Design of Robust Control Techniques for a Small Satellite with Flexible Appendages

In the latest years, small satellites are becoming more and more utilised by space agencies, thanks to their reduced costs. The technological improvement and the large choice of Components of the Shelf, allowed the space industry to develop smaller and cheaper satellites, able to operate in different missions and scenarios. Due to their limited mass and volume, they can be launched simultaneously with only one launcher, cutting enormously the launch costs. They can be disposed as a constellation and provide services for communications, Earth observation, science experiments or debris removal. All these aspects allowed the non-governmental companies and universities to have access to the space, improving the research of reliable and increasingly smaller satellites, like CubeSats. Another important characteristic of these satellites is the presence of deployable appendages, like solar arrays, space manipulators, antennas or debris capture systems, to perform different missions and reduce the launch volume. Recent works are focusing the space sector attention to the expandable and inflatable structure, based on flexible materials, in order to cut even more the spacecrafts mass. But small dimensions involve a higher sensibility to external disturbances. Besides, the coupling between the main body of the satellite and the flexible appendages could origin relative oscillations, making the attitude control really hard. Therefore, the attitude control system needs to be robust and reliable enough to dampen the oscillations and maintain the desired attitude. The aim of this work is to design an attitude control systems, based only on the use of reaction wheels as actuators. In order to do so, a small satellite with two flexible appendages is modelled and two different control techniques are considered: a Linear Quadratic Regulator and a Sliding Mode Control. Eventually, the control system is tested in different mission scenarios.