Abdollah Madadkar; Ahmad Kalhor; Amirreza Kosari
Volume 9, Issue 2 , September 2016, , Pages 1-9
Abstract
In order to overcome the nonlinear terms in the flight equations of a launch vehicle, an appropriate control strategy has to be designed. In this paper, the fundamentals of designing a simple controller in order to control a typical launch vehicle for tracking the optimum launch vehicle path is presented. ...
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In order to overcome the nonlinear terms in the flight equations of a launch vehicle, an appropriate control strategy has to be designed. In this paper, the fundamentals of designing a simple controller in order to control a typical launch vehicle for tracking the optimum launch vehicle path is presented. The principals of this strategy are based on on-line linearization of the nonlinear equations in each sampling interval during the flight and eventually representing system equations as extended Jacobean equations. It is important to note that equations linearization does not work in some areas and equilibrium points of the system but in each sampling interval is trying the system of nonlinear equations can be transformed into linear equations and then by using the pole placement theory, a good tracking controller proposed for the system. Design and simulation results show good accuracy and proper convergence of the reference signals (speed and pitch angle signals) and eventually, the success of the mission.
Mohsen Dehghani Mohammad-Abadi; Seyed Hamid Jalali Naini
Volume 9, Issue 3 , December 2016, , Pages 1-12
Abstract
In this paper, an approximate solution of required velocity with final position constraint is derived using a piecewise linear gravity assumption for elliptical earth model. In this approach, the total flight time is divided into several time intervals and the gravitational acceleration is assumed to ...
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In this paper, an approximate solution of required velocity with final position constraint is derived using a piecewise linear gravity assumption for elliptical earth model. In this approach, the total flight time is divided into several time intervals and the gravitational acceleration is assumed to be linear at each interval. The solution gives an explicit relation in terms of the current position vector, desired final position and flight time in three dimensions. The accuracy and computational burden of the method are obtained numerically in terms of the number of time intervals, and compared with linearized solution and Zarchan's iterative algorithm. Numerical solution shows that the present method has better accuracy than the two mentioned approaches with the same computational burden up to a range angle of 18 deg for minimum energy trajectory in an elliptical earth model. The presented method can be extended for two or multi-body problem and also for the computation of sensitivity matrix of required velocity.
Hasan Naseh
Volume 9, Issue 4 , April 2017, , Pages 1-12
Abstract
The major purpose of this paper is to present Space Launch System (SLS) family technology development from propulsion system aspect. Thus, the models of cost estimation for two types of propulsion systems (cryogenic and semi-cryogenic) are derived based on the statistical method and are then compared ...
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The major purpose of this paper is to present Space Launch System (SLS) family technology development from propulsion system aspect. Thus, the models of cost estimation for two types of propulsion systems (cryogenic and semi-cryogenic) are derived based on the statistical method and are then compared with each other. The SLS family modernization model includes five main steps:(1) SLS family propulsion system mass and energetic calculations; (2) Cost estimation and analysis; (3) Sensitivity analysis of propellant volume tanks; (4) Sensitivity analysis of propulsion system performance based on cost; (5) mass, energetic and cost calculations of cryogenic and semi-cryogenic propulsion systems. Finally, the results of the modernization methodology execution are verified by an existing propulsion system.
Ghasem Kahe; Maysam Mohammadi-Amin; Arash Sefidan Benisi
Volume 10, Issue 1 , June 2017, , Pages 1-13
Abstract
Various strategies have been developed to increase the safety of spacecraft crews, among which the Launch Abort System has been widely considered by the space centers across the world. The launch abort system should be able to carry the crew module away from the failed launcher or rocket in a short time ...
