project09:2025Msc2JIP

Problem Statement

After more than 50 years since the Apollo 17 mission left the moon, many space agencies are eyeing a return of crewed missions to the lunar surface, and unlike the short visits in the past, plans are being made for permanent human settlement. Yet, transforming this vision into reality comes with unparalleled challenges.

The lunar environment is characterized by serious threats, ranging from frequent micrometeorite impacts, intense radiation levels (up to 2200 mSv/event during solar flares and CMEs [1]), extreme temperature fluctuations between day (420 K) and night (100 K) [2], and moonquakes, which can reach body wave magnitudes mb up to 5 during shallow (most energetic) events [3]. Many recent studies have consistently advocated for the establishment of lunar outposts inside lunar lava tubes [4], [5], [6]. These large (100-300 m in diameter) cave-like natural, which are formed by ancient lava flows, could protect astronauts and structures from radiation [7], meteorite impacts, and the extreme temperature variations [8]. Some of these sub-surface tunnels are thought to be accessible by the superficial pit entrance [9], [10], and therefore are of great interest for future lunar settlements and for the following study.

A major challenge for lunar construction is the prohibitively high cost of transporting payloads, estimated at approximately $1 million per kilogram. In situ resource utilization (ISRU) offers an appealing potential solution to this problem by leveraging lunar soil (regolith) as a primary building material, reducing dependence on costly Earth-supplied resources, which is essential for making the construction of the first lunar habitat both economically viable and sustainable. The high transportation costs also render delivering heavy construction equipment, such as cranes or excavators, to the moon impractical. Furthermore, given that the construction of a lunar habitat is likely to require an extended period, relying on human labor is infeasible. Human involvement would necessitate temporary shelters and expose crews to severe life-threatening risks. Consequently, we envision the possibility to deploy robotic swarms and additive manufacturing systems ahead of human arrival. These autonomous systems could collect lunar soil and construct a fully functional habitat, ensuring that the environment is safe and ready for incoming astronauts.

Within the ISRU context, Additive Manufacturing (AM) technology [11] is receiving increasing attention due to its potential to produce various geometrically complex building blocks and structures in extreme environments. Sintering, particularly through Selective Laser, Solar, or Microwave techniques, is a promising solution under investigation for its ability to fuse regolith into structural geometries without additives (unlike concrete-like 3D printing), offering material-efficient methods for lunar construction. Up to date, various experiments have successfully sintered and formed parts [12], [13], rendering this fabrication method appealing for extraterrestrial construction.

While many concepts for lunar habitats have already been developed and proposed [14], [15], [16], these often fail to address many of the core challenges inherent to lunar construction. Some concepts rely heavily on the costly transport of large construction equipment/robots and additives from Earth (Chinese Super Mansion [17] and Project Olympus [18]), while others rely on the use of heavy ready-to-live modules [19]. Therefore, the primary objective of this project is to develop and outline an autonomous robotic construction process to enable practical and scalable lunar construction of a lunar habitat within a lava tube using In-Situ Resource Utilization (ISRU) methods.

Sub-objectives include:

• Outline the construction process from gathering and processing lunar material to the creation of construction geometries using Selective Laser Sintering
• Defining requirements for several aspects of the robots used in the construction process, including coordination strategies, traversal mechanisms, required tools and support systems such as charging infrastructure.
• Characterizing an ideal lunar regolith composition for construction and outlining how to acquire this material, from gathering the material to processing/filtering the material.

General Requirements

The design of the structure and construction process is also guided by several other factors, which are partly driven by the robotic construction process and factors such as occupant well-being. The infeasibility of using heavy lifting machinery means that the structure should facilitate traversal of construction robots, requiring either external ramps or shallow wall angles. The enclosed environment of the lava tube will provide protection against a significant amount of radiation, however, the design should be flexible and scalable enough to support thicker walls for surface applications or to facilitate the construction of larger or interconnected habitats. At the same time, current plans indicate that mission durations will be approximately 6 months, meaning that the habitat should offer a somewhat comfortable environment for its occupants. This means that the total livable habitable volume of at least 160 m3 for a crew of four people [20], and the ceiling height should be at least 2.4 meter for 2/3 of the total surface area. A structure geometry that best satisfies these demands is a catenary dome, which allows for a large range of wall thicknesses and can be designed with low angles between the wall and ground.

