous thermal and electrical energy for the lunar base. Methodologically, the performance assessment of these systems in the current literature relies predominantly on numerical simulations and theoretical analyses. These studies generally indicate that such systems are capable of supplying essential thermal and electrical energy to lunar bases, thereby ensuring survival during the lunar night.

The systems can be integrated with power generation technologies to ensure energy supply during lunar base nights. Li et al.51 proposed a system architecture combining a parabolic dish concentrator with regolith-based thermal storage. The model showed the system could generate an average of 10.8 kW of electrical power during the lunar day and a stable 7.0 kW during the night, achieving an overall cycle efficiency of up to 48.0%. Similarly, Hu et al.52 indicated that an ISRU-based solar thermal power system could produce an average of 6.5 kW of electricity during the lunar night, with a solar energy utilization efficiency of approximately 19.6%. Thermoelectric generators (TEGs) are also often combined with thermal storage systems to power the lunar bases (Fig. 3a)53. Fleith et al.54 optimized a regolith-based TEG system that achieved a minimum guaranteed power of 36 W during the lunar night. Liu et al.55 integrated regolith thermal storage with heat pipes and TEGs, achieving a total energy output of 1.75 MJ over the lunar night. Structurally, Kim et al.56 found that adopting a multi-body thermal storage architecture could increase the power output of a TEG system by approximately 48.9% in the lunar environment.

Fig. 3: Lunar regolith solar thermal energy storage system.
Fig. 3: Lunar regolith solar thermal energy storage system.
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a Schematic diagram of the lunar energy storage and conversion system based on in situ resource utilization, reproduced from Liu et al.53 with permission from Elsevier (license number: 6164200097456). b Schematic diagram of solar thermal energy storage system using Stirling engine, reproduced from Cheng et al.57 with permission from Elsevier (license number: 6164200531178). c Lunar base energy storage photovoltaic thermal system, reproduced from Chen et al.59 with permission from Elsevier (license number: 6164201217301).

As understanding of lunar base energy requirements has matured, more advanced and diversified system architectures have been proposed (Fig. 3b)57. To meet the complex power and heating demands of large-scale bases, Zhang et al.58 designed a combined heat and power system incorporating ISRU thermal storage. The system can meet the heating demand of 15 kW, while achieving a net power output of 101.25 kW and a specific power of 13 W kg−1. Photovoltaics with good absorption rate can generate a lot of heat while generating electricity, which can be combined with heat storage to improve the efficiency of the system. Chen et al.59 integrated a photovoltaic array with regolith thermal storage (Fig. 3c), using the storage unit to co-generate 0.13 GJ of electricity, 3.5 GJ of heat, and 10.5 GJ of cooling energy, potentially reducing launch mass by approximately 53.6%. Furthermore, Liu et al.60 established a model for a lunar thermal storage system using a combined approach of numerical analysis and multi-objective optimization, assuming natural regolith acted as the primary insulation layer to mitigate heat dissipation. The results indicated that the heat storage efficiency of the system remained at 0.59 after long-term operation.

In summary, in situ solar TES systems exhibit significant promise and offer multiple technological pathways for lunar night survival. However, the current performance evaluations largely depend on idealized numerical assumptions regarding boundary conditions and material homogeneity. These theoretical predictions often underestimate the complexities of the unique lunar environment, where technologies mature on Earth may perform unpredictably. Specifically, the practical implementation is impeded by the inherently low thermal conductivity of lunar regolith, which restricts efficient heat transfer, alongside the substantial engineering challenges associated with autonomous excavation and complex in situ construction in the unstructured lunar environment.

Active nuclear power systems

As a high-density, highly reliable energy source independent of environmental conditions, nuclear power exhibits significant potential for lunar exploration. Lunar nuclear power is advancing along two primary pathways: radioisotope heat sources and fission reactors (Fig. 4a)61. Radioisotope heat sources leverage the thermal energy, providing a durable and stable source of heat for equipment. These systems are characterized by their simplicity, reliability, and high energy density, and have been successfully deployed on various lunar missions, demonstrating robust and long-lasting performance12. However, because of very low conversion efficiency, radioisotope power systems cannot meet the megawatt-class energy demand of a long-term lunar base.

Fig. 4: Nuclear energy utilization of lunar base.
Fig. 4: Nuclear energy utilization of lunar base.
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a Structure of the nuclear power system, reproduced unchanged from Xia et al.61 under the CC BY 4.0. b A schematic diagram of direct heat source supply and indirect power generation utilization of nuclear fission in lunar base.