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Various strategies have been developed to increase the safety of spacecraft crews, among which the Launch Abort System has been widely considered by the space centers across the world. The launch abort system should be able to carry the crew module away from the failed launcher or rocket in a short time in accordance with the predetermined profile and recover the crew module on the ground. While the main part of the vehicle flight consists of the tracking, reorientation, and settling phase; attitude control in the flight path is done via the roll and pitch channel. Non-linear dynamic inversion flight control is considered for the attitude control of the LAS. Tracking the predetermined profile for the angle of attack as well as the sideslip angle and maintaining the stability of the vehicle in the flight path are considered as the control objectives based on the requirements. Simulations and analytical evaluations indicate the outperformance of the proposed controller for the attitude control of LAS in line with the predetermined profile.
farshad shamlu; Abolghasem Naghash
Volume 10, Issue 2 , September 2017, , Pages 1-8
Abstract
In this study, a different approach to the prediction of satellite position is introduced.All methods are based on the Kepler’s laws of planetary motion and the orbitalperturbations such as the Earth’s oblateness, atmospheric drag, third-body perturbationand the solar-radiation pressure. ...
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In this study, a different approach to the prediction of satellite position is introduced.All methods are based on the Kepler’s laws of planetary motion and the orbitalperturbations such as the Earth’s oblateness, atmospheric drag, third-body perturbationand the solar-radiation pressure. All these perturbations are modeled and are includedseparately in the equation. However, this paper offers a new view of the prediction whichsuggests the use of artificial neural networks and observation data. The advantage of thismethod is based on the usage of observation data, so that all disturbances are taken intoaccount and there is no need to use perturbation models. For this reason, the use of theTLE as the most reachable actual data is considered. Comparison of the output of thismethod with actual data shows the accuracy of the proposed method which is very high.
Mehran Mirshams; Ehsan Zabihian
Volume 10, Issue 3 , December 2017, , Pages 1-14
Abstract
This study introduces a new computer code termed AZMIN developed by Space Research Laboratory (SRL). This efficient tool which benefits from the Statistical Design Model (SDM) has been developed for the system design of GEO communication satellites. The main advantage of the AZMIN is to determine technical ...
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This study introduces a new computer code termed AZMIN developed by Space Research Laboratory (SRL). This efficient tool which benefits from the Statistical Design Model (SDM) has been developed for the system design of GEO communication satellites. The main advantage of the AZMIN is to determine technical specification parameters of a satellite at both system and subsystem levels, with a high accuracy and time performance. System-level parameters encompass mass, power, dimension and cost; while, subsystem parameters contain mass, power, and solutions for components configurations of each subsystem. Actual computations of this tool are carried out by means of SDM, leading to a dramatic decrease in the conceptual design time and consequently, its cost. The database utilized is composed of records of 462 GEO communication satellites launched from the year 2000 to 2017. The accuracy of the AZMIN code is amply verified through an example and also a statistical method, demonstrating the mean error of approximately 15% in the obtained results.
Hadiseh Karimaei; Mostafa Hossein Alipour; F Ommi; Ehsan Movahednejad; Reza Sharifzadeh
Volume 10, Issue 4 , March 2018, , Pages 1-7
Abstract
A swirl injector is tested to investigate the instability of the liquid sheet emanating from it and determine the main microscopic characteristics of the spray. The injector, which is tested, was already approved by doing the characterization tests (macroscopic). Due to the fact that the PDPA systems ...
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A swirl injector is tested to investigate the instability of the liquid sheet emanating from it and determine the main microscopic characteristics of the spray. The injector, which is tested, was already approved by doing the characterization tests (macroscopic). Due to the fact that the PDPA systems to measure the spray characteristics are very expensive and high-tech, and therefore inaccessible for us , it is attempted to investigate the specifications and instability of the liquid sheet as much as possible, by photography. The liquid sheet emanating from the injector has perturbations on its surface which originate from inside the injector. Due to the aerodynamic interactions, these perturbations grow and eventually lead to break up the liquid sheet and form the ligaments. The growth of these unstable waves can be observed in the images. Also the breakup length can be measured using the images recorded. Also ligaments in the primary breakup zone and droplets were shown.
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.
