Space subsystems design: (navigation, control, structure and…)
hamid reza ali mohamadi; Hassan Naseh
Articles in Press, Accepted Manuscript, Available Online from 25 September 2023
Abstract
Achieving to new technologies with high reliability, along with reducing the cost and time of the design cycle, is one of the most important challenges in complex systems. In this paper, reliability based design of a space system is discussed in the conceptual design phase. Normally, there are eight ...
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Achieving to new technologies with high reliability, along with reducing the cost and time of the design cycle, is one of the most important challenges in complex systems. In this paper, reliability based design of a space system is discussed in the conceptual design phase. Normally, there are eight steps in the design for reliability. The first step, planning, and the next seven steps that applied for the liquid propellant engine with electro-pump technology included: determination of failure modes; reliability modeling; reliability allocation; propagation of uncertainty; Implementation of the chosen method in reliability analysis; reliability prediction and reliability evaluation. Therefore, in this research has been performed to achieved method and implementation steps of reliability design in the conceptual design phase of a space system.
H. Bolandi; B. Ghorbani-Vaghei; F. Fani- Saberi
Volume 1, Issue 2 , December 2008, , Pages 27-33
Abstract
Attitude control system of satellite with Gravity Gradient stabilization requires high moments of inertia ratio for providing stability and continuous orientation toward Earth. Although, this high ratio causes satellite has small body and reduce mission capability. In this paper, moments of inertia ratio ...
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Attitude control system of satellite with Gravity Gradient stabilization requires high moments of inertia ratio for providing stability and continuous orientation toward Earth. Although, this high ratio causes satellite has small body and reduce mission capability. In this paper, moments of inertia ratio is reduced using a closed form formula based on our previous work, in such a way that it could be provided more missions by augmented solar panels to satellite. Solar orientation could be yielded by rotating satellite about gravity gradient boom (yaw rotation). Interaction between yaw rotation and satellite rotation around Earth causes biased-attitude error in roll axis. To overcome this problem, it is necessary to reduce yaw rotation by adding a reaction wheel toward boom direction. To realization this method, stability criteria of gravity gradient is developed and control law for small and large angles rotation is designed in such a way that angular momentum and moment constraints of reaction wheel to be satisfied. Finally, fine performance of attitude control system will be illustrated with simulation based on specification of an on-orbit satellite and actual consideration
Y. Ghaderi-Dehkordi
Volume 2, Issue 3 , December 2009, , Pages 27-34
Abstract
Corrugated tunnel is a pipe, which its outer surface is corrugated and is generally used for fluid transfer in different industries. Owing to complicated geometrical structure of corrugated tunnels, very limited numbers of closed-form equations have been presented for analysis of their mechanical behavior. ...
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Corrugated tunnel is a pipe, which its outer surface is corrugated and is generally used for fluid transfer in different industries. Owing to complicated geometrical structure of corrugated tunnels, very limited numbers of closed-form equations have been presented for analysis of their mechanical behavior. In the present study, a mathematical model is proposed for strength and buckling analysis of corrugated pipes. In addition, an algorithm is presented for designing of corrugated tunnels. In order to verify the presented model, its results were compared with those obtained by finite element method (the ABAQUS software was used) and a good agreement was observed. Finally, some corrugated tunnels were designed, fabricated and tested for a special industrial application. Critical pressure values obtained from the tests were less than those calculated from the theoretical method, which could be due to fabricated flaws.
Mohammad Reza Mortazavi; Ali Reza Alikhani
Volume 8, Issue 1 , April 2015, , Pages 27-41
Abstract
This paper presents a suitable technique for nonlinear control of a flexible spacecraft in proximity operations. To do proximity operations well, the pursuer spacecraft must place itself in a pre specified location relative to target and align its docking port to target’s docking port while keeping ...
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This paper presents a suitable technique for nonlinear control of a flexible spacecraft in proximity operations. To do proximity operations well, the pursuer spacecraft must place itself in a pre specified location relative to target and align its docking port to target’s docking port while keeping their attitude compatible. This procedure usually needs large, fast and accurate manoeuvres which can cause flexible structure vibrations. In addition, external disturbances, actuator saturation and model uncertainties increase difficulties of achieving such a goal. Consequently it is necessary to utilize an effective and nonlinear controller design approach to overcome these challenges. To perform considered scenario successfully, in this paper we use a method in nonlinear optimal control called State Dependent Riccati Equation (SDRE). Simple formulation and tuning as well as good performance and satisfactory robustness are some advantages of this approach in unified control of the spacecraft position, attitude and flexible motion during a proximity operation. 6DoF simulations show good performance of controller in presence of structure flexibility, parametric uncertainties, input uncertainty and saturation and external disturbance.
