Structure
Yaser Vahidshad; Faegheh Soltanmohammad
Abstract
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 ...
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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.
Propulsion
Mohammad Hossein mansouri Moghari; Hassan Naseh; Sahar Noori
Abstract
Accurate solving of complex systems such as space systems and specifically space propulsion system is very costly and time consuming. By developing and 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 ...
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Accurate solving of complex systems such as space systems and specifically space propulsion system is very costly and time consuming. By developing and 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 of great value in solving complex systems. The purpose of this paper 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.
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 the deform 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 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.
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. 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.
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 seriously endanger the satellite telecommunication components. The purpose of this paper is to investigate ...
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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 seriously endanger the satellite telecommunication components. 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 components. First, the surface charging phenomenon is simulated in an aluminum satellite in low earth orbit and then in polar aurora by SPIS software. Then multi-layer thermal insulation is applied to the system and its effects on the charging phenomenon are 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 leads to the achievement of an optimal system.
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 supercapacitor, and a solar energy picker to power supply itself. The life of a system is defined in terms of 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 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.
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 control subsystems (sensor-actuator-system). Direct access to spacecraft is not always possible, therefore fault-tolerant control has become even ...
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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 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.
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 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.
Propulsion
masumeh kiantaj; morteza farhid; mohammadmehdi shafie; Mohammad reza morad
Abstract
In this article, the characteristics of the hollow cathode plasma particles in the spt-100 hall effect thruster are 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 ...
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In this article, the characteristics of the hollow cathode plasma particles in the spt-100 hall effect thruster are 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 the 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. The behavior of the potential, the density of electrons and ions and the temperature of particles has been studied. The results show that corresponding the electrons, the ion density also decreases exponentially from the maximum value in the cathode ionization region 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.
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.
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 the increase 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 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.
dynamics
Hossein Maghsoudi Dehaghani; Amirreza Kosari; Mahdi Fakoor; Masoud Khoshsima
Abstract
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 ...
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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.
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, twisting pattern of fibers, materials, etc. which can play a significant role in this process. In this regard, the twisting pattern has been less studied by researchers 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, glass/epoxy cylinders with 4 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 radial displacement of cylinders due to the internal pressure was 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 pattern having finer texture has a higher compressive strength. Also, the simulation results showed a good agreement with the experimental results.
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 static and scanning types. In the static type, a 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 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.
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, fabricated. Operational characteristics including discharge coefficient and breakup length ...
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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, 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.
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, it is necessary to test the performance by pre-evacuating its internal space. In this research, the suitability of an exhaust diffuser for this type of test is investigated numerically. 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.
Structure
mohamad bagher bahrami
Abstract
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 ...
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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.
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. Consequently, ...
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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. 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.
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 to be aided to complement its discontinuity. Using gyroscope unit is the most suitable choice for aiding the star tracker. However, using these two kinds of sensor ...
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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 to be aided to complement its discontinuity. 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 biases lead to low accuracy in the 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 based only on their measurements, and the mathematical formulation is presented in detail. Then, 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, for which the results are reported.
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, the optimal rheological properties of highly filled suspensions after mixing process, ensure its transfer to the mold and complete filling of complex geometries. ...
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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.
Material science
Sajede Aghasi; Seyed Hassan Jafari; Mahdi Golriz
Abstract
One of the methods for improving thermal conductivity of epoxy adhesives is the incorporating of conductive ceramic, metal or carbon fillers. As the main goal of this research, is to improve thermal conductivity of epoxy resin and keep its electrically insulating property, Alumina (Al2O3) ceramic filler, ...
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One of the methods for improving thermal conductivity of epoxy adhesives is the incorporating of conductive ceramic, metal or carbon fillers. As the main goal of this research, is to improve thermal conductivity of epoxy resin and keep its electrically insulating property, Alumina (Al2O3) ceramic filler, individually and in combination with Boron Nitride (BN) ceramic filler with high thermal conductivity and electrical resistivity. Scanning Electron Microscopy (SEM) observations showed a good dispersion and an acceptable connection between fillers. Thermal diffusivity measurements revealed that by incorporating conductive ceramic fillers, either individually or in combination with each other, regardless of the type of the hardener, thermal diffusivity would increase as a result of 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 show that the thermal conductivity of hybrid system of Alumina/BN have been raised to 1.7 (W/mK) instead of 0.4 (W/mK) which is belong to pure epoxy system. The most important point of this work is that the good thermal conductivity obtained by kept of mechanical properties, dielectric constant, as well as lap shear strength of Alumina/BN hybrid system meet all acceptable range of thermal conductive adhesive for space application.
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.
Propulsion
Hadiseh Karimaei
Abstract
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 ...
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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.