Vahid Behnamgol; Ahmadreza Vali; ali mohammadi
Volume 11, Issue 2 , September 2018, , Pages 1-10
Abstract
Nonsingular terminal sliding mode (NTSM) guidance for intercepting the desired line of sight (LOS) angle in terminal phase is proposed in this paper. In order to satisfy the predefined LOS angle and to intercep into target, a nonsingular terminal sliding variable is introduced. In reaching phase, in ...
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Nonsingular terminal sliding mode (NTSM) guidance for intercepting the desired line of sight (LOS) angle in terminal phase is proposed in this paper. In order to satisfy the predefined LOS angle and to intercep into target, a nonsingular terminal sliding variable is introduced. In reaching phase, in the presence of uncertainties such as target maneuvers, robust NTSM guidance law is designed in order forzeroing the sliding variable in finite reaching time. Then, in sliding phase, due to introducing nonsingular terminal sliding variable, finite time stability of line of sight angle and line of sight angular rate is granteed without singularity in commanded acceleration as control signal Numerical simulations are presented to illustrate the potential of the proposed guidance law.
mehran mirshams; Mohammad Teshneh lab; Morteza Ramezani
Volume 11, Issue 3 , December 2018, , Pages 1-8
Abstract
Modeling and analyzing systems, especially in complex systems with high dynamics, noise and uncertainty in understanding the behavior of systems and decision making is very important problem from long time ago. This paper shows that neuro-fuzzy systems can be used effectively to design the solar arrays ...
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Modeling and analyzing systems, especially in complex systems with high dynamics, noise and uncertainty in understanding the behavior of systems and decision making is very important problem from long time ago. This paper shows that neuro-fuzzy systems can be used effectively to design the solar arrays of electrical power subsystem of a remote sensing satellite in conceptual design phase. In the design of neuro-fuzzy system, Takagi-Sugeno inference system, hybrid training algorithm and Gaussian membership functions are used. The simulation results obtained in this modeling have an accurate accuracy compared to the experimental data and classical calculations of remote sensing satellites.
Hadiseh Karimaei; Ramin Ghorbani; Seyed Mostafa Hoseeinalipour
Volume 11, Issue 4 , December 2018, , Pages 1-10
Abstract
In the atomization process, small disturbances grow in liquid jet or sheet and eventually cause to disintegrate it into ligaments and smaller droplets. Concerning to the motion of waves on the liquid sheet surface, the stage of primary breakup is deterministic and can be predicted by instability analyzes. ...
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In the atomization process, small disturbances grow in liquid jet or sheet and eventually cause to disintegrate it into ligaments and smaller droplets. Concerning to the motion of waves on the liquid sheet surface, the stage of primary breakup is deterministic and can be predicted by instability analyzes. In early studies, the theories of linear and weakly nonlinear instability have been implemented on a cylindrical liquid sheet and the effect of spray cone angle was not included in the model. Therefore, in this paper in order to improve the model, the linear instability theory is implemented on a cone-shaped liquid sheet for the first time, and therefore radial velocities of liquid and gas phases are also considered moreover than axial and tangential velocities. The results of this improved model such as maximum wave growth rate and its corresponding wave number can be used to estimate mean droplet diameter and breakup length.
Alireza Fathi; Mahdy Ahangar
Volume 12, Issue 2 , September 2019, , Pages 1-10
Abstract
corona discharge which had been considered undesired before, has become popular for different uses in the past decades; including space thrusters. The basic corona discharge has a simple setup including two electrodes with unequal cross-sections; one of which connected to a high voltage and the other ...
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corona discharge which had been considered undesired before, has become popular for different uses in the past decades; including space thrusters. The basic corona discharge has a simple setup including two electrodes with unequal cross-sections; one of which connected to a high voltage and the other connected to ground or opposite voltage. By changing the number of electrodes, the efficiency of corona discharge can be improved. In this paper, number of electrodes have been changed from 2 to 3 in order to study an electrohydrodynamic thruster. Flow characteristics have been studied by solving the electrostatics and Navier-Stokes equations by finite element method (FEM). The results show that with increasing the number of cathodes the thrust, electric current and thrust efficiency will also increase. In similar condition and geometry, maximum produced velocity resulted by applying any electric potential to anode, increases by about 30% in comparison with one-cathode setup.
