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In this paper, the structural optimization of a space capsule has been discussed by approximating a thin-walled cylindrical shell with a certain length under the axial compression force and constant lateral pressure. Design variables... more
In this paper, the structural optimization of a space capsule has been discussed by approximating a thin-walled cylindrical shell with a certain length under the axial compression force and constant lateral pressure. Design variables include the outer diameter and cylinder thickness. The purpose of optimization is to minimize the mass and maximize the frequency of the first vibration shape mode of the cylinder. The design constraints include the buckling load multiplier (buckling safety factor) above 1.5 and Von Mises stress below 100 MPa. In this article, first, according to the permissible limits of the design variables, a design of experiment (DOE) and then a sensitivity analysis was carried out to check the sensitivity of the objective functions and constraints to the design variables. After numerically solving the output values with the help of Ansys software and preparing the response surface, the optimal design point has been identified with the help of the two objectives optimization Genetic algorithm. Then, with the numerical simulation of the optimal point, the accuracy of the values obtained from the response surface method was checked and their accuracy was confirmed. The results show that at the selected design point, Von Mises stress becomes less than its allowed value, i.e. 100 MPa, and also the buckling load factor is more than twice its minimum allowed value. However, this point has the smallest distance from the origin and the optimum point has been chosen as the knee point.
PARS1 Satellite is a Remote Sensing satellite with a 3-years mission. The main mission of this satellite is imaging the earth by three cameras named MS, SWIR and TIR. PARS1 OnBoard Software (OBSW) is developed as a performance platform,... more
PARS1 Satellite is a Remote Sensing satellite with a 3-years mission. The main mission of this satellite is imaging the earth by three cameras named MS, SWIR and TIR. PARS1 OnBoard Software (OBSW) is developed as a performance platform, satellite components control, manage their data, algorithm management included normal status control and event handling. OBSW is more important than other satellite subsystems due to its complexity and different features. So, the design, development and test of the PARS1 satellite OBSW is a useful platform to gain valuable experiences in the field of satellite onboard software which is very wide and complicated in its field. Therefore, in this paper decided to present experiences which gained in this field, in the form of summary of achievements and lessons learned. These experiences is gained from development and test phase of the satellite and using of these experiences will be very useful and effective in smoothing of test and development path in future projects of the Satellite Research Institute
In This paper, a domestic regional and independent satellite navigation system, known as "IRANSS" has been designed and analyzed to cover user needs in the Middle East Region. The Space Segment of this constellation is composed of nine... more
In This paper, a domestic regional and independent satellite navigation system, known as "IRANSS" has been designed and analyzed to cover user needs in the Middle East Region. The Space Segment of this constellation is composed of nine satellites in four orbits, in such a way three satellites have been considered in one GEO orbit [1] and two satellites are considered in each of three IGSO orbits [2]. Two main Tracking and Control Ground Stations and twenty wide area reference stations, assigned only for augmentation, form the Ground Segment. The focus of this research is on space segment and specially design a navigation constellation and satellites' system design, and evaluation of the performance of the navigation system in combination with other satellite-based navigation systems, since Augmentation Systems prepare correction signals for a specific Navigation System by ground segment. STK is the main software used to design and analyze the performance of the system by DOP as a reference for Ranging Errors based on Constellation Geometry. All of design parameters are computed in a way to minimize GDOP with four satellites. The parameters of navigation accuracy have been compared with other active GNSS [3] constellations to evaluate error in the designed system. Analysis results express that the geometric accuracy of the designed system is solely 16 meters in 95% of a day in all points of the desired area and would be improved to 14 and 12.5 meters in the case of combination with BeiDou and GPS, respectively.
Due to various and complex phenomena in hybrid dynamical systems, the control of these types of systems has faced a challenge. Space systems also have hybrid dynamics due to different missions and operational modes. Therefore, to deal... more
Due to various and complex phenomena in hybrid dynamical systems, the control of these types of systems has faced a challenge. Space systems also have hybrid dynamics due to different missions and operational modes. Therefore, to deal with these systems, we must first familiarize ourselves with the standard examples that have been studied before. Consequently, in the field of hybrid control science, various examples have been reviewed and researched. In order to improve the performance comparison of control methods or to check their comprehensiveness, some of these examples are used as benchmark examples. Therefore, this article has been tried to collect benchmark examples with different characteristics in the hybrid control field and compare them with each other. It should be noted that benchmark examples were selected based on the number of repetitions and recognition. Therefore, the performance of the developing controllers can be examined on these examples and compared with the results of other controllers. As a result, the researchers can choose their desired benchmark more accurate and efficient with the investigation and design of the controller.
One of the methods for improving thermal conductivity of epoxy adhesives is the incorporation of conductive ceramic, metal or carbon fillers. As the main goal of this research is to improve the thermal conductivity of epoxy resin and keep... more
One of the methods for improving thermal conductivity of epoxy adhesives is the incorporation of conductive ceramic, metal or carbon fillers. As the main goal of this research is to improve the thermal conductivity of epoxy resin and keep its electrical insulating property, the effect of Alumina (Al2O3) ceramic filler individually, and in combination with Boron Nitride (BN) ceramic filler with high thermal conductivity and electrical resistivity is investigated. Scanning Electron Microscopy (SEM) observations showed a proper dispersion and an acceptable connection between fillers. The results of the thermal diffusivity measurements revealed that by incorporating conductive ceramic fillers, either individually or in combination, regardless of the type of the hardener, thermal diffusivity would increase due to the formation of thermal conductive networks. Although, in hybrid system, because of bridging effect between particles, thermal diffusivity will notably increase; therefore, using hybrid system of Alumina/BN along with long chain polyamine curing agent is a suitable choice for the preparation of thermally conductive yet electrically insulating epoxy adhesives in space industries. The results showed that the thermal conductivity of hybrid system of Alumina/BN has raised to 1.7 (W/mK), which is about 0.4 (W/mK) for epoxy system without filler. The most important achievement of this research is to achieve proper thermal conductivity while keeping mechanical properties, dielectric constant, and lap shear strength of Alumina/BN hybrid system within acceptable range of thermal conductive adhesive for space applications.
Star tracker is one of the most important devices used on satellites for attitude determination. Since its output is discontinuous, it needs a complementary unit to cover its discontinuities. Using gyroscope unit is the most suitable... more
Star tracker is one of the most important devices used on satellites for attitude determination. Since its output is discontinuous, it needs a complementary unit to cover its discontinuities. Using gyroscope unit is the most suitable choice for aiding the star tracker. However, using these two kinds of sensor simultaneously has some challenges. In other words, not only not only sensor biases decrease the accuracy of attitude determination, but also the installation error has a significant effect on the accuracy. In this paper, after presenting the important role of installation errors between star tracker and gyroscope in the accuracy of attitude determination, an effective method is proposed to determine the misalignment error between these two sensors which is only based on their measurements, and the mathematical formulation is presented in detail. Finally, to validate the performance of the proposed method, it is implemented to calculate the instantiation error of an experimental dataset gathered in the Mount Pooladkaf, And the results are reported in the form of graphs and tables.