Nuclear fission reactors are widely regarded as the core energy solution for future long-term lunar bases, providing continuous, megawatt-scale electrical and thermal power. Leading spacefaring nations are actively advancing the development of reactors for extraterrestrial applications. Methodologically, the development of these systems relies on ground-based experimental validation and numerical simulations. The Kilopower project in the United States has completed testing of reactors in the 1–10 kW class62,63; China’s 1.5 MW-class ground-based experimental reactor has passed preliminary validation64; and nations such as Russia, Japan, and the United Kingdom are actively pursuing related research65,66,67. The substantial thermal output from a nuclear reactor can be converted into electricity using advanced technologies. These are broadly categorized into static methods, such as thermoelectric conversion68 and alkali metal thermal-to-electric conversion69, and more efficient dynamic systems, including the closed-baryton cycle70,71, Rankine cycle72, and Stirling engines73 (Fig. 4b). Recent studies indicate that nuclear power concepts utilizing heat pipe cooling and Stirling engine power conversion are garnering significant attention74,75. For example, Wang et al.76 developed a dynamic model for a lunar nuclear system using Stirling engine and heat pipe, assuming simplified fluid dynamics, and demonstrated that the high thermal conductivity and passive reliability of heat pipes enable stable, isothermal heat transfer. Furthermore, the hot-end operating temperature of lunar fission reactors is typically maintained at around 900 K77,78. Because thermoelectric conversion efficiencies remain limited, approximately 60–70% of the thermal power must still be rejected as waste heat. According to previous studies, vacuum-sintered lunar regolith simulants exhibit good structural integrity and thermophysical stability in the temperature range of 1300–1350 K48. This temperature matches the waste-heat rejection range of fission power systems. If reactor waste heat directly charges regolith-based thermal storage modules, the thermally coupled nuclear-regolith TES system can be established without any additional solar collection. This form of integration exploits the thermal inertia of in situ regolith to improve system reliability through passive thermal storage and provides the lunar base with a mass-efficient in situ energy buffer.

However, most existing research on high-power space nuclear fission systems is still conducted under terrestrial conditions. System-level analyses typically treat stable fluid behavior in cooling loops and heat pipes under lunar gravity as a design assumption, which has not yet been rigorously validated. In addition, the nuclear-regolith TES system faces practical limitations, primarily because of the mass penalties associated with the inherently low thermal conductivity of lunar regolith.

Passive thermal control systems for lunar base

The passive thermal protection plays a crucial role in ensuring the long-term habitability and energy efficiency of lunar bases. By relying on the intrinsic properties of local materials and the space environment, passive measures can buffer the extreme diurnal temperature swings on the Moon, thereby reducing the reliance on power-intensive active thermal-control systems and enhancing system robustness.

Natural lunar regolith, characterized by high porosity and extremely low thermal conductivity, is widely regarded as an ideal passive thermal insulation material for lunar bases79,80 (Fig. 5a). Vasavada et al.81 combined Lunar Reconnaissance Orbiter/Diviner observations with a thermal diffusion model. Their results show that diurnal temperature perturbations within the regolith decay rapidly within several tens of centimetres to about 1 m, while at depths of a few meters, the subsurface is already in a quasi-steady thermal regime. Consequently, the numerical studies and system-level design analyses have evaluated the feasibility of employing regolith as an external insulating overburden for lunar habitats. Malla et al.82 developed a transient heat-transfer model spanning the lunar surface, regolith and habitat, and introduced regolith shields of varying thickness to examine the effect of the 0.5–2.0 m regolith cover on the propagation of the thermal wave. Their results show that an external regolith layer of about 1 m is sufficient to significantly reduce the heat flux through habitat walls and thereby stabilize the internal thermal environment. Akisheva et al.80 constructed a multiphysics model that couples regolith bulk density. Their analysis indicates that a low-density regolith layer 2–3 m thick can effectively smooth diurnal temperature variations, thereby greatly reducing the power demand of active thermal-control systems.

Fig. 5: Passive thermal wall of lunar base.
Fig. 5: Passive thermal wall of lunar base.
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a Lunar base model. reproduced from Akisheva et al.80 under the CC BY license. b Sketch of habitat concept and the associated 1-dimensional model, reproduced from Borshchak et al.85 under the CC BY license.

