Journal of Space Science and Technology
Year:2012 | Volume:5 | Issue:1|Papers Count:9

The increase in capability and performance of digital cameras, processors and image processing algorithms has caused vision-aided navigation of aerial vehicles to be a hot research of interest. In order to determine pose parameters form vision-aided navigation methods, it is common to use automatic image registration using information of reference databases. However, solving registration issue in automatic navigating of aerial vehicles has been considered a complex manner. In this paper, a novel method for vision-aided navigation of aerial vehicles to increase reliability and accuracy of geo-referencing aerial image is proposed. To have robust evaluation, different aerial images with variety of conditions are utilized to assess this method. Obtained results show high performance of proposed method to solve issues related to automatic GEO-referencing of aerial images.

Instantaneous grain geometry is one of the most affecting parameters on the performance of the solid rocket motors (SRMs). This paper presents the simulation of geometrically complicated solid propellant grain burn back using the level set method. The initial form of the grain is assumed in this method. Propagation of the grain boundaries in a velocity field is described using the Hamilton-Jacobi type equation. The solution of this equation in successive time steps gives the new burning boundaries of the grain. For this purpose, the initial geometry of grain is modeled in any CAD software. Then, the initial burning surfaces of grain are implicitly defined by the sign distance function and are used as the initial conditions of the level set equation. The geometrical characteristics of grain, such as burning surface area, port area, burning perimeter, and port volume are determined by Heaviside and Delta Dirac functions. The result of simulation is validated by an analytically predictable case, which shows excellent agreement. Burn back analysis is done for some practical grains including two cases that the test data were available. Using an unsteady zero dimension interior ballistic analysis, the resulting motor pressure curves are compared with the experimental data showing good agreement. The capability of the approach to handle the analyzing of problems, including non uniform burning velocity and arbitrary burnout configurations of grain are shown in examples.

A Fault Tolerant attitude control system has been designed in this paper, which provides abilities of fault detection, identification and recovery. For this purpose, nonlinear dynamics of satellite is modeled based on Takagi-Sugeno method, which enables us to extend advantages of linear adaptive observer for nonlinear dynamics of satellite. In the designed adaptive observer, occurrence of fault in satellite reaction wheels are estimated based on an adaptive law which provides abilities of fault detection and identification in these actuators. Also, a back stepping feedback linearization control law has been applied for recovery which uses estimated fault term provided by adaptive observer as a compensation term in control law. So, bounded error of attitude control has been guaranteed even in faulty conditions. Finally, fault detection, identification and recovery algorithms have been verified by simulation results.

In this paper the mechanical behavior of satellite carrier adapter made of composite lattice shell is examined. First, the geometrical parameters of the composite lattice shell are analyzed. Choosing the direction for winding the fibers (geodesic route), geometric equations of the structure is elicited. Then, stiffness matrix of the structure is obtained according to these equations. Finally using finite element modeling of a conical lattice shell sample, the comparison between finite element and analytical results are presented. The analytical and numerical results show that with increasing rib's thickness and Width, axial strain of the structure decreases nonlinearly.

Relative motion of satellites in a formation can be studied in several forms of dynamics models. In this paper, some of the most applicable models each implying particular assumptions, constraints and specifications are described in Cartesian and orbital element spaces. Despite the significant applications of models based on linear equations of motion in modeling orbital rendezvous and ducking maneuvers, it is shown that the modeling errors of these simplified models limits their application in long term missions such as formation flying. Nonlinear equations of relative motion are derived in addition to6 other dynamical models to simulate a low earth two satellite formation with projected circular relative orbit. Models are evaluated under the effects of non-spherical earth perturbation, relative distance between the satellites, and the eccentricity of the chief orbit. Analyzing the results of simulations emphasizes the importance of accuracy of the system.

One of the most important problems that nowadays are common in aerospace societies in Iran and also around the world is how to optimize the designing of the flight objects. Since the flight objects like LVs, which are the subject of this paper, are composed of several subsystems that have influences to each others, the multidisciplinary design optimization methods (MDO) are commonly used for doing design optimization of them. In usage of the multidisciplinary design optimization methods for different objects, to select the proper optimization algorithm is one of the very important problems. In this research the conceptual design of a lightweight liquid propellant LV is done with the all at once (AAO) method. The object of optimization is to minimize gross launch weight and four disciplines of structure, aerodynamics, trajectory, and propulsion are considered. Performance of gradient based algorithm of SQP and heuristic algorithm of GA and traditional method (statistical method) by solving an example are compared and is shown that if the output of statistical method is used as start point of optimization using gradient based algorithm of SQP, the global answer will be derived.

Failures identification of vital and sensitive products and their reliability estimation, before applying affects design improvement of them. On the other hand, because of lack of data, reliability estimation of some systems such as space products is hard and sometimes impossible. Bayesian networks method is a graphical model with high efficiency for reliability estimation of complex systems and it can a/so eliminate problem of data shortage. Accordingly, at this paper, first, fault tree related to structure of launch vehicle with liquid fuel has been designed and then mapped into Bayesian networks. Finally using expert decision of system and estimation of model conditional parameters with Monte Carol Markov Chain, reliability of launch vehicle structure has been estimated.

The responsibility of the satellite thermal control system is to maintain equipments temperature in all external environments and under operational modes within an allowable temperature range. The geometric math model of satellite with available relations in references is obtained and certified with Thermal Desktop software. The outputs of geometric math model are external heating rates and radiation interchange factors. In this paper, the electrical simulation method is proposed as a tool for thermal math model of rotating satellite as equipments and structure of satellite are divided into several nodes and each term of thermal balance equation is simulated with equivalent electrical elements (capacitor, resistance, current source and etc.) and obtained circuit is solved fast and easily with HSPICE code. The values of voltage and current in each node are equivalent to temperature and heat flux, respectively. The results are illustrated the low run time with exact temperature responses of electrical simulation method in thermal modeling of satellite. By using the semi active thermal control, the thermal requirements are achieved and the effect of radiator paint is investigated.