A Brush Wheel System Sampler for Regolith and Lunar Soil Developed within the APOSSUM Mission Study

A Brush Wheel System Sampler for Regolith and Lunar Soil Developed within the APOSSUM Mission Study. M. Patzek1, M. Goldmann1, B. Gundlach1, C. Güttler1, G. S. Klingenberg1, L. Bannemann1, B. Aussel1, J. T. Grundmann2, M. Hilchenbach3, 1Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany. 2Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany. 3Institute of Space Systems (DLR), Robert-Hooke-Straße 7, 28359 Bremen, Germany. [email protected] Introduction: The recent sample return missions Hayabusa2 and OSIRIS-REx to the Near-Earth Asteroids Ryugu and Bennu, respectively, were able to collect considerable amounts of samples from the surfaces of these objects [1,2]. While the sampling mechanism of HAYABUSA and HAYABUSA2 are based on the collection of grains via contact mobilization through impact, OSIRIS-REx utilized a Nitrogen-gas pressurized system that flushes material into the sampling mechanism. While Touch-And-Go (TAG) manoeuvrers are popular for asteroids, recent sampling approaches on the Moon (i.e., the Luna and the Chang’e programs, [3,4]) use drilling and scouping approaches performed by landers in a more controlled manner. During the Apollo era, sampling was done mainly manually by astronauts using various instruments. During the MARCOPOLO-R mission study [5], an alternative approach was developed and tested, but ultimately stopped. This approach used a Brush Wheel System (BWS) to brush material into a sampling container during a landing manoeuvre [6]. In order to further develop and study another sampling mechanism that can be used during TAG and landing manoeuvres, the previous developments [6-8] have been reviewed and will be adapted and optimized for a different mission profile when compared to MARCOPOLO-R capable of sampling a wide range of grain sizes ranging from the Moon to asteroids. The APOSSUM Mission Study: The APOphiS SUrface saMpler (APOSSUM) has been studied and developed in two Concurrent Engineering studies at DLR Bremen in 2024 together with DLR and MPS Göttingen [9,10]. The concept foresees a fast sample return mission from a NEO passing by Earth at low distance (<20 lunar distances) by arriving at the asteroid before close encounter, sample acquisition and return could be performed with low Δv requirements. This can save considerable amount of fuel and mission time and consequently its financial costs can be kept low. The initial mission design was developed for Apophis’ flyby on Friday April 13th, 2029, when it will fly by Earth closer than 32,000 km. The BWS (see Fig. 1) was developed as the main instrument allowing to sample grains with a diameter of up to 5 cm during a TAG manoeuvre [9,10]. Sampler Design: The presented design of the BWS currently consists of two cylindrical brushes with a length of 100 mm and a diameter of 100 mm, each driven by individual brushless DC motors. The breadboard design uses aluminium stringers to adapt for multiple test scenarios. Surface particles in the sub-mm to cm range are grabbed, lifted, and transported into the sampling tube, where they shall be collected afterwards. A test facility was designed to simulate a TAG maneuver inside a 45 cm squared sample box (Fig. 1c). To achieve this, the sampler is suspended on four Dyneema strings, which allow a controlled descent up to 20 cm/s at variable angle wrt. gravity and/or sample surface. The design for the flight instrument facilitates two cameras with viewing directions towards the surface interaction zone as well as into sampling tube (Fig. 1a). A flap is foreseen above the brushes to avoid material loss after successful sampling, speFig. 1: a) CAD model of the BWS flight design consisting of 4 diamondshaped brushes, a flap to close the sampling tube and two cameras (blue) to observe surface interaction and material inside the sampling tube. b) BWS breadboard with two cylindrical brushes. c) Test facility to simulate TAG maneuver under Earth gravity and atmospheric pressure using various surface analogue materials. a b c cifically in ascent after TAG. In contrast to the breadboard, the flight design will possibly follow a 4-brush design, which will be traded against the 2-brush design in terms of sampling efficiency, system redundancy and system complexity. First Test Results: The breadboard design in Fig. 1 was tested under a wide range of parameters in our test facility. Key parameters that determine the sampling efficiency are particle size and BWS motor speed. Particles up to 5 cm in diameter can be sampled with satisfying efficiency even under Earth’ gravity. Porous clay (LECA) and broken Ytong rocks are currently used as an analogue material, which can optionally be mixed with sand to simulate finer material. Using lunar and Martian soil analogue is also possible and planned as proof of concept for specific grain size frequency distributions. Motor speeds of 300 - 400 rpm as shown by previous studies provided a good compromise between sampling efficiency and required motor power [5,6], which is verified in our tests. Figure 2 shows a qualitive impression of sampling at 400, 300, and 200 rpm, respectively. Blocking of the brushes happens for lower rotation speeds (i.e., 200 rpm) more often than at higher speeds (i.e., 400 rpm), and the ~40 mm particles are ejected several decimetres from the surface at 400 rpm. Other parameters that have been tested are, among others, the relative surface angle, particle shapes and sizes and contact force via approach speed. Overall, the concept is robust against these variations although sampling efficiency is affected. If the brushes get stuck by a particle exceeding the free-length between the brushes, a reverse rotation is able to clear the entry for a second sampling attempt. Upcoming Development: The BWS is currently being updated to comply with vacuum conditions and will be tested in zeroand Moon-g campaigns at the Drop-Tower and GraviTower Facilities at ZARM in Bremen during two campaigns in June and October. Key questions are 1) study the interaction between the brushes and the surface material, 2) verify the system efficiency under zeroand low-g for various system parameters. These system parameters are those tested also in the air setup depicted in the previous section. Simultaneously, a breadboard utilizing 4 brushes as foreseen in the flight-model design is built and tested under 1g and atmosphere. Preliminary test results of the zeroand Moon-g campaign will be presented on the conference. Acknowledgement: We acknowledge financial support by the DLR Agency (50OO2511). References: [1] Watanabe S. I., et al. (2017) Space Science Reviews, 208, 3-16. [2] Lauretta D. S. et al. (2024) Meteorit. Planet. Sci., 59, 2453-2486. [3] Florensky et al (1977) Proc. 8th Lunar Sci. Conf., 3257-3279. [4] Xiao et al. (2021), Sample return missions, 195206. [5] Barucci M. A. et al. (2012) Exp. Astron., 33, 645–684. [6] Bonitz R. (2012) IEEE Aerospace Conference, Big Sky, MT, USA, pp. 1-6. [7] Zhang J. et al. (2022) Acta Astronautica, 198, 329-346. [8] Luo H. et al. (2023) Front. Mech. Eng., 18, 16. [9] Grundmann J. T. et al. (2025) Apophis T-4 Workshop. [10] Goldmann M. et al. (2025) Apophis T-4 Workshop. Fig. 2: Snapshot from a video during a test with a brush rotation speed of 400 rpm and an approach velocity of 20 cm/s on ~30-40 mm LECA clay and Ytong rocks. After surface contact many particles are lifted and partially flying up to a meter high (arrow) reaching velocity of ~1 m/s. a b c