Sharif Digital Repository

An autonomous method for attitude and position determination of a satellite without using data from ground stations and also without the need for human interference is proposed using the image that the satellite has taken at each moment. The proposed method is based on recognition of stable features in the image and using them in order to match the satellite image with a source image from the Earth and the latitude and longitude of the features become known.SIFT and SURF algorithms have been examined. Using the perspective equation and camera coordinate system, a model has been developed that relates the coordinates of a point in the image with its equivalent coordinates in the real world.... 

This paper presents a novel method for satellite attitude determination, using Electrostatically Suspended gyroscope (ESG). In this method, two superconducting rings rotated around a spherical rotor, which causes a variable flux in rings. So according to faraday’s law of induction, a voltage will be induced in the rings. Using this voltage and a kalman filter, attitude of satellite will be determined. ESG works precisely, when the rotor is maintain at the center of gyroscope cavity, between three pairs of circular electrode, so a backstepping control algorithm will be designed In order to this purpose. The performance of attitude determination using this ESG and designed control algorithm is... 

By using of raw measurements of GPS receivers including carrier phase and Doppler frequency we can estimate attitude parameters of a platform on which the receivers are installed in a proper orientation. In this research attitude parameters are estimated based on quaternions. To this end a discrete Kalman filter was designed to predict the attitude parameters by using of carrier phase double difference measurements and then update the predicted parameters by using of Doppler frequency double difference measurements. Doppler frequency measurements were used to estimate the quaternion rates which are used in update step of Kalman filter algorithm. A robust algorithm for carrier phase ambiguity... 

In this Thesis, attitude and orbit of a satellite is estimated using a star sensor and an earth sensor. An algorithm has been developed to estimate satellite attitude and orbit that can be implement on a satellite as strap-down hardware. This system has an uncomplicated implementation compared with platform based systems. That mentioned algorithm estimates satellite orbit by using identified star vectors via star sensor and identified earth vector via earth sensor simultaneously. It also knows the stars vectors according to Star Catalog. Attitude estimation is also executed using both star and earth sensor. It has to be said that an Unscented Kalman Filter synthesize both sensors output data... 

In this study the problem of position and attitude control of a Spacecraft has been investigated under position and attitude constraints as well as uncertainties in mass, moments of inertia, thrust vector error, and external disturbances. The Lyapunov theory is utilized for deriving the appropriate controls. Two kinds of controls are derived in the first step. The first kind has been derived using direct Lyapunov method and the second by the use of back-stepping method. Obtained simulation results prove that the first control scheme is more suitable for a Spacecraft control, since it has less computational effort, convenient selection of control parameters, and especially it has less... 

In this research, INS error will be corrected with the help of the unscented kalman filter, by combining the IMU sensors and flight consecutive images information. Measurement equation of the Kalman filter is the epipolar Constraint of geometry of two consecutive images of the camera. In epipolar Constraint, the common points of two consecutive images of the camera field of view have an important role. This points will be extracted by SIFT and SURF algorithms. These algorithms have many mistakes in the process of images matching, but in this research, a solution based on the error covariance of the position of the ground point corresponding to the two common points of two images is presented... 

One of the most dangerous phases of the flight is landing. Newly automatic landing is noticed. The vital element in an automatic landing system is navigation system. In this document, a PL/INS/DGPS auto landing system is introduced.In a PL based navigation system, accuracy is highly under the influence of relative geometry between PLs position and flight path. Therefore, it is necessary to locate PLs on the best position. An optimization is used to find PLs best configuration that increases the navigation performance. Tightly coupling of INS and GPS/PL is preferred, because some problems lead to GPS satellite signal unavailability  

Pregroups as a mathematical structure, are replacement for Lambek's type caregorial grammar which much used in Computational Linguistics. Because of computational and logical properties of pregroups, we can use them as strong tool to analyse the sentence structure of many natural languages. This kind of analysis has been done for English, French, German, Polish, Italian, Arabic and Japanese. In case of Persian language, analysis of simple and compound sentences structure with simple tense verbs and explicit subjects and objects has been studied. In this M.Sc. thesis, we will extent analysis of Persian sentence structure to sentences with compound tense verbs and implicit subjects and objects... 

An ontology is a formal description of a domain by definition a set of concepts and the relationships between those concepts. Ontologies defined by different applications usually describe their domains in different terminologies,even when they cover the same domain. Thus, we need to resolve the semantic heterogeneities problem and align terms in different ontologies. Ontology alignment plays the central role in these areas to identify correspondences among elements of two or more ontologies. It should be noted that,finding an optimize mapping between two ontologies with respect to search space is an NP-hard [6] problem.
In This thesis we focused on large ontologies and alignment among...