Nonlinear Observability Analysis of Spacecraft Angular Rates Estimation Based on Gyrowheel

Gyrowheel (GW) is an integrated servo device which is used as both sensor and actuator in a small spacecraft. In order to realize three-dimensional torque output, the rotor of GW needs to tilt in large angles, which leads to the difficulty of the spacecraft angular rate sensing with the GW by the algorithm measurement method since the compensation of GW modeling error can hardly be realized. Therefore, combining with the GW dynamics equations, the spacecraft attitude dynamics model is introduced to construct the dynamic filtering equations by momentum exchange principle, which contributes to the application of advanced filtering method for compensating the noise from the modeling error and random factors. Moreover, the nonlinear observability of the dynamic filtering model is analyzed and validated by Lie derivatives and extremum principle, respectively.