Space subsystems design: (navigation, control, structure and…)
M. Navabi; F. Malekpour
Volume 15, Issue 2 , June 2022, , Pages 15-25
Abstract
In the variable parameter linear method, which is used to express systems with time-varying state-space matrices, the stability and performance of the feedback system are guaranteed, and there is a significant potential for improving efficiency. The dynamics of these systems depend on a variable parameter ...
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In the variable parameter linear method, which is used to express systems with time-varying state-space matrices, the stability and performance of the feedback system are guaranteed, and there is a significant potential for improving efficiency. The dynamics of these systems depend on a variable parameter with time, considered in this research as the angular velocity of the reaction wheel. The values of this parameter are during an unknown period but can be measured by system performance. Using the tabulation gain technique, the stability of the variable parameter system is checked, and the tabulation parameter is selected for estimating practical control factors. The convex algorithm can solve the extracted sufficient conditions converted into linear matrix inequality conditions. By solving these controlling conditions, the tabulated gain is obtained to guarantee the stability and performance of the variable parameter system. Numerical simulation results show the success of the proposed method.
Space subsystems design: (navigation, control, structure and…)
M. Navabi; P. Zarei
Volume 14, Issue 4 , December 2021, , Pages 77-83
Abstract
The use of four reaction wheels to control the three-axis attitude of the spacecraft, considering its mechanical performance and the possibility of its failure, is a practical solution in the face of a defect in one of the wheels. In this article, the optimal control of the spacecraft, which has four ...
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The use of four reaction wheels to control the three-axis attitude of the spacecraft, considering its mechanical performance and the possibility of its failure, is a practical solution in the face of a defect in one of the wheels. In this article, the optimal control of the spacecraft, which has four reaction wheels, is investigated. Controlling the attitude of a spacecraft with just two reaction wheels is a significant issue that conventional controllers are not able to do. Therefore, the use of nonlinear model-based predictive controller is used to control the attitude of this spacecraft and compared with optimal nonlinear control in a discrete-time comparison, which satisfies the acceptable results.
Space subsystems design: (navigation, control, structure and…)
M. Navabi; Ahmad Ebrahimi
Volume 14, Issue 3 , September 2021, , Pages 15-22
Abstract
Turbulence in the spacecraft tanks has undesirable effects during maneuvers. Therefore, considering the importance of the correct orbit maneuver to reach the target orbit, it is necessary to model and select a proper method to control it before performing the orbital maneuvers. In this paper, by using ...
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Turbulence in the spacecraft tanks has undesirable effects during maneuvers. Therefore, considering the importance of the correct orbit maneuver to reach the target orbit, it is necessary to model and select a proper method to control it before performing the orbital maneuvers. In this paper, by using a new method for modeling turbulence in reservoirs and for the first time, spacecraft attitude control and turbulence control are simulated using this model. Fuel turbulence is modeled using a moving pulsed ball model, and the whole system's dynamic equations are derived using Krishehoff equations. The maneuver of the spacecraft and the motion of the moving pulsed ball is considered in the plane; therefore, the spacecraft and pulsed ball system will have four degrees of freedom. simulation results show successful modeling and simultaneous control of turbulence and situation
Space subsystems design: (navigation, control, structure and…)
M. Navabi; Nazanin Safaei Hashekvaei
Volume 14, Issue 2 , June 2021, , Pages 77-88
Abstract
Adaptive control technique is taken into consideration because of overcoming the problem of existence of uncertainties in the space missions. In this paper, a novel optimal direct adaptive control technique which is based on Markov parameters is presented. In this technique, the system's performance ...
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Adaptive control technique is taken into consideration because of overcoming the problem of existence of uncertainties in the space missions. In this paper, a novel optimal direct adaptive control technique which is based on Markov parameters is presented. In this technique, the system's performance is expressed based on rotation matrices, and this method doesn't have a singularity problem. The problem of satellite attitude control using this method and nonlinear thruster actuator in existence of uncertainty in moment of inertia is analyzed. The novel adaptive controller using on-off thrusters is robust to inertia changes. In this paper, a mamdani fuzzy logic is used to schedule the gains of PD control method, and the satellite attitude control problem using a fuzzy controller is simulated. With considering the settling and rise times, it's shown that the fuzzy controller is better than the presented adaptive controller. Also, the problem of satellite attitude control using the novel adaptive controller in presence of a constant disturbance is analyzed, and simulation results illustrate that the new adaptive control is robust to a constant disturbance.
