Control of a Planar Satellite with an Unactuated Movable Solar Panel

In this paper, the dynamic behavior of a satellite with an unactuated movable solar panel is examined as governed by two different controllers. This two-body system is dynamically underactuated because it has two outputs of concern, which are the angles of the satellite and the panel, but it has only one actuator, which is the reaction wheel attached to the main body of the satellite. Nevertheless, this system is still stabilizable owing to the spring supported joint of the panel. To describe and discuss the panel-satellite interactions plainly and clearly, a planar dynamic model is preferred. Thus, it has been possible to get an idea quickly about the effects of the stiffness of the panel joint spring and the type of the implemented controller on the attitude control of the satellite. However, a similar study can as well be extended without much difficulty to the general case of a multi-panel satellite with three-dimensional attitude control requirements. In this work, two different controllers are studied by assigning three different values to the stiffness of the spring between the panel and the satellite. With the support of the simulation results, this work has led to the conclusion that, if the spring is stiff enough, it is possible to implement the simple controller that requires feedback only from the satellite motion. On the other hand, if the spring is not very stiff, then it becomes advisable to implement the complicated controller that requires feedback not only from the satellite attitude but also from the relative panel motion, which further requires either extra sensors to use or an observer to implement. In this work, the complicated controller is implemented together with an observer

Measurement correction of a set of analog sun sensors via neural network

A Neural Network (NN) based method to improve the accuracy of a set of analog Sun sensors is presented. Analog Sun Sensors are commonly used on satellites due to their reduced cost, small size and low power consumption. However, especially in Earth imaging satellites, they are prone to the Earth albedo effects. Magnitude and direction of albedo change depending on the reflection characteristics of the Earth's surface, position and attitude of the satellite and position of the Sun. The albedo may deteriorate Sun direction measurements by the analog Sun sensor as much as 20°. In this study, a multilayer NN, which is trained using the Sun direction vector and available attitude information, is applied to the Sun sensor readings to correct the voltage output for the corresponding measurements. Then the corrected Sun angles in sensor x and y axes are obtained by combining NN outputs with the sensor measurements. The proposed algorithm is tested in various simulation scenarios of differing training and interrogation periods for the NN. Results show that the Sun sensor measurements can be corrected up to an accuracy of 1° using the NN approach. Generalization of the NN by tuning the parameters enables using the same trained NN for extended durations of time