نشریه علوم و فناوری فضایی
پیاپی 1 (پاییز 1387)

Current practical methods of pitch programming design for multi-stage launch and ballistic vehicles suffer from several deficiencies. For many applications they are often determined for various phases of ascent trajectory utilizing simplified dynamics that results in non-optimal trajectories. Trial-anderror design techniques coupled with flight simulation usually results in a more accurate pitch program, but that may not satisfy all the required constraints simultaneously and is also very time consuming. In this study, an integrated design environment is developed which enables a novice designer to generate optimal pitch program for the whole part of the ascent trajectory while satisfying all the required flight path constraints as well as the final time boundary conditions. Since, the preset guidance program is naturally known as an openloop steering program, this method utilizes optimal control theory using full nonlinear system state equations together with a functional performance index to determine the optimal steering command. Evaluation of the proposed technique is demonstrated through application on a typical two stage ballistic vehicle, for which the resulting trajectory fully satisfies all the flight related and final time constraints.

In this paper, attitude control system of an axisymmetric satellite will be designed in such a way that required stability is provided with slow spinning about yaw axis. In this regard, dynamic of motion and coupling between satellite’s axes is modeled. As a result, a closed form formula is yielded included moment of inertia ratio, angular velocity about yaw axis and pointing accuracy of control system. Then, magnetic control is designed for providing capture range of gravity gradient stabilization and requirements of pointing accuracy. Finally, fine performance of designed control system will be illustrated with simulation based on specification of a near axisymmetric satellite.

The principle goal of this paper is developing of Launch Vehicle Conceptual Design (LVCD) method based on combinational optimization of major design parameters. To this end, ten sub-algorithms will be presented in this design approach. Mass distribution of different stages to launch maximum payload mass to the orbit, pitch program trajectory to get to the maximum final velocity, and providing minimum velocity loss due to gravity, and also minimum axial acceleration of various stages of launch vehicle will be optimized as the results of the presented approach. The optimization process is performed subject to the restrictions. Also, the performance index is optimized in a mutual iteration mechanism. Evaluation and verification of the presented method is performed using available data of two and three-stage launch vehicles.

This Paper presents a dynamic model of a micro-satellite in Mesbah class. At this model aerodynamic torque and solar radiation pressure torques are considered as disturbance torques. Gravity gradient torque is assumed as stabilizing torque and acts as a passive controller. Magnetic torquers act as an active controller. There are three methods of optimization of power consumption; first using LQR controller, secondly using the mapping function (which is suggested to ensure that the generated magnetic moment by the coils is perpendicular to the local magnetic field vector), and finally powering on control system over the earth stations only for the purpose of power saving.

Multidisciplinary Design Optimization (MDO) approaches have significant effects on aerospace vehicle design methodology. In designing next generation space launch systems, MDO processes will face new and greater challenges. Needs to improve conceptual design capabilities have required an increase in the fidelity of empirical disciplinary models, improved design solutions and optimization methods, and reduced workload and design cycle time through advanced frameworks. Such a procedure could identify feasible designs and generate comparison and sensitivity data during optimization. This study uses a System Sensitivity Analysis method to optimize multidisciplinary design of a two-stage Small Solid Propellant Launch Vehicle (SSPLV) based on minimum launch mass. Suitable design variables and technological and functional constraints are considered, both at the system and discipline levels. Propulsion, weight, geometry and trajectory simulation disciplines are used in an appropriate combination. A Generalized Sensitivity Equation (GSE) is derived and solved, and the results of this equation are used for optimization. Comparing the results with the well known gradient based optimization methods proves the ability of the SSA method to reduce computation time.

In this paper, the effects of future solar activities, drag coefficient and atmospheric wind on altitude loss and life time of a LEO satellite is investigated. For this purpose, an orbit propagator is used whose results have been verified by STK software. To analyze the satellite position, the effect of no spherical earth is also considered. In this investigation, simulation of the atmosphere, estimation of wind, and prediction of future solar activity have been implemented using MSIS-90, HWM-93, and 13-month Zurich smoothed models, respectively. Our investigation shows that the effect of future solar activity on satellite life time is a function of the predicted percentile. The effect of drag coefficient is almost linear while the effect of atmospheric wind is a function of inclination.

In this paper, the effects of orbital–environmental parameters on the maximum delivered power of silicon solar cells in various orbits are investigated. The survey consists of the effects of radiation, irradiance, and temperature on solar cell electrical characteristics in LEO and GEO orbits. Applying radiation effect to “One-Diode” model of the solar cell and implementation of the model in MATLAB environment has been done. Then the verification of the model by the existing data, and simulation of radiation effects at AM0, in LEO and GEO orbits is implemented. Comparison of electrical characteristics of the cell at BOL and EOL in various orbits is a part of the results of the survey.

Utilization of the GPS and telemetry systems in sounding rockets are described in this paper. The GPS system is composed of a GPS receiver and its special antennas for this mission. Telemetry system consists of data transmitter, data receiver, and antennas. Each system undergoes some tests to being verified for accurate performance in flight situation after design and fabrication. These tests are also explained in this paper.