Accurate Three-Axis Control of Spacecraft with Non-Uniform Mass Distribution
Authors
Dibbern, Danny ; Pathania, Siddharth
Term
4. term
Education
Publication year
2023
Submitted on
2023-06-02
Pages
51
Abstract
This thesis investigates how to achieve high-precision three-axis attitude control for satellites with non-uniform mass distribution using reaction wheels. The system is modeled with quaternions for kinematics and Euler’s equations for dynamics, and over-actuated reaction wheel torque allocation is handled via the Moore–Penrose pseudoinverse. Linear (PD, LQR, MPC) and nonlinear (SMC) control strategies are implemented and compared, including linearization and transformation to the principal-axes frame to decouple the inertia matrix. Controllers are evaluated in MATLAB on a simulated low Earth orbit satellite and additionally implemented in C for testing in a high-fidelity simulator from Space Inventor. Results indicate that transforming linear control problems to the principal-axes frame improves pointing accuracy, while SMC remains robust to such changes. In nadir-pointing scenarios, all methods performed comparably, with LQR in the principal-axes frame slightly better. In landmark-pointing with target switches, MPC settled the fastest but exhibited substantial chatter, suggesting room for refinement. For large-angle maneuvers, SMC outperformed PD and LQR for equivalent control effort, underscoring SMC’s suitability for large slews.
Denne afhandling undersøger, hvordan højpræcis tre-aksers attitude-kontrol kan opnås for satellitter med ikke-uniform massedistribution ved brug af reaktionshjul. Systemet modelleres med kvaternioner for kinematik og Eulers ligninger for dynamik, og reaktionshjulenes overaktuerede momentfordeling håndteres via Moore–Penrose-pseudoinvers. Der implementeres og sammenlignes lineære (PD, LQR, MPC) og ikke-lineære (SMC) strategier, herunder linearisering og transformation til hovedakserammen for at afkoble inertimatricen. Controllerne evalueres i MATLAB på en simuleret lav-jordsbane-satellit og desuden implementeret i C til test i en højfidelitet-simulator fra Space Inventor. Resultaterne viser, at transformation af lineære kontrolproblemer til hovedakserammen forbedrer pegepræcisionen, mens SMC er robust over for sådanne ændringer. I nadir-pegningsscenarier havde alle metoder sammenlignelig ydeevne, med LQR i hovedakserammen som en let forbedring. Ved målskift under landmærke-pejling opnåede MPC hurtigst indsvingsning, men med betydelig chatter, hvilket indikerer forbedringspotentiale. For store vinkelmanøvrer overgik SMC både PD og LQR ved samme styreindsats, hvilket understøtter SMC’s relevans til store slews.
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