Space subsystems design: (navigation, control, structure and…)
M. Navabi; Nazanin Safaei
Volume 13, Issue 4 , December 2020, , Pages 25-35
Abstract
Several novel control techniques have been created as a result of the diversity of researches which are conducted about the problem of satellite attitude control. There are always uncertainties in the problem of satellite attitude control in the space missions. Therefore, Adaptive control is a method ...
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Several novel control techniques have been created as a result of the diversity of researches which are conducted about the problem of satellite attitude control. There are always uncertainties in the problem of satellite attitude control in the space missions. Therefore, Adaptive control is a method which is taken into consideration. High computational volume is one of the problems of adaptive control technique. In this paper, a control technique which is based on optimization concepts is introduced for the problem of satellite angular velocity and attitude control. Also, it's developed based on the three-dimensional special orthogonal group, and it's not faced by a singularity problem. For comparison, the linear quadratic regulator (LQR) control technique is simulated. Finally, the results of the simulations show that the performance of the presented adaptive control technique is optimal, and this method is robust to inertia changes.
Space subsystems design: (navigation, control, structure and…)
M. Navabi; H. Ghanbari
Volume 13, Issue 2 , June 2020, , Pages 79-86
Abstract
In this paper, attitude control of spacecraft in the presence of uncertainties and disturbances has been simulated. Access to rapid maneuver in spacecraft decreased accuracy. Therefore, to enhance the accuracy of spacecraft rapid maneuver and to resist uncertainties the adaptive control L1 is suggested. ...
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In this paper, attitude control of spacecraft in the presence of uncertainties and disturbances has been simulated. Access to rapid maneuver in spacecraft decreased accuracy. Therefore, to enhance the accuracy of spacecraft rapid maneuver and to resist uncertainties the adaptive control L1 is suggested. The controller is able to control the attitude of the spacecraft due to rapid adaptation and robustness against uncertainties simultaneously. In this paper, an adaptive control of L1 is compared with reference model. The dynamics of the multi-input-multi-output system. Simulation results show the desired performance of the L1 controller.
M. Navabi; ُshahram Hosseini
Volume 12, Issue 4 , December 2019, , Pages 79-89
Abstract
افزایش دقت و پایداری در تخمین آنلاین مدل یک فضاپیما، به دلیل همزمانی وجود نامعینی در دینامیک سیستم و نویز در خروجی حسگرهای وضعیت، یکی از چالشهای کنترل وضعیت است. ...
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افزایش دقت و پایداری در تخمین آنلاین مدل یک فضاپیما، به دلیل همزمانی وجود نامعینی در دینامیک سیستم و نویز در خروجی حسگرهای وضعیت، یکی از چالشهای کنترل وضعیت است. یکی از روشهای مؤثر تخمین این نوع از مدلهای دینامیکی، روش کمترین مربعات خطا در ترکیب با فیلتر کالمن است. برای افزایش عملکرد روش تخمین ذکر شده، الگوریتم آنلاین فرا ابتکاری جدیدی بر اساس توسعه روش کمترین باقیمانده تعمیمیافته ارائه میگردد. این الگوریتم یک روش مبتنی بر تکرار است که با استفاده از اطلاعات مرحله قبل و بر اساس تجربه کاربر، و یا یک روش فرا ابتکاری آنلاین نوین، تعداد گامهای حل دستگاه در زیر فضای کریلف را تعیین کرده و همگرایی کلی به پاسخ را بهبود میبخشد. برای بررسی دقت تخمین این روش، روشهای کمترین باقیمانده تعمیمیافته ساده، گرادیان دو مزدوجی، گرادیان مزدوج مربعی و گرادیان دو مزدوجی پایدار مقایسه شده است، که روش فرا ابتکاری کمترین باقیمانده تعمیمیافته تطبیقی بیشترین دقت و پایداری در پاسخ را نشان میدهد.