On Earth, the integration of PCMs into building envelopes for passive thermal control has been widely studied83,84. For lunar habitats, this concept can be extended to passive thermal walls, in which an inner pressure shell is combined with a PCM-containing layer and an outer regolith shield. The regolith provides basic thermal resistance and radiation protection, while the PCM layer acts as a reversible heat sink that absorbs heat during the lunar day and releases latent heat at night. Kachalov et al.85,86 investigated filling the cavities of 3D-printed regolith structures with PCMs. During the lunar day, the PCM absorbs heat and melts; at night, it solidifies and releases this stored heat, acting as a thermal buffer that mitigates the impact of the external temperature extremes on the internal environment. In another study, Ongil et al.85 modeled an igloo-shaped habitat using water as the PCMs (Fig. 5b), confirming that such materials are a viable option for passive thermal control in lunar bases. The large mass of high-heat-capacity material required for these passive thermal walls would be prohibitively expensive to launch from Earth, thus necessitating the use of in situ construction techniques. In practice, such walls may be realized by 3D-printing or sintering porous regolith blocks with cavities subsequently filled with encapsulated PCMs.

However, passive thermal protection is constrained by challenges related to in situ construction complexity and long-term material stability. In particular, the substantial logistical burden associated with large-scale regolith modification, together with the inherent heterogeneity of the material. Moreover, the encapsulation reliability of PCMs in vacuum environments and their thermo-mechanical compatibility with the regolith matrix still require rigorous validation. Consequently, future research should prioritize the optimization of in situ fabrication processes and the establishment of systematic material-compatibility verification frameworks in order to advance these technologies toward practical engineering deployment.

Multidimensional evaluation and integrated architecture design of lunar base active thermal systems

In the design of night-time survival strategies for lunar bases, passive thermal protection technologies remain present at all development stages and consistently play a fundamental role. Therefore, the following discussion on “trade-off analysis”, “technical roadmap for the development of lunar-base active thermal energy systems,” and “integrated multi-source thermal supply in future base” does not provide a detailed discussion of passive measures, but instead shifts the focus to energy systems capable of actively supplying heat throughout the prolonged lunar night.

Trade-off analysis

Informed by the multi-criteria assessment methodology of Palos et al.29 and drawing on existing study with RTGs, solar-regolith TES and fission surface power (FSP) systems, this study develops a multidimensional evaluation matrix, as summarized in Table 2. The assessment dimensions include technology readiness level (TRL), initial mass and cost, heat supply capability, deployment complexity, and operation and maintenance. This qualitative scoring scheme is intended to elucidate the suitability of different options for various stages of lunar base development and to provide a basic decision-making reference for future thermal-system selection.

Table 2 Trade-off of active heat supply technologies
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Technology readiness level: level of technical maturity and reliability, based on past operational experience and demonstrated performance in relevant environments.

Initial mass and cost: combined metric representing the total launch mass and the research and development costs (R&D) of the system’s components.

Heat supply capability: capacity of the system to generate thermal power output and the duration it can sustain this output to meet lunar base thermal loads.

Deployment complexity: difficulty of installation, required infrastructure, on-site preparation, and associated construction risks.

Operation and maintenance: difficulty of operation, required human intervention, maintenance frequency, and likelihood of component failures.

As illustrated in Fig. 6, the performance envelopes of the three technologies align clearly with different evolutionary stages of a lunar base. RTGs, owing to their mature high-reliability and low-maintenance87,88, constitute the preferred option for the early robotic exploration phase. Solar-regolith TES, enabled by ISRU and offering a favorable balance between mass input and thermal performance52,89, is well suited to the constraints of the initial outpost-construction stage. FSP systems require higher upfront investment and involve greater deployment complexity90,91; however, their greatly extended heat-supply capability makes them the most appropriate choice for supporting the high energy demand associated with long-term industrialization of the lunar surface.

Fig. 6
Fig. 6
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Multi-criteria performance comparison of lunar-night active heat supply technologies.

Technical roadmap for the development of lunar-base active thermal energy systems

To accommodate the anticipated evolution of lunar bases from short-duration missions to long-term habitation and industrial development, this study proposes an overarching development roadmap (Fig. 7). The roadmap organizes technical requirements by construction stage and outlines a progressive transition in primary night-time heat-supply technologies from RTGs to solar-regolith TES and, ultimately, to multi-source hybrid systems, thereby providing guidance for the staged development of lunar night survival technologies.

Fig. 7
Fig. 7
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Night survival strategies corresponding to different lunar base periods.