The purpose of this research is to evaluate a ground test bed of an orbital transmission engine with pre-evacuation of the engine's internal space. In the usual tests on the ground, the initial pressure of the engine is atmospheric... more
The purpose of this research is to evaluate a ground test bed of an orbital transmission engine with pre-evacuation of the engine's internal space. In the usual tests on the ground, the initial pressure of the engine is atmospheric pressure. While during the orbital mission, the internal space of the engine may be in the vacuum pressure. Therefore, to ensure the proper performance of internal ballistics, it is necessary to test the performance by pre-evacuating its internal space. In this research, first, the suitability of an exhaust diffuser for this type of test is investigated numerically. Then, the unsteady numerical simulations have been done by applying the pressure-time profiles of the engine as the boundary condition of the inlet pressure. Investigations show that the two phenomena of flow being supersonic in the diffuser at very low engine pressures and the discharge of the return flow to the vacuum chamber prevent the significant influence of environmental conditions on the flow inside the nozzle. So, from the initial moment to the stable working of the diffuser, the flow in the first half of the nozzle is in the supersonic state. Therefore, the internal ballistics of the engine is evaluated independently of the conditions of the outside environment.
The filament winding process is one of the most important and widely used processes in the manufacture of composite structures in order to achieve high strength and rigidity. In this process, there are important parameters such as fiber... more
The filament winding process is one of the most important and widely used processes in the manufacture of composite structures in order to achieve high strength and rigidity. In this process, there are important parameters such as fiber tension, how the fibers are twisted, the effect of layering, twisting angle, fiber twisting pattern of fibers, type of material suitable for twisting, etc. , which can play a significant role in this the strength of the processstructure. In this regard, the twisting pattern has been less studied by researchers less than other parameters. In this research, the effect of fiber twisting pattern on the hydrostatic pressure threshold of epoxy glass cylinder has been investigated. For this purpose, first, glass/epoxy cylinders with 4 four different twisting patterns were made with ± 54 arrangement and subjected to hydrostatic test with internal pressures of 5-50 bar, where the amount of radial displacement in the middle of the cylinder was measured experimentally. In the following, the amount of radial displacement of cylinders due to the internal pressure was is also modeled using numerical analysis (Abaqus) and compared with experimental results. In order to validate the experimental and numerical results, theoretical model was used and the results were compared. All of the results obtained were in acceptable limits and showed that the twist pattern having with finer texture has a higher compressive strength. Also, the simulation results showed a good agreement with the experimental results.
This research is going to present design of a LEO Constellation for Navigation service with minimum number of Satellites. The goal is to achieve Dilution Of Precision (DOP) less than 6. This Requirement is going to be achieved using... more
This research is going to present design of a LEO Constellation for Navigation service with minimum number of Satellites. The goal is to achieve Dilution Of Precision (DOP) less than 6. This Requirement is going to be achieved using predefined launch vehicles limitation on orbit which is 500 km in circular orbit altitude and 55 degrees for orbit inclination. Design has been done based on Analyses resulting in Optimization for least number of Satellites in this orbit, to satisfy all requirements for Navigation Performance and in conformance with the constraints related to launch and orbit. Multiple analyses have been done resulted in Constellation with 324 satellites, formed in 18 Orbits with 18 Satellites in each. This design shows the performance of 4.7 in DOP for a User located in Tehran, however, the distribution of DOP over the target area shows that the requirement has been passed through the whole region.
The this article the characteristics of the hollow cathode plasma particles in the spt-100 hall effect thruster have been investigated by two-dimensional particle-in-cell simulation. One of the main and important components of the hall... more
The this article the characteristics of the hollow cathode plasma particles in the spt-100 hall effect thruster have been investigated by two-dimensional particle-in-cell simulation. One of the main and important components of the hall thruster is hollow cathode which plays two important tasks: one part of the electrons that come from the cathode used for anode propellant ionization, and the other part plays an important role of neutralizing the ion beam coming out of the thruster. Therefore, the study of the hollow cathode characteristic is importance. Krypton is used as fuel in this system. Potential changes, density of electrons, ions and temperature of particles have been studied throughout the simulation area. The results show that corresponding to the electrons, the ion density also decreases from the maximum value in the cathode ionization region exponentially through outer chamber. Also, analyzing normalized radius regard to electron density shows that the cathode effective area in which the radius electron temperature reaches maximum value is located about 1.5mm from the center line of the hallow cathode.
The ions in the space environment cause the surface and internal charging phenomenon in satellites. The accumulated potential during the charging phenomenon can cause electrostatic discharge and expose the satellite telecommunication... more
The ions in the space environment cause the surface and internal charging phenomenon in satellites. The accumulated potential during the charging phenomenon can cause electrostatic discharge and expose the satellite telecommunication components such as antennas and electronic circuits to serious risk. The purpose of this paper is to investigate the possibility of electrostatic discharge on satellite surfaces in low earth orbit (LEO) environment and to reduce this possibility in order to reduce the risk of damage to satellite surfaces and telecommunication components. Therefore, First, the surface charging phenomenon was simulated in an aluminum satellite in low earth orbit and then in polar aurora by SPIS software and the possibility of damage to the antennas was investigated. Then, multi-layer thermal insulation was applied to the system and its effects on the charging phenomenon were investigated. Research has shown that adding MLI layers will increase the risk of electrostatic discharge. Therefore, in the next steps, the effect of the grounding system in reducing the risk was investigated. By connecting the layers to the ground in a proper way, the possibility of discharge between the layers and the body and between the layers with each other is minimized, which led to the achievement of an optimal system in terms of electrostatic aspects.
Accurate solving of complex systems such as spacecraft is very costly and time consuming. By building a surrogate model, the solution time and the cost can be reduced. The closer the surrogate model is to the actual model, the more... more
Accurate solving of complex systems such as spacecraft is very costly and time consuming. By building a surrogate model, the solution time and the cost can be reduced. The closer the surrogate model is to the actual model, the more accurate the solution and the lower the error rate. Highprecision successor models are called metamodels. The basis of producing a high-precision metamodel is to perform high-precision sensitivity analysis with a suitable method. Sensitivity analysis can show the effect of input variables on output variables and produce a surrogate model by eliminating ineffective input variables. Therefore, sensitivity analysis is highly valuable in solving complex systems. The purpose of this article is to analyze the sensitivity of the multidisciplinary design of a monopropellant liquid propulsion system by the Latin Hypercube Sampling method. In this article, the topics related to the liquid monopropellant propulsion system are divided into six parts: High pressure gas tank, liquid fuel tank, injector, decomposition chamber, catalytic bed and nozzle. By determining the input and output variables of each subject, the results of sensitivity analysis are displayed in two ways: the sensitivity of the input variables to the output and the twoby-two correlation of the parameters with each other. In the results, as can be seen, the specific impulse input variable, in the high-pressure gas tank and the liquid fuel tank, has no effect on the output variables. In the injector, the number of grooves, groove angles and fuel tank pressure do not have a significant effect on the output variables. In the decomposition chamber sensitivity analysis diagram, the radius of the granule and for the catalyst bed, in addition to the radius of the granule, the percentage of ammonia decomposition are also ineffective. Finally, the sensitivity analysis for the nozzle shows that the ratio of specific heat has no effect on the output variables.
