Ferrofluid reaction wheel development and in-orbit verification

Abstract

In contemporary satellite systems, the Attitude and Orbit Control System (AOCS) manages internal torque generation primarily through Reaction Wheels (RW) and Control Moment Gyros (CMG), which use mechanically mounted rotating disks to control orientation without expelling mass. Unlike magnetorquers, which interact with Earth’s magnetic field, or thruster-based Reaction Control Systems (RCS), which generate external forces by expelling propellant, RW and CMG systems rely solely on momentum exchange within the spacecraft. While state-of-the-art RWs are highly reliable and have demonstrated exceptional performance over decades of operation, their design still presents inherent challenges, such as wear, nonlinear friction effects, and tribological degradation of contact surfaces. These challenges are critical in space, where repairs are impractical and/or resource-intense. Consequently, engineers have devoted significant effort to developing robust and reliable mechanical reaction wheels. This paper explores an innovative proof-of-concept design based on a fluid-magnetic system utilizing ferrofluids and permanent magnets. This study aims to address limitations of traditional RWs by eliminating mechanical interfaces susceptible to wear and tear and replacing them with a low friction ferrofluidic bearing. Ferrofluid-based system concepts can offer a longer life due to reduced wear and tear, lower production costs by requiring less exotic materials and tolerances, self-center within the provided magnetic potential field and can therefore exhibit reduced vibration behavior. The Ferrowheel experiment, flown as part of the FARGO mission ( Überflieger 2 competition of the space agency within DLR) in March and April 2023, demonstrated the feasibility of ferrofluidic bearings for attitude control in ISS microgravity. These results contribute to exploration of innovative reaction wheel technologies, highlighting the potential of fluid-based systems for applications requiring enhanced robustness and reduced mechanical wear.