An attitude control system for the deployment and stabilisation of a tethered dual CubeSat mission

[摘要] ENGLISH ABSTRACT: The use of electrodynamic tethers on-board satellites is an exciting scientific prospect. These conductive tethers provide the means for satellites to generate power and to do propulsion by electrodynamic interaction with the geomagnetic field. Although well researched in theory, the concept has not enjoyed much success in practice. This study aims to utilise low-cost CubeSats as experimental tool to verify many of the theoretical principles that govern the behaviour of conductive tethers in orbit. The study provides a theoretical background of the concept by evaluating past tether missions and analysing existing theory. A feasible application of an electrodynamic tether within the size and weight limitations of a Nano-satellite is formulated. Existing theoretical work is adapted to model the dynamics and electrodynamics of specifically Nano-satellites. Using these mathematical models, control and estimation algorithms are designed which would provide stable deployment of a tethered CubeSat pair and stable control of the orientation of the tethered system. To be able to implement these algorithms on a satellite mission, a prototype of a sensor capable of measuring the angle of the tether using a CMOS camera is designed and built. A hardware platform is built to test the deployment of the tether using an electric motor. Electronics are designed to control the operation of the camera, to do motor control, and to run control and estimation algorithms. Using the results obtained from the practical tests done on the hardware, and using the theoretical models and control algorithms designed, a full orbital simulation of the deployment was done. This simulation includes the performance of the deployment system, the electrodynamic performance of the tether in earth‟s plasmasphere, and the estimation and control algorithms to control the system. Different deployment strategies are analysed and their performance are compared.

[发布机构] Stellenbosch University