The design and implementation of a stellar gyroscope for accurate angular rate estimation on CubeSats

[摘要] ENGLISH ABSTRACT: Until recently, small form factor satellites (such as CubeSats) relied almost exclusivelyon micro electromechanical system (MEMS) gyroscopes for attitude propagationpurposes. Unfortunately, the nature of MEMS gyros is such that they exhibit ameasure of bias drift. This drift must be compensated for, a task for which stellargyros have proved to be exceptionally useful.Stellar gyros are satellite subsystems capable of inferring three-axis attitude propagationbased on the displacement of a series of stars between successive image frames.Their design is analogous to that of star trackers, using many of the same hardwaredesigns and algorithms. When used in combination with MEMS solutions,stellar gyros provide not only a means for drift compensation, but also a measure offunctional redundancy with regard to attitude propagation.This thesis presents the design and implementation of stellar gyroscope algorithmscapable of operating alongside existing orientation algorithms on traditional startracker hardware. The CubeStar star tracker module is used as development platform.The proposed stellar gyro solution retains CubeStar's existing star extractionalgorithms, while investigating alternative methods for star centroiding in addition tothe existing centre of gravity (CoG) approach. A dynamic proximity based matchingalgorithm is suggested to determine star correspondence between image frames.Finally, various well established estimation algorithms are considered for the purposeof rate determination, including singular value decomposition (SVD), Davenport'sq-Method and weighted least-squares (WLS).An initial evaluation of the proposed algorithms is made based on simulations in theMATLAB environment. Simulation results are confirmed through means of practicaltests, performed on a simulated night sky in a controlled environment. With a focuson low angular rates, results suggest reliable operation up to ±1 deg/s in all threeaxes of rotation. As expected for stellar imaging solutions, angular rates estimatedin both cross-boresight axes are almost an order of magnitude more accurate thanthe corresponding estimates in the boresight axis itself.

[发布机构] Stellenbosch University