# An Automatic Dry Sieving Mechanism for a Lunar Brick Payload
## 2 Materials and Methods
### Regolith Simulant Selection  
The sieving device was tested with lunar regolith simulants. Several candidate simulants were initially selected through the, now discontinued, Colorado School of Mines Planetary Simulant Database and then further evaluated for their mechanical properties (see Table 1). Specifically, particle size distribution and particle shape were considered most relevant for testing the sieve [15].  
The first simulant considered was CUMT-1, developed by the China University of Mining and Technology. This simulant is reported to have similar particle size distribution and particle sphericity and roundness to those of real lunar regolith [16], suggesting comparable results to test on the sieve. However, this product was excluded due to difficulty in obtaining a sufficient quantity in time for this study.  
The second set of simulants evaluated were TUBS-M (mare) and TUBS-T (highland) from the Technical University Braunschweig [17; 18]. The main advantage of these simulants is their high degree of customization. Additionally, the grain size distribution falls right in between the upper and lower limits measured in Apollo samples, making them representative of lunar regolith. For these simulants, the angle of repose is measured [18], which is a good indicator of the adhesiveness of the material. This is connected to the angularity and is therefore also a good indicator to assess the sieving performance [19]. The angle of repose for lunar regolith typically ranges from 41 to 55 degrees. For TUBS-M, this value would fall between 41.9 and 45.8 degrees, while for TUBS-T it is reported at 37.91 degrees. These values suggest that TUBS-M is mechanically a closer match to lunar regolith. Aspect ratios were also considered, they influence how many times a particle needs to be compared to the sieve before passing through [20]. The TUBS simulants exhibit an average aspect ratio of 0.635 which is near the upper limit of lunar regolith, as shown in Table 1[18]. The availability of both mare and highland simulant variants makes this material strong candidate for these particular tests.  
When considering availability, EAC-1A stands out as the most accessible option. This in-house simulant was developed for the European Astronaut Center with the LUNA facility in mind. This simulant exhibits a grain size distribution closely resembling lunar regolith, except for a slight dip below the lower lunar threshold. [PERSON] et al. [21] estimated a cohesion of 0.38 kPa at a density of 1.95 g/cm\({}^{3}\), which is a relatively low value for these simulants. The roundness of the EAC-1A particles is comparable to the lunar regolith roundness. However, due to the absence of data on the angle of repose and aspect ratio, this simulant was eventually excluded as a viable option.  
Ultimately, two regolith simulants, LMS-1 (mare) and LHS-1 (highland), were selected with mechanical properties and availability in mind. These simulants were developed by Space Resource Technologies (formerly known as Exolith Lab). In this study, LHS-1 was the main test material because the current mission planning focuses heavily on the lunar south pole, a region which is dominated by highland terrain [22]. LMS-1 was also used in some tests to compare results with LHS-1. These materials have similar particle size distribution and mechanical properties to the ones stated before, as shown in Table 1. Moreover, their widespread availability makes them highly practical choices for extensive experimentation [23; 24].