Short-time lunar base (−2030)

During the early phase of lunar exploration, missions rely primarily on orbiters, landers and uncrewed rovers to characterize the surface environment, accomplish key scientific observations and identify candidate sites for future base construction. Mission durations in this phase are relatively short, and the thermal power required for night-time survival is generally below 1–2 kW. The core design challenge lies in the combination of severe launch-mass constraints and the need for fully autonomous survival in an extreme environment. RTGs offer extensive flight heritage, continuous and stable heat supply, and virtually negligible installation and maintenance requirements, and therefore, represent the preferred heat-source option at this stage. The main technical issues concern the assurance of thermal safety for critical payloads in the absence of redundant chains and switching mechanisms, and the prevention of fault amplification in architectures that rely on a single heat source. Although this phase does not yet involve complex load-sharing strategies, the stable operation of RTGs demonstrates their feasibility as standalone heating units and provides initial experience for the later development of distributed, redundant systems.

Primary permanent lunar base (2030–2035)

As the first permanent outpost emerges through progressive human-robot collaboration, the nighttime heat demand rises to several tens of kilowatts. Solar-regolith TES systems exhibit marked advantages at this stage. Solar collection technologies are mature and can provide reliable daytime heat input, while lunar regolith is an abundant local storage medium that can accumulate heat during the day and release it during the night, thereby satisfying the thermal loads associated with early base survival and initial ISRU experiments. Although deployment requires excavation, insulation measures and the installation of solar collection hardware, the ISRU nature of regolith significantly alleviates transportation burdens. At the same time, regolith TES systems introduce a series of potential challenges, particularly the continuity of system operation across day-night transitions, and the ability to compensate in real time for performance degradation caused by dust on solar collectors. To address these issues, the regolith-TES system gradually assumes the role of primary heat source, whereas RTGs are integrated as compensating backup units within a redundant architecture. Load management thus evolves from support of a single mission load to a coordinated primary backup configuration, leading to a tangible improvement in overall system reliability.

Future permanent lunar base (2035+)

In the subsequent phase of future permanent lunar bases, the lunar infrastructure enters a stage of long-term habitation and industrial development, and the energy demand increases substantially. High and sustained thermal power is required to support continuous crewed presence, large-scale scientific experiments, ISRU processing facilities and initial industrial activities. Thermal power requirements are expected to reach several hundred kilowatts or even the megawatt level, and long-term maintenance of high-temperature thermal loads becomes a critical constraint. FSP systems, with continuous output, high energy density (>100 kW thermal power) and strong scalability, are expected to form the core of base-level energy supply. At this stage, the energy system evolves into a multisource architecture in which nuclear fission and solar input together charge thermal storage systems, while RTGs support distributed and emergency loads. The associated challenges become more systemic and include power coordination among multiple sources, rapid switching between different operating modes, the stability of redundancy links across sources, and increased coupling complexity and fault propagation risk as system scale grows. Further progress requires more advanced multisource energy management strategies and improved control stability, fault tolerance and system-level diagnostic capabilities to ensure the high reliability and long-term sustainable operation of lunar bases.

Integrated multi-source thermal supply in future base

For future permanent lunar bases, this study proposes an integrated thermal supply and management system that combines several energy sources within a unified architecture. The system consists of a nuclear reactor coupled to solar concentrators, a thermal energy storage unit based on lunar regolith or other media, a central supervisory controller and a set of distributed RTG units located near critical modules and mobile platforms (Fig. 8). The reactor and solar concentrators provide the main high-power heat input, the storage unit acts as a thermal buffer to smooth the strong day-night variations, and the RTGs support distributed and emergency demands at the habitat and rover level.

Fig. 8
Fig. 8
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The conceptual architecture of a multi-source thermal supply system for a future permanent lunar base.

A multi-source thermal system also introduces richer potential failure modes. Risks arise not only from individual components, such as high-temperature fatigue in TES vessels, shielding degradation in RTGs, and coolant-loop anomalies in FSP units. System-level hazards also emerge, including failures of the energy management controller, loss of coordination among subsystems, and adverse interactions between different energy sources. These effects can manifest as uncontrolled power oscillations, delayed fault isolation or propagation of local failures into system-wide outages, especially when the base operates close to its thermal capacity limits.

