فهرست مطالب مسعود ابراهیمی کچویی

In the last decades, the visual navigation system has been investigated by many researchers as an aided navigation system for Inertial Navigation System (INS) in the Unmanned Aerial Vehicles (UAV). In this research, for improving the INS errors a new approach based on feature tracking algorithm is used. In this approach, in order to estimate the feature points in the current image, the INS states, the feature points of the previous image and dynamic equations are used. Also, in this approach, for improving the estimation of terrain points, the outlier estimated feature points delete. Furthermore, in this article, for improving the altitude error, a barometer is used by the mentioned vision navigation system. The simulation results illustrate the desirable accuracy of the vision system and barometer observations in the update step of Extended Kalman Filter (EKF) and remarkable performance of integrated navigation system for calculating the UAV navigation parameters.

The present study aims to present a safe, robust and fast orbital rendezvous guidance. The scheme improves the rate of convergence to equal point until the chaser spacecraft reaches the proximity target. Then, the robust guidance structure is transformed in order to avoid singularity and provide safe rendezvous for reaching the target. Switching is conducted in the guidance scheme by utilizing a self-defined sign function. Moreover, a new modified saturation function is employed instead of the discontinuous part of the sliding mode. The Lyapunov function approach guarantees the asymptotic stability. Numerical simulations are conducted by both linear and nonlinear models of relative dynamics. Mean anomaly, angular velocity, and eccentricity of target orbit are considered as the uncertainties. Finally, the results indicate the performance and robustness of the proposed guidance in the presence of non-linearity, uncertainties, and disturbances, compared to the conventional sliding mode.

The main objective of this research is to improve the distribution of electrical potential on spacecraft surfaces by changing the surface coatings to reduce the risk of electrostatic discharge in the spacecraft. For this purpose, SPIS software, the EU standard software for modeling and simulating the interaction of space plasma with the spacecraft is used. The spacecraft has 8 nodes, and each node is related to a particular substance. The simulations were compared with the variation in the materials of these nodes in terms of differential electric and floating potential. Investigating materials that differed in the differential electric potential of zero showed that they are conductive materials. In order to choose among several conductive materials, these materials were compared in terms of electric floating potential. Simulations on satellite surfaces showed an average of 11% improvement in the electrical potential on surfaces

Dielectric barrier discharge (DBD) plasma actuators are one of the new devices for active flow control, which has received substantial attention during the last decade. The performance of the actuator is optimum when it induces the highest velocity per unit of power consumption. Since the induced velocity and the power consumption of the actuator depend on many different variables, finding the optimal set, which results in the best performance, is of immense importance. In this paper, in order to optimize the performance of these actuators, at first, by using full factorial design of experiments the effect of electrical variables (including voltage and frequency) and geometrical variables (including the gap between electrodes, dielectric thickness, and covered electrode width) on induced flow velocity and power consumption in steady actuation is experimentally investigated. Then, by using the multi-layer perceptron neural network, a model is created for the ratio of induced velocity to power consumption. The model is validated both statistically and experimentally. The results indicate that the coefficient of determination for training and test data is higher than 95 percent. Finally, the surrogate model is optimized by genetic algorithm and the optimal value of electrical and geometrical variables is determined. In order to validate the result, an actuator is designed based on the optimal set of variables and it’s ratio of velocity to power is measured to be 29.71 (m/s)/(kW/m). The difference of 3 percent between the measured and the predicted value demonstrates high accuracy and correctness of the proposed model and method.

Inertial navigation system error increases due to sensor errors with the increase in time. Usually, to prevent the growth of navigation system error, inertial navigation systems are integrated with sensors or auxiliary systems. The importantly aided system is GNSS. Because of GNSS outage or its invalidity, the other auxiliary sensors are used to increase the accuracy of the inertial navigation system. In this article, the types of methods which are used by imaging camera for navigation or for the accuracy improvement of an inertial navigation system for UAVs are discussed. After reviewing the literature in the field of vision navigation in UAVs, the proper classification for vision navigation methods and the development of these methods are presented. In UAVs, the vision navigation techniques are based more on Map metric, optical flow, feature tracking, odometers and simultaneous localization and mapping.

Satellite Thermal Control subsystem has the responsibility of maintaining the temperature of different parts and other subsystems in an allowable range. The purpose of this paper is to optimally design the satellite thermal control subsystem. In order to achieve this goal, at first a software for thermal analysis of satellite was developed and validated. Receiving orbital data and Satellite’s properties, the software simulates the position of the satellite in any desired orbit and calculates input and output thermal flux. Meanwhile, the software calculates the temperature of each sides of satellite in cold case and hot case. At the end, it computs the minimum and maximum temperature of the satellite. Combination of three commonly used thermal control methods for small satellite was used. Insulation thickness, thickness of radiator’s cover, and the power of radiator are considered as design parameter and allowable temperature of surfaces (minimum and maximum allowable temperature) are considered as design constraints. A weighted function of mass, cost, and power consumption of thermal control system are chosen as objective function that can be an indicator of the cost. Sequential Quadratic Programming as a powerful method in nonlinear optimization was used to optimize thermal control properties.The results demonstrated that the objective function improved dramatically comparing to initial design. High speed, appropriate precision, and extensibility of this software to thermal control design of vast majority of small satellites, makes this research superior. Therefore, this software could be cooperated as the thermal control design module in multidisciplinary design optimization of satellites.

Processor memory capacity and update frequency are one of the main restricting constraints in star tracker design and development. In order to decrease the volume of the data required onboard, uniforming the star catalog which is eventually used as pattern recognition database is considered. Three different methods of uniforming the star catalog have been applied. Spherical patches, fixed slope curve and charged particles or Thomson’s problem. After generation of a sphere with uniform distribution of points, a star is assigned to each point according to its spherical distance or best magnitude. In order to evaluate the performance of each method, seven evaluation criteria are defined. Point distribution minimum energy, catalog size, minimum star required for pattern recognition, mean and standard deviation of star distribution in each frame, database size and pattern recognition true recognize percentage. These seven criteria are combined in weighted equation of “average” to choose the best star catalog uniforming method with respect to the star tracker mission. After having implemented the average equation it is demonstrated that uniforming the star catalog using charged particle or Thomson’s problem has better results.