Space systems design (spacecraft, satellites, space stations and their equipment)
Mohammad Razmjooei; Mohammad Shahbazi; Fathollah Ommi
Volume 14, Issue 2 , June 2021, , Pages 1-26
Abstract
In this paper, the heat transfer and ablation thermal insulators in solid rocket motor are investigated. Therefore, by collecting and solving the thermal ablation equations, a computer program, using MATLAB software, is developed which can predict the thermal response of insulators in different operating ...
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In this paper, the heat transfer and ablation thermal insulators in solid rocket motor are investigated. Therefore, by collecting and solving the thermal ablation equations, a computer program, using MATLAB software, is developed which can predict the thermal response of insulators in different operating conditions and compare the performance of these insulators. The heat and mass transfer equations are considered in two dimensions in a solid body. We used the equations, finite volume method with implicit formulation for time dependency to solve equations. The reaction equation which written in the form of Arrhenius, is solved using Runge-Kutta method, and the density and the flux of the gas produced at each step are obtained. Also we represent a model for the rate of recession.
space law
Payman Namamian; Sobhan Tayebi; Sajad Tayebi
Volume 12, Issue 1 , April 2019, , Pages 1-12
Abstract
Following the beginning of human activities in outer space, such issues as governance, jurisdiction and other legal matters were investigated by jurists. It should be accepted that technological advancement cannot be made possible in the presence of legal gaps, and it should be acknowledged that law ...
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Following the beginning of human activities in outer space, such issues as governance, jurisdiction and other legal matters were investigated by jurists. It should be accepted that technological advancement cannot be made possible in the presence of legal gaps, and it should be acknowledged that law is easily changing and developing constantly. With increasing progression law of outer space is essential. humans having access to the outer space, it is extremely essential and important to develop international law governing the outer space and celestial Bodies.As the most resent branch of international law, therefore, International Space law provides new concepts related to criminal jurisdiction for this reason, present paper attempts to explain criminal jurisdiction within international law system while evaluating its position in the framework of international outer space law on interrelated issues such as command authority, authority of commanding the international space stations, and Command of the International Space Station and commanders in light of U.N outer space treaty
Fathollah Ommi; Dooman Poorrajab Sufinai; Davood Doomiri Ganji; Seyed Hossein Moosavi
Volume 13, Issue 1 , March 2020, , Pages 1-11
Abstract
In this research, it is attempted to determine the diameter and velocity distribution according to the flow characteristics of the upstream and without needing experimental measurements.Firstly, Fluent software has been used to simulate the turbulent flow of inside nozzle by k-? model to obtain the nozzle ...
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In this research, it is attempted to determine the diameter and velocity distribution according to the flow characteristics of the upstream and without needing experimental measurements.Firstly, Fluent software has been used to simulate the turbulent flow of inside nozzle by k-? model to obtain the nozzle turbulence energy at the nozzle outlet. Then, nonlinear growth rate analysis of instability is used to determine spray breakup length and the frequency of maximum instability and the mean diameter of primary breakup. Four equation maximum entropy model has been developed according to the inlet of upstream flow. Subsequently, the terms of momentum source as well as the energy of maximum entropy model has been determined using the results of simulated nozzle turbulence flow and instability analysis. In the following, first the results of maximum entropy model have been evaluated with the experimental input and then determined with upstream input. The obtained results which have been compared with experimental tests show well agreement.
Space systems design (spacecraft, satellites, space stations and their equipment)
Hamed Moeini; Ebrahim Afshari; Karim Mazaheri
Volume 15, English Special Issue , May 2022, , Pages 1-13
Abstract
In the present study, the effects of geometrical properties of gas flow channels on both current density and temperature distributions inside a polymer electrolyte membrane (PEM) fuel cell are investigated. The main purpose here is to clarify the effects of the variation of width, depth, and the ribs ...
