Descent Modeling and Attitude Control of a Tethered Nano-Satellite

This paper describes a method to determine the rate of descent of a nano-satellite which uses an electrodynamic tether for de-orbiting. Also described, is an orbit propagator model of the continuously varying orbit and a control algorithm during its descent. An elaborate attitude control model is also proposed which is complemented by a set of sensors and actuators. Use of tethers provides an economical way to deorbit satellites. In order to aid the design of the satellite's attitude control, an orbit propagator has been developed. Sun sensors and magnetometers have been chosen as sensors for attitude determination and magnetorquers have been chosen as actuators. The dynamics of the satellite has been modeled in order to facilitate the design of the control system. This model considers disturbances acting on the satellite. A proportional derivative controller algorithm was used for attitude stabilization. The attitude control algorithm was tested using on-board models and a stability of less than 5 degrees per second was achieved. This enables the satellite to achieve the desired descent with attitude control enabling it to perform payload duties while deorbiting.