Proceedings of the Canadian Society for Mechanical Engineering International Congress 2021 CSME Congress 2021 June 27-30, 2021, Charlottetown, PE, Canada Multi-Shaft Reaction Wheel Design for a 2U CubeSat Nicholas R.H. Popp 1,2 , Vignesh Krishnan 1,2 , Elijah Vautour 1,2 , Maxwell Bauer 1,2 , Annalisa Wailand 1,2 , Anthony Newton 1,2 , Silas Eastwood 2 , Suraj Chandrasekaran 1,2 , Robert Bauer 1,2, * 1 Department of Mechanical Engineering, Dalhousie University, Halifax, Canada 2 Dalhousie Space Systems Lab, Halifax, Canada *Robert.Bauer@dal.ca Abstract — In this paper, a reaction wheel design is presented and proposed for use in Dalhousie University’s Low Earth Orbit Reconnaissance Imagery Satellite (LORIS) 2U CubeSat. After estimating a cumulative maximum disturbance torque of 7.16 × 10 -7 Nm in low Earth orbit, a flywheel design was developed with a momentum storage of 1.01 × 10 -2 Nms. The authors propose to machine the flywheel in a skate-wheel shape to provide a large inertia-to-mass ratio compared to solid- cylindrical designs. A novel three-shaft system is employed wherein a Brushless DC motor shaft is rigidly connected to a spline-toothed inner shaft which transmits power to an outer shaft rigidly fixed to the flywheel. The inner shaft provides torsional flexibility to the system and ultimately reduces the transfer of vibration due to shaft misalignments. Splines and back-to-back angular contact bearings accommodate axial and radial misalignments between the inner and outer shaft experienced during mounting and operation. Finite element analysis was employed to validate the design across worst-case loading scenarios including rocket launch and misaligned inner and outer shafts. Keywords-CubeSat; reaction wheel; design; disturbance torques; momentum storage; inertia; pointing; ADCS I. INTRODUCTION There is a wide range of reaction wheel (RW) designs presented in the existing literature. This paper focuses on a novel reaction wheel design proposed for the Dalhousie University Low Earth Orbit Reconnaissance Imagery Satellite (LORIS) 2U CubeSat. LORIS plans to achieve three-axis attitude control by aligning three of these RWs along mutually- orthogonal axes within the satellite. In terms of designs, Takehana and Uchiyama [1] propose a spherical RW design to miniaturize conventional reaction wheel systems. Their design rotates a spherical rotor using omni-directional wheels. Krishna et al. [2] propose a spoked- flywheel design for a 2U CubeSat to try to obtain high moments of inertia for a given mass of the wheel. They point out, however, that spoked wheels can be challenging to machine and balance. Additionally, Oland and Schlanbusch [3] present a reaction wheel design for CubeSats where the flywheel exhibits a thin inner disc and a thicker outer ring around its periphery to enable a high moment of inertia for a given flywheel mass. The difference in thickness between the inner and outer ring creates what appear to be symmetrical cavities on either side of the flywheel. Kumar et al. [4] studied different flywheel shapes for a nanosatellite including a conical disc, modified constant stress disc, and a flat unpierced disc. They selected a solid disc and arranged four RWs in a tetrahedral configuration to retain three- axis control if one RW fails. Manggala et al. [5] designed a micro reaction wheel for a 1U CubeSat that consists of a bowl- shaped flywheel that fits the motor in its cavity. Munter et al. [6] present a flywheel design for CubeSats that uses a thin inner disc and thicker outer ring, similar in design to Oland and Schlanbusch [3], except that the two cavities on either side of the thin inner disc are not symmetric. Their reaction wheel design uses two deep-groove ball bearings, a stainless-steel flywheel, and a Faulhaber 1509T006 brushless DC motor. The LORIS RW adopts a design that is similar in geometry and dimensions to Munter et al. [6]. While Munter et al. [6] use a stainless-steel flywheel, the present authors are considering the use of the MT18C Tungsten alloy due to its high density. Furthermore, instead of using two deep-groove ball bearings, the proposed LORIS RW design uses a pair of angular-contact ball bearings similar to the high-torque reaction wheel design proposed by Nigo et al. [7]. The reasoning behind the decision to use a pair of angular-contact ball bearings is because these types of bearings offer high resistance to any misalignments in the shaft [8]. A nut is then used to clamp the inner races of the two bearings together to establish the necessary preload. Reaction wheels are one of the primary sources of micro- vibration disturbances onboard spacecraft [9] including CubeSats [6]. Sources of these vibrations include unbalanced rotors, misaligned rotors, and defective bearings [10]. Flexibility is, therefore, needed in the system to accommodate any misalignments between the motor shaft and the outer The authors received financial support from the Canadian Space Agency (CSA) Canadian CubeSat Project and the Natural Sciences and Engineering Research Council of Canada (NSERC).