Forest biomass is one of the most important parameters in the ecosystem changes assessment and global carbon cycle modelling. In the other hand, the forest height is an effective parameter in the allometric equations which are used for... more
Forest biomass is one of the most important parameters in the ecosystem changes assessment and global carbon cycle modelling. In the other hand, the forest height is an effective parameter in the allometric equations which are used for biomass estimation. In this research, the effect of two physical factors forest height and forest density, will be evaluated in the applicability of the four common inversion algorithms for forest height estimation based on the polarimetric Interferometry SAR (PolInSAR) technique. The applicability of the digital elevation model (DEM) differencing, volume coherence amplitude, hybrid and three-stage methods are studied for different forest height and forest density by using simulated polarimetric interferometric SAR data in L-band. The experimental results of the forest height estimation in simulated data with a density of 100 to 900 trees per hectare and a height of 10 to 18 meters show that the results of the hybrid method show high sensivity to changes in both height and density. The root mean square of error was 5.8, 5.6, 3.2 and 4 m for data with variable height and 11.6, 6.7, 5.8 and 5.3 m for data with different densities, respectively.
One of the key subsystems in satellites is the attitude determination, and the sun sensor is one of the most common sensors in this field. Today, due to the increasing development of satellites, the need to increase the accuracy of... more
One of the key subsystems in satellites is the attitude determination, and the sun sensor is one of the most common sensors in this field. Today, due to the increasing development of satellites, the need to increase the accuracy of satellite subsystems seems very necessary. In this paper, the design of a sun sensor made with an optimized slit in the entire field of view is examined. In this sensor, two orthogonal linear detectors are used, on top of each of the detectors, an optimal gap perpendicular to the detectors is required at an optimal distance according to the field of view. Due to the light passing through the optimized slits and its effect on the detectors and the slit, a peak can be seen in the output of the detectors, which according to the location of the peak, the angle of the incoming light can be calculated with high accuracy. The sun sensor made in Shiraz Mechanics Research Institute has an absolute error (2 sigma) of 0.14 in the 50 degrees of field of view
In this paper, a passive fault tolerant control method is proposed for the satellite attitude tracking in the presence of external disturbances, the inertia matrix uncertainties, and reaction wheel faults. To achieve this goal, a modified... more
In this paper, a passive fault tolerant control method is proposed for the satellite attitude tracking in the presence of external disturbances, the inertia matrix uncertainties, and reaction wheel faults. To achieve this goal, a modified fast terminal sliding model approach is used due to its robustness against the un-modeled uncertainties and being suitable for the nonlinear system model. The sliding surface variable is chosen to avoid singularity, converge to zero in a finite time, and also reduce the Chatting phenomenon. The stability and finite time convergence of the attitude variables are also demonstrated by the extended Lyapunov method. In order to increase the accuracy of the designed controller, the dynamic model of the mentioned actuators is considered. Finally, in order to evaluate the performance of the proposed method, the simulation is performed on a satellite with four reaction wheels under the mentioned conditions. The results show that the proposed method can maintain the stability of the system despite the occurrence of actuator faults, and it makes the state variables converge to the desired trajectories in a finite time and also produce chattering-free control signals.
The use of thermal knives as holding mechanism and non-explosive release in the field of space mechanisms has always been considered. In these mechanisms, the use of materials with high melting points and low weight, as well as the... more
The use of thermal knives as holding mechanism and non-explosive release in the field of space mechanisms has always been considered. In these mechanisms, the use of materials with high melting points and low weight, as well as the possibility of production on a small scale is a major challenge. Therefore, the use of platinum / alumina catalysts can be a good solution to the leading problems in this field. The purpose of this paper is to prepare a high specific surface alumina base using the process of anodizing aluminum and coating it with platinum particles. Thus, the present study consists of two stages; In the first stage, aluminum is anodized in oxalic acid solution and its parameters are optimized in order to achieve aluminum nanotubes with various diameters and wall thicknesses, as well as the applied voltage, electrolyte concentration and anodizing conditions. In the next step, platinum nanoparticles were precipitated in different amounts using metal salt and suitable solvent using electrochemical method. The results showed that the obtained nanowires have a diameter of about 200 nm and a length of several micrometers. All samples were mechanically polished and it was shown that the aluminum anode oxide membranes were completely filled with a combination of metals. Also, the performed analyzes showed that the obtained nanowires are stable inside the membrane.
In this paper, the effects of different weight percentage of iridium (Ir) nanoparticles loadings on performance parameters of hydrazine catalyst and monopropellant thruster have been studied. Nanoparticles of iridium with different... more
In this paper, the effects of different weight percentage of iridium (Ir) nanoparticles loadings on performance parameters of hydrazine catalyst and monopropellant thruster have been studied. Nanoparticles of iridium with different contents of 10 wt%, 20 wt%, and 30 wt% has been coated on gamma-alumina of 1 to 2 mm size for decomposition of hydrazine during some various steps of calcination. These catalysts then have been tested in a 1 N thruster. The tests were conducted using a scenario of different stages of steady and pulsating fires of different times and duty cycles. The test results showed that catalyst loss was minimum with 30 wt% of iridium nanoparticles loading. Despite of this, there were no meaningful difference between other parameters such as pressure roughness, thrust, specific impulse, and catalyst crushing. The results showed a good value of characteristic velocity. All parameter values of three type of catalysts were in the expected and desired range.
In this paper, a satellite attitude control system (SACS) based on tube-based robust model predictive control (TMPC) methodology is designed which is robust to bounded disturbances. All Euler angles and their derivatives are ensured not... more
In this paper, a satellite attitude control system (SACS) based on tube-based robust model predictive control (TMPC) methodology is designed which is robust to bounded disturbances. All Euler angles and their derivatives are ensured not to deviate more than a determined limit under those disturbances with known bounds. It is conducted based on the concept of the minimal robust positive invariant (mRPI) set. Actuators and Euler variables constraints could be considered in the SACS. The dynamics are guaranteed to be robustly stable. Given that the satellite dynamics consists of a great number of states, it is not possible to implement a TMPC scheme on the SACS in real-time. The number of satellite system states in this article is 6. Which has practically increased the volume of calculations. In order to solve this challenge, the proposed solution of tube estimation is presented to reduce the volume of satellite calculations. With this estimation, the process of increasing the volume of computations for tube-based robust predictive control design for satellite is stopped. For the desired system, simulation has been done in the presence of uncertain and limited disturbance. The results show satellite attitude control by reducing the amount of computation when designing a tube-based robust Model predictive control.
