Characterization of CubeSat Reaction Wheel Assemblies

This paper characterizes three different CubeSat reaction wheel assemblies, using measurements from a sixaxis Kistler dynamometer. Two reaction wheels from Blue Canyon Technologies (BCT) with momentum capacities of 15 and 100 milli-N-m-s, and one wheel from Sinclair Interplanetary with 30 milli-N-m-s were tested. Each wheel was tested throughout its specified wheel speed range, in 50 RPM increments. Amplitude spectrums out to 500 Hz were obtained for each wheel speed. From this data, the static and dynamic imbalances were calculated, as well as the harmonic coefficients and harmonic amplitudes. This data also revealed the various structural cage modes of each wheel and the interaction of the harmonics with these modes, which is important for disturbance modeling. Empirical time domain models of the exported force and torque for each wheel were constructed from waterfall plots. These models can be used as part of pointing simulations to predict CubeSat pointing jitter, which is currently of keen interest to the small satellite community. Analysis of the ASTERIA mission shows that the reaction wheels produce a jitter of approximately 0.1 arcsec RMS about the payload tip/tilt axes. Under the worstcase conditions of three wheels hitting a lightly damped structural resonance, the jitter can be as large as 8 arcsec RMS about the payload roll axis, which is of less importance than the other two axes.