Multi-degree of Freedom Position and Attitude Control of RINGS Dipoles Using Electromagnetic Forces and Torques
Alvarez, David Andres
MetadataShow full item record
Satellite formation flight (SFF) is likely to transform and advance the scope of space missions in the near future. Some considerable benefits of SFF to a mission include robustness, adaptability, and potential cost savings. However, satellite formations face a fuel expenditure issue: the more spacecraft there are to control, the more fuel will be expended on alignment and maneuvering. A solution to this problem is Electromagnetic Formation Flight (EMFF), which is the application of conductive coils in producing electromagnetic fields that can interact with the fields of other coils in a formation to exchange forces and torques. With three orthogonal coils, it is possible to control all the relative degrees of freedom of the spacecraft. With a functionally infinite source of electrical energy from solar panels, mission length for satellite formations would not be so limited by fuel capacity. In this thesis, control schema for electromagnetic (EM) assist maneuvers are proposed to solve the control problem caused by the inherent non-linearity of the EM forces and torques, but for a two-dimensional three degree-of-freedom system. An EM assist is then defined as an EMFF restricted to one of three axes, while an optimal controller restricts the other two degrees-of-freedom. The near-field model of electromagnetic force and torque is then simplified and interpolated into a polynomial expression. A feed-forward control method is then devised that inverts the polynomial expression and system dynamics to estimate command currents that satisfy a time function of the desired position and its derivatives. To account for saturation limits, un-modeled disturbances, and stochastic effects, a Sliding Mode (SM) controller contributes feedback error handling; EMFF is also demonstrated with only SM control and no feed-forward. Fuel savings are exhibited through a variety of arbitrary EMFF assist maneuvers in simulation. Finally, a Resonant Inductive Near-field Generation System (RINGS) actuator is shown performing axial and shear translations and torque rotations for the first time, demonstrating the potential that EMFF has in the future of SFF.