In this paper, the computational fluid dynamics simulation of a tactical aerostat is conducted and the longitudinal static coefficients of the aerostat are evaluated. In this simulation, Fluent software and Spalart-Allmaras turbulent... more
In this paper, the computational fluid dynamics simulation of a tactical aerostat is conducted and the longitudinal static coefficients of the aerostat are evaluated. In this simulation, Fluent software and Spalart-Allmaras turbulent model are used. First, in order to validate the numerical method and the applied turbulent model, a famous airship hull is simulated and the drag coefficient at zero angle of attack is compared with the references and the CD0 is in very good agreement with references. Then, the designed aerostat is simulated in the angle attack of)-10 to 30(degrees then the pressure, Y+ contours and the streamlines around the aerostat are presented. Furthermore, the aerodynamic longitudinal coefficients are calculated for 5 and 20 m/s. The results show that the aerodynamic coefficients do not vary significantly with the change of velocity and the pitch moment coefficient about the nose of the designed aerostat has a negative slope. Finally, Comparing the pitch moment coefficient of the designed aerostat with two American and Korean aerostats indicate that, the designed aerostat has more static stability.
In recent years, extensive research has been focused on the key materials of vanadium redox flow batteries (VRFBs) to improve the power and energy density. In a VRFB system, the ion-exchange membrane is an important component, because it... more
In recent years, extensive research has been focused on the key materials of vanadium redox flow batteries (VRFBs) to improve the power and energy density. In a VRFB system, the ion-exchange membrane is an important component, because it is used to separate the positive and negative electrolytes and to allow the transfer of ions. Nafion membrane is now widely used in VRFBs due to its high proton conductivity and remarkable chemical stability. In the present study, the Nafion 117 membrane was subjected to acid-heat pretreatment for utilizing in VRFBs. Three-cell stacks of VRFB were assembled using bare and pretreated membranes, and their performances were evaluated during charge/discharge cycles. The results indicate that acid and heat pretreatment on the Nafion 117 membrane improves the VRFB energy density up to 30%. In addition, the average discharge voltage, which is one of the key parameters in the VRFB performance, is increased from 3.57 V (for the bare membrane) to 3.9 V (for the pretreated membrane). This helps to reduce the weight of the VRFB stack as well as the cost of the battery manufacturing. On the other hand, the acid and heat pretreatment of the membrane improves the energy and voltage efficiencies of VRFB from 66.9% and 76.8% to 73% and 87%, respectively. How to Cite this article
One of the most common methods to increase the adhesion of aluminum surfaces is the use of anodized coatings. However, if we heat the manufactured products before adhering due to the hydration of the anodized coating, cracking and... more
One of the most common methods to increase the adhesion of aluminum surfaces is the use of anodized coatings. However, if we heat the manufactured products before adhering due to the hydration of the anodized coating, cracking and morphological changes, the adhesive capacity will be severely reduced. As part of the research presented in this study, methods such as non-sealing of the anodize, primer application before heating the coating, sandblasting before and after the anodizing coating, and use of FPL (Forest Products Laboratory) replacement coating have been used to investigate the adhesive behavior of the coating. According to the results, not sealing the anodized coating and priming it before heating will increase the adhesiveness of the coating in all cases. Sandblasting after coating had no significant effect on adhesion. Sandblasting before anodizing improves adhesion by altering the texture of roughness and morphology. FPL can also be used to replace anodized coatings. They were less sensitive to heating and storage.
The aim of this study is to evaluate the performance of water-jacket cooling system for thermal protection of exhaust large dimension diffuser at high heat fluxes in a wide range of coolant pressure. For this purpose, using the developed... more
The aim of this study is to evaluate the performance of water-jacket cooling system for thermal protection of exhaust large dimension diffuser at high heat fluxes in a wide range of coolant pressure. For this purpose, using the developed calculation code, the parameters of the water-jacket cooling system are determined so that in addition to satisfying the temperature conditions of the metal body, the total pressure drop has remained in the desired range. In the following, the capability of numerical code to design and performance analysis of the cooling system has been evaluated in coolant pressure of 3 to 50 bar and high heat fluxes up to 3.5 MW/m2. The present studies show that the proper selection of coolant pressure is very important in the design of the cooling system with optimal mass flow rate and minimum coolant dimensions, especially at high heat fluxes, so that increasing the coolant pressure from 3 to 10 bar, in addition to significantly reducing the dimensions of the cooling system, reduces the mass flow rate by 75%.
One of the reasons for the increasing popularity of lithium-ion batteries is the improvement of their rate capability and power density. All components of a battery, including the anode, cathode, electrolyte, and separator, can limit the... more
One of the reasons for the increasing popularity of lithium-ion batteries is the improvement of their rate capability and power density. All components of a battery, including the anode, cathode, electrolyte, and separator, can limit the capability of lithium-ion batteries. While most efforts have focused on the new electrode architecture and electrolyte formulation to improve battery performance, studies on separators have focused mainly on their mechanical and physical properties and little attention has been paid to their effect on the performance of lithium-ion batteries. In this study, a comprehensive study of the physical, thermal and electrochemical properties of disassembled high drain lithium-ion battery separator (HDLIB) with high discharge rate capability and commercial polyethylene separator with a thickness of 16µm (G16) is reported. According to the research, it has been shown that HDLIB separator has 26% less contact angle and better wettability than commercial polyethylene separator. Also, HDLIB separator at 150°C has shrunk by 55.6% less than G16, which may be due to the presence of boehmite ceramic particles in its structure. In addition, it shows that HDLIB separator can play an important role in improving the rate performance and safety of lithium-ion batteries.
In this paper, a wideband high-gain microstip patch array antenna for high resolution synthetic aperture radar applications is presented. The antenna operation frequency is in the X-band and the antenna structure is a four-layer... more
In this paper, a wideband high-gain microstip patch array antenna for high resolution synthetic aperture radar applications is presented. The antenna operation frequency is in the X-band and the antenna structure is a four-layer configuration consisting of radiating patches, slots, coupling cavities, and a corporate feeding network, which in turn is fed by a coaxial probe. The increased frequency bandwidth of the radiating patch is achieved by employing a square slot, which appears as a cavity for it, and improves the gain and impedance bandwidth of the antenna array by isolating the patch feeding slot and eliminating the mutual coupling effect. The whole antenna structure is fabricated by using a combination of the milling process and printed circuit technology. Measurement results show a relative gain bandwidth of more than 10%, in which the antenna gain is measured above 28.8 dBi over the frequency band of more than 1 GHz. Moreover, the relative impedance bandwidth of the antenna for VSWR>2 is more than 16%.
One of the key issues in the operations of on orbit servicing to unmanned satellites is to provide a safe and reliable docking process. This paper investigates the dynamic behavior of a flexible probe in the central docking mechanism of... more
One of the key issues in the operations of on orbit servicing to unmanned satellites is to provide a safe and reliable docking process. This paper investigates the dynamic behavior of a flexible probe in the central docking mechanism of unmanned satellites. For simulating the impact phenomenon, a dynamic analysis software (MSC. Adams) has been applied and a three-dimensional model has created based on the assumption of a flexible clamped beam as a shock absorber. The results are in good agreement with similar theoretical and experimental results. additionally, it is possible to consider the parameters such as the type of connection between the beam and the concentrated mass, angular and translational velocity of chaser and target satellites, in order to determine the optimum condition to perform a successful docking operation. The results of this study indicate that the use of a spherical joint for the ball attached to the probe, significantly reduces the maximum value of impact force. Also, the rotation of the sphere leads to less change in the linear and angular velocity of the target satellite and increases the probability of successful mating of the satellites. On the other hand, the movement of the conical area relative to the target satellite reduces the maximum impact force and shock resulting on the satellites structure. As a result, the chance of successful docking increases.
