Research Paper
atefeh hoseinzadeh; Amirhossain Adami; Asghar Ebrahimi
Volume 11, Issue 1 , June 2018, Pages 1-12
Abstract
The atmospheric reentry phase is one of the most important mission steps in space missions, therefore, the guidance and control of reentry vehicles in this phase of mission is important. In this article, a reentry vehicle guidance algorithm is proposed which has suitable robustness in the presence of ...
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The atmospheric reentry phase is one of the most important mission steps in space missions, therefore, the guidance and control of reentry vehicles in this phase of mission is important. In this article, a reentry vehicle guidance algorithm is proposed which has suitable robustness in the presence of initial reentry parameters uncertainty. To use any conductive method, first the motion equations must be obtained. In this paper, quadratic nonlinear control method is used to guide the vehicle. In this regard, the equations of motion of reentry vehicles are developed in form of state space and the system and control matrices depending on the state and control variables are extracted. In this article, it is tried to minimize the landing errors at terminal point using Nonlinear Quadratic Tracking (NQT) and chasing a reference trajectory. In order to define a trajectory with different initial states using evolutionary genetic algorithm with changes in weighting matrices Q and R, it is tried to reduce the errors of landing at terminal point. Monte Carlo analysis is used to evaluate the performance of the proposed algorithm. According to the results, the proposed algorithm can reduce the errors more than 90% in the presence of reentry initial parameter uncertainties.
Research Paper
S.Hamid Jalali-Naini
Volume 11, Issue 1 , June 2018, Pages 13-29
Abstract
In this study, the preferred regions of Pulse-Width Pulse-Frequency Modulator (PWPFM) are obtained analytically for the static analysis. For this purpose, a comprehensive parametric study is carried out based on the two performance indices of fuel consumption and the number of thruster firings. The preferred ...
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In this study, the preferred regions of Pulse-Width Pulse-Frequency Modulator (PWPFM) are obtained analytically for the static analysis. For this purpose, a comprehensive parametric study is carried out based on the two performance indices of fuel consumption and the number of thruster firings. The preferred regions are presented by normalized relations and curves. Moreover, the exact analytical solutions of the two performance indices are obtained for a class of modulators with the assumption of constant inputs. The advantages of the present study are non dimensional analysis and obtaining the preferred regions in terms of each others, resulting in more accurate regions as opposed to inequality relations using constant values for a specified input signal. In addition, in the case of specified minimum pulse width (having the update frequency and thruster time constant), determining the preferred regions becomes more limited. In this regard, useful relations and curves based on the maximum possible value for the number of the thruster firings are derived and presented.
Research Paper
Valiollah Ghaffari; Paknoosh Karimaghaee
Volume 11, Issue 1 , June 2018, Pages 31-40
Abstract
Usually vehicles are equipped with guidance algorithm based on line of sight (LOS) angle. In this way, some measurements like target acceleration, LOS rate, and closing velocity are provided for the guidance algorithm. The noise effect on the guidance loop would be neglected when the variance of the ...
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Usually vehicles are equipped with guidance algorithm based on line of sight (LOS) angle. In this way, some measurements like target acceleration, LOS rate, and closing velocity are provided for the guidance algorithm. The noise effect on the guidance loop would be neglected when the variance of the measurement noise is small. However, the stability property and/or performance of the guidance loop may be effected when the measurement noise is considerable. In this paper, a suitable guidance law is proposed in the presence of measurement noise. Then, a numerical example is provided. The effectiveness of the proposed method in the simulation results is shown in comparison with the previous results.
Research Paper
mehdi alemi rostami; Morteza Aghaei
Volume 11, Issue 1 , June 2018, Pages 41-48
Abstract
In this paper, a high efficiency DC-DC converter for variable input voltage and high output voltage applications is presented. This converter is specially appropriate for driving travelling wave tube amplifier with a variable input source (i.e. solar panels). The proposed converter consists of a boost ...
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In this paper, a high efficiency DC-DC converter for variable input voltage and high output voltage applications is presented. This converter is specially appropriate for driving travelling wave tube amplifier with a variable input source (i.e. solar panels). The proposed converter consists of a boost converter to remove the variations of its input voltage and regulate its output voltage. Afterwards, a full bridge inverter controls the phase angle between the output inverter voltage and the current. Keeping the value of this angle at zero, the switching losses are reduced. A series-parallel resonant circuit uses the parasitic elements of the transformer as its elements and makes switches work in soft switching conditions. This reduces the converter power losses and increases the efficiency. Simulation results show the behavior of the proposed converter.
Research Paper
Maryam Kiani; Amir Shakouri; S.H Pourtakdoust; Mohammad Sayanjali
Volume 11, Issue 1 , June 2018, Pages 49-57
Abstract
A new strategy is presented for the optimal transfer of non-coplanar elliptical orbits based on sequential multi-Lambert trajectories. The proposed method tries to minimize the control effort during the orbit transfer. The main advantages of the proposed method include transfer between arbitrary initial ...
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A new strategy is presented for the optimal transfer of non-coplanar elliptical orbits based on sequential multi-Lambert trajectories. The proposed method tries to minimize the control effort during the orbit transfer. The main advantages of the proposed method include transfer between arbitrary initial and final orbits, utilizing desired number of impulses, and covering all possible transfer trajectories to achieve the target. The position and time instant of impulses are considered as the design variables which determine utilizing the well-known optimization method of pseudo-Newton. Performance of the proposed method is investigated and verified through some numerical simulations. It is also shown that the proposed method converges to the celebrated Hahmann’s maneuver in transfer between two coplanar orbital orbits.
Research Paper
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.
