Nor Hazadura Hamzah

Mathematical model and attitude estimation using Kalman filter technique for low earth orbit satellite

In space, attitude analysis of a satellite is constantly being computed within the system of the satellite. In this paper, a rigorous derivation of mathematical model of satellite’s attitude with gravity gradient moment, which is inherent in low-orbit satellite is presented. Additionally, attitude estimation using Kalman filter technique is employed to predict the actual satellite’s attitude despite the noise presence in the system. As for demonstration purpose, a simulation of the attitude estimation via Kalman filter is carried out using MATLAB software. Through the simulation result, the importance of filtering technique for attitude estimation is realised.

Analysis of the residual between the model and the data using autocorrelation function for satellite attitude estimation

Objective of this paper is to investigate whether the noise in attitude dynamics model and measurement model is Gaussian white noise process or not. This is important because if the assumption regarding the noise is wrong, this will lead to unreliable and inaccurate estimation. The residual between the standard model and the real data is computed and is analyzed using autocorrelation function via Minitab software. The result shows that the error in the attitude dynamics model is not Gaussian white noise, while the error in measurement model is Gaussian white noise.

A study on correlation between ECI and satellite’s velocity based on RazakSAT data

This paper presents the analyzed on Earth Centered Inertial (ECI) of Attitude Determination System (ADS) and satellite velocity data of RazakSAT by using analysis method. ADS are one sub-system in satellite as function to control the orientation of satellite relative with inertial references frame. ECI is one of inertial references frame of RazakSAT with three dimension axis. ECI and velocity of satellite data of RazakSAT are analyzed with normality test by using Minitab software. The results show ECI and velocity data of RazakSAT are non-normal distribution, and correlation between ECI and satellite velocity is ellipse shape.

Unmodeled disturbances torque exerted on RazakSAT’s attitude during sun tracking mode

In space, environmental torques exerts continuously on a satellite and may influence and affect the satellite’s attitude dynamics. The relative strength of the various torques will depend on both spacecraft environment and the structure of the spacecraft itself. RazakSAT is the world first remote sensing satellite launched into Near Equatorial Orbit (NEqO). Hence, the objective of this paper is to study the properties and behaviour of disturbance torque that perturb RazakSAT’s attitude during orbiting in NEqO in sun tracking mode using in-flight attitude data. The results show that the environmental torques exerted on RazakSAT during sun tracking mode is periodic and the magnitude of the torques vary from 10−4 to 10−7. Understanding the behaviour of disturbance torque can be utilized in spacecraft design to improve the satellite’s performance for future mission.

Updated model of RazakSAT’s attitude during sun tracking mode using time series

The accuracy of control and estimation tasks can strongly depend on the accuracy of the underlying model. In space, there are many sources that contribute to the uncertainty in the dynamics model of satellite attitude. Hence, the aim of this paper is to update the dynamical attitude model using grey modeling technique. In this paper, the residual error between the nominal dynamics model and in-flight attitude data is modeled using time series data analysis. Then the time series model of the residual error is augmented in the nominal dynamics model. The updated model is simulated and its performance is analyzed. The results show that the updated model is adequate describing the data.

omparative Study of Extended Kalman Filter and Particle Filter for Attitude Estimation in Gyroless Low Earth Orbit Spacecraft

This paper presents attitude determination using a designed observer for gyroless Low Earth Orbit spacecraft using two different estimation approaches which are Extended Kalman Filter (EKF) and Particle Filter (PF) algorithms. This designed system contributes as an alternative or backup system during rate data absence resulted from the unexpected failure of existing gyros. The performance of EKF and PF as the estimator in the observer are compared in terms of statistical and computational aspects. The performance of the nonlinear observer to estimate the states is also verified using real flight data of Malaysian satellite.

The study of gravity gradient effect on attitude of low earth orbit satellite

Simulations and mathematical models are increasingly used to assist the process of decision making in engineering design. The objective of this paper is to simulate the linear attitude dynamics of small satellites under gravity gradient torque which is inherent in low earth orbit. The equations were first derived in their nonlinear form, and then manipulated and simulated in their linear form. Simulation results demonstrate the importance of choosing the appropriate values of satellites moment of inertia in designing phase of a satellite.