Martian biolith: A bioinspired regolith composite for closed-loop extraterrestrial manufacturing

Abstract

Given plans to revisit the lunar surface by the late 2020s and to take a crewed mission to Mars by the late 2030s, critical technologies must mature. In missions of extended duration, in situ resource utilization is necessary to both maximize scientific returns and minimize costs. While this present a significantly more complex challenge in the resource-starved environment of Mars, it is similar to the increasing need to develop resource-efficient and zero-waste ecosystems on Earth. Here, we make use of recent advances in the field of bioinspired chitinous manufacturing to develop a manufacturing technology to be used within the context of a minimal, artificial ecosystem that supports humans in a Martian environment.

Fig 1. Micro-scale organization of biolith.

(A) Regolith particles are dispersed within the chitosan solution after mixing. After the evaporation of the water, the chitosan crystalizes, reduces volume, and pulls the regolith particles together; (B) SEM imaging of regolith particle showing irregular size and morphology. Crystallized chitosan in the biolith can be seen enveloping and agglutinating the particles; (C) FTIR between chitosan, regolith, and biolith did not show conclusive evidence of a chemical reaction between chitosan and regolith; (D) Similarly, differential scanning calorimetry results did not reflect the heat flow patterns indicating phase changes between regolith and biolith.

Fig 2. Mechanical characteristics of biolith composite.

(A) Flexural strength and elastic modulus of biolith with varying chitosan to regolith ratio. There is a significant increase in flexural strength as regolith is increasingly added to a 1:75 ratio. At a 1:100 ratio, a significant decrease in flexural strength was observed. A similar relationship for elastic modulus was also observed; (B) A significant drop of compressive strength occurred beyond the 1:100 ratio; (C) Shear thinning behavior and increasing complex viscosity with added regolith was observed, likely due to the presence of chitosan; (D) Ashby plot showing dried biolith with mechanical properties similar to refractory brick; (E) Three different uses of biolith were demonstrated. From the prepolymer solution, the pliable liquid crystal-regolith mixture was cast into different geometries including a wrench that was later tested, used to repair a broken pipe, and used in additive manufacturing to produce a scaled habitat model; (F) The versatility to be shaped, printed, or casted without modification positions biolith as a unique material obtainable in a basic Martian ecosystem.

Fig 3. Demonstration of biolith utility in general manufacturing.

(A) Custom-designed wrench casted with biolith that avoids failure at the handle; (B) The casted wrench was subjected to increasing vertical load after tightening to obtain maximum torque before failure; (C) The wrench sustained a maximum torque of more than 2.5 Nm before failure. In the absence of a torque wrench, the casted wrench can be designed to the desired failure load to prevent over tightening; (D) Molded samples of varying geometry intricacies to demonstrate biolith’s ability to replicate object geometries; (E) The ability of biolith to form a mechanical sealing is critical to stop leakage from a drilled hole in a chemically inert acrylic tube; (F) Differences in substrate material properties, such as material stiffness, could affect the maximum pressure sustained before the sealing is compromised via rupture or substantial leakage; (G) Initial hypothesis for enhanced sealing due to surface interaction was not validated as there was no significant difference in the shear strength of biolith applied onto aluminum or PLA surfaces.

Fig 4. Usage of biolith in additive manufacturing.

(A) A scaled model was created in three sections with varying degrees of overhang; (B) The additive manufacturing setup features a pneumatic ram extruder mounted onto a 6-axis robotic arm. Pressure is regulated to directly control the flow of material and used to match the translational speed of the robotic arm. Hot air is manually focused on extruded layers to accelerate water evaporation; (C) Printed sections after drying; (D) Sections joined using biolith as mortar; (E) Completed model with a 3D-printed lander module illustrating a possible scenario of fabricating habitats on Mars.