In the present study, the effect of pre-evacuation on starting process of a second throat exhaust diffuser has been investigated experimentally by examining a thrust optimized parabolic nozzle. An experimental setup called high-altitude... more
In the present study, the effect of pre-evacuation on starting process of a second throat exhaust diffuser has been investigated experimentally by examining a thrust optimized parabolic nozzle. An experimental setup called high-altitude test facility has been used with compressed air as operating fluid. According to the importance of area ratio parameter (Ad/Ast) of a second throat diffuser, the effect of this parameter variation has been examined on the start-up performance of the nozzle and diffuser. In all of the diffuser geometries, to evaluate the instantaneous performances, the pressure in the nozzle chamber has charged instantly in two modes; with and without pre-evacuation. then, the vacuum chamber pressure and static pressure distribution along the diffuser are measured by a data acquisition system. The results show that pre-evacuation in the test chamber reduces the start-up time of the diffuser by 50 to 60%. In addition, pre-evacuating the test chamber eliminates the destructive transition phenomenon from the flow separation pattern during start-up of the nozzle and diffuser. Also, It is observed that with the narrowing of the diffuser’s second throat duct, the minimum starting pressure of the diffuser increases and eventually flow chocks at the second throat in a certain area ratio.
This paper studies the time-optimal 6 degrees of freedom (6DOF) orbital rendezvous maneuver problem for an inertially asymmetric rigid spacecraft with independent attitude and position control actuators. It is assumed that the spacecraft... more
This paper studies the time-optimal 6 degrees of freedom (6DOF) orbital rendezvous maneuver problem for an inertially asymmetric rigid spacecraft with independent attitude and position control actuators. It is assumed that the spacecraft equipped with the thruster actuators and the control forces and torques are generated along the three principal axes of the spacecraft. In order to obtain the time-optimal 6DOF maneuver state and control trajectories, at first, the relative translational and rotational dynamics of the spacecraft are described. Then, the Gauss pseudospectral method is used to solve the time-optimal control problem in the presence of constraints on control forces and torques. Also, the costates are estimated to first-order optimality proof of the obtained solutions. Numerical simulation results show that for the assumed time-optimal 6DOF maneuver problem, the control structure for all of the control forces and torques is ‘bang-bang’. Eventually, the optimality of the obtained solutions is verified by checking the fulfillment of Pontrygain’s minimum principle.
In this paper, we investigate the orbital characteristics of a constellation consisting of 24 LEO satellites. All the configurations are based on the Walker Delta model, which include single-regulated (one constellation) and... more
In this paper, we investigate the orbital characteristics of a constellation consisting of 24 LEO satellites. All the configurations are based on the Walker Delta model, which include single-regulated (one constellation) and double-regulated (intertwined two constellations) models. For the sake of comparability, it is assumed that the orbital period of all satellites is 127 minutes and regarding the maximum altitude of 2000 km, the three eccentricities of zero (circle), 0.19 (with an apogee of 2000 km) and 0.097 (=0.19/2) with the longest presence time on the mission area, are considered. In order to limit the search space, the inclination of all orbits is assumed to be 40 degrees and three values of 320, 340 and 360 degrees are considered for the argument of perigee in elliptical orbits. Assuming the need for at least two satellites observable, basically, it can be found that for the argument of perigee of 320 degrees pertains the best coverage beside the least standard deviation. As expected, the higher eccentric orbits perform better regardless of changes in signal strength. Double-regulated configurations, on the other hand, can be associated with a larger number of satellites in view, which generally is accompanied by higher standard deviations. In essence, a configuration may be chosen only based on the pertaining mission requirement and no one should be regarded as the absolute optimum.
In this research, the performance of a monopropellant hydrazine thruster in atmospheric conditions has been investigated experimentally. For this purpose, after designing and constructing the thruster according to the functional... more
In this research, the performance of a monopropellant hydrazine thruster in atmospheric conditions has been investigated experimentally. For this purpose, after designing and constructing the thruster according to the functional requirements of the thruster, a test was designed and after that, the desired thruster was tested in atmospheric conditions. The test results show that the tested thruster can generate 2000 pulses with a width of 0.5 seconds and a periodicity of one second with reproducibility. It was shown that the life of this thruster is more than 2000 pulses and the thruster was able to produce very small beats of 3 mNS in reproducibility. Also, comparing the results of the current thruster sample with the experimental results of other thrusters showed how by selecting the appropriate dimensions for the injector, catalyst chamber and nozzle, the characteristics of pressure rise time, minimum impulse, pulse centroid and pressure drop time in the Thruster can be well controlled. Reducing the injector diameter (by keeping the flow rate constant by increasing the injection pressure) reduces the impulse (within a constant pulse width) and increases the pressure rise time. Reducing the dimensions of the catalyst chamber also reduces the increase and decrease time of the pressure, resulting in a smaller pulse centroid.
In this paper, the results of the process of analyzing potential failure situations on the operational product of the reaction wheel condition control operator are discussed and the effects of the identified failure situations are... more
In this paper, the results of the process of analyzing potential failure situations on the operational product of the reaction wheel condition control operator are discussed and the effects of the identified failure situations are eliminated or reduced. The technique of analyzing failure modes and their effects is the first technique in meeting the requirements of reliability in design. In this regard, the block diagram of the functional flow of the reaction wheel is presented for the first time and the dependence of the functions is presented statically in the form of a matrix. To achieve this goal, the different parts of this operation are identified and their failure modes and the cause of failures of each part are determined. Also, the effects of failure of different levels will be determined locally, at the equipment level, at the subsystem level and at the system level. In addition, the way to diagnose failure and deal with the effect of failure is presented and related analysis is performed, which is a quantitative analysis and will determine the parameters of severity of error effect, probability number and criticality number, calculation and critical items. Took. Then, based on the identified critical sections, a list of critical items is also extracted. The information extracted from the analysis of failure modes and their effects, while helping to improve the reliability of the design of the reaction wheel operator, will provide the designer with important data for fault and error management during the test and mission stages.
