Control dynamics
Ehsan Maani miandoab; Ehsan Zabihian; Hossein Najafi
Abstract
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 deforming antenna ...
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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 deforming antenna pattern, creating noise and reducing 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 is very accurate and this model can be used to determine the dynamic behavior of the antenna in different satellite secondary structures.
Structure
Yaser Vahidshad; Faegheh Soltanmohammad
Abstract
Many factors affect the quality of brazing process, including 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 ...
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Many factors affect the quality of brazing process, including 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
Propulsion
Mohammad Hossein mansouri Moghari; Hassan Naseh; Sahar Noori
Abstract
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. High-precision successor ...
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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. High-precision successor models are called metamodels. The basis of producing a high-precision meta-model 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 two-by-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
Remote Sensing
Tayebe Managhebi; Mohammadreza Mobasheri
Abstract
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 ...
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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. for this purpose, 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 water content modelling
Power Electronics
Mahmoud Hasanloo; Mahdi Kargahi; Shahrokh Jalilian
Abstract
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 super capacitor, and a solar energy picker to power supply itself. The lifetime of a system in this document is the moment the system ...
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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 super capacitor, and a solar energy picker to power supply itself. The lifetime of a system in this document is the moment the system starts until the moment its tasks are disrupted due to lack of energy. Due to the nonlinear properties of batteries and super capacitors 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. Ultimately, its 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, the main idea of this paper is to influence the charge/ discharge pattern of the tank by adjusting the pattern of energy consumption to improve the lifetime 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, then using the MCG policy, which at any time, Decisions are made on the use of one of these algorithms according to the conditions. Experimental results show that we can increase system lifetime between 5% and 16%. Considering that in recent years the issue of using super capacitors 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.
Heat control
Mehrnoosh Farahani; Vafa Sedghi; seyed mostafa safavi homami; Hamid Mesforoush
Abstract
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 ...
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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
control
Rouzbeh Moradi
Abstract
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 controlling subsystems (sensor-actuator-system). Direct access to spacecraft is not always possible, Therefore fault- tolerant control has become ...
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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 controlling 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. So, 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 shown, 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 these inputs can be obtained through integration.. This will prevent computational problems associated with differentiation.
Structure
Arvin Taghizadeh Tabrizi; Hossein Aghajani; Farhad Farhang Laleh
Abstract
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 ...
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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 is effective. The physical parameters of wear resistance, adhesion and surface microhardness are impressive and could avoid occurance of cold weld. Therefore, in the present study, by applying plasma nitriding on chromium layer on titanium used in space structures, its tribological behavior (wear resistance, adhesion and surface microhardness) has been investigated. The results confirmed the formation of nitride chromium thin layer on titanium substrate due to the applying plasma nitriding on the chromium layer , which increasing the surface microhardness up to 1109 HV and improving the wear resistance and adhesion subsequently. The coefficient of friction is also decreased to 0.16,which can well prevent the occurrence of cold weld
Propulsion
masumeh kiantaj; morteza farhid; mohammadmehdi shafie; Mohammad reza morad
Abstract
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 ...
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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
space climate
Omid Shekoofa; Masoud Khoshsima; Sajad Ghazanfarinia; Farhad Bagheroskouei
Abstract
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 ...
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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
Propulsion
seyed alireza Jalali chimeh; Ali Madadi; seyed mostafa safavi homami; javad Emami
Abstract
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 increasing in space trash, the propulsion subsystems are introduced to avoid ...
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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 increasing 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 a 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 according to all properties. The design of the nozzle and the heater is also introduced, The overall layout of the system is presented and finally, an algorithm of electrical propulsion systems for a specified mission is proposed.
mechanic
Sajjad Ghazanfarinia; Ehsan Mousivand; Masoud Khoshsima; Yaser Saffar
Abstract
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 ...
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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
dynamics
Hossein Maghsoudi Dehaghani; Amirreza Kosari; Mahdi Fakoor; Masoud Khoshsima
Abstract
Due to the unique characteristics of the geostationary 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 ...
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Due to the unique characteristics of the geostationary 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 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
Flight dynamics
Behrooz Raeisy; Fatemeh Ghofrani
Abstract
Various sensors can be used to attitude determination of a satellite, including the Earth Horizon Sensor. These sensors generally divided into two types: static and scanning types. In the static type, two- dimensional array or several linear arrays capture instantly the Earth image information to attitude ...
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Various sensors can be used to attitude determination of a satellite, including the Earth Horizon Sensor. These sensors generally divided into two types: static and scanning types. In the static type, 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 parameters are estimated by numerical solving of the unknown equations.
Structure
Alireza Zarezadeh; Mohammad Hossein Allaee; Mohsen Heydari Beni; Ali Davar; Jafar Eskandari Jam
Abstract
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 ...
