Development of a ground testing facility and attitude control for magneticallyactuated nanosatellites

Abstract

Growing popularity of the highly capable small- and nano-satellites, driven by components miniaturization, face new technological challenges and at the same time provides new opportunities for the whole space sector. Low cost of nanosatellites launches make them accessible. Reliability is an exigency: especially challenging is design and testing of Attitude and Determination Control Systems (ADCS). Demand for nanosatellitesdedicated attitude control algorithms and careful performance assessment of the spacecrafts motivates the research work presented in this thesis. In the first part of the manuscript, development and assessment of the three degreesoffreedom ADCS testbed for nanosatellites testing is described. The facility was developed within the Microsatellites and Space Microsystems Lab at University of Bologna, and designed to meet strict low-cost requirements. The facility includes several integrated subsystems to simulate the on-orbit environment: i) an air-bearing based, three degree of freedom platform with automatic balancing system, ii) a Helmholtz , iii) a Sun simulator, and iv) a metrology vision system . Experimental assessment of the subsystems guarantee necessary level of performance. Control law design for smallsats is addressed in the second part. Limited power availability and reliability makes magnetic actuation particularly suited for ADCS design, but, the control system faces inherent underactuation. To overcome the intrinsic limits of existing control designs, a novel approach to the three-axis attitude control of a magnetically actuated spacecrafts is proposed, based on hybrid systems theory. A local H-inf regulator with guaranteed performance and a global nonlinear controller used for ensuring global stability and robustness, are combined. Hybrid control theory is employed to develop a mixed continuous-discrete controller able to switch between different feedbacks. Analytical results are verified by means of realistic numerical simulations: errors on the state comply with the computed bounds and stability is guaranteed.