Available at: https://digitalcommons.calpoly.edu/theses/3194
Date of Award
12-2025
Degree Name
MS in Aerospace Engineering
Department/Program
Aerospace Engineering
College
College of Engineering
Advisor
Eric Mehiel
Advisor Department
Aerospace Engineering
Advisor College
College of Engineering
Abstract
The Cal Poly Spacecraft Attitude Dynamics Simulator (SADS) is an ongoing project to develop an air-bearing platform capable of recreating on-orbit rotational dynamics with near frictionless and torque-free rotations. However, any offset between the platform's center of rotation and its center of mass will introduce a torque due to gravity.
This thesis presents the design, implementation, and experimental evaluation of a low-cost, automatic mass balancing system for the SADS to address this challenge. A new modular sliding mass system was developed that overcomes issues faced in previous iterations of the SADS, providing real-time positional control of the masses and a customizable center of mass envelope. An STM32-based onboard computer was developed that implements control laws, balancing algorithms, and attitude estimation using a combination of Simulink code generation and C/C++ drivers. A variety of balancing methods found in the literature are tested experimentally, including active feedback control, least-squares batch estimation, and Kalman filtering. The best balancing results are obtained using a PID controller to compensate for the horizontal imbalance, and an unscented Kalman filter for the vertical imbalance. This approach reduces the torque due to gravity to the order of 1x10^-4 Nm, which aligns with results achieved by comparable simulators at other universities. This work also contributes to the literature by demonstrating an experimental PID-based balancing approach and benchmarking its performance against alternative methods.