S. H. Pourtakdoust; R. Moradi; R. Kamyar
Volume 2, Issue 2 , July 2009, Pages 1-16
Abstract
In this work the coupled nonlinear problem of optimal spacecraft rendezvous and docking (RVD) is addressed. In most of the previous studies on the subject of optimal RVD, decoupling is presumed to exist between the trajectory translational and the attitude motions and hence the optimal coupled analysis ...
Read More
In this work the coupled nonlinear problem of optimal spacecraft rendezvous and docking (RVD) is addressed. In most of the previous studies on the subject of optimal RVD, decoupling is presumed to exist between the trajectory translational and the attitude motions and hence the optimal coupled analysis has not been yet addressed properly. However there are circumstances where these two motions are in fact coupled and interdependent and one such situation is investigated and analyzed in this article. By utilizing thrusters for the translational control and reaction wheels for the attitude control, one can uncouple the translational and rotational control to a high degree of approximation. However it can be shown that due to even very small thrust misalignments, the uncoupled problem changes to a highly coupled one. In this article, the nonlinear rendezvous and docking problem is assumed to be coupled and its optimal fuel-trajectory closed loop solution is obtained using two approaches of local linearization and Gauss Pseudospectral methods. Therefore the designed controllers are able to handle the highly nonlinear coupled rendezvous and docking optimally in the presence of system uncertainties as well as environmental disturbances. The results of the two solution approaches and their pertinent control strategies are compared and the merits and weaknesses of each are fully analyzed. Finally, a sensitivity analysis is also performed that shows the effects of thrust misalignments levels on the final state diversions.
H. Bolandi; F. Fani-Saberi
Volume 2, Issue 2 , July 2009, Pages 17-26
Abstract
In this paper, a novel and highly accurate attitude estimation method for a LEO satellite is designed. The method is based on multiple model adaptive estimation (MMAE) structure. In this method, the satellite dynamic equation is linearized in a few points in order to increase the computational rate compared ...
Read More
In this paper, a novel and highly accurate attitude estimation method for a LEO satellite is designed. The method is based on multiple model adaptive estimation (MMAE) structure. In this method, the satellite dynamic equation is linearized in a few points in order to increase the computational rate compared with extended Kalman filter (EKF) method. The attitude determination and control system of the satellite is consists of a star sensor, gyroscope and reaction wheels. As known, star sensor is a very power consuming sensor in attitude determination of the satellite; therefore, a lesser power consuming method, using the dynamic model of the satellite along with angular momentum of the reaction wheels, is proposed to estimate the satellite attitude. This method assures the proper operation and the attitude estimation of the satellite in eclipse mode as well. By applying this method, the star sensor is used for a short period of time which reduces power consumption considerably. The performance and effectiveness of the proposed algorithm are investigated through numerical simulations and is compared with extended Kalman filter.
M. A. Sharifi; F. Samadzadegan; Saeed Saeed Farzaneh
Volume 2, Issue 2 , July 2009, Pages 27-38
Abstract
Celestial positioning has been used for navigation purposes for many years. Stars as the extra-terrestrial benchmarks provide unique opportunity in absolute point positioning. However, astronomical field data acquisition and data processing of the collected data is very time-consuming. The advent of ...
Read More
Celestial positioning has been used for navigation purposes for many years. Stars as the extra-terrestrial benchmarks provide unique opportunity in absolute point positioning. However, astronomical field data acquisition and data processing of the collected data is very time-consuming. The advent of the Global Positioning System (GPS) nearly made the celestial positioning system obsolete. The new satellite-based positioning system has been very popular since it is very efficient and convenient for many daily life applications. Nevertheless, the celestial positioning method is never replaced by satellite-based positioning in absolute point positioning sense.The invention of electro-optical devices at the beginning of the 21st century was really a rebirth in geodetic astronomy. Today, the digital cameras with relatively high geometric and radiometric accuracy has opened a new insight in satellite attitude determination and the study of the Earth’s surface geometry and physics of its interior, i.e., computation of astronomical coordinates and the vertical deflection components. In the automatic star detection, high precision and reliable in extraction of the star’s centers from the captured images and corresponding them with the astronomical coordinates is the most important point. In this article, the star’s centers are extracted by the advanced image processing technique with sub-pixel precision. Relating the parameters of the presented technique to star’s Mag is one of it’s exclusive properties
O. Shekoofa; M. Taherbane
Volume 2, Issue 2 , July 2009, Pages 39-49
Abstract
This paper intends to study the impacts of orbit parameters change and evaluate their importance in Electrical Power Subsystem (EPS) design. Two main objectives have been followed in this research: 1) understanding the impacts of the orbital parameters change and the mechanisms of their interactions ...
