Development of an advanced nano-satellite VELOX-II : attitude control system

The VELOX series of satellite was started in Nanyang Technological University as an initiative to train it undergraduate students in space technology. The attitude of satellite refers to its orientation in space. Attitude Determination and Control System (ADCS) consists of Attitude Determination System (ADS) and Attitude Control System (ACS). ACS is responsible for achieving the desire orientation with the help of on board reaction wheels and actuator. An ADS is responsible for determining current orientation with the help of sensors such as GPS, Gyroscope. However just relying on Gyroscope to measure body rate would be insufficient. When the Gyroscopes fail, there is no way to find out the body rate of the satellite. If we are unable to determine or estimate the body rate, it would not be possible to control the movement of the satellite. Hence, this paper presents the method to estimate the body rate with the use of Magnetometer and Accelerator sensors. Firstly three methods namely the method of estimating body rate using sun sensor, Error Quaternion method and Quaternion method were put to simulation. The input to the simulation was the body rate and using ODE to extract the position of the satellite. By using the quaternion approach, it is able to determine the body rate of the satellite. From the simulation, it was found that the limitation of the sun sensor method was, it able to estimate the body rate up to rotation on two axes of the satellite. However, the simulation results of the other two methods have proven to be able to determine the body rate of the satellite. The method using Quaternion method was then further developed. To be able to test the algorithm in real time, the quaternions were extracted from Magnetometer sensor vector and Accelerometer sensor vector using TRIAD. The method was then further modified and improved to remove the noise and to provide better estimation of body rate, while satellite is rotating at different speed about its three axes.Bachelor of Engineerin