Space subsystems design: (navigation, control, structure and…)
Valiollah Shahbahrami; Milad َAzimi; َAlireza Alikhani
Volume 16, Issue 4 , December 2023, , Pages 1-13
Abstract
In this paper, a robust adaptive hybrid control approach based on a combination of super-twisting and non-singular terminal sliding mode control (STNSMC) approaches for vibration and attitude control of a flexible spacecraft with fully coupled dynamic is developed. The proposed adaptation law eliminates ...
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In this paper, a robust adaptive hybrid control approach based on a combination of super-twisting and non-singular terminal sliding mode control (STNSMC) approaches for vibration and attitude control of a flexible spacecraft with fully coupled dynamic is developed. The proposed adaptation law eliminates the need for bounds knowledge of external disturbances and uncertainties. Then an ST-based NSMC generates a continuous control signal to reject the Chattering phenomenon, the non-singular terminal switching control law with the ability to generate continuous control commands to eliminate the chattering phenomenon. Moreover, finite-time convergence is achieved, and the singularity problem has been avoided. The overall stability of the system has been demonstrated using the Lyapunov theory. One of the essential features of the proposed control algorithm is to prevent overestimation of control gains and faster convergence rates comparing to conventional ST and non-singular terminal SMC approaches. The simulations in the form of a comparative study for large-angle maneuver reveal the advantage of the proposed approach.
Space subsystems design: (navigation, control, structure and…)
Amirhossein Mirzaei; S. Hamid Jalali-Naini; Ali Arabian Arani
Volume 15, Issue 4 , December 2022, , Pages 1-18
Abstract
The miss distance analysis of the first-order explicit guidance law (EGL) is carried out using linearized equation of motion in the normalized form in order to obtain normalized miss distance curves. The initial heading error, constant target, acceleration limit, radome refraction error, and fifth-order ...
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The miss distance analysis of the first-order explicit guidance law (EGL) is carried out using linearized equation of motion in the normalized form in order to obtain normalized miss distance curves. The initial heading error, constant target, acceleration limit, radome refraction error, and fifth-order binomial control system are considered. Moreover, body rate feedback is added to the explicit guidance law as a well-known classical compensation method of the radome effect as in proportional navigation. The analysis is performed for different values of the power of the alpha function, defined as the time decrease rate of the zero-effort miss to unit control input. As a special case, the EGL with unit power gives the first-order optimal guidance strategy for minimizing the integral of the square of the commanded acceleration during the total flight time. For the performance/stability analysis, the rms miss distance versus turning rate time constant and radome slope can be plotted for different values of the power of alpha function.
Space subsystems design: (navigation, control, structure and…)
Morteza Tayefi; Ramin Kamali Moghadam
Volume 15, Issue 3 , September 2022, , Pages 1-9
Abstract
To create drag and reduce the speed of space payloads in the phase of entering the atmosphere, the payload body itself can be used as brake mechanisms without using additional tools. The approach analyzed in this paper is the separation of the nose and then the stability of the cylindrical body in horizontal ...
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To create drag and reduce the speed of space payloads in the phase of entering the atmosphere, the payload body itself can be used as brake mechanisms without using additional tools. The approach analyzed in this paper is the separation of the nose and then the stability of the cylindrical body in horizontal or vertical mode. First, by numerical solution, the cylindrical body is aerodynamically simulated in the flight conditions entering the atmosphere, and the location of the center of mass is designed to achieve static stability. Then, by developing the equations of motion of atmospheric reentry using aerodynamic coefficients and derivatives calculated by DATCOM, the flight parameters for both modes are compared and evaluated. The simulation results show that the horizontal flight is more efficient and is able to create better conditions for opening the parachute and landing. Another advantage of atmospheric reentry flight in horizontal mode is the proper distribution of aerodynamic heating and reduction of heat load in certain points of the payload.
Remote sensing
Javad Haghshenas; Reza Sharifi Hafshejani
Volume 16, Issue 1 , March 2023, , Pages 1-9
Abstract
In this paper, a step-by-step laboratory procedure for performing a satellite's payload’s alignment measurement is presented. Four highly accurate theodolites are used along with two or more alignment corner cube to accurately extract the final attitude. Theodolites are arranged around the satellite ...