Hossein Darabi; Jafar Roshanian
Volume 8, Issue 2 , July 2015, , Pages 27-39
Abstract
Collaborative optimization is one of bi-level multidisciplinary optimization methods which consists of system level and discipline level and is applied for complex engineering problems. since this method is rigidly convergent at discipline level because of noisy constraints at system level on one hand ...
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Collaborative optimization is one of bi-level multidisciplinary optimization methods which consists of system level and discipline level and is applied for complex engineering problems. since this method is rigidly convergent at discipline level because of noisy constraints at system level on one hand and minimizing objective function necessity at system level on the other hand, this optimizationmethod is forced to use evolutionary algorithms in order to minimize objective function at system level, also, It has been proved that, applying this algorithms according to their nature is expensive and time consuming. This paper with performed inspections is a new method for applying innovated optimization algorithms through which considerable results are obtained in solving sample problems. It is shown that using this method will decrease function calls number or problem solving time and therefore calculating costs will decrease considerably. Also it is shown that this method sometimes increase accuracy.
Ehsan Daneshnia; Mehrzad Nasirian; S. Mohammad Mahdi Dehghan
Volume 5, Issue 4 , January 2013, , Pages 29-38
Abstract
One of the mostimportant issuesin theproductivityof thesatellites is the mode timingand the automatic writingof thescenarioon-boardof thesatellite with regard environmental conditions. In order to have the capability to make flight scenariosformissionssent fromgroundstationsormissions that aregenerated ...
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One of the mostimportant issuesin theproductivityof thesatellites is the mode timingand the automatic writingof thescenarioon-boardof thesatellite with regard environmental conditions. In order to have the capability to make flight scenariosformissionssent fromgroundstationsormissions that aregenerated automatically, on board timing forecast along with the time to reach thestationor thephoto target will be necessary. on board automatic generation of thescenarioswill reduce the dependency of the satelliteto groundstation. Calculation of the satellite riseandsettimes,without thesatellite passesand orbitdisturbances simulation, would not be possible. This paperpresentsformulaforthesatellite passessimulation, algorithmandtime prediction computation modelingusing keplerianorbitalparametersandreduces the size ofthecalculation utilizing of semimajor axis of the orbit to be usedonthe boardof satellite. Toreduce thevolume ofcalculations,it will be necessary to use numericalmethods forfindingfunction minimums orroots. semimajor axis of the orbitwill decrease the numerical computation to a great extent using the algorithmpresentedinthis paper.
H. Bolandi; M. H. Ashtari; M. Nadi; M. Esmaeelzade
Volume 6, Issue 2 , July 2013, , Pages 29-42
Abstract
In this article by analyzing the TLE data of Navid satellite from IranUniversityofScienceand Technology the effects of these data on tracking operation of ground station has been studied. Then the prediction accuracy of satellite position, the error rate of antenna ground station, the error rate of satellite ...
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In this article by analyzing the TLE data of Navid satellite from IranUniversityofScienceand Technology the effects of these data on tracking operation of ground station has been studied. Then the prediction accuracy of satellite position, the error rate of antenna ground station, the error rate of satellite rise time and the sensitivity survey of these toward the variation of drag term () of TLE data has been investigated. The results show that the accuracy of TLE data, the intervals of updating them and the time elapsed the epoch related to TLE data directly effected on accuracy prediction of thesatellite position and atracking operation. In some cases such as the limitation of ground antenna beam, tracking satellite is not succeeded. Therefore it has been suggested that tracking operation of satellite is done by ground station and independent of the TLE data and using TLE data as a reserve state has been considered. In this case TLE data must be updated daily.
R. Esmaelzadeh
Volume 6, Issue 4 , January 2014, , Pages 29-36
Abstract
An explicit guidance law is developed for a reentry vehicle. Motion is constrained to a three-dimensional Bezier curve. Acceleration commands are derived by solving an inverse problem that combined with differential flatness approach. Trajectory is related to Bezier parameters. A comparison with pure ...
