Modeling and simulation of an orbit controller for a communication satellite

It is of critical importance to control the altitude of a satellite especially one used for worldwide communications in a geo-stationary orbit. The objective of this work is to evolve a design based on modeling and simulation of an orbit controller for a satellite orbiting into a circular orbit. This involves a good understanding of the system dynamics. Once a satellite is launched in a desired orbit, it never remains in that ideal orbit. The external forces present in space cause perturbations to this ideal orbit. To bring back the satellite into the desired orbit, on-board thrusters provide in-orbit propulsion. In this work, the altitude of the satellite is controlled by the thrust produced by the on-board thrusters installed in the radial and tangential directions. However, dictated by the controllability requirement, we have analyzed the dynamic system stabilization with the application of two thrusters as well as one thruster. Thus the feedback dynamic control system considers both the two-input and the single-input cases. The model developed is essentially a linearized, normalized and state-space model. The simulation of this model is based on the MATLAB software package. The design thus evolved is used to study the effect of pole-placement on the controlling parameters like settling time, peak time, overshoot, and damping ratio of the closed-loop system. This enables us to make predictions about the stability requirements for any dynamic system of the type considered. The design tool thus developed is applied to a current actual communication satellite design. The design results are compared and recommendations are made.