Ferrofluid Reaction Wheel Development and in-orbit Verification

Abstract In contemporary satellite systems, Reaction Control Systems (RCS) serve as one of the primary means for generating internal torques within the Attitude and Orbit Control System (AOCS). Notably, these systems encompass Reaction Wheels (RW) and Control Moment Gyros (CMG), both characterized by mechanically-mounted rotating disks engineered for maximized moment of inertia. However, this design inherently introduces challenges common to movingmechanical systems, including wear, (non-linear) friction effects, and potential degradation. For in space applications these challenges are more severe, as repairs are usually not possible or would entail significant resource allocation. An alternative to this is provided by fluid-based systems, which can prevent wear and tear of mechanical systems by completely replacing the mechanical interfaces in conventional system with a design based on a ferrofluid mechanism. Ferrofluid-based system concepts offer longer life due to reduced wear and tear as well as potentially lower production costs and overall increased durability and reliability. This paper aims to describe the development of a potential replacment of a reaction wheel by a fluid-based concept from the basic idea and proof of concept up to the data evaluation of the in-space verification of the system in the zero-gravity environment on the ISS (International Space Station). This ACS (Attitude Control System) experiment is called Ferrowheel as it is based on a stator of a brushless DC motor in combination with a rotor on a ferrofluidic bearing. This research was completed as part of the student project FARGO (Ferrofluid Application Research Goes Orbital). FARGO is part of the Überflieger 2 student competition hosted by the space agency within DLR (German Aerospace Center). The experiment was operated on the ISS in March and April 2023. The project objective was to test and analyze three separate ferrofluid applications in the ISS micro-gravity environment.