Building Cube Satellites Frictionless ADCS Testing Framework for Testing B-dot Algorithm

Abstract

Cube satellites increased the potential of utilizing space and its applications. Lower manufacturing and operating costs, compared to larger scale satellites, are what makes cube satellites appealing for many research and academic institutes. However, it is critical to ensure the functionality and reliability of these systems prior to launching into space. On-orbit maintenance cannot be justified for satellites, thus, extensive, and thorough on ground testing is crucial for ensuring successful operation and fulfilling the objectives of the mission. ADCS subsystem is considered one of the most critical and complex subsystems on a satellite and it was always a domain for satellites' research topics. Many testbeds were designed for testing ADCS systems; however, most of them are limited by their high cost, complexity in implementation, difficulty of operation and poor simulation of space's frictionless environment. Magnetic levitation system, on the other side, has proven its ability to overcome most of these issues and opens the doors for various testing opportunities if combined with other testbeds and sensors. This type of testbeds has never been used before for testing cube satellite's magnetic control system. To do so, it has to be combined with specially designed Helmholtz cage which will accommodate and enclose only the magnetically levitating satellite and not the electromagnet core thus, not disturbing the levitation process by the magnetic field produced by the cage. In this work, a magnetic levitation testbed was designed with a Helmholtz cage enclosing it. By measuring the external magnetic field and controlling the current through coils of the cage, the designed cage was capable of producing a uniform magnetic field within a region of 12 cm which is sufficient to host 1U cube satellite. The uniformity of the magnetic field was measured to be within ±2% the value at the center of the cage. The magnetic levitation system was designed to maintain a 0.3mm air-gap with a feedback control system based on PD controller with one linear Hall-effect sensor for measuring the distance which is the feedback signal. The system was simulated on SIMULINK first to study the feasibility of implanting the system. The equation used in simulation that relates the supplied current to the produced electromagnetic force was found empirically and the system has proven to be feasible. In the final implementation however, although, the PD controller was tuned, noisy measurements from the Hall-effect sensor affected the output of the controller leading to unstable response from the system. It has been concluded that one linear Hall-effect sensor is not sufficient to provide stable response as it is prone to noise from external magnetic fields. Future work shall consider including multiple Hall-effect sensors which can reduce the effect of noise by fusing the measurements from the multiple sensors together. Optical displacement sensor, although expensive, is considered the most accurate sensor for such applications.

Date of Award	May 2021
Original language	American English