M. Navabi; A. Davodi
Volume 11, Issue 4 , December 2018, , Pages 11-22
Abstract
Sloshing phenomenon in spacecraft fuel tank during orbital maneuver, causes adverse effects on spacecraft attitude. Therefore, before orbital maneuvers, modeling fuel sloshing and determining appropriate method for controlling it has to be carried out. The aim of this paper is to model slosh dynamics ...
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Sloshing phenomenon in spacecraft fuel tank during orbital maneuver, causes adverse effects on spacecraft attitude. Therefore, before orbital maneuvers, modeling fuel sloshing and determining appropriate method for controlling it has to be carried out. The aim of this paper is to model slosh dynamics by using double pendulum model in two-dimensional space. Spacecraft maneuver and pendulums motion are considered in 2D-coordinate, so coupled spacecraft and pendulums dynamic system are 5 degrees of freedom systems. Here, linear control methods (PD and LQR), and also nonlinear control methods (Lyapunov and fuzzy) are determined to stabilize dynamic parameters of the introduced system. Simulation results show that designed controllers have good performance to achieve stabilization of the parameters.
M. Navabi; M.R. Hosseini
Volume 11, Issue 1 , June 2018, , Pages 59-71
Abstract
Using nonlinear control theories is common for the attitude control problem of spacecraft.Feedback linearization theory is a nonlinear control method which tries to transform nonlinear dynamics of system into linear.In this control theory, outputs choice will have a direct impact on the stability ...
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Using nonlinear control theories is common for the attitude control problem of spacecraft.Feedback linearization theory is a nonlinear control method which tries to transform nonlinear dynamics of system into linear.In this control theory, outputs choice will have a direct impact on the stability of system.In order to control the spacecraft attitude by this method, parameters that describe the spacecraft attitude are considered as outputs.The aim of this study is to investigate the effect of using quaternion parameters as a conventional representation in the kinematic equations compared with modified Rodrigues parameters.According to designed controller and simulation results, it is evident that in maneuvers with zero scalar part of quaternion, the controller efficiency is reduced due to singularity in the calculations.This is while by using modified Rodrigues parameters, singularity does not occur and in this way the controller, in the same maneuvers as the previous method, is faster and more efficient with less effort.
M. Navabi; M. R Akhlomadi
Volume 8, Issue 3 , October 2015, , Pages 27-40
Abstract
In this paper a nonlinear optimal control is suggested. Spacecraft intended to rendezvous and dock with the target is controlled by actuators to have a safe and stable course while satisfying requirements. The Nonlinear optimal controller is designed using nonlinear equations of relative position and ...
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In this paper a nonlinear optimal control is suggested. Spacecraft intended to rendezvous and dock with the target is controlled by actuators to have a safe and stable course while satisfying requirements. The Nonlinear optimal controller is designed using nonlinear equations of relative position and attitude of spacecraft for circular and elliptical orbits with and without reaction wheels. Cost function of the optimal control problem is expressed in the form of nonlinear quadratic regulator and control constraints are applied to the problem to gain controls in the allowable domain which is produced by the wheels. For the sake of robustness to the uncertainties as one of the most important element of the control design, nonlinear optimal control is derived using state dependent Riccatti equation based on analytical method of eigen vectors of Hamiltonian matrix. Simulation results show that this nonlinear control method achieves a good performance for rendezvous and docking problem.
M. Navabi; M. Tavana; H.R. Mirzaei
Volume 7, Issue 4 , January 2015, , Pages 39-49
Abstract
Attitude control of spacecraft in order to nonlinear and high order dynamics is fundamental and challenging issue. With respect to these nonlinearities, linear control theories are not suitable choices and spacecraft may be unstable or lose performance. In this paper, State Dependent Riccati Equation ...
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Attitude control of spacecraft in order to nonlinear and high order dynamics is fundamental and challenging issue. With respect to these nonlinearities, linear control theories are not suitable choices and spacecraft may be unstable or lose performance. In this paper, State Dependent Riccati Equation (SDRE) method is utilized to 3-axis stabilization using four reaction wheels. State dependent Riccati equation method is systematic approach for optimal control of nonlinear systems which satisfies constraints of systems. In order to solve time consuming problem of this method in practical systems, Theta-D method is used. Results demonstrate the effectiveness of Theta-D in compare with Riccati method.
