Original Article
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.
Original Article
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.
Original Article
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
Original Article
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.
Original Article
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.
Original Article
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
Original Article
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
Original Article
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.
Original Article
Propulsion
Sahar noori; Rojin Shokri Khanghah; mohammad nadafipour meibody
Abstract
Microwave electrothermal thruster is the propellant that converts microwave energy into heat energy. nowadays, with the technology development of electric thrusters are very important in terms of producing high specific impact and low fuel consumption. These thrusters can produce acceptable thrust over ...
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Microwave electrothermal thruster is the propellant that converts microwave energy into heat energy. nowadays, with the technology development of electric thrusters are very important in terms of producing high specific impact and low fuel consumption. These thrusters can produce acceptable thrust over a long period of time, which are suitable for spiral orbital transfer missions. In this type of propulsion, the propellant gas is heated and expanded, which produces the propulsion force. This paper presents the conceptual design process of a microwave thermal thruster. The propulsion system includes propellant, propulsion storage tank, amplification chamber, and power plant, which includes batteries and solar arrays. In this paper, the method of calculating the mass and the characteristics of each 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.
Original Article
Structure
Maedeh sadat Zoei; hadi gorabi; mohammadreza asharf khorasani; saeed asghari; S. Javid Mirahmadi
Abstract
Space systems in Low Earth Orbit (LEO) expose 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 ...
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Space systems in Low Earth Orbit (LEO) expose 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 has 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 has used by DC plasma equipment. Initially, the parameters of the atomic oxygen corrosion ground test 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. 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 has achieved