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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
Structure
mohamad bagher bahrami
Abstract
One of the most critical design points in satellites is to achieve the minimum mass (weight) by meeting all the requirements and constraints (strength, location and vibration). In this regard, the structure can play a very important role because the structural designer has more freedom of action in determining ...
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One of the most critical design points in satellites is to achieve the minimum mass (weight) by meeting all the requirements and constraints (strength, location and vibration). 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 such as vibration constraints hasbeen investigated. The process used to achieve the above goal is to change the geometric dimensions of the structure. Satellite modeling steps with all subsystems have been performed in SolidWorks software and modal, quasi-static and random vibrations analyzes have been performed in ansys software. Also, By using the ability to optimize the genetic algorithm in this software, the geometric parameters of the structure such as the thickness of the amplifiers have been obtained in such a way that the structure has reached the lowest possible weight and meet the prevailing conditions for vibration constraints, strength and random vibrations. The results show that by choosing the right thickness of amplifiers, the weight and frequency of the first satellite mode can be reduced significantly, and at the same time, the optimal final structure can satisfy all the constraints applied by the launcher and provide sufficient strength and rigidity
Propulsion
ALI RASTGAR; Hojat Ghasemi
Abstract
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 and fabricated. Operational characteristics including discharge coefficient and breakup ...
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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 and fabricated. Operational characteristics including discharge coefficient and breakup length were expressed in terms of different injection pressures for internal and external injectors. Utilizing fast shooting, based on the backlighting method, the interaction between of 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. The reason for this increase in this range of external injector injection pressure differences is that, 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.
Propulsion
Nematollah Fouladi; Alireza Mohammadi
Abstract
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 ...
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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
control
Zeinab Talebi; Amir Labibian; Hossein Salimi
Abstract
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. Therefore, ...
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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. Therefore, the accuracy of magnetometer data and its calibration is essential in the success of the missions. 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 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 the AE filter. The results show that the attitude error gradually decreases and the final accuracy increases
Structure
S. Javid Mirahmadi; Mohsen Hamedi; Maedeh sadat Zoei
Abstract
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 ...
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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
control
Elham Kowsari; Hadi Makarem
Abstract
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 ...
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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
Material science
Majid Haghgoo; Ahmad Ramezani Saadat Abadi
Abstract
Achieving a flawless solid composite propellant requires proper processability of its corresponding filled polymer slurry. In other words, a highly filled suspension with optimal rheological properties makes it possible to transfer to the mold and complete filling in complex geometries. In this dynamic ...
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Achieving a flawless solid composite propellant requires proper processability of its corresponding filled polymer slurry. In other words, a highly filled suspension with optimal rheological properties makes it possible to transfer to the mold and complete filling in complex geometries. In this dynamic study, the rheological properties of the obtained suspensions have been investigated after adding molybdenum disulfide nanoparticles to the model materials. In order to study the effect of molybdenum disulfide nanosheets on the rheological behavior of the suspensions, polyethylene glycol matrix and glass beads, with particle distribution of 60 to 103 microns were used as a model.Single- layer and multi- layer molybdenum disulfide nanosheets with thickness of 50 to 100 nm was obtained using 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. The results of frequency sweep and temperature sweep tests showed that by increasing the percentage of molybdenum disulfide nanosheets by less than 0.1%,The mixed viscosity has a significant decreasing in all microfiller values while maintaining the storage modulus and increasing the loss modulus. Finally, the dynamic shear flow test demonstrated that the dynamic viscosity also decreased significantly after the addition of nanoparticles.
Computer
Athena Abdi; shahrokh jalilian
Abstract
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 ...
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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.
Material science
Sajede Aghasi; Seyed Hassan Jafari; Mahdi Golriz
Abstract
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) ...
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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
Propulsion
Hadiseh Karimaei
Abstract
The monopropellant thrusters of the situation control system are a requirement for the development and application of satellites and space capsules in space, which are high-tech and expensive. In this paper, the design and simulation of a pressure- swirl injector with full-cone spray as a fuel injector ...
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The monopropellant thrusters of the situation control system are a requirement for the development and application of satellites and space capsules in space, which are high-tech and expensive. In this paper, the design and simulation of a pressure- swirl injector with full-cone spray as a fuel injector of a monopropellant thruster are presented. For this injector, internal flow simulation was performed in order to predict its output flow characteristics including spray cone angle, output velocity distribution, mass flow rate, spray pattern, etc. For this purpose, VOF fluid volume method is used and the flow turbulence is simulated using the k-eps model. This type of injector is actually a combination of straight flow injector and swirl flow 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. 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. Based on the results, it was ensured that the injector provides the desired mass flow rate (about 5.8 gr/s) at a certain design pressure difference (3 bar) and determines a suitable spray pattern. It also provides the desired spray angle (about 35).