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In this paper, a step-by-step laboratory procedure for performing a satellite's payload’s alignment measurement is presented. Four highly accurate theodolites are used along with two or more alignment corner cube to accurately extract the final attitude. Theodolites are arranged around the satellite in such a way that they have a clear direct view of the alignment cubes mounted on the payload and the satellite. Two theodolites should point to the payload’s alignment cube and the other two theodolites must point to the satellite’s alignment cube. Each theodolite must see at least one other theodolite, directly. Finally, by forming the coordinates systems of the payload and satellite in the theodolites coordinate system along with using the coordinate transfer matrices, the payload alignment correction matrix will be extracted in detail. The total method accuracy is within the order of few arcseconds.
Space systems design (spacecraft, satellites, space stations and their equipment)
Vahid Rahimi Ghoradel; Hossein Mahdavy-Moghaddam
Volume 16, Issue 2 , June 2023, , Pages 1-17
Abstract
Each missile has a payload section and an engine section. In the path of the missile, there is a time when the mission of the engine section is over and after that the engine will not play an effective role and will be as extra weight and consequently reduced range or factor for easy detection of the ...
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Each missile has a payload section and an engine section. In the path of the missile, there is a time when the mission of the engine section is over and after that the engine will not play an effective role and will be as extra weight and consequently reduced range or factor for easy detection of the warhead by enemy agents. In such a situation, after completing the engine mission, the mechanism of separating the steps and separating the head from the body is used. One of the separation methods is to use the thrust termination system method. In this paper, with the studies performed on the thrust termination system and the presentation of mathematical relations, the pressure drop and inverse thrust created in the chamber after opening the reverse thrust valves are predicted. Also, cold type separation and thrust termination system were used and the combustion chamber pressure drop is simulated. Then, the effect of important and influential factors on the thrust termination system has been investigated.
space sciences and exploration
Iman Shafieenejad
Articles in Press, Accepted Manuscript, Available Online from 25 July 2023
Abstract
The aim of this research is to optimize the trajectory of a low-trust spacecraft carrying biological cargo. Reducing the radiation stresses of the Van Allen belt is the optimal criterion of the optimal control problem of the orbital transfer from the low orbits to the high orbits. Since the minimum radiation ...
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The aim of this research is to optimize the trajectory of a low-trust spacecraft carrying biological cargo. Reducing the radiation stresses of the Van Allen belt is the optimal criterion of the optimal control problem of the orbital transfer from the low orbits to the high orbits. Since the minimum radiation stress criterion introduced in this article is not among the conventional optimality criteria, solving the above optimal control problem will be complicated and the honey bee optimization method has been used. The optimization of the path in this article is done by rewriting the motion equations based on the control variable and solving the new motion equations with the help of bee optimization. The main advantage of the method used in this problem is the use of optimal control theory and population-based optimization methods with a global approach. In the presented new method, the optimal control problem is simplified by redefining the differential equation system, and the results show the accuracy and ease of solution. Results of the optimal criterion of the minimum time and the minimum radiation stresses presented in this article, the criterion of the minimum radiation causes an increase of 8.89% in the transfer time.
GPS and navigation GPS)، GLONASS، GALILEO
Seyed Ali Zahiripour
Volume 17, Issue 1 , March 2024, , Pages 1-9
Abstract
A method for increasing the accuracy of the initial alignment process of inertial navigation systems with a stable platform is presented through state feedback control in flight mode. In the presented method, the state feedback controller is designed by using the stable plate deviation angles and the ...
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A method for increasing the accuracy of the initial alignment process of inertial navigation systems with a stable platform is presented through state feedback control in flight mode. In the presented method, the state feedback controller is designed by using the stable plate deviation angles and the sensor error which is extracted with the help of Kalman filter. To do this, while checking the observability of the system, by adding suitable flight maneuvers and expressing the equations of propagation of navigation error, in the form of a fixed piece system with time, it is possible to estimate the angles and errors of the sensors in the align phase. The groundwork is provided for the design of state feedback. Then, taking into account the stable platform motion equations and using the principle of separation of observer and controller design, a state feedback controller is designed. In the end, the simulation results of the proposed method show an increase in the accuracy of the alignment process and, consequently, an increase in the accuracy of the navigation, compared to the conventional output feedback method.
Space systems design (spacecraft, satellites, space stations and their equipment)
Hamed Hashemi Mehneh; amirreza Ghedamini Harouni
Volume 12, Issue 4 , December 2019, , Pages 1-17
Abstract
The robust multi-disciplinary, multi-objective shape optimization of re-entry capsule with aero-thermodynamic, trajectory, stability and the geometry considerations are presented in this paper. In this research, the results of maximizing the volumetric efficiency of the capsules while minimizing the ...
