An assessment of the orbital elements of RazakSAT for attitude determination using extender Kalman Filter

Malaysia has successfully developed and launched RazakSAT, the first mini satellite at the Near Equatorial Orbit (NeqO). The mission was focus on a technology demonstrator and one of the payloads is a high-resolution camera to capture images at the equatorial region. The purpose of RazakSAT’s Attitude Determination System (ADS) is to ensure that the orientation is relative to Earth. Any misalignments or disturbances on the ADS can affect the orientation of the satellite in terms of the orbital position. Therefore, this research focuses on determining the attitude of a satellite in order to determine the orbital position for control requirement purposes. However, conducting experiments in the space environment to determine the accuracy and computation time is impossible due to cost constraints and the fact that facilities are scarce resources. As RazakSAT data is NEqO based orbits, so it proposed to use as reference to the actual data to substitute for the experiments in the space environment. The main aim is to give accurate information and computation time for the attitude estimation of ADS. In this thesis, RazakSAT data are used as a reference to give accurate information and computation time for the attitude estimation of ADS. Keplerian orbit model is implementing as an orbital model and compares with the NEqO of RazakSAT data. Besides that, Satellite Tools Kit (STK) software were used to conduct and validate the reliability analysis for orbital elements of RazakSAT such as the Earth-Centered Inertial (ECI), Earth Centered Earth Fixed (ECEF) and Latitude Longitude Altitude (LLA) based on the Two-Line Element (TLE) provided by Astronautic Technology Sdn Bhd (ATSB). The sun vector and magnetic field vector in the field in the orbit frame were analysed using the sun model, and International Geomagnetic Reference Field (IGRF). The sun vector in the body frame is the measurement from the sun sensor and magnetometer. The result on ECI and ECEF was analysed as well using the STK. The Keplerian orbit model was found to be more accurate than STK for LLA where the error yield is less compared to the Keplerian orbit model. The overall result for ECI, ECEF, and LLA is less than 5%, which also meets the error requirement of ATSB for RazakSAT orbit. For the sun model analysis, due to the difficulties in obtaining information about the RazakSAT sun sensor from ATSB, the analysis for the sun model utilized the results from STK and mathematical model developed in this thesis. The result shows that the percentage error for the sun in the orbit frame and body frame is acceptable, less than 5%. The magnetic field in the body frame and orbit frame from STK is more accurate compared to IGRF model. From the overall orbital results, RazakSAT was found are able to fulfill the requirement of the orbital specification while entering its orbit. For the attitude estimation of the satellite, a recursive approach known as an Extended Kalman Filter (EKF) is used to estimate the attitude. In this thesis, the kinematic and dynamics models for the EKF method are derived and analyzed in terms of controllability, observability, and stability. The result proved that the model could be controllable, observable, and marginally stable condition where it can be used for estimation by using EKF.