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In the present study, the effects of geometrical properties of gas flow channels on both current density and temperature distributions inside a polymer electrolyte membrane (PEM) fuel cell are investigated. The main purpose here is to clarify the effects of the variation of width, depth, and the ribs of flow channels on the fuel cell performance. To do this, the fuel cell is numerically simulated in two dimensions. The governing equations consist of the conservation of the electrical potential, Darcy’s law as alternative to the momentum equation, Maxwell-Stefan equation for mass transport, energy conservation, and electro-thermal equations along with the Butler–Volmer equation. Numerical results indicate that the width of channels and their ribs have more sensible effects than the depth of flow channels on the current density and temperature distributions and fuel cell performance. While the maximum temperature of the cell is increased by increasing the width of the flow channels, the current density distribution and fuel cell performance can be improved. By decreasing the width of their ribs or depth of channels, the performance of the fuel cell is improved and its maximum temperature is decreased.
Space systems design (spacecraft, satellites, space stations and their equipment)
Mehran Nosratollahi; Mohammad Fatehi Fatehi; Amirhossain Adami
Volume 13, Issue 3 , September 2020, , Pages 1-16
Abstract
Orbital transfer blocks has the task of transferring satellites to objective orbits from parking orbit. In this paper, Attention will be given to multidisciplinary optimal design of the propulsion system of two liquid component which is one of the most important subsystems of Orbital transfer blocks. ...
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Orbital transfer blocks has the task of transferring satellites to objective orbits from parking orbit. In this paper, Attention will be given to multidisciplinary optimal design of the propulsion system of two liquid component which is one of the most important subsystems of Orbital transfer blocks. Designing with multi objective bipropellant system, based on minimum total mass and maximum Isp, and at the end mentioned to costs and compared. For combinations of NTO as Oxidizer and fuels which are: UDMH, MMH, Hydrazine and RP-1 then for usual structures that utilized in this systems, design and optimization occurred by multi objective hybrid Particle Swarm Optimization (PSO) algorithms.
Space subsystems design: (navigation, control, structure and…)
Mahdi Jafari Nadoushan; Kosar Aramkhah
Volume 14, Issue 1 , March 2021, , Pages 1-13
Abstract
In this paper, the dumbbell model is used for gravity field of asteroid 216 Kleopatra. Utilizing the model results in governing equations of motion of a spacecraft around an asteroid similar to those of motion of a spacecraft in the restricted circular three-body problem. The equilibrium points and Jacobi ...
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In this paper, the dumbbell model is used for gravity field of asteroid 216 Kleopatra. Utilizing the model results in governing equations of motion of a spacecraft around an asteroid similar to those of motion of a spacecraft in the restricted circular three-body problem. The equilibrium points and Jacobi regions are calculated and symmetric periodic orbits are computed utilizing grid search and shooting methods. The xz-plane is considered as the symmetry plane. Stability of the periodic orbits is evaluated by Floquet theory that shows all the computed orbits are unstable. By adding the solar radiation pressure term to the governing equations of motion, the symmetric periodic orbits are recomputed and index of stability are examined. The results show that the solar radiation pressure, though change the values of the index of stability, does not affect the stability of computed periodic orbits. Therefore, stabilizing a spacecraft on the unstable periodic orbits requires controlling spacecraft.
Space subsystems design: (navigation, control, structure and…)
S. Hamid Jalali-Naini; Ali Arabian Arani
Volume 13, Issue 2 , June 2020, , Pages 1-12
Abstract
In the present work, the performance of True Proportional Navigation (TPN) with different profiles for effective navigation ratio in terms of the relative velocity angle with respect to line-of-sight is investigated due to initial heading errors and target maneuvers. Since an appropriate profile of effective ...