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The robust multi-disciplinary, multi-objective shape optimization of re-entry capsule with aero-thermodynamic, trajectory, stability and the geometry considerations are presented in this paper. In this research, the results of maximizing the volumetric efficiency of the capsules while minimizing the ballistic coefficient and the longitudinal stability derivative with considering uncertainties are discussed in presence of some constraints on geometry, heating load, and load factor. To reduce the time and cost of robust optimization, the Adaptive Monte Carlo Simulation technique is used which decreases the number of required evaluations within the robust optimization process. Utilizing the constrained multi-objective genetic algorithm will result in a collection of robust optimal solutions. The results show that the performance of obtained robust optimal configurations is in a way that the considered constraints aren’t violated with 99.8% of confidence level even in the presence of uncertainties.
S. Hossein Pourtakdost; M. Fakhri; Nima Asadian
Volume 1, Issue 1 , September 2008, , Pages 1-10
Abstract
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-and-error ...
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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-and-error 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 open-loop 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.
H. Bolandi; F. Fani- Saberi; B. Ghorbani-Vaghei
Volume 1, Issue 2 , December 2008, , Pages 9-15
Abstract
In this paper, the main stereo-imaging methods by high resolution satellites, including Along-Track and Across-Track, have been evaluated and then we will combine the two main stereo-imaging configurations of along track and across track as a new idea to obtain the advantages of both methods. In the ...
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In this paper, the main stereo-imaging methods by high resolution satellites, including Along-Track and Across-Track, have been evaluated and then we will combine the two main stereo-imaging configurations of along track and across track as a new idea to obtain the advantages of both methods. In the proposed stereo-imaging scenario, fast and simultaneous large maneuvers of the satellite around pitch and roll axes is one of the versatile methods. So, highly nonlinear characteristics of the governing equations because of large angle slewing maneuvers are very effective on pointing accuracy and stability and should be considered to design control laws. The purpose of this paper is to design a nonlinear control method using four reaction wheels based on PD controller that can be used to perform a spacecraft large angle maneuver using quaternion attitude variables. The configuration of reaction wheels in the simulated spacecraft has been arranged as a skewed four-wheel reaction. Reaction wheels unloading is also accomplished through the use of three magnetic torquers to prevent the speeds of the reaction wheels exceeding their designed limits, largely as a result of the action of secular components of disturbing torque. Simulation study has verified the performance and effectiveness of the proposed algorithm to achieve the proposed stereo-imaging scenario.
Tahereh Broomandnezhad; Mohammad Abdollahi Azgomi; Shahrokh Jalilian
Volume 5, Issue 4 , January 2013, , Pages 9-18
Abstract
Satellite software is a kind of application that are exposed to soft-errors or transient faults because they work in an environment, which is full of radiations. This kind of fault has caused error in the execution of software. Satellite designers have used different methods, such as hardware shielding ...
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Satellite software is a kind of application that are exposed to soft-errors or transient faults because they work in an environment, which is full of radiations. This kind of fault has caused error in the execution of software. Satellite designers have used different methods, such as hardware shielding and component hardening, for removing the effects of this type of errors. These methods will increase the cost, weight and power consumption. Also, thesemethods decrease the performance. Recently, researches have shown that instead of spatial components,, COTS components can be used in LEO satellites. In addition, software implemented hardware fault tolerance (SIHFT) techniques can be added to these components for dealing with transient faults. In this paper, a branch of these techniques, which is called control flow based techniques, are investigated and the useful method among them is highlighted. The result of the implementation, testing and evaluation of the selected method (i.e. RSCFC) is also presented in this paper.
H. Fazeli; H. Naseh; M. Mirshams; A.B. Novinzadeh
Volume 7, Issue 3 , October 2014, , Pages 9-21
Abstract
Designing space propulsion systems as one of the important subsystems of the spacecrafts and upper stage space launch systems needs to bypass different and complicated steps. In this article the comprehensive process of designing liquid fuel low-thrust space propulsion systems was illustrated. In the ...
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Designing space propulsion systems as one of the important subsystems of the spacecrafts and upper stage space launch systems needs to bypass different and complicated steps. In this article the comprehensive process of designing liquid fuel low-thrust space propulsion systems was illustrated. In the presented pattern, first of all according to the requirements and mission constraints, the main characteristics of the system were determined and then other characteristics were extracted. Finally, for the evaluation of the presented pattern, a low-thrust space propulsion system was designed based on a special mission and the results were compared with a real model. Comparison between the designed space propulsion system and the real one showed an appropriate accuracy of the presented pattern
Milad Behzadi; Mohammad Farshchi
Volume 8, Issue 1 , April 2015, , Pages 9-18
Abstract
Dynamics of laminar premixed conical flame in acoustic-velocity field was studied via numerical simulation. Methane/air combustion was modeled using a single-step, irreversible reaction and diffusion phenomena with a simple but efficient method. First, the steady flame was obtained and its corresponding ...