To address these risks, the system operates in two distinct modes. Under normal conditions, the controller uses a main-heat mode. In this mode, all available heat sources supply scientific and habitation demands, while thermal storage is maintained at a target state of charge. When sensors detect anomalies at the source or distribution level, such as abnormal coolant temperatures, loss of solar input, or degraded TES performance, the controller switches to a life-saving heat mode. In the life-saving mode, noncritical loads, including industrial processes and nonessential experiments, are shed in a controlled sequence. The remaining thermal capacity is directed to predefined survival loops. RTG units are dedicated to life-support systems in crewed modules and to essential communication and control equipment. This configuration maintains minimum survival conditions even during severe degradation of the primary thermal supply.

This integrated design links the technological roadmap outlined earlier with a concrete system-level implementation. RTGs validated in the early exploration phase act as robust survival units, solar-regolith TES developed for the first outposts provides an effective thermal buffer, and FSP systems deliver the high-capacity backbone for long-term industrial activity. Through coordinated control of these elements and explicit emergency operating modes, the proposed architecture aims to enhance fault tolerance, limit the spread of local failures and ensure the long-term safe operation of future permanent lunar bases.

Challenge and future direction

A survey of lunar-exploration stages and technologies shows that core challenges evolve in step with the developmental phase of the lunar base. These challenges can be categorized into four primary aspects:

  1. 1.

    Radioisotope heat sources: while sufficient for powering uncrewed probes or critical equipment, their hundred-watt-class output is insufficient to meet the energy demands of a large-scale human base.

  2. 2.

    In situ solar thermal storage: the materials engineering problem of efficiently transforming lunar regolith from a natural insulator into an effective thermal storage medium, and ensuring the long-term engineering reliability of the complex thermodynamic systems involved.

  3. 3.

    Space fission reactors: the high initial deployment mass and cost, significant safety risks, and the formidable difficulty of efficiently rejecting megawatt-scale waste heat in a vacuum.

  4. 4.

    Passive thermal walls: the technology remains immature and depends on advances in lunar in situ construction.

Future research should not be on single technology but could proceed within a framework that considers the synergistic development of lunar construction and thermal energy systems. There are three main aspects:

  1. 1.

    Research should establish a dedicated experimental validation pathway to advance concepts toward engineering readiness by generating empirical data through ground-based thermal-vacuum tests, material characterization, subsystem demonstrations, and future small-scale lunar surface experiments.

  2. 2.

    Research should focus on breakthroughs in lunar construction, particularly ISRU-based building materials, structural optimization, and intelligent construction processes, to provide more effective insulation, radiation shielding, and integrated energy storage.

  3. 3.

    Research should pursue multi-source, system-level integration by architecting dynamic coupling and redundancy among radioisotope power, in situ solar-thermal storage, and fission reactors, tailored to mission epoch and scenario to enhance energy resilience and reliability.

Through co-evolution of construction and energy technologies, future lunar bases can progressively reduce their heavy reliance on terrestrial logistics and make the critical transition from survival to sustainable development.

Conclusion

This paper has reviewed the evolutionary trajectory of thermal energy architectures for sustainable lunar bases and outlined the transition from passive survival to active development. By analyzing the impacts of passive and active thermal control on lunar base night survival, the work has summarized recent research progress in passive insulation/thermal storage structures, radioisotope heat sources, solar-regolith TES and FSP. On this basis, a conceptual framework has been constructed for coping with the extreme thermal environment of the long lunar night. In parallel, a multidimensional assessment scheme has been introduced, which evaluates candidate options in terms of TRL, initial mass and cost, heat supply capability, deployment complexity, and operation and maintenance.

Application of the assessment framework identifies preferred technical pathways for different stages of lunar base development. In the short-term exploration phase, radioisotope heat sources, with their high reliability, independence from the external environment and negligible maintenance requirements, emerge as the most suitable option for meeting early autonomous heating needs. During the phase of primary permanent base, solar-regolith TES offers clear advantages in launch-mass reduction, cost control and scalability, and can complement conventional electric heating and a limited number of radioisotope units. At the stage of a long-term permanent base, an architecture that combines FSP for base-load cogeneration with solar-regolith TES for thermal buffering and local RTGs for redundancy is identified as a key solution for supporting megawatt-class industrial loads.

The research on solar-regolith TES and FSP systems is largely confined to numerical studies and ground-based tests, and lacks experimental data for fluid dynamics and heat-transfer behavior under lunar vacuum and low gravity. In addition, large-scale regolith modification and the fabrication of in situ thermal storage and protection structures still require validation in lunar environments. This study establishes a structured framework and roadmap that can guide future experimental efforts and mission demonstrations. In this sense, the work bridges conceptual system design and engineering realization, providing a foundation for subsequent empirical validation and technology maturation toward sustainable lunar base construction.