The monopropellant thrusters of the position control system are a requirement for the development and application of satellites and space capsules in space, which are also high-tech and expensive. In this paper, the design and simulation... more
The monopropellant thrusters of the position control system are a requirement for the development and application of satellites and space capsules in space, which are also high-tech and expensive. In this paper, the design and simulation of a pressure-swirl injector with full-cone spray as the fuel injector of a monopropellant thruster were presented. For this injector, internal flow simulation was performed in order to predict its output flow characteristics. These characteristics include spray cone angle, output velocity distribution, mass flow rate, spray pattern, and etc. For this purpose, the VOF fluid volume method was used and the flow turbulence was simulated using the k-eps model. The results of these studies are presented and discussed in detail in the article. This type of injector is actually a combination of jet injector and swirl injector. Jet straight flow in the center of the injector and swirl flow along the injector wall are flowed. Both flow regimes are combined in the swirl chamber and the spray is formed as a full-cone in the injector discharge nozzle. If the ratio of the outlets is selected correctly, the radial and environmental distribution of the liquid jet will be uniform. This injector is preferred to the capillary type (straight flow) and the swirl type. The pressure-swirl injector spray angle is larger than the capillary type, which improves the coverage of the catalyst bed, at the same time, spray angle is not as large as the swirl injector, which enlarges the radial dimensions of the decomposition chamber.
Achieving a flawless solid composite propellant requires proper processability of its corresponding filled polymer slurry. In other words, the optimal rheological properties of highly filled suspensions after mixing process, ensure its... more
Achieving a flawless solid composite propellant requires proper processability of its corresponding filled polymer slurry. In other words, the optimal rheological properties of highly filled suspensions after mixing process, ensure its transfer to the mold and complete filling of complex geometries. In this dynamic study, after adding molybdenum disulfide nanoparticles to the model materials, rheological properties of the obtained suspensions have been investigated.
In order to study the effect of molybdenum disulfide nanosheets on the rheological behavior of the suspensions, polyethylene glycol matrix and glass beads, as model, with particle distribution of 60 to 103 microns were employed.
Single-layer and multi-layer molybdenum disulfide nanosheets with thickness of 50 to 100 nm was obtained after acid washing, oxidation and heat shock of raw molybdenum disulfide. Then, after preparation of suspensions containing 10-40 vol% glass beads, the effect of obtained molybdenum disulfide (less than 0.1 vol% of the matrix) on the rheological properties of the mixture was studied. Results of frequency sweep and temperature sweep tests showed that complex viscosity of the suspensions had a significant decrease with increasing nanoparticles, while simultaneously, storage modulus was fixed and loss modulus was increased. The test also confirmed this. Finally, the dynamic shear flow test demonstrated that the dynamic viscosity also decreased significantly after addition of nanoparticles.
Magnetometer is one of the main sensors in Attitude Determination and Control Subsystem (ADCS) of Low Earth Orbit (LEO) satellites and since it is operable in all times during an orbital period, it can be utilized in almost all functional... more
Magnetometer is one of the main sensors in Attitude Determination and Control Subsystem (ADCS) of Low Earth Orbit (LEO) satellites and since it is operable in all times during an orbital period, it can be utilized in almost all functional modes like detumbling, nadir pointing and orbit transfer. Consequently, the accuracy of magnetometer data and its calibration have vital roles in mission success. In this paper, regarding to the importance of real-time approaches in practical applications, an Extended Kalman Filter (EKF) is used for magnetometer calibration. Then, in order to study the role of magnetometer calibration in attitude estimation (AE) results, calibrated data is employed in the structure of a Multiplicative Quaternion EKF (MQEKF). Finally, a Hardware in the Loop (HIL) test bed which is equipped with a three axis Helmholtz coil and a three degree of freedom platform is utilized to measure the performance of developed algorithms experimentally. In the calibration process, magnetometer parameters are estimated and used in AE filter. The results show that the attitude error decreases gradually and the final accuracy increases.
The purpose of this paper is to present experimental data for merging two outlet fluid skirts in a dual pressure-swirl coaxial injector. In this study, a dual pressure-swirl external mixing injector was designed, fabricated. Operational... more
The purpose of this paper is to present experimental data for merging two outlet fluid skirts in a dual pressure-swirl coaxial injector. In this study, a dual pressure-swirl external mixing injector was designed, fabricated. Operational characteristics including discharge coefficient and breakup length with injection pressures difference for internal and external injectors were expressed. Utilizing fast shooting, based on backlighting method, the interaction between the two outlet skirts were investigated and the merge performance map was extracted. The merge performance map results indicated, when the pressure difference of the external injector increases from 0.3 bar to 0.95 bar, the pressure difference of the internal injector for the merge to occur increases. Because the effect of the internal injector injection pressure for merge in this area is greater than the external injector injection pressure, the external injector skirt is pulled toward the internal injector skirt. For injection pressures difference of more than 0.95 bar in the external injector, because the effect of the external injector injection pressure for merge is greater than the internal injector injection pressure, the internal injector injection pressure difference is reduced for the merge to occur and the internal injector skirt is pulled toward the external injector skirt.
Due to the unique characteristics of the geo-synchronous orbit and the importance of establishing a satellite in this flying corridor, it is necessary to investigate the effect of environmental disturbances on the orbital elements and to... more
Due to the unique characteristics of the geo-synchronous orbit and the importance of establishing a satellite in this flying corridor, it is necessary to investigate the effect of environmental disturbances on the orbital elements and to maintain the satellite orbital elements in order to increase the longevity and operation of a satellite in this orbit. A satellite in earth orbit is also always exposed to various environmental disturbances such as earth gravity gradient force, gravity of the moon and sun, solar radiation pressure, and so on. For this reason, it is constantly deviating from its original path and needs to study the effect of environmental disturbances on the orbital elements in order to properly correct the disturbed orbital parameters. To achieve the above goals, in this paper, we try to investigate the effect of the environmental perturbations on the orbital characteristics by simulating the satellite translational dynamic behavior in the presence of environmental disturbances. Then, utilizing the genetic algorithm and fuzzy logic approach, an attempt was made to modify the compensation logic of the orbital elements correction, so that, the satellite may be forced to remain in its limited operational orbital window during the mission lifetime. The proposed method could improve the problem-solving operational effectiveness to maintain the position of the satellite with the criterion of minimizing fuel consumption. The case study simulation results may indicate the capability of the proposed approach in satisfying the performance requirements of the satellite station-keeping maneuver.
This article discusses the need for research, monitoring and forecasting services related to space weather events and the establishment of a national center to achieve these goals. It starts with an introduction to the growing dependence... more
This article discusses the need for research, monitoring and forecasting services related to space weather events and the establishment of a national center to achieve these goals. It starts with an introduction to the growing dependence of human civilization on advanced technologies, including space technology, and with an overview of the big investments and costs incurred in building critical infrastructures on Earth and in space. Then, this paper investigates the vulnerability of these infrastructures to space weather events and the need to monitor and predict these phenomena. In the next section, some examples of monitoring and forecasting systems created by different countries and space organizations are introduced. Also, the need to establish a national center in Iran is proposed. The initial organizational structure and mechanism for the activities and cooperation between this center and other national and international institutions are discussed. Finally, different types of actions and the most important activities that can be carried out in this center are presented.