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An explicit guidance law is developed for a reentry vehicle. Motion is constrained to a three-dimensional Bezier curve. Acceleration commands are derived by solving an inverse problem that combined with differential flatness approach. Trajectory is related to Bezier parameters. A comparison with pure proportional navigation shows the same accuracy, but a higher capability for optimal trajectory to some degree. Other advantages such as trajectory representation with minimum parameters, applicability to any reentry vehicle configuration and any control scheme, and Time-to-Go independency make this guidance approach more favorable.
Amir Mahdi Tahsini; Samaneh Tadayon Mousavi
Volume 8, Issue 4 , January 2016, , Pages 29-34
Abstract
The aim of this paper is to identify the unknown properties of an industrial hot air gun using inverse heat transfer approach. A combination of experiments and numerical analyses is used to define the convection coefficient and the produced temperature of this device. A numerical solver is developed ...
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The aim of this paper is to identify the unknown properties of an industrial hot air gun using inverse heat transfer approach. A combination of experiments and numerical analyses is used to define the convection coefficient and the produced temperature of this device. A numerical solver is developed by employment of a straightforward and powerful inverse heat transfer method: “The conjugate gradient method for parameter estimation”. The variation of temperature versus time in a fixed point of a steel-304 rod is sensed by a thermocouple and is given as an input to the numerical solver. The produced temperature of the hot air gun and the variation of convection heat transfer coefficient of this device as a function of distance between gun and rod are estimated in this research. Two non-dimensional distances between hot air gun and head of rod, H/D, are considered in this research: 2 and 6. These distances are chosen based on the hot jet potential core, the former is inside the potential core and the latter is outside it. The identifications of this gun are used in the process of determining unknown thermal properties of insulating and ablative materials, which are essential components of ablative heat shields, by inverse heat transfer methods.
atefeh hoseinzadeh; Amirhossain Adami; Asghar Ebrahimi
Volume 10, Issue 4 , March 2018, , Pages 29-40
Abstract
The atmospheric re-entry phase is one of the most significantmission steps in the space missions;hence, theguidance and control of reentry vehicles in this phase of mission is important. In this article, a reentry vehicle guidance algorithm has been proposed which has suitable robustness in the presence ...
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The atmospheric re-entry phase is one of the most significantmission steps in the space missions;hence, theguidance and control of reentry vehicles in this phase of mission is important. In this article, a reentry vehicle guidance algorithm has been proposed which has suitable robustness in the presence of initial reentry parameters uncertainties. Here,it has been tried to minimize the landing errors at terminal point using Nonlinear Quadratic Tracking (NQT) and chasing a reference trajectory. In order to define several trajectories with different initial states using evolutionary genetic algorithm with changes in weighting matrices Q and R, it hasbeen tried to reduce the errors of landing at terminal point. The reentry position of the reentry vehicles may be different from the desired ones with respect to several events. In this situation, reentry vehicles start to move in a new trajectory which is not suitable. Therefore, the reentry vehicles should be guided to come back into the desired trajectory or a new optimum trajectory needs to be redesignedto have the same target position on the ground. To do this, we need optimum weighting matrices R and Q for every new trajectory. In this article, this problem has been resolved using partial least squares regression; meanwhile, obtaining the optimal matrices by genetic algorithms needed many times. Also,it is shown that using this method, in the presence of reentry uncertainties, weighting matrices for each new initial condition hasbeen quickly derived. Additionaly,through the matrices obtained and the nonlinear quadratic tracking controller, reentry vehicle was directedto the target with a good accuracy. The Monte Carlo analysis has been used to evaluate the performance of the proposed algoritm. According to the results, the proposed algoritm has a suitable accuracy level and it can generate the online optimum trajectory.
M. Naderi Tabrizi; S. A. R. Jalali Chimeh; H. Karimi
Volume 3, Issue 2 , January 2011, , Pages 31-43
Abstract
In this article the Propellant Utilization system (PU) has been simulated. The objective of this system is to adjust the consumption ratio of the propellants in order to ensure the minimum propellant residuals at engine’s shutdown phase. Using the PU system, the orbital or range and also the payload ...
