# An Automatic Dry Sieving Mechanism for a Lunar Brick Payload
## 1 Introduction  
According to the International Space Exploration Coordination Group (ISECG), in situ resource utilization (ISRU) is pivotal for in situ manufacturing applications such as hardware fabrication, shielding, and potential landing pad construction [1]. Consequently, researchers across various institutions are actively engaged in developing solutions for these proposed applications. [PERSON] et al. introduced a novel approach involving a low-binder composite brick utilizing regolith particles optimized up to 500 \(\upmu\)m in size [2]. Additionally, other manufacturing techniques like spark plasma sintering require maximum particle sizes of 200 \(\upmu\)m [3]. Overall, the properties of lunar regolith are influenced by particle size [4], which affect any ISRU activities and necessitate particle size separation before use. Given that lunar regolith particle size varies from sub-micrometer to several millimeters [5], these approaches demand that we process the feedstock material to obtain particles in the desired size range. In the mining industry, water is frequently used to aid the beneficiation process. However, this method is impractical due to the lack of atmosphere, requiring an enclosed system. Additionally, it requires a 1:1 water-to-mineral ratio, which would require substantial water usage in an environment where this resource is critical for survival [6]. To address this, this study explores the performance of a sieving equipment prototype designed to separate particles at 500 \(\upmu\)m, 250 \(\upmu\)m, and 125 \(\upmu\)m, acknowledging that aperture-based beneficiation is limited to particles sizes above 40 \(\upmu\)m and is increasingly challenging as particle size decreases [6]. State-of-the-art lunar beneficiation techniques currently include two main approaches for particle size separation [6], dry sieving [7; 8] and electrostatic methods [9; 10]. Circular dry sieving benefits from the apparent centrifugal forces generated in low-gravity environments like the Moon, which propel particles outward to the sieve. However, this method has issues such as sieve blocking, necessitating an additional cleaning step [9; 10]. Electrostatic beneficiation, on the other hand, avoids using a mesh to separate the particles but relies on the forces generated by the electrostatic charge and the weight of the particles. This approach requires a vacuum chamber to mitigate air turbulence that hinders particle motion, particularly for smaller particles [10]. Another type of electrostatic beneficiation is dependent on the parameters of the traveling wave. Research by [PERSON] et al. [11] demonstrated a separation method in which the frequency of the wave will define if the charged particles are more likely to move with or against the wave, resulting in a 90% desired particle concentration and a recovery rate of 79% [11]. Despite its simplicity and automation potential, the resulting separation lacks the precision achieved with meshes [9; 10; 11]. An alternative dry-sieving solution was proposed by [PERSON] et al. [7]. Their proposed system consists of a scoop with an integrated dry sieving mechanism that sieves the material during the excavation using a shaking motion. After separation, the compartments can be emptied and cleaned using a shaking motion [7]. While this reduces the sieve blocking issue, it introduces extra steps and complexity due to the robotic arm's requirements. To address potential sieve blocking issues [12] and complexity, the equipment used in this research employs a specific technique using natural frequencies. The sieve unit (depicted in Figure 1) is based on the design of [PERSON] et al. [13] and is akin to industrial screening devices. The paper by [PERSON] et al. [13] introduces an approach called a toss indicator K (Equation (1)) and suggests that this indicator's value correlates with sieve blocking. For hard-to-screen grains, a value between 7 and 10 is recommended [13].