Concepts

To address the challenges of constructing a safe and sustainable lunar habitat, two concepts have been developed. Concept 1 envisions prefabricated modular blocks made from lunar regolith using stationary SLS machines, which are then assembled into the habitat by swarm robots. Concept 2 proposes in-situ layer-bylayer sintering of the entire structure, using either a centralized laser directed by mobile robots with mirrors or robots carrying the sintering equipment themselves. In both approaches, an inflatable membrane is deployed inside the lava tube before the start of construction. This membrane provides a habitable environment for the astronauts and, if necessary, serves as a supportive formwork during the assembly of the structure.

Concept 1: Modular Components

Figure 1: System diagram of concept one

In the first concept, the lunar habitat is constructed from modular components that are prefabricated inside the lava tube using stationary Selective Laser Sintering (SLS) machines. Lunar regolith is collected on the surface and transported into the lava tube by a swarm of autonomous robots. Once inside, the regolith is filtered and pre-processed before being fed into the SLS machines. Producing the components in a controlled environment ensures stable operating conditions and consistent quality of the resulting building blocks.

The building elements are designed as brick-like modules, small enough to be handled by robotic systems while still forming a robust and scalable construction system. Each block is equipped with interlocking and/or aligning features, that enable precise placement and structural stability. These features also allow the swarm robots to reliably assemble the structure in an incremental manner.

Two specialized groups of robots operate together in this concept. The first type is responsible for collecting, transporting, and delivering pre-processed regolith to the SLS units. The second type is tasked with trans- porting the finished components to the construction site, moving them along integrated ramps or stairs that are incorporated into the developing structure itself. Once a block reaches its designated position, the robots align it with the existing structure and lock it into place.

The modular components serve a dual purpose: they act as the primary load-bearing system of the habitat while also providing radiation shielding and thermal protection. This integration of structural and protective functions reduces complexity and makes the building process more efficient.

Concept 2: In-Situ Sintering

Figure 2: System diagram of concept two

In the second concept, the lunar habitat is constructed by direct in-situ sintering of lunar regolith to form a continuous outer shell around the inflatable membrane. Lunar regolith is collected on the surface and transported into the lava tube by autonomous robots, where it is filtered and pre-processed.

The process relies on SLS, in which the processed regolith, is spread in thin layers and locally fused by high energy lasers. This technique enables the formation of a continuous, load-bearing structure without the need to transport prefabricated blocks. To optimize time and energy consumption, the structure would not be fully sintered, instead, a controlled infill pattern, such as voronoi or honeycomb geometries, would provide the necessary strength while reducing material use. Regolith deposition can be achieved through an ultrasonic spreading system, which releases precise and uniform layers of powder. Ensuring the uniformity of these layers is essential, as irregularities or holes could compromise subsequent sintering steps. This requirements also imposes constrains on rover mobility: their wheels must be adapted to avoid disturbing unsintered regions while maintaining reliable locomotion.

A major challenge remains the positioning of the laser. Currently, two solutions are being investigated. The first solution uses a centralized laser where the beam is guided to the sintering location using a set of mirrors/reflectors. In the second option, the sintering will be conducted by robots equipped with lasers. In the second option, the sintering material can be deposited by the same robots that are performing the sintering process, while the first option would require separate robots for depositing material.

Concept Selection

To evaluate the two proposed construction concepts in a fair and structured way, a set of criteria was defined that reflects the technical challenges, operational risks, and long-term mission goals of building a lunar habitat in a lava tube. Each criterion was chosen to capture a distinct aspect of performance or feasibility that is critical to the success of the project.