M. Navabi; R. Hamrah
Volume 6, Issue 1 , April 2013, , Pages 57-67
Abstract
In this paper, a precise propagation model which takes into account the effects of the atmospheric drag and gravitational harmonies is developed and presented using available Two Line Element (TLE) data. Moreover, the prediction of the trajectory of space objects (e.g. the operational and non-operational ...
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In this paper, a precise propagation model which takes into account the effects of the atmospheric drag and gravitational harmonies is developed and presented using available Two Line Element (TLE) data. Moreover, the prediction of the trajectory of space objects (e.g. the operational and non-operational satellites and space debris) and their orbital data is performed. Then, the 2009 prominentcollisionbetween the Cosmos2251 and Iridium33 satellite is simulated and the maximum probability of their collision is computed by implementing the propagation algorithm and probabilities Theory, and finally the results are discussed. Therefore, the precise position and velocity of each space object at any time, as well as their collision probability will be determined, and if necessary, the time available to enact collision avoidance maneuver will be obtained. The success and accuracy of an avoidance maneuver is affected by the precision of the propagation model, the exact computation of collision probability, and finally the maneuver mechanism which are utilized.
M. Navabi; M. Barati
Volume 5, Issue 1 , April 2012, , Pages 51-59
Abstract
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 ...
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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 to 6 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.
M. Navabi; N. Nasiri
Volume 3, Issue 2 , January 2011, , Pages 45-52
Abstract
Since last decades utilizing satellites in low earth orbits have had increasing tendency. These satellites experience the earth magnetic field due to their low altitude to the earth. The Earth magnetic intensity can be used in order to control the attitude of spacecraft utilizing the interaction between ...
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Since last decades utilizing satellites in low earth orbits have had increasing tendency. These satellites experience the earth magnetic field due to their low altitude to the earth. The Earth magnetic intensity can be used in order to control the attitude of spacecraft utilizing the interaction between the earth magnetic field and magnetic dipoles which are generated in the body of satellite. First of all, for using this phenomenon the magnitude and direction of the Earth magnetic field have to be obtained. There are various ways in order to simulate the earth magnetic field, that the most accurate one is utilizing the harmonic coefficients and mathematical model of the earth magnetic field. In this study, the earth magnetic field is modeled based on the 10thgeneration of the IGRF coefficients and the results are verified with the most valid reference. Due the Earth magnetic field is used in order to attitude control of a spacecraft, it is necessary to transform the results into the spacecraft Body frame. This transformation can be obtained utilizing linear and nonlinear transformation. In the next step, based on the comparison of the results of the spacecraft attitude dynamics utilizing linear and nonlinear transformation the validity margin of linear transformation is studied.
M. Navabi; M. Sabatifar
Volume 3, Issue 1 , July 2010, , Pages 67-74
Abstract
Orbital transfer has a significant role in any space mission. This transfers generally categorized in impulsive and continuous maneuvers. An important challenge is fuel consumption in the maneuver. This problem is considered as a required Δυ problem. Hence, minimization of Δυ ...
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Orbital transfer has a significant role in any space mission. This transfers generally categorized in impulsive and continuous maneuvers. An important challenge is fuel consumption in the maneuver. This problem is considered as a required Δυ problem. Hence, minimization of Δυ means minimization of fuel consumption orbital transfer. In simple cases, the problem has closed form solution for example transfer between coplanar circular orbits or transfer between coplanar coaxial elliptical orbits. The conventional methods cannot solve complex cases of initial and target orbits. In this paper the impulsive optimal transfer between two coplanar- noncoaxial elliptical orbits is considered. The numerical solution of optimality nonlinear equations is necessary to obtain the solutions of complex problems. According to nonlinearity of equations two issues arise, firstly numerical solution is sensitive to initial guess, secondly the local minimum solutions only may be find. In this paper some equations have been derived that using them behavior of required Δυ function can be investigate based on various values of independent variables and can be find the boundary of global solution. In this way one can be determined a reasonable and proper initial guess for nonlinear solver. The proposed methodology is applied to an example and the results are provided. The results include the local and global solutions and they show a good ability of the proposed method.
