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Improving the guidance, navigation and control design of the KNATTE platformLundström, Lars January 2023 (has links)
For complex satellite missions that rely on agile and high-precision manoeuvres, the low-friction aspect of the space environment is a critical component in understanding the attitude control dynamics of the spacecraft. The Kinesthetic Node and Autonomous Table-Top Emulator (KNATTE) is a three-degree-of-freedom frictionless vehicle that serves as the foundation of a multipurpose platform for real-time spacecraft hardware-in-the-loop experiments, and allows emulation of these conditions in two dimensions with the purpose of validating various guidance, navigation, and control algorithms. The data acquisition of the vehicle depends on a computer vision system (CVS) that yields position and attitude data, but also suffers from unpredictable blackout events. To complement such measurements, KNATTE incorporates an inertial measurement unit (IMU) that yields accelerometer, gyroscope, and magnetometer data. This study describes a multisensor data fusion approach to obtain accurate attitude information by combining the measurements from the CVS and the IMU using nonlinear Kalman filter algorithms. To do this, the data fusion algorithms are developed and tested in a Matlab/Simulink environment. After that, the algorithms are adapted to the KNATTE platform and their performance is confirmed in various conditions. Through this work, the accuracy and efficiency of the approach can be checked by numerical simulation and real-time experiments. In addition, the quality of the CVS measurements are further improved by the introduction of a neural network to the image processing pipeline of the original system.
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Wheel-terrain contact angle estimation for planetary exploration roversVijayan, Ria January 2018 (has links)
During space missions, real time tele-operation of a rover is not practical because of significant signal latencies associated with inter planetary distances, making some degree of autonomy in rover control desirable. One of the challenges to achieving autonomy is the determination of terrain traversability. As part of this field, the determination of motion state of a rover on rough terrain via the estimation of wheel-terrain contact angles is proposed. This thesis investigates the feasibility of estimating the contact angles from the kinematics of the rover system and measurements from the onboard inertial measurement unit (IMU), joint angle sensors and wheel encoders. This approach does not rely on any knowledge of the terrain geometry or terrain mechanical properties. An existing framework of rover velocity and wheel slip estimation for flat terrain has been extended to additionally estimate the wheel-terrain contact angle along with a side slip angle for each individual wheel, for rough terrain drive. A random walk and a damped model are used to describe the evolution of the contact angle and side slip angle over an unknown terrain. A standard strapdown algorithm for the estimation of attitude and velocity from IMU measurements, is modified to incorporate the 3D kinematics of the rover in the implementation of a nonlinear Kalman filter to estimate the motion states. The estimation results from the filter are verified using tests performed on the ExoMars BB2. The obtained contact angle estimates are found to be consistent with the reference values.
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