Novel Attitude Control Challenges for an Earth-Observing CubeSat

This paper presents a novel attitude determination and control solution for a three cube nanosatellite performing science operations in low Earth orbit. The spacecraft is tasked with studying the water content of Earth’s upper atmosphere by taking radiometer measurements along the 183 GHz absorption line. The radiometer must be calibrated against the cold of deep space, and this calibration necessitates spinning the spacecraft at approximately 5 RPM about the minor axis—an inherently unstable configuration. Along with this angular velocity requirement, the spacecraft must be able to resolve its attitude to approximately 1.5° about all axes in order to geo-locate the radiometer data, a relatively high level of accuracy for a CubeSat. This paper will describe in detail the Earth observation science mission as well as the development of the spacecraft attitude determination and control subsystem. A commercially available kit of parts was assembled to satisfy the attitude determination and control requirements, and the challenges of integrating this hardware into the power-limited spacecraft system in a relatively short period of time will also be discussed.