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Dynamics of laminar premixed conical flame in acoustic-velocity field was studied via numerical simulation. Methane/air combustion was modeled using a single-step, irreversible reaction and diffusion phenomena with a simple but efficient method. First, the steady flame was obtained and its corresponding parameters were verified. Then this steady state solution was excited by modulation of the inlet velocity. After the initial transients, heat release rate of the flame kept fluctuating with the forced frequency. The response function for various modulation intensities and frequencies agrees satisfactorily with experiments. Also, like the experimental observations the flame wrinkles and the convex sections which convert to sharp edges travel from the base to the tip of the cone at the speed of the flow.
Vahid Behnamgol; Ahmad Reza Vali; Ali Mohammadi
Volume 8, Issue 4 , January 2016, , Pages 9-17
Abstract
In this paper, a new procedure for designing the guidance law considering the control loop dynamics is proposed. The nonlinear guidance loop entailing a first order lag as the control loop dynamics is formulated. A new finite time and smooth backstepping sliding mode control scheme is used to guarantee ...
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In this paper, a new procedure for designing the guidance law considering the control loop dynamics is proposed. The nonlinear guidance loop entailing a first order lag as the control loop dynamics is formulated. A new finite time and smooth backstepping sliding mode control scheme is used to guarantee the finite time convergence of relative lateral velocity. Also in the proposed algorithm the chattering is removed and a smooth control signal is produced. Moreover, the target maneuver is considered as an unmatched uncertainty. Then a robust guidance law is designed without requiring the precise measurement or estimation of target acceleration. Simulation results show that the proposed algorithm has better performance as compared to the proportional navigation, augmented PN and the other sliding mode guidance law.
sahand majidi; Mostafa Esmaili
Volume 10, Issue 2 , September 2017, , Pages 9-21
Abstract
Liquid sloshing of a partially filled container subject to surge and pitch motions isnumerically investigated using a sophisticated numerical algorithm. The algorithm isdeveloped based on the finite volume methodology and volume of fluid (VOF) technique isutilized to capture the interface evolution and ...
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Liquid sloshing of a partially filled container subject to surge and pitch motions isnumerically investigated using a sophisticated numerical algorithm. The algorithm isdeveloped based on the finite volume methodology and volume of fluid (VOF) technique isutilized to capture the interface evolution and deformation. Also, the interface capturingquality of the developed flow solver is enhanced due to its coupling to THINC interfacesharpening technique. The numerical results are validated through the comparison of theinterface deformation amplitude and the frequency with the available experimental andanalytical data for liquid sloshing caused by lateral sinusoidal accelerations withresonance and non-resonance frequencies. Moreover, liquid sloshing due to angularexcitations are studied for two different tank geometries with and without dampingbaffles. The resulting pressure oscillations of the pressure exerted on the side walls aremonitored and compared to the experimental data.
Alireza Sharifi; Mahdi Foroughi; H. Nobahari
Volume 10, Issue 4 , March 2018, , Pages 9-17
Abstract
In this paper, an adaptive-neuro-fuzzy controller is implemented online for a temperature control system using model-based design. First, the time domain identification approaches are utilized for the dynamic model identification. Then, the identified model is used in the adaptive-neuro-fuzzy controller. ...
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In this paper, an adaptive-neuro-fuzzy controller is implemented online for a temperature control system using model-based design. First, the time domain identification approaches are utilized for the dynamic model identification. Then, the identified model is used in the adaptive-neuro-fuzzy controller. The simulated model of the proposed controller, created in the Simulink environment, is translated into C code using Simulink Coder. The generated C code is compiled into a hardware device and is successfully embedded on a microcontroller. In the next step, the experimental setup of a temperature controller is done to verify the adaptive-neuro-fuzzy controller. Finally, a comparison was made between the proposed controller and a classical proportional-integral-derivative controller to investigate the performance of the proposed approach. The results demonstrate that the proposed approach provides an excellent performance for a temperature control system.
Hadiseh Karimaei
Volume 11, Issue 3 , December 2018, , Pages 9-19
Abstract
Monopropellant thruster of atitude control system is a requirement for the development and functionalization of satellites in space, which have expensive and high-tech technology. Hydrazine thrusters are currently the most widely used thrusters for guidance and control systems of re-entry and manned ...