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In the present work, the performance of True Proportional Navigation (TPN) with different profiles for effective navigation ratio in terms of the relative velocity angle with respect to line-of-sight is investigated due to initial heading errors and target maneuvers. Since an appropriate profile of effective navigation ratio for heading error is almost in contrary with the appropriate profile for maneuvering targets, a variable effective navigation ratio in terms of the relative velocity angle and its rate is introduced. In this way, the miss distance (MD) for the first two peaks of the normalized MD graph versus normalized final time, for example under an effective navigation ratio of 4, is reduced together. The analysis is carried out using normalized equations in polar coordinates for perfect and binomial fifth-order control systems without acceleration limit. Due to practical consideration, the effective navigation ratio is tuned and limited between 3 and 5.
Zoheir Saboohi
Volume 12, Issue 3 , September 2019, , Pages 1-13
Abstract
In this paper, the design of a diffuser for a suction type subsonic wind tunnel equipped with three axial fans has been taken into account by CFD. The tunnel test section has a 140 cm height and 195cm width. For numerical modeling the axial fans that contains 10 rotor blades and 13 stator blades 3D modeling ...
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In this paper, the design of a diffuser for a suction type subsonic wind tunnel equipped with three axial fans has been taken into account by CFD. The tunnel test section has a 140 cm height and 195cm width. For numerical modeling the axial fans that contains 10 rotor blades and 13 stator blades 3D modeling to simulate the impeller have been used. The 3D modeling to simulate the impeller method provides an adequate means for simulating the swirl effects of air flow. The best geometrical characteristics have been selected for designing the optimal performance for the diffuser. The final design includes a circular diffuser which incorporates a 4 degree equivalent cone angle. This study also suggests that the circular scheme is superior to the triangular and fitted design aspect of the total pressure loss and the volumetric flow rate.
Space subsystems design: (navigation, control, structure and…)
S. Hamid Jalali Naini; Ali Arabian Arani
Volume 13, Issue 4 , December 2020, , Pages 1-13
Abstract
In this paper, a modified proportional navigation (PN) with weighted combination of linear acceleration and line-of-sight (LOS) acceleration feedback is suggested. For this purpose, a comprehensive miss distance analysis is carried out for PN with linear acceletation feedback and PN with LOS acceleration ...
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In this paper, a modified proportional navigation (PN) with weighted combination of linear acceleration and line-of-sight (LOS) acceleration feedback is suggested. For this purpose, a comprehensive miss distance analysis is carried out for PN with linear acceletation feedback and PN with LOS acceleration feedback using a fifth-order binomial guidance and control system. The miss distance (MD) due to initial heading error, target acceleration, and seeker noise is separately analysed. As a special case, a modified PN with acceleration feedback using variable gains is suggested based on MD analysis for infra red seekers. The comparison of PN strategies is carried out using an equivalent effective navigation ratio, defined by using LOS rate profile solution. In addition, the first-order optimal guidance law is converted into PN with PD block with variable gains.
Space systems design (spacecraft, satellites, space stations and their equipment)
Alireza Toloei; Mohammad Fatehi; Behrooz Keshtegar
Volume 14, Issue 3 , September 2021, , Pages 1-14
Abstract
In this paper, a design of a hydrazine monopropellant system is proposed based on the maximum likelihood for the presentation of uncertainties, without any specific assumptions about the type of distribution and even uncertainty in distribution parameters by the johnson distributions family. The maximum ...
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In this paper, a design of a hydrazine monopropellant system is proposed based on the maximum likelihood for the presentation of uncertainties, without any specific assumptions about the type of distribution and even uncertainty in distribution parameters by the johnson distributions family. The maximum likelihood method for the combination of spars point and interval data has been added to a separate formulation for design variables and parameters. This formulation is also suitable for both epistemic and aleatory uncertainty with three presentation types of spars points, single interval, and multi-interval.
