project09:2025Msc2JIP

Problem statement

After more than 50 years since the Apollo 17 mission left the moon, many space agencies are eyeing a returnof 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 forthe 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 solutionto 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.