Design, analysis, and testing of a precision guidance, navigation, and control system for a dual-spinning Cubesat

Abstract

The Microsized Microwave Atmospheric Satellite (MicroMAS) combines two traditional control approaches: a dual spinner and a three-axis gyrostat. Unlike typical dual spinners, the purpose of MicroMAS 's 2U bus and spinner assembly is to actuate a iu payload, not to add gyroscopic stiffness. An orthogonal triple reaction wheel assembly from Maryland Aerospace, Inc., will both counter the angular momentum from the payload and rotate the satellite's bus about its orbit-normal vector to maintain bus alignment with the orbital frame. The payload spins about the spacecraft velocity axis to scan successive swaths of the Earth. However, the CubeSat form factor restricts the velocity axis to be along the spacecraft minor axis of inertia. This orientation leaves the spacecraft at a gravity-gradient-unstable equilibrium. Further, imperfect cancellation of the payload's angular momentum induces nutation behavior. An extended Kalman filter is implemented on a 16-bit P1C24 microcontroller to combine gyroscope, limb sensor, and magnetometer data to provide attitude estimation accuracy of approximately 20 arcminutes. Simulations show that the reaction wheels can consistently maintain pointing to within 30 arcminutes for orbits above 400 kilometers with the payload rotating at 0.83 hertz.