Design of a Low Micro Vibration High Precision CubeSat Reaction Wheel

Rolling element bearings are known to generate higher order harmonics. These harmonics can reach up to the 10th or higher engine order [1]. When wheels are used in a wide speed range, these higher order harmonics can pass and excite rotor eigenfrequencies and rotor modes, severely increasing the exported μ-vibrations at these frequencies. The amplification of these frequencies will then be governed by the quality factor (Q-factor) of the rotor. Single piece rotors have several advantages such as affordable tight tolerances, uniform mass and elimination of assembly errors, but such monolithic metallic structure feature high Q-factors. Material choice is a first way to address this [2], but damping will stay limited. To further increase the internal damping and reduce the Q-factor, Constrained layer damping is employed

CubeSpec, A Mission Overview

CubeSpec is an in-orbit demonstration CubeSat mission in the ESA technology programme, developed and funded in Belgium. The goal of the mission is to demonstrate high-spectral-resolution astronomical spectroscopy from a 6-unit CubeSat. The prime science demonstration case for the in-orbit demonstration mission is to unravel the interior of massive stars using asteroseismology by high-cadance monitoring of the variations in spectral line profiles during a few months. The technological challenges are numerous. The 10x20cm aperture telescope and echelle spectrometer have been designed to fit in a 10x10x20cm volume. Under low-Earth orbit thermal variations, maintaining the fast telescope focus and spectrometer alignment is achieved via an athermal design. Straylight rejection and thermal shielding from the Sun and Earth infrared flux is achieved via deploying Earth and Sunshades. The narrow spectrometer slit requires arcsecond-level pointing stability using a performant 3-axis wheel stabilised attitude control system with star tracker augmented with a fine beam steering mechanism controlled in closed loop with a guiding sensor. The high cadence, long-term monitoring requirement of the mission poses specific requirements on the orbit and operational scenarios to enable the required sky visibility. CubeSpec is starting the implementation phase, with a planned launch early 2024