Microvibration test bench for tiny reaction wheels

Abstract

Reaction wheels are often the main contributor to microvibrations on satellites. These vibrations are a source of pointing errors and therefore need to be limited as much as possible. The miniaturization trend in the space industry and universities fostered the production of very small reaction wheels, suited to Cubesat and PocketQube scales. A novel method to measure microvibrations for these kinds of wheels is proposed in this thesis. Due to budget and resolution constraints, a standardized method is indeed not available for this
scale yet. The main idea behind this method is to amplify vibrations through a flexible mounting bracket on which the wheels are fixed and later calculate the source disturbance via a transmissibility function. This measurement method will be studied for validation against some initial requirements. Two types of tests are proposed for this purpose: In the first, a MEMS accelerometer is attached to the mounting bracket to measure accelerations, while in the second a laser is pointed to a mirror on the mounting bracket to measure displacement. The tests will be compared with two models: the empirical model, which is a parameter estimation model with test results as input; and the unified model, which combines the empirical model and an analytical model, simulating the equations of motion of the system with input parameters from a CAD model. The main results will include microvibration waterfall plots and static and dynamic imbalance values. Although it was not possible to entirely validate the test bench prototype within the scope of this thesis, room for improvement is left, with some hints for possible future work.