• Technical Complexity: Measures both the number of subsystems involved and the difficulty of implementing them under lunar conditions. A concept with fewer, simpler technologies is generally more robust and easier to realize, while high complexity introduces more interfaces and potential failure points. Concept 1 involves higher complexity due to block transport, precise placement, and the need for multiple robotic systems, which add many failure points. Concept 2 has a simpler production chain, requiring only raw material handling, even though laser sintering remains technically challenging. Overall, Concept 2 is less complex and therefore the more favorable option for this criteria.

• Technological maturity and Risk: How close the technology is to practical application. This is evaluated together with the associated risks, including uncertainties and potential showstoppers. Concept 1 benefits from previous small scale experiments, but has high operational risk related to aligning and placing blocks. Concept 2 relies on less tested technology, with multi layer large-scale regolith sintering still untested and potential hazards such as dust and membrane damage. Due to the lack of experiments on large scale, for this criteria, concept 1 presents as the best solution.

• Adaptability: Measures how modular and scalable the design is, referring to the potential to scale up or modify the habitat design for different sizes, geometries, or mission requirements over time, without redesigning the entire system. Concept 1 requires the design both the block elements and the ramp geometry, according to the requirements of the structure itself, even small changes in geometry could make necessary to re-design the components making the concept not very adaptable. Concept 2 in contrast allows for a great variety of geometries for the final product, without requiring major adjustments, making it substantially more adaptable.

• Reliability and Maintenance:Construction and operation must be carried out with minimal human intervention, as astronauts cannot be expected to perform extensive maintenance during or after construction. Measures the robustness of autonomous systems, their ability to continue functioning over time, and the ease of maintenance or replacement are therefore central considerations. Concept 1 presents challenges in terms of maintenance, as replacing a damaged block would require partial disassembly of the structure. However, since the blocks are produced in a closed and controlled environment, the sintered material generally achieves higher and more consistent quality. In contrast, structures built with Concept 2 are easier to repair, as damage can be addressed by simply piling and sintering new material directly on-site.

• Structural Integrity and Durability:The habitat must not only stand structurally once assembled but also be able withstand the lunar environment for a long period of time. This includes resilience against radiation, micro-meteorite impacts, seismic vibrations, and extreme temperature cycles. Concept 1 relies primarily on compression, which is where sintered regolith performs best. However, its performance is highly dependent on the quality of the interlocking system. Concept 2, with its Voronoi infill, is highly durable and capable of withstanding high-energy impacts. Its continuous structure minimizes weak points, though it is somewhat less resilient against moon quakes. Given the relatively low intensity of lunar seismic activity and the greater structural resilience of Concept 2, it is better suited to this criterion.

• Construction Time:Timely construction is important for mission planning and logistics. Assesses the total duration of the construction process, from regolith gathering to completion, and how effectively timelines can be accelerated by, increasing the amount of construction equipment. Concept 2 is favored here since it 2 will likely be the most time efficient process. It does not require the block transport step, which is likely the most complex step of Concept 1. Concept 1 may be slightly more scalable since the addition of more sintering machines may have a greater impact on the construction timeline, however, the ramps that are required may cause potential bottlenecks during the process.

• Logistical Cost:Launching material from Earth is the main cost driver of any space mission. This criterion focuses on the total mass that needs to be shipped from Earth to realize the concept. Concept 1 is anticipated to require a broader range of unique robots and machines, which is likely to result in higher logistical costs than Concept 2.

Together, these criteria provide a balanced framework to compare the two construction approaches, covering immediate feasibility, operational reliability, and long-term mission sustainability.

Based on the evaluation across all criteria, Concept 2 emerges as the more favorable option for our mission objectives. Its lower technical complexity, higher adaptability, ease of maintenance, and stronger structural resilience under lunar conditions make it better aligned with the long-term sustainability and operational requirements of constructing a habitat in a lava tube. However, the feasibility of large-scale regolith sintering remains the most critical open question. To address this, further discussions with domain experts in sintering technologies are planned in the coming weeks, which will be essential before a final decision can be made.

