Characterization of reaction wheel torque instabilities

J.J.A.M. Borgharts

    Research output: ThesisEngD Thesis


    Cutting edge earth observation and scientific missions require high spacecraft pointing stability. The limiting factor for pointing stability is unsatisfactory reaction wheel torque performance, of which so-called torque instabilities are the main drivers. To gain insight in these phenomena, the European Space Agency (ESA) has set up the ’Mitigation of wheel friction torque instabilities’ project. The aim is to properly characterize these instabilities and find possible routes to reduce these disturbances.
    The first task of the project is to characterize five main torque instabilities:
    1. Noise
    2. Stiction
    3. Friction change
    4. Oil jog
    5. Torque jump
    To this end a reaction wheel ground test design is developed at MOOG Bradford. A dedicated test instrument is designed and built (both hardware and software) to meet the specifications set by ESA. Additionally, a test plan is developed to provoke torque instabilities to allow proper characterization. In this test plan five reaction wheels are selected of which some are known to exhibit severe torque instabilities. In the test plan four screened variables are varied: reaction wheel bearing design, wheel speed, temperature and lubrication condition. The test matrix orthogonality is ensured.
    The ground test campaign is successfully completed and data is analyzed using custom algorithms. Only the friction change is not observed in the test data. The other torque instabilities could be analyzed and quantified for modeling purposes. The results are implemented in an existing high fidelity functional model of reaction wheel operation to allow proper torque instability generation.
    The influence of torque instabilities on pointing stability is analyzed, showing that the torque jump is the most severe instability. The impact of oil jogs is up to a factor 100 less than that of the torque jump. The other instabilities are not considered in this analysis as their impact is negligible (noise) or considered irrelevant (stiction, friction change).
    At this moment there is an on-going mitigation task in which several methods are considered to prevent torque instabilities from occurring or at least reduce the impact they have on pointing stability. These methods exist at two levels: reaction wheel level and control system level. The exploration of mitigation methods is primarily focused on torque jumps, as they have largest impact on pointing stability.
    Original languageEnglish
    Awarding Institution
    Place of PublicationEindhoven
    Publication statusPublished - 2014

    Bibliographical note

    PDEng thesis. - Confidential forever.


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