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In this article the Propellant Utilization system (PU) has been simulated. The objective of this system is to adjust the consumption ratio of the propellants in order to ensure the minimum propellant residuals at engine’s shutdown phase. Using the PU system, the orbital or range and also the payload capabilities of missiles or launch vehicles will be enhanced. In this article, after studying and simulation of the PU system, the necessity of using such system is compared with a missile without the PU system. At the end of this paper it is proven that using PU system on a desired missile has enhanced its range up to 7 percent and has also reduced the propellant residuals up to 25 percent.
H. Bolandi; M. Abedi; M. Haghparast
Volume 6, Issue 1 , April 2013, , Pages 31-46
Abstract
This paper presents robust fault detection based on adaptive thresholds for a three axis satellite. For this purpose, first we described the attitude control system (ACS) as a quasi linear parameter model. Next, an interval observer has been designed that based on, effect of the satellite parameter uncertainties ...
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This paper presents robust fault detection based on adaptive thresholds for a three axis satellite. For this purpose, first we described the attitude control system (ACS) as a quasi linear parameter model. Next, an interval observer has been designed that based on, effect of the satellite parameter uncertainties has been propagated into the alarm limits and so the adaptive thresholds are generated. In this paper, it is shown that the developed method minimizes the missing alarm rates; also this approach detects small or incipient faults more effectively than the classical fault detection algorithms with constant thresholds. In the next part of paper, we propose an isolation algorithm using the fault tree approach. Also, an accommodation system has been designed based on reconfiguration of available actuators. Accordingly, after isolation of faulty reaction wheels, the accommodation system turns them off and replaces the suitable magnetic tourqers instead of the faulty reaction wheels and so the attitude control error is maintained limited.
Javad Shams; Jafar Roshanian
Volume 11, Issue 4 , December 2018, , Pages 31-42
Abstract
In this paper, an analytical solution to deflection mission of asteroid as potentially hazardous spatial mass that threat humanity in future is investigated . The mission of deflecting potentially hazardous asteroids in recently years with possibility of their collision with Earth and the priority to ...
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In this paper, an analytical solution to deflection mission of asteroid as potentially hazardous spatial mass that threat humanity in future is investigated . The mission of deflecting potentially hazardous asteroids in recently years with possibility of their collision with Earth and the priority to carry out the mission of mitigate risk of these objects from its original space trajectory in recent years has been studied with interest in scientific research. Different methods have been proposed for execute the deflecting these celestial objects, among which the use of gravity tractor technology has become more widely used. In addition, the increasing use of formation flying technology in space missions is increasingly increasing, which has led to the use of this technology in this survey.
Shervin Amiri; Mohammad Ali Dalir; Hossein Talaiee
Volume 5, Issue 3 , October 2012, , Pages 33-40
Abstract
The NAVSTAR Global Positioning System (GPS) is a satellite-based navigation and positioning system which includes a constellation of 32 satellites, remote control stations and its receivers and can be used for determination the geographical positions of its users. GPS signal simulator needs for test ...
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The NAVSTAR Global Positioning System (GPS) is a satellite-based navigation and positioning system which includes a constellation of 32 satellites, remote control stations and its receivers and can be used for determination the geographical positions of its users. GPS signal simulator needs for test and verification of GPS receiver's performances in special applications at the Laboratory. For this mission we should simulate the various static and dynamic scenarios for GPS receiver tracks and generate GPS signals for all the satellites. For GPS signals, generation of all its elements like the Navigation messages, C/A codes, frame and subframe structures should be defined and used in this project.
S. A. Hosseini; S. Noori
Volume 7, Issue 1 , April 2014, , Pages 33-40
Abstract
In the present work, an engineering method is developed to predict laminar and turbulent heating-rate solutions for blunt reentry spacecraft at hypersonic conditions. The calculation of aerodynamic heating around blunt bodies requires alternative solution of inviscid flow field around the hypersonic ...