Project Plan Progress

In the upcoming weeks, our focus will shift toward validating the feasibility of Concept 2 through consultations with domain experts in sintering and lunar construction. These discussions will help refine our technical assumptions regarding regolith handling, energy requirements, and layer deposition strategies. Parallel to this, we will continue developing the robotic system concepts, with emphasis on mobility, coordination, and mapping the lava tube environment.

At the same time, we will maintain Concept 1 as a fallback option. Should large-scale sintering prove unfeasible within the current technological constraints, our efforts will redirect toward refining the modular block approach, with particular attention to block design, ramp geometry, and robotic assembly methods.

Finally, we aim to consolidate our findings into a preliminary design framework that can serve as the basis for the final report and presentation.

References

[1] Masayuki Naito et al. “Radiation dose and its protection in the Moon from galactic cosmic rays and solar energetic particles: at the lunar surface and in a lava tube”. In: Journal of Radiological Protection 40.4 (2020), p. 947. DOI: 10.1088/1361-6498/abb120.

[2] Tyler Horvath, Paul O. Hayne, and David A. Paige. “Thermal and Illumination Environments of Lunar Pits and Caves: Models and Observations From the Diviner Lunar Radiometer Experiment”. In: Geophysical Research Letters 49.13 (2022), e2022GL099710. DOI: 10.1029/2022GL099710.

[3] Neal R Goins, Anton M Dainty, and M Nafi Toksöz. “Seismic energy release of the Moon”. In: Journal of Geophysical Research: Solid Earth 86.B1 (1981), pp. 378–388.

[4] Friedrich Horz. “Lava tubes-potential shelters for habitats”. In: Lunar bases and space activities of the 21st century. 1985, pp. 405–412.

[5] Cassandra R Coombs and BRAY Hawke. “A search for intact lava tubes on the Moon: Possible lunar base habitats”. In: NASA. Johnson Space Center, The Second Conference on Lunar Bases and Space Activities of the 21st Century, Volume 1. HIG-CONTRIB-2165. 1992.

[6] A. Theinat et al. “Geometry and structural stability of lunar lava tubes”. In: 2018 AIAA SPACE and Astronautics Forum and Exposition. 2018, p. 5185.

[7] De Giovanni Angelis et al. “Lunar Lava Tube Radiation Safety Analysis”. In: Journal of Radiation Research 43.Suppl (Dec. 2002), S41–S45.

[8] N. J. Lindsey. “Lunar Station Protection”. In: Lunar Regolith Shielding, International Lunar Conference. 2003.

[9] R. Wagner and M. Robinson. “Lunar Pit Morphology: Implications for Exploration”. In: Journal of Geophysical Research: Planets 127.8 (Aug. 2022), Add pages if available.

[10] R. V. Wagner, M. S. Robinson, and the LROC Team. Lunar Reconnaissance Orbiter Camera Catalog of Lunar Pits. Tech. rep. Version 1. Lunar Reconnaissance Orbiter Camera (LROC) Team, Mar. 2021.

[11] BJ Pletka. “Processing of lunar basalt materials”. In: Resources of near-Earth space (1993), p. 325.

[12] Vamsi Krishna Balla et al. “First demonstration on direct laser fabrication of lunar regolith parts”. In: Rapid Prototyping Journal 18.6 (2012), pp. 451–457. DOI: 10.1108/13552541211271904.

[13] Athanasios Goulas et al. “Assessing extraterrestrial regolith material simulants for in-situ resource utilisation based 3D printing”. In: Acta Astronautica 137 (2017), pp. 357–370. DOI: 10.1016/j.actaastro. 2017.05.003. URL: https://www.sciencedirect.com/science/article/pii/S009457651631059X.

