Attitude Determination and Control System for AAUSAT3
Authors
Jensen, Kasper Fuglsang ; Vinther, Kasper
Term
10. term
Publication year
2010
Submitted on
2010-06-02
Pages
224
Abstract
Afhandlingen udvikler og analyserer et Attitude Determination and Control System (ADCS) til CubeSats, motiveret af behovet på AAUSAT3, Aalborg Universitets næste satellit. ADCS er det system, der bestemmer satellittens orientering (attitude) og styrer, hvordan den peger. For at evaluere ydeevnen er der opbygget et simuleringsmiljø for AAUSAT3 i MATLAB Simulink som et bibliotek. Biblioteket er gjort genbrugeligt, så det nemt kan udvides til fremtidige satellitter. Der er udviklet en hardwareprototype til at afprøve udvalgte sensorer og aktuatorer: et 3-aksers magnetometer, et 3-aksers gyroskop, solsensore og magnettorquer (elektromagneter, der interagerer med Jordens magnetfelt). Afhandlingen foreslår en kvaternion-baseret Unscented Kalman-filter (UKF) til attitudebestemmelse med et lavpris, standard sensor-setup. Implementeringen er gjort tilgængelig for andre CubeSat-udviklere via pseudokode, og resultaterne indikerer, at man kan opnå acceptabel attitudebestemmelse selv under skyggeperioder uden sollys (eclipse), hvis sensorernes bias (systematiske afvigelser) estimeres. Det vises desuden, hvordan pålidelig afspin (detumbling) kan opnås med en B-dot-regel, som sammen med en permanent magnet giver 2-aksers attitudestabilitet i forhold til det lokale geomagnetiske felt. Afhandlingen skitserer også idéer til en globalt stabiliserende attitude-erhvervelsesregulator baseret på modelprædiktiv regulering (MPC) og beskriver udfordringer forbundet med magnetisk aktuation og ikke-lineær MPC.
This thesis develops and analyzes an Attitude Determination and Control System (ADCS) for CubeSats, motivated by the needs of AAUSAT3, Aalborg University’s next satellite. ADCS determines a satellite’s orientation (attitude) and controls how it points. To evaluate performance, a simulation environment for AAUSAT3 was built as a MATLAB Simulink library. The library is designed to be reusable and easily extended for future satellites. A hardware prototype was created to test selected sensors and actuators: a 3-axis magnetometer, a 3-axis gyroscope, sun sensors, and magnetorquers (electromagnets that interact with Earth’s magnetic field). The thesis proposes a quaternion-based Unscented Kalman Filter (UKF) for attitude estimation using a low-cost, off-the-shelf sensor setup. The implementation is made accessible to other CubeSat developers through pseudocode, and results indicate acceptable attitude estimation even during eclipse (periods without sunlight) when sensor biases (systematic offsets) are estimated. It is also shown how reliable detumbling (stopping uncontrolled rotation) can be achieved with a B-dot control law, which, together with a permanent magnet, provides 2-axis attitude stability relative to the local geomagnetic field. Finally, the thesis outlines ideas for a globally stabilizing attitude acquisition controller using model predictive control (MPC) and discusses challenges associated with magnetic actuation and nonlinear MPC.
[This abstract was generated with the help of AI]
Keywords
Attitude Determination and Control System ; ADCS ; CubeSat ; AAUSAT3 ; Matlab Simulink simulation environment ; satellite ; quaternions ; Unscented Kalman Filter ; UKF ; Extended Kalman Filter ; EKF ; SVD-method ; Wahba's problem ; Detumbling ; B-dot ; 2-axis attitude stability ; globally stabilizing attitude acquisition ; Model Predictive Control ; MPC ; Nonlinear MPC ; magnetic actuation ; ADS ; ACS ; Attitude estimation ; MPC with re-linearization
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