Space subsystems design: (navigation, control, structure and…)
Milad َAzimi; Samad Moradi
Volume 15, Issue 2 , June 2022, , Pages 1-13
Abstract
This paper presents a study concerning active vibration control of a smart flexible spacecraft during attitude maneuver using thrusters and reaction wheels (RW) in combination and piezoelectric (PZT) sensor/actuator patches. The large-angle maneuver and residual vibration of the spacecraft are controlled ...
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This paper presents a study concerning active vibration control of a smart flexible spacecraft during attitude maneuver using thrusters and reaction wheels (RW) in combination and piezoelectric (PZT) sensor/actuator patches. The large-angle maneuver and residual vibration of the spacecraft are controlled using an extended Lyapunov-based design (ELD) and strain rate feedback (SRF) theory for a two-mode mission. The single-axis fully coupled nolinear rigid-flexible dynamic of the system is derived applying a Lagrangian approach and Finite Element Method (FEM). The overall stability of the system including energetic terms covering a hub and two flexible appendages, torsional spring, RW, and PZT dynamics, has been proved and the control law has been derived accordingly. A pulse-width pulse-frequency (PWPF) modulation is used to alleviate the excitations of high-frequency flexible modes. However, due to the fast maneuver, there are still residual vibrations in the system. Hence, the SRF algorithm using PZT is applied to prepare further vibration suppression. A great feature of the proposed hybrid actuator system is the switching time of the thrusters and RW, which is based on total system energy. The numerical results for a flexible spacecraft with large-angle, agile, and precise maneuver requirements through a comparative study verify the merits of the proposed approach.
Space systems design (spacecraft, satellites, space stations and their equipment)
Amirreza Kosari; Asad Saghari; Masoud Khoshsima
Volume 14, Issue 4 , December 2021, , Pages 1-9
Abstract
This article investigates an operational orbit's design and sensitivity analysis for Earth observation (EO) missions in non-sun-synchronous orbits. Sun-synchronous orbits are the primary choice for deploying EO satellites, but in the absence of access to such orbits, alternative options can be considered, ...
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This article investigates an operational orbit's design and sensitivity analysis for Earth observation (EO) missions in non-sun-synchronous orbits. Sun-synchronous orbits are the primary choice for deploying EO satellites, but in the absence of access to such orbits, alternative options can be considered, including multi-sun-synchronous orbits (MSSO) capable of repeating ground track (RGT).In this research, sets of such orbits are designed, taking into account the defined mission and considering the available altitude and inclination of the orbit. To achieve this, a constrained search problem is formulated, considering the constraints related to the characteristics of multi-sun-synchronicity and repeating ground tracks to search for orbit characteristics.Furthermore, to identify the allowable range of injection errors, a sensitivity analysis of the designed orbit's characteristics has been conducted to assess their sensitivity to uncertainties in injection accuracy during a case study investigation.
Space New Technologies
Reza Kohandani; Ali Davar; Mohsen Heydari Beni; Jafar Eskandari Jam; Majid Eskandari Shahraki
Volume 15, Issue 1 , March 2022, , Pages 1-20
Abstract
In this research the free vibration analysis of simply supported grid stiffened doubly curved shells by using a refined higher order theory is presented. The advantage of the present theory in comparison with other higher order theories is investigation of the effects of trapezoidal shape factor in the ...
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In this research the free vibration analysis of simply supported grid stiffened doubly curved shells by using a refined higher order theory is presented. The advantage of the present theory in comparison with other higher order theories is investigation of the effects of trapezoidal shape factor in the stress resultants in order to obtain more accurate frequency results. The governing equations of motion and boundary conditions are obtained using Hamilton’s principle and solved by using the Galerkin method. In the case of grid stiffened shells, a distribution function is introduced for describing the physical discontinuity between the ribs and the bays. The results are validated by making comparison to those existed in the literature or those obtained using the present numerical simulation in ABAQUS/Standard solver. In most cases, validations illustrated excellent agreement between the results . Finally, the effects of geometrical properties, material property and layup on the frequency responses of the shell are discussed.