Fault-tolerant control is one of the important issues in automatic control. The reason for this importance is the probability of fault/failure occurrence in control subsystems (sensor-actuator-system). Direct access to spacecraft is not... more
Fault-tolerant control is one of the important issues in automatic control. The reason for this importance is the probability of fault/failure occurrence in control subsystems (sensor-actuator-system). Direct access to spacecraft is not always possible, therefore fault-tolerant control has become even more important in space systems. On the other hand, due to the necessity for weight reduction in these systems, employing hardware redundancy has limitations. Therefore, analytical redundancy has gained much attention in such systems. In this paper, reference inputs are corrected based an open-loop control command adjustment. Using simulation, it is shown that without reference input adjustment, the controller will not be able to satisfy mission requirements when actuator faults occur. Then, the proposed method is used and the desired requirements are satisfied. The advantage of the proposed method is that, there is no need for taking the first and second derivatives of the reference inputs and it is possible to obtain these inputs using integration. This will prevent computational problems associated with differentiation.
The leaf water content is a specific index for the assessment of the physiological status of the plant based on the water content of the vegetation. This research provides an appropriate model based on the reflectance spectra between 400... more
The leaf water content is a specific index for the assessment of the physiological status of the plant based on the water content of the vegetation. This research provides an appropriate model based on the reflectance spectra between 400 and 2500 nm to estimate the leaf water content. We examined 53 different species of the well-known Leaf Optical Properties Experiment and a total of 263 spectral curves were employed in a supervised modelling procedure. In doing so, three different linear models were proposed based on the two different indices and their combination. The first index refers to the ratio of reflectance value in two wavelengths and the second one is the ratio of the derivative of the spectral curve slop in two wavelengths. The experimental results indicate the dependence between the water absorption bands and leaf water content. Finally determination of coefficient for hybrid linear model, which is used both indices, resulted to be 87 percent, indicating a very good fit. Also, the 0.06 relative root mean square error represents the aceptable accuracy in the wáter content modelling.
Properties of brazed joints could be affected by some factors like temperature, time, clearance, surface roughness and alloy elements. Actually they influence on the formation of intermetallic compounds in brazed joints. Since... more
Properties of brazed joints could be affected by some factors like temperature, time, clearance, surface roughness and alloy elements. Actually they influence on the formation of intermetallic compounds in brazed joints. Since intermetallic compounds are brittle, they considerably degrade the mechanical properties of joints. In this study the mechanical strength and microstructural characterization of AISI 316 brazed joints with BNi2 filler metal in different temperature has been investigated. Brazing temperatures changed from 1050 °C, 1100 °C, 1150 °C and 1200 °C for a holding time of 60 min then, the influence of this variable on the brazing strength were examined. Tensile test samples were evaluated at room temperature and metallography samples and fractured tensile sample scanned by a microscope. The results showed that the higher brazing temperature leads to diffusion of boron element into base metal and less volume formation of intermetallic compound phase in the brazing joint and consequently more tensile strength.
Space systems in Low Earth Orbit (LEO) are exposed to the destructive parameter of atomic oxygen. In long-term missions, the rate of degradation of the material resulting from the reaction with atomic oxygen is significant and reduces the... more
Space systems in Low Earth Orbit (LEO) are exposed to the destructive parameter of atomic oxygen. In long-term missions, the rate of degradation of the material resulting from the reaction with atomic oxygen is significant and reduces the performance of the structure. Due to the harmful effects of atomic oxygen on materials, the choice of atomic oxygen resistant materials or the use of durable surface coatings is very common. In this study, the corrosion resistance of atomic oxygen of an interconnector part of a solar cell was studied by applying a silicone base coating. In order to investigate the corrosion behavior of atomic oxygen, ground test method with equivalent conditions of LEO orbit was used by DC plasma equipment. Initially, the parameters of the atomic oxygen corrosion ground test were determined under the equivalent conditions of the LEO orbit. The results of atomic oxygen application in this study showed that the amount of atomic oxygen erosion yield of silicon coating is significantly lower than the amount of atomic oxygen erosion yield of silver substrate. Also, the study of the coating surface after applying atomic oxygen by SEM images led to the determination of the optimal coating thickness. EDX results showed that after applying atomic oxygen, no significant change in the chemical composition of the coating was achieved.
The microwave electrothermal thruster is the propellant that converts the microwave energy into thermal energy. Nowadays, with the development of technology, electric thrusters are very important in terms of producing high specific impact... more
The microwave electrothermal thruster is the propellant that converts the microwave energy into thermal energy. Nowadays, with the development of technology, electric thrusters are very important in terms of producing high specific impact and low consumption. These thrusters are capable of producing acceptable thrust over a long period of time that are suitable for helical orbital transfer missions. In this type of propulsion, the propellant gas is heated and expanded, which produces propulsion force. In this paper, the conceptual design process of a microwave electrothermal thruster is presented. The propulsion system includes propulant gas, propulsion storage tank, amplification chamber and power generation source, which includes batteries and solar arrays. In the text of the article, the method of calculating the mass and the specifications of each part are presented in detail. Finally, in order to validate the conceptual design process presented in this study, the necessary studies have been discussed.Conceptual design has been done for a 100 kg satellite, which is desirable to travel in a week from an orbital height of 300 to 800 km during a spiral treansfer. The propulsion system and mass of each subsystem are obtained.
In this paper, a task scheduling and mapping method based on multi-objective particle swarm optimization (MOPSO) algorithm is presented to improve lifetime reliability of multiprocessors systems on chip. This method considers power... more
In this paper, a task scheduling and mapping method based on multi-objective particle swarm optimization (MOPSO) algorithm is presented to improve lifetime reliability of multiprocessors systems on chip. This method considers power consumption temperature and performance along with the lifetime reliability due to the antagonistic relations of these parameters. These antagonistic and dependent relations make the design space exploration and optimization processes complex. The proposed method is based on MOPSO algorithm and starts with an initial population of candidate solutions which are generated randomly and represents valid task scheduling and mapping solutions. By changing the scheduling and mapping parameters during the MOPSO algorithm, new solutions are produced and the design space is explored based on the objective of the target problem of this method. Several experiments on random and real-life benchmarks are performed to verify the effectiveness of our proposed method. The results demonstrate the capability of the proposed method in effective design space exploration and generating the Pareto front. Moreover, comparisons to the related research show 35%, 23%, 19% and 3% improvements in performance, lifetime reliability, temperature, and power consumption on average.
Ti-6Al-4V is one of the most common materials in the aerospace industry. For example, satellite fuel tanks are made of this alloy. Among manufacturing processes, forming processes is one of the most widely used areas in the manufacture of... more
Ti-6Al-4V is one of the most common materials in the aerospace industry. For example, satellite fuel tanks are made of this alloy. Among manufacturing processes, forming processes is one of the most widely used areas in the manufacture of Ti-6Al-4V components. Due to the importance of determining the allowable deformation limit in the successful design of the Ti-6Al-4V forming process, in this paper, the amount of critical damage was studied. For this purpose, parts with double-cone geometry with grooves on the maximum diameter with two initial microstructure, lamellar and equiaxed, were fabricated and subjected to hot compression testing. The results showed that the initial equiaxed microstructure provides good accumulated damage tolerance. Up to 2.38, 2.67, and 5.89 accumulated damage values, according to Cockcroft-Latham, Brozo, and McClintock criteria, respectively, no crack was observed on the samples. However, with an initial lamellar microstructure, the damage tolerance was significantly reduced. The critical damage value based on Cockcroft-Latham, Brozzo and McClintock criteria was 1.05±0.02, 1.03±0.02, and 2.56±0.05, respectively.
