Browsing by Author "Ehrpais, Hendrik"

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Development and Performance Analysis of UKF Models for Satellite Position and Attitude Determination
(Tartu Ülikool, 2020) Kütt, Johan; Ehrpais, Hendrik; Tartu Ülikool. Loodus- ja täppisteaduste valdkond; Tartu Ülikool. Tehnoloogiainstituut
This theses focuses on the development of models of satellite physics and attitude sensors, adaption of environmental models to be used in a highly optimised UKF algorithm for satellite attitude and orbit determination and the performance analysis of the system based on simulation data. During the writing of this theses a basic framework was set up to adapt the UKF algorithm for use in a satellite attitude determination environment and the star tracker, gyro and sun sensor models were developed. Several environmental models were adapted to work with the sensor models. Regarding orbital dynamics, a satellite communication ground station based orbital position correction method was proposed that, according to the knowledge of the author, has not been used on small satellites before. The method utilises the precise measurement of the communication signal return time to apply a correction factor to the orbital location of the satellite. To test the method, a ranging sensor model was devised. All sensors and the sensor fusion capability of the UKF were tested under varying operating conditions, which included different sensor combinations, sensor errors and different attitude manoeuvres. The required simulation data was generated using a simulation environment developed by the author. It contains the necessary physics and environmental models to produce realistic data. All models and the UKF algorithm were found to work well and the results match the accuracy configurations of the different sensors. The ground station ranging based orbital correction was shown to work well with considerably larger errors than would be encountered in actual orbit.
EST-Cube-1 in-orbit attitude determination validation
(Tartu Ülikool, 2015) Ehrpais, Hendrik; Slavinskis, Andris, juhendaja; Kuuste, Henri, juhendaja; Tartu Ülikool. Loodus- ja tehnoloogiateaduskond; Tartu Ülikool. Füüsika instituut
ESTCube-2 attitude and orbit control system design
(Tartu Ülikool, 2017) Ehrpais, Hendrik; Slavinskis, Andris, juhendaja; Tartu Ülikool. Loodus- ja täppisteaduste valdkond; Tartu Ülikool. Tehnoloogiainstituut
This thesis presents the design and analysis of the attitude and orbit control system for the ESTCube-2 CubeSat. The objective of the system is to spin up the satellite to high angular rates, perform accurate pointing and should also be able to operate outside of the Earth’s magnetic influences, for example in a Lunar orbit. For this thesis various requirements for the subsystem and payloads of the nanosatellite have been gathered. From these requirements the design drivers for the attitude and orbit control system are identified. Additionally the thesis analyses the ESTCube-1 nanosatellite attitude determination and control performance and presents the lessons learned, which provides input to the design of the ESTCube-2 nanosatellite. Based on the requirements a set of actuators and sensors are presented that fulfil the various ESTCube-2 mission objectives. The thesis also covers the attitude estimation process. This is done by describing the data generation from the simulation environment and the different potential algorithms to be used for sensor fusion. A sensor fusion algorithm for nanosatellite attitude determination is proposed and the first implementation was made to work on the ESTCube-2 microcontroller. Initial results for the algorithm are described and the future improvements are identified.