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Monopropellant thruster of atitude control system is a requirement for the development and functionalization of satellites in space, which have expensive and high-tech technology. Hydrazine thrusters are currently the most widely used thrusters for guidance and control systems of re-entry and manned spacecraft. In this paper, design and computation of an injector with hollow-cone spray with two tangential inlets as a fuel injector of a 10N monopropellant hydrazine thruster is presented. This injector has designed based on Bazarov method so that can generate a spray with a common (not so big) spray angle and very thin liquid sheet. Therefore it will be suitable from aspect of limitation of the catalyst bed length and also gives finer atomization.The phenomenon of creating and developing an air core in the internal flow of these injectors and its simulation is complex due to the existence of two turbulent swirl flows in two different phases, liquid and gas, which have an interface. For this injector, simulation of the internal flow has been performed to predict the output flow characteristics and ensure the formation of the gas core inside it. These characteristics include the spray cone angle, liquid sheet thickness, the output velocity distribution of the injector nozzle, and etc. For this purpose, volume of fluid (VOF) method has been used and flow turbulence has been simulated using the k-emodel. The results of this study is presented in detail in the paper.
H. Bolandi; B. Ghorbani Vaghei
Volume 1, Issue 1 , September 2008, , Pages 11-19
Abstract
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 ...
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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.
M. Nosratollahi; A. h. Adami-Dehkordi
Volume 3, Issue 2 , January 2011, , Pages 11-22
Abstract
This paper presents the multidisciplinary design optimization of monopropellant propulsion system of the nanosatellite for planner maneuver. Mass, configuration and internal ballistic equations are derived for any part of propulsion system (thruster, tank, pressurized gas, ...). Minimizing total mass ...
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This paper presents the multidisciplinary design optimization of monopropellant propulsion system of the nanosatellite for planner maneuver. Mass, configuration and internal ballistic equations are derived for any part of propulsion system (thruster, tank, pressurized gas, ...). Minimizing total mass of the propulsion system and satisfying all constrains such as Thrust limitation 5 (N) and 10 (N), Minimum specific impulse () and minimum throttle area (). AAO framework is developed and the direct search is selected for optimization method. Finally optimum designs are introduced and compared for 10(N) and 5(N) monopropellant propulsion system.
M. Mirshams; L. Khalaj-Zade
Volume 4, Issue 2 , January 2012, , Pages 11-22
Abstract
To design a manned spacecraft carrying one to two crews to the low Earth orbits, design phases should be completed in various levels. It also needs to gather manned spacecrafts technical data which is developed in the same category. In the system design algorithm presented in this paper, the conceptual ...
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To design a manned spacecraft carrying one to two crews to the low Earth orbits, design phases should be completed in various levels. It also needs to gather manned spacecrafts technical data which is developed in the same category. In the system design algorithm presented in this paper, the conceptual design sequences of a manned spacecraft named Dousti is accomplished systematically.
First of all, in accordance with a target group of manned spacecrafts’ mission, Dousti’s mission profile is defined and system level requirements are recognized. User’s requirements are also considered in the mission profile and subsequently in system level requirements.
General characteristics of Dousti spacecraft as well as its mass and dimensional features are derived in the next step. Statistics and parametric models are systematically applied in design sequence. Then, final characteristics of the spacecraft’s main subsystems designed through engineering methods and applying parametric models are introduced.
Afterwards, resulting characteristics of the spacecraft are traded off to reform and then validated by statistics and parametric models to present the final plan.
Mahdi Jafari; Arash Sangary; Jafar Roshanyan
Volume 5, Issue 3 , October 2012, , Pages 11-19
Abstract
The Inertial navigation system is an ideal solution for motion detection with high accuracy with fast dynamics, but the precise location and status of the system output can be significantly reduced over time. On the other hand, global positioning system is able to determine its position with an average ...
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The Inertial navigation system is an ideal solution for motion detection with high accuracy with fast dynamics, but the precise location and status of the system output can be significantly reduced over time. On the other hand, global positioning system is able to determine its position with an average accuracy around the earth. But the GPS alone isn’t enough for navigation of orbital modules, because it doesn’t have situation of orbital modules. The integrated inertial navigation system with global positioning system is a low cost method of providing an accurate and reliable navigation system in the civilian and military aerospace applications. In this paper, using the extended Kalman filter, we design an algorithm to estimate error of sensors, navigation and GPS. This method can be widely used in the integrated navigation INS / GPS in aerospace applications and provides an accurate navigation.