One of the most critical design points in satellites is to achieve the minimum mass (or weight) by meeting all the requirements and constraints (constraints on strength, location and pointing vibrations). In this regard, the structure can... more
One of the most critical design points in satellites is to achieve the minimum mass (or weight) by meeting all the requirements and constraints (constraints on strength, location and pointing vibrations). In this regard, the structure can play a very important role because the structural designer has more freedom of action in determining the design of the structure compared to other subsystems. In the present study, the process of designing the structure of a small satellite, with the aim of achieving the lowest possible weight and maintaining the prevailing requirements (vibration constraint), has been investigated. The process used to achieve the above goal is a change in the geometric dimensions of the structure. Satellite modeling steps with all subsystems have been performed in solidwork software and in ANSYS software, modal analysis, strength and random vibrations have been performed. Also, using the optimization of genetic algorithm in this software, the geometric parameters of the structure such as the thickness of the frame have been obtained in such a way that the structure has reached the lowest possible weight and by satisfying the prevailing conditions for vibration constraints, strength and random vibrations. The results show that by choosing the right thickness of frame, the weight and frequency of the first satellite mode can be significantly reduced, and at the same time, the optimal final structure satisfies all the constraints applied by the launcher and has sufficient strength and rigidity. Is.
Various sensors can be used to attitude determination of a satellite, including the Earth Horizon Sensor. These sensors generally divided into two static and scanning types. In the static type, a two-dimensional array or several linear... more
Various sensors can be used to attitude determination of a satellite, including the Earth Horizon Sensor. These sensors generally divided into two static and scanning types. In the static type, a two-dimensional array or several linear arrays capture instantly the Earth image information to attitude determination. In the scanning type sensors, a narrow-band optical beam mechanically sweeps a ring of space to find the crossing point of the beam to the Earth using a single spot detector. In this research, a new algorithm for a static earth horizon sensor with a two-dimensional array is presented. The algorithm does not need elevation of the sensor and this is the main advantage with respect to old ones. To extract the equations, a tangent vectors from the aperture of the pine-hole camera to the Earth is considered and this vector is extracted in two different body coordinates and base coordinates that are connected to the ground. By equating the two, an equation with three unknowns of pitch, roll and elevation is obtained. The equation is satisfied by each pixel on the Earth horizon Thus; the system of equations is formed by the number of the Earth horizon pixels in the camera image and by numerical solving of the equations unknown parameters are estimated.
In complicated systems such as satellites, each subsystem's design can affect the design of the overall system. In the design procedure, the effect of each technology on the other components should be determined. Because of the increase... more
In complicated systems such as satellites, each subsystem's design can affect the design of the overall system. In the design procedure, the effect of each technology on the other components should be determined. Because of the increase in space trash, the propulsion subsystems are introduced to avoid collision in space. One of the methods to attain high altitude orbits is flight maneuvers using propulsion systems. Several types of propulsion systems are utilized in satellites. Resistojets can be employed as low-cost propulsion systems for satellites because they do not use complicated technologies. In the present research, a resistojet propulsion system is designed for a CubeSat for the mission of orbital altitude reduction. The propellant is selected considering all properties. The design of the nozzle and the heater is also introduced. The overall layout of the system is presented. In the end, an algorithm is proposed for electrical propulsion systems for a specified mission.
Although regarding low density and high ratio of strength to weight of titanium, the application of this metal is restricted in space industry due to its low surface properties including low wear resistance which could lead to the cold... more
Although regarding low density and high ratio of strength to weight of titanium, the application of this metal is restricted in space industry due to its low surface properties including low wear resistance which could lead to the cold weld. For improving this property of titanium, applying protective coatings are effective. Physical parameters, wear resistance, adhesion of applied layer, and surface microhardness are impressive and could avoid occurrence of the cold weld. Therefore, by applying plasma nitriding on chromium layer in titanium used in space constructions, tribological properties (wear resistance, adhesion and surface microhardness) were studied. Results confirmed the formation of nitride chromium phase on titanium substrate due to the applying plasma nitriding on chromium layer and increasing the surface microhardness up to 1109 HV and improving the wear resistance and adhesion subsequently. The value of the friction coefficient was decreased down 0.16 which could avoid the cold weld occurrence.
In this paper, we investigate the effect of task scheduling on the lifetime of a real-time hard drive system that uses a composite energy tank consisting of a battery, a supercapacitor, and a solar energy picker to power supply itself.... more
In this paper, we investigate the effect of task scheduling on the lifetime of a real-time hard drive system that uses a composite energy tank consisting of a battery, a supercapacitor, and a solar energy picker to power supply itself. The life of a system is defined in terms of the moment the system starts up to the moment its tasks are disrupted due to lack of energy. Due to the nonlinear properties of batteries and supercapacitors, which cause their internal charge to be divided into available (IAC) and inaccessible (IUC), the lifetime of such a system depends entirely on the charging and discharging pattern of the energy tank, as this pattern ultimately leads to the amount of charge stored in the IUC section and the amount of charge extracted from this section. Therefore, we can influence the lifetime of the system and increase it by managing the charge / discharge pattern of energy tanks. Since the pattern of energy delivery from the environment is beyond the control of the system, we try to influence the tank charge / discharge pattern by adjusting the consumption pattern to ultimately improve the life of the system. In this regard, we have presented two scheduling algorithms MCF and MGF, which are respectively trying to perform the most consumed and least consumed task in the system, and then using the MCG policy, which at any time according to the conditions for using one of these decision algorithms are presented. Experimental results show that we can increase system lifetime by between 5% and 16%. Considering that in recent years the issue of using supercapacitors along with batteries and solar cells in space systems has been raised, so the results of this research can be investigated for use in satellites.
In all types of satellites, communication systems are utilized for data transmission between satellite and ground stations. pointing the communication antennas to the ground is necessary for the correct mission transmission information.... more
In all types of satellites, communication systems are utilized for data transmission between satellite and ground stations. pointing the communication antennas to the ground is necessary for the correct mission transmission information. The vibration of the satellite antenna leads to the deform antenna pattern, creating noise and reduction of connection quality. Moreover, working the attitude control actuators near the antenna's natural frequency leads to its resonance and large amplitude vibration in the antenna and satellite structure. Thus it is necessary to identify the satellite antenna dynamic behavior as natural frequency and damping ratio. In this paper the satellite antenna is intended as a smart beam, based on the free vibration of clamped-free beam shape of satellite antenna and sensing its vibration by the piezoelectric sensor, its dynamic characteristic as damping and frequency is identified and verified by comparing the results with experimental ones. The considered mathematical model has very accurate and this model can be used to determine the dynamic behavior of the antenna in different satellite secondary structures.