Analysis, Simulation, and Measurement of Micro-Vibrations in Reaction Wheels for High-Performance Imaging Missions

High-performance imaging satellite missions require exceptional pointing stability to ensure image quality and geometric fidelity. This stability is often degraded by micro-vibrations originating from reaction wheels, which are the primary attitude actuators. These vibrations, resulting from mechanical unbalance, torque ripple, and bearing imperfections, propagate through the satellite structure and induce line-of-sight (LoS) jitter. This thesis presents the analysis, simulation, and measurement of reaction wheel micro-vibrations to characterise their effect on LoS stability and to evaluate mitigation strategies aimed at improving overall pointing performance. A complete analytical model was developed to describe the disturbance forces and torques generated by a reaction wheel, including static and dynamic unbalance and structural resonances. The model was implemented in a Matlab Simulink simulation environment to predict the resulting LoS disturbances for a four-wheel pyramid configuration. Experimental measurements were performed using a six-axis Kistler force-torque sensor to quantify the disturbance spectra of single and pyramid reaction wheel assemblies. The results were used to validate the analytical and simulation models. Additional testing on a reaction wheel pyramid mounted to an elastomeric isolation system quantified the attenuation of transmitted vibrations and demonstrated the effectiveness of passive isolation at high frequencies, as well as its limitations at low frequencies. Finally, an air-bearing platform experiment was used to relate the measured disturbances to spacecraft-level pointing errors. The combined modelling, simulation, and experimental framework provides a validated method for predicting reaction-wheel induced micro-vibrations and assessing their impact on LoS stability. The results confirm that unbalance-related disturbances are the dominant contributor to LoS instability in small, high-resolution imaging satellites and demonstrate how the developed framework can be used to evaluate and optimise isolation techniques and balancing strategies for future missions.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Du Plessis, Maria Richardt

Advisors dc:contributor.advisor

• Steyn, W. H.
• Jordaan, H. W.

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135768

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135768