H. R. Ali Mohammady; D. Ramesh; M. R. Heidary; R Farrokhi; H. Karimi
Volume 6, Issue 1 , April 2013, , Pages 11-19
Abstract
Providing of sufficient input pressure of pumps is Pressurizing system tank mission. In structure of objective propulsion system, pressurizing system of fuel tank is hot gas kind that is feeding with engine which caused of operation relational. In this paper, interaction of pressurizing system of fuel ...
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Providing of sufficient input pressure of pumps is Pressurizing system tank mission. In structure of objective propulsion system, pressurizing system of fuel tank is hot gas kind that is feeding with engine which caused of operation relational. In this paper, interaction of pressurizing system of fuel tank and liquid rocket engine has been surveyed. Objective system consists of four main subsystems: liquid rocket engine, fuel tank, gas mixer and pipes. The procedure is based on a nonlinear mathematical model that dynamically describes operation of favorite system by regard to interaction of subsystems. Then all of the equations have been simulated in Matlab Simulation environment. Finally, results of propulsion system hot test are compared with model that shows acceptable accuracy of simulator code.
A. Hosseini; S. A. Feghhi; H. Jafari; M.B Aghaei
Volume 6, Issue 2 , July 2013, , Pages 11-19
Abstract
When the electronic components are exposed to neutron irradiation, electrical properties change by interaction of neutrons in these parts such as capacitance, reverse bias current, the minority carrier lifetime, etc. These changes are very important, so that may impair the performance of the device and ...
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When the electronic components are exposed to neutron irradiation, electrical properties change by interaction of neutrons in these parts such as capacitance, reverse bias current, the minority carrier lifetime, etc. These changes are very important, so that may impair the performance of the device and disable it. So the measurement of the damage by neutrons in these parts is necessary. One of the most important parameters for expressing the damage to electronic components is a constant, α that is the inverse current of the damage.The constant (α) is the slope of the reverse current curve versus the radiation flux. The aim of this work is measurement of the damage reverse current of constant α for diodes 1N4007, BYV27 and BYV95 in various voltages and temperatures.These diodes have been irradiated at the Tehran Research Reactor by fission neutron spectrum.The results are in good agreement with the theoretical relations.
H. Taheri Shahraaini
Volume 7, Issue 2 , July 2014, , Pages 11-21
Abstract
In this study, univariate linear regression model was developed for monitoring secchi depth in the Caspian Sea using level 1b and level 2 data. The in-situ measurements were carried outduring 25 one-day campaigns in the Caspian Sea. In this study, 25 level 1b MERIS images were utilized and then converted ...
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In this study, univariate linear regression model was developed for monitoring secchi depth in the Caspian Sea using level 1b and level 2 data. The in-situ measurements were carried outduring 25 one-day campaigns in the Caspian Sea. In this study, 25 level 1b MERIS images were utilized and then converted to level 2 data using C2R processor. The ability of univariate linear regression for the extraction of secchi depth from level 1b and level 2 wasinvestigated. The results demonstrated that the level 2 data lead to better performance than level 1b data. The level 2 data are able to retrieve the secchi depth in the Caspian Sea with correlation coefficient and percent of absolute error about 0.86 and 28.6%, respectively. Finally, secchi depth map of Caspian Sea was retrieved from MERIS level 2 images using developed univariate empirical model.
Seyed Hossein Mortazavi
Volume 7, Issue 4 , January 2015, , Pages 11-21
Abstract
Satellite formation flying is one of the most recent research topics in space field owing to various operational projects. The first and the most important step in facing with this concept is studying and modeling of dynamics of the problem. In this paper, the relative dynamics of a satellite formation ...
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Satellite formation flying is one of the most recent research topics in space field owing to various operational projects. The first and the most important step in facing with this concept is studying and modeling of dynamics of the problem. In this paper, the relative dynamics of a satellite formation flying including the leader-follower satellites based on the concept of control for geostationary vehicles, has been examined. As a consequence, an analytical solution for determination of relative position and velocity of the formation in local horizontal coordinate system which is set on leader-follower satellites has been derived. Dynamics modeling of the problem is done based on parameters which are normally used for control of geostationary maneuvers like station keeping. The advantages of utilizing these parameters are non singularity of equations and having physical sensation to these parameters. The analytical solution has been resulted from two supposes: the relative orbit is semi circular and the leader-follower satellites are close to each other in the formation.Â
