Optimization of geosynchronous satellite constellation for independent regional navigation and positioning in Middle East region

Regional Navigation and positioning systems using geosynchronous satellites are emerging for different parts of the world. Optimal constellation geometry achievement for a set of geosynchronous satellites is a key sector in designing of such systems. Genetic algorithm is applied for optimization of constellations with 6 and 7 satellites which is to be used in Middle East region where these systems have been deprived of. Based on the fact that the coverage criterion is not sufficient enough to guarantee a good navigation service, positioning process by the satellite systems is discussed and the performance of the system on the basis of position dilution of precision is collected as the fitness criterion. Placing the satellites in groups to pass over the same ground track is applied as a constraint to the genetic algorithm. By simulation, performance of the best obtained results and GPS are compared in terms of position dilution of precision, visibility and the required epochs (time span) to resolve the ambiguities with a 99% success rate, in this region. Also, capability of the GA for such problems is demonstrated.     

Modeling the ionospheric gradient by using VSS base functions and GPS data over Iran

The spatial and temporal variations of ionosphere play an important role in positioning and navigation by the space geodetic techniques. Therefore, the ionospheric gradient should be calculated, analyzed, and applied in both space and time. Spatial gradients of the ionosphere have remarkable delay on the propagation of electromagnetic waves. This study intends to propose a new method for simultaneous modeling of the spatial gradients of ionosphere and VTECs in the local scale for Iran. Vector Spherical Slepian (VSS) base functions are used for the development of this method.Five VSS models with the maximal degrees of L = 30, 35, 40, 45 and 50 are taken into account. For implementing the VSS method, 24 permanent GPS stations from the Iranian Permanent GPS Network (IPGN) have been used. The unknown coefficients are estimated with the observations of these stations with least squares technique. Four other stations are used for evaluating the accuracy of the models. Repeatability of baselines is the measure that is used for this purpose. Based on the results obtained, L = 40 is the optimum degree for the VSS model with this input data over Iran.The baselines’ repeatability showed that ionospheric gradients have more influence on the north–south component. Moreover, the spatial gradient is negligible in the east–west and up-down component when a short baseline is processed. In other words, this kind of ionospheric modeling has significant application for baseline, which is longer than 1000 km. In the study, proposed method has improved the long baselines' solution by more than 12%, 18% and 10% in east–west, north–south and up-down components, respectively.     

Experimental Investigation of the Effects of Various Plasma Actuator Configurations on Lift and Drag Coefficients of a Circular Cylinder Including the Effects of Electrodes

In this paper, the effects of the existence of plasma actuator electrodes and also various configurations of the actuator for controlling the flow field around a circular cylinder are experimentally investigated. The cylinder is made of PVC (Polyvinyl Chloride) and considered as a dielectric barrier. Two electrodes are flush-mounted on the surface of the cylinder and are connected to a DC high voltage power supply for generation of electrical discharge. Pressure distribution results show that the existence of the electrodes and also the plasma are able to change the pressure distribution around the cylinder and consequently the lift and drag coefficients. It is found that the effect of the existence of the electrodes is comparable with the effect of plasma actuator in controlling the flow field around the cylinder and this effect is not reported by other researchers. Eventually it is concluded that the existence of the electrodes or any extra objects on the cylinder and also the existence of the plasma are capable of changing the flow field structure around the cylinder so that the behavior of the lift and drag coefficients of the cylinder will be changed significantly.