Read More
This paper intends to study the impacts of orbit parameters change and evaluate their importance in Electrical Power Subsystem (EPS) design. Two main objectives have been followed in this research: 1) understanding the impacts of the orbital parameters change and the mechanisms of their interactions with the EPS design and operation, 2) evaluation of the importance of their effects. To this end, a typical cube satellite has been considered in different LEO orbits, to investigate the impacts of variation in the main orbit parameters e. g. altitude and inclination angle. Then the sizing, operation and performance of power sources have been evaluated via comparing the results of in-orbit simulations of EPS operation. In addition, some indirect impacts of the orbit parameters change are evaluated, by analysis and calculation of the interaction between EPS and other subsystems such as Telecommunication and Telemetery (TMTC), Attitude Determination and Control Subsystem (ADCS) and Thermal Control. The results show how the sizing and operation of solar array and battery are under the influence of orbit parameters change via certain factors such as orbit period, duration and the fraction of eclipse to sunlit phases, received solar irradiance by solar panels, and received thermal fluxes from the sun. According to the acquired results, any altitude increment leads to have better margins in power source sizing but there is an optimum value for inclination angle from this point of view.
A. Tavakoli; M. Nikusokhan; J. Roshanian; M. Mirshams
Volume 2, Issue 2 , July 2009, Pages 51-60
Abstract
Design of launch vehicle (LV) trajectory is among the problems in which the use of optimization is of high significance. Implementing optimization using optimal control problem leads to a two point boundary value problem (TPBVS) that can be solved only numerically. On the other hand, development of optimal ...
Read More
Design of launch vehicle (LV) trajectory is among the problems in which the use of optimization is of high significance. Implementing optimization using optimal control problem leads to a two point boundary value problem (TPBVS) that can be solved only numerically. On the other hand, development of optimal control problem for sophisticated model is very intricate and therefore simulation-based optimization plays an Important role in these problems. In this paper, a LV trajectory defining control input as a parameteic function with linear, Spline and Bezier functions was designed and its fuel consumption was optimized using Genetic Algorithm. Result analyses speculate that Bezier and Spline functions arrives to favorable consequences in terms of meeting terminal Boundary Condition (B. C), optimality of LV payload and also number of optimization parameters.
S.H. Miri Roknabadi; M. Mirshams; A. A. Nikkhah
Volume 2, Issue 2 , July 2009, Pages 61-68
Abstract
This paper presents a technical note of mathematic model, design and manufacturing steps of a Reaction Wheel, one of the most important active actuators of satellite. After that Reaction Wheels are tested for the satellite simulator of K.N.Toosi University of Technology, Iran. There were some requirements ...
Read More
This paper presents a technical note of mathematic model, design and manufacturing steps of a Reaction Wheel, one of the most important active actuators of satellite. After that Reaction Wheels are tested for the satellite simulator of K.N.Toosi University of Technology, Iran. There were some requirements and restrictions such as needed maximum torque and control accuracy for attitude maneuver, receivable power, voltage and current. Accordingly fundamental components of Reaction Wheel have been designed and selected. Wheel, motor, bearings and retentive are the significant components. At the rest of the paper, the substantial parameters of the Reaction Wheels are confirmed by a new test set. The results of test guarantee a satisfactory stabilization and accurate maneuver.
M. Karbasian; A. Bagheri
Volume 2, Issue 2 , July 2009, Pages 69-73
Abstract
Recognition of any type of failures in systems and prediction of its reliability have important role in improvement of design of systems. Fault Tree Analysis (FTA) is one of the best techniques in analysis and improvement of complex systems. In this paper first, we show reliability block diagram (RBD) ...
Read More
Recognition of any type of failures in systems and prediction of its reliability have important role in improvement of design of systems. Fault Tree Analysis (FTA) is one of the best techniques in analysis and improvement of complex systems. In this paper first, we show reliability block diagram (RBD) of Rocket Engine and then its fault tree is analyzed. Finally based on FTA, reliability of combustion of rocket engine is calculated.
R Zardashti; M Bagherian
Volume 2, Issue 2 , July 2009, Pages 75-79
Abstract
In this paper a new guidance technique for ballistic missiles and launch vehicles is proposed. Generally the Lambert guidance is used to generate missile nominal (correlated) parameters through powered flight to put it in a ballistic flight path. Because of uncertainties and undesired factors, the nominal ...
Read More
In this paper a new guidance technique for ballistic missiles and launch vehicles is proposed. Generally the Lambert guidance is used to generate missile nominal (correlated) parameters through powered flight to put it in a ballistic flight path. Because of uncertainties and undesired factors, the nominal position and velocity obtained by Lambert technique need to be followed in actual flight. In this paper the Flight Path angle Steering (FPS) procedure is used to accomplish the tracking of nominal parameters. The numerical simulations indicate that the integrated procedure is a cost-effective and suitable scheme for guiding ballistic missiles and launch vehicles especially in design process. In spite of the simplifications made in FPS procedure, numerical simulations show that there is very little difference between the results obtained by FPS and the results obtained by Q-guidance method.