Journal of Space Science and Technology
Year:2012 | Volume:5 | Issue:2 (11)|Papers Count:8

In this study, a fault tolerant Attitude Determination System (ADS) has been designed which provides fault detection, isolation and tolerant abilities in this system. Suggested approach is based on derivation of all possible rotations between body and orbital frames and comparison of Euler angles provided by them. In this regard, significant changes in the variance of Euler angles set are considered as criteria for fault detection. Moreover, fault isolation and tolerant mechanisms are based on classification of rotation matrices which are not affected by faulty components. The above features present a quite analytical and computational approach which does not impose additional mass, power consumption and cost in the satellite. Also, designed diagnosis and fault correction algorithms are model-free based mechanisms which always provide tolerated attitude angles for the attitude control subsystem. The mentioned abilities combined with the model based FDI mechanisms utilized in the attitude control system, provide an advanced decision support system capable of isolation of faults which have been simultaneously occurred in the satellite sensors and actuators. Finally, performance of the designed algorithm is approved by simulation results.

Star trackers are one of the most accurate attitude determination devices of a spacecraft. Star trackers are able to determine the spacecraft attitude with the use of recognizing the stars within their field of view. One of the major subsystems of star tracker software is the star pattern recognition algorithm. In this research a novel star pattern recognition algorithm called Non-Dimensional is considered. This algorithm can recognize the stars within its field of view without using the information of camera calibration. In order to fulfill this goal, the algorithm requires a database which contains the star inertial information. Afterwards a fast search method is used to compare the combinations on the image with database. Eventually there has been a tradeoff between database volume and the update frequency for a better performance.

Flexible manipulators have plentiful applications in Aero-Space fields, due to their less weight and maneuverability. In fact, the ratio of their load carrying capacity to their weight, make them more excellent over their rigid ones. Moreover, these manipulators are known as good candidates in Aero-Space applications because of their less energy consumption, and smaller actuators. In this paper, the dynamic modeling of the flexible manipulators are performed using Finite Element Method (FEM), and optimal control of point-to-point motion of robot is done via optimal control method. To dynamic modeling of flexible manipulator, each link of the robot is divided into sufficient elements, and total displacement of the element is presumed as summation of a rigid displacement and a displacement because of flexibility. By means of Lagrange’s principle, dynamic equations of the flexible robot are derived, and the effect of number of the on dynamic motion of the robot is considered. Also, for the optimal point-to-point motion planning of the elastic manipulator, the nonlinear dynamic equations of the robot is assumed as constraints of optimal control problem, and a proper cost function is defined including torque and speed terms. Then, variation of calculus and Pontryagin’s minimum principle are employed and optimality conditions are resulted in a set of nonlinear differential equations, which is solved numerically. The priority of the optimal control method on the optimal motion planning of the flexible manipulator is discussed, and simulations for a single-link elastic robot illustrate the applicability of the method.

The international system proposed the liability convention 1972 for compensating damages occurred while utilizing space. However, certain key principles of liability such as some rules of conflict law and jurisdictions have been neglected there. This convention failed to provide a unified regime like that of established by the Warsaw system for air carrier liability against passengers and cargo. Because of this failure and due to the international nature of space activities, during the past two decades, states inclined toward bilateral and multilateral space agreements for determining liability and compensating probable damages. In this paper it is argued that international law system is capable of finding common points in the said agreements and taking a new step toward uniformity of international regulations of space liability by modifying the convention 1972.

The goal of this paper is presenting a methodology for reliability allocation to launch vehicle subsystems using Analytical Hierarchy Process (AHP) method in conceptual design phase. In this methodology, the goal function is reliability and the main considered criterions are technology, complexity, operational time of each subsystem and cost. For applying AHP method to launch vehicle subsystems reliability allocation, a Matlab code ( for investigating compatibility and determining allocation weight factors by employing Matrix Eigen Vector Method) and a Excel sheet (for forming the comparison matrix) are employed. To this point, by using the outcomes of liquid-propellant launch vehicle conceptual design software (LVCD) which developed by authors, the launch vehicle specifications and operational time of each subsystems is derived and is feed to this methodology as input. The results of applying this method to launch vehicle reliability allocation for the second stage of a launch vehicle, shows the error of this method below 2%. It is clear that this small error in reliability issues in conceptual design phase is acceptable.

In this paper the performance of a three Degrees Of Freedom simulator is evaluated. This platform is considered as an important instrument generally used in performance tests of spacecraft attitude determination and control subsystem on the ground. A hemispherical air bearing is used to provide micro gravity condition. Reaction wheels produce required control torques and an integrated sensor is used for attitude determination. Commanding and visualization of the platform in monitoring station are provided by a wireless LAN. PD, QEF and LQR controllers are designed and implemented for slew maneuver to show the ability of the simulator. The desired attitude accuracy is obtained using these controllers. The test results verify the designed controllers and show the ability and functionality of the system, as a simulator for evaluating attitude controllers.

Outer space ballistic missiles use thrust vector control system and it is because aerodynamic surfaces are not efficient in thin air. Flexible joint is the most useful type of thrust vector control system through satellite transporters and ballistic missiles based on solid fuel. Most common type of elastomer in these structures is rubbers and especially natural rubber, which require special preparation and cure processes. The goal defined in this article is to introduce a process which is much easier to apply. Based on flexible joint design in Japanese MV booster missile, an elastomer based on polyurethane resin, which is easily applicable and consists of two liquid parts, is used instead of original Polyisoperne. This elastomer has achieved a good rank in both sealing test in eight-bar pressure and hydrostatic test in the pressure of 70 bars. It also has been fire tested and the results were satisfactory.

In this study, solid rocket motor internal ballistic, has been investigated. Flow field consists of internal grain space and converging-diverging nozzle. Axisymmetric, compressible and transient Euler equations have been considered as governing equations and erosive burning has been considered as an important phenomenon in solid rocket motors. Fluent software and its moving mesh capability have been used to flow field modeling. At the first time, an appropriate UDF has been utilized to achieve a good simulation of erosive burning. The results show very good agreement with other numerical results.