[14] Nicos Kalapodis, Georgios Kampas, and Olga-Joan Ktenidou. “A review towards the design of extraterrestrial structures: From regolith to human outposts”. In: Acta Astronautica 175 (2020), pp. 540–569. ISSN: 0094-5765. DOI: https : / / doi . org / 10 . 1016 / j . actaastro . 2020 . 05 . 038. URL: https : //www.sciencedirect.com/science/article/pii/S0094576520303210.

[15] Gani B. Ganapathi, Joseph Ferrall, and P. K. Seshan. Lunar Base Habitat Designs: Characterizing the Environment, and Selecting Habitat Designs for Future Trade-offs. Tech. rep. NASA-CR-195087. NASA Report No. N94-27934, 78 pages. Pasadena, California: NASA Jet Propulsion Laboratory, California Institute of Technology, May 1993.

[16] Haym Benaroya. “Lunar habitats: A brief overview of issues and concepts”. In: REACH 7-8 (2017), pp. 14–33. ISSN: 2352-3093. DOI: https://doi.org/10.1016/j.reach.2018.08.002. URL: https: //www.sciencedirect.com/science/article/pii/S2352309318300014.

[17] Cheng Zhou et al. “In-situ construction method for lunar habitation: Chinese Super Mason”. In: Automation in Construction 104 (2019), pp. 66–79. ISSN: 0926-5805. DOI: https : / / doi . org / 10 . 1016/j.autcon.2019.03.024. URL: https://www.sciencedirect.com/science/article/pii/ S0926580518311026.

[18] Melodie Yashar et al. “Project Olympus: Off-World Additive Construction for Lunar Surface Infrastructure”. In: 50th International Conference on Environmental Systems (ICES). ICES-2021-279, 12–15 July 2021. Online, July 2021.

[19] Werner Grandl. “Lunar Base 2015 Stage 1 Preliminary Design Study”. In: Acta Astronautica 60 (2007). Available online 25 October 2006, pp. 554–560. URL: https://www.sciencedirect.com/science/ article/pii/S009457650600350X.

[20] Minimum Acceptable Net Habitable Volume for Long�Duration Exploration Missions: Subject Matter Expert Consensus Session Report. Tech. rep. NASA Behavioral Health and Performance Element. Johnson Space Center, Houston, TX: NASA Human Research Program (HRP), Jan. 2014. URL: http: //humanresearchroadmap.nasa.gov/.

Introduction

More than 50 years after Apollo 17, space agencies are planning permanent human settlement on the Moon rather than brief visits. The lunar environment presents serious challenges, including frequent micrometeorite impacts, radiation levels up to 2200 mSv per event during solar flares and coronal mass ejections, temperature swings from 375 K during the day to 100 K at night, and moonquakes reaching body wave magnitudes up to 5 in shallow events. Numerous studies have proposed lunar outposts inside lava tubes, large natural structures 100 to 300 m in diameter formed by ancient lava flows that shield against radiation, meteorites, and thermal extremes, with some accessible via surface pits.

Transporting payloads to the Moon costs approximately €1 million per kilogram, making heavy equipment like cranes or excavators impractical and human labor infeasible due to the need for temporary shelters and exposure to severe risks over an extended construction period. In-Situ Resource Utilization (ISRU) addresses this by using lunar regolith as building material, while autonomous robotic swarms with additive manufacturing can prepare a habitat ahead of crew arrival. Selective laser melting (SLM) of regolith is a promising technique for fusing material into structures without the need for additives.

The 2025 Joint Interdisciplinary Project (JIP) Group 1.13.1 developed a conceptual design for an autonomous swarm to construct a habitat in a lava tube via in-situ SLM. Two concepts were evaluated, prefabricated blocks and direct in-situ melting, with the in-situ approach selected for lower technical complexity and higher adaptability. A heterogeneous swarm of collectors that also serve as depositors, processors with centrifugal sieves, flatteners, and melters operates during the 14-day lunar daylight using solar panels and batteries, fusing regolith around an inflatable substructure with an unmelted buffer layer to form a radiation-shielded dome in approximately two years.

Documents

[Final Report]