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In the present work, an engineering method is developed to predict laminar and turbulent heating-rate solutions for blunt reentry spacecraft at hypersonic conditions. The calculation of aerodynamic heating around blunt bodies requires alternative solution of inviscid flow field around the hypersonic bodies. In this paper, the procedure is of an inverse nature, that is, a shock wave is assumed and calculations proceed along rays normal to the shock. The solution is iterated until the given body is computed. The inverse method is practical for the calculation of flow field between the shock wave and the body surface. Body calculation with the body analysis is contrasted and according to the entire differences between those; the shape of shock with the coefficient scales is implemented. The normal momentum equation is replaced with a Maslen’s second order pressure equation. This significantlysignificantly decreases machine computation time. The present method predicts laminar and turbulent heating-rates that compare favorably with other researches. Since the method is very high-speed, it can be used for preliminary design, or parametric study of aerodynamics vehicles and thermal protection of hypersonic flows.
H. Kazemi
Volume 7, Issue 3 , October 2014, , Pages 33-42
Abstract
When space vehicles did not take off horizontally (like airplanes), they had to cross airspace of states other than the launcher state. This phenomenon exists still now for the states who intend to launch space objects, especially when launch pads are located near borders of adjacent states. What has ...
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When space vehicles did not take off horizontally (like airplanes), they had to cross airspace of states other than the launcher state. This phenomenon exists still now for the states who intend to launch space objects, especially when launch pads are located near borders of adjacent states. What has been the attitude of the international law toward the issue of passage of space object through a foreign territory during its launch and re-entry into the atmosphere? Are the states allowed to use territory of other states, while launching their space objects? Do the international instruments or customary international law provide precise answers for this issue? In this paper, the researcher investigates sovereignty of states over their territorial air-space and discusses different legal viewpoints on passage of space objects through territory of other states. It clear that states cannot launch space objects without first obtaining permission of the concerned state. It is asserted that up to now no international law instrument have been linked to that effect, i.e. regarding innocent passage of space objects without consent of the concerned state(s).
Masoud Ebrahimi Kachoie; Mohammadvali Arbabmir; Mohammad Norouz
Volume 10, Issue 2 , September 2017, , Pages 33-52
Abstract
Inertial navigation system error increases due to sensor errors with the increase intime. Usually, to prevent the growth of navigation system error, inertial navigationsystems are integrated with sensors or auxiliary systems. The importantly aided system isGNSS. Because of GNSS outage or its invalidity, ...
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Inertial navigation system error increases due to sensor errors with the increase intime. Usually, to prevent the growth of navigation system error, inertial navigationsystems are integrated with sensors or auxiliary systems. The importantly aided system isGNSS. Because of GNSS outage or its invalidity, the other auxiliary sensors are used toincrease the accuracy of the inertial navigation system. In this article, the types ofmethods which are used by imaging camera for navigation or for the accuracyimprovement of an inertial navigation system for UAVs are discussed. After reviewing theliterature in the field of vision navigation in UAVs, the proper classification for visionnavigation methods and the development of these methods are presented. In UAVs, thevision navigation techniques are based more on Map metric, optical flow, featuretracking, odometers and simultaneous localization and mapping.
Vahid Behnamgol; Ahmadreza Vali; ali mohammadi; َAshknaz Oraee
Volume 11, Issue 2 , September 2018, , Pages 33-39
Abstract
A new adaptive smooth second-order sliding mode control is proposed for uncertain nonlinear systems in this paper. The finite time stability is proved using a Lyapunov technic. The proposed controller consists of an adaptive term equal to the uncertainty in finite time. This algorithm is used to design ...
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A new adaptive smooth second-order sliding mode control is proposed for uncertain nonlinear systems in this paper. The finite time stability is proved using a Lyapunov technic. The proposed controller consists of an adaptive term equal to the uncertainty in finite time. This algorithm is used to design terminal guidance law for homing interceptors to intercept maneuvering targets. The guidance law generates smooth acceleration commands and the control signal is able to stabilize relative lateral velocity in a desired time. Finally, the proposed guidance law is compared with the second-order sliding mode guidance law from carried out simulations.
Mohammad Rezaei; mohammad mirzaei; hamid gholami baie
Volume 11, Issue 3 , December 2018, , Pages 33-45
Abstract
Demand for positioning services with proper coverage and high accuracy has been increased rapidly in recent years. A global positioning system solves many users’ requirements and presents positioning services with global coverage and proper accuracy. However, satellite-based positioning systems ...
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Demand for positioning services with proper coverage and high accuracy has been increased rapidly in recent years. A global positioning system solves many users’ requirements and presents positioning services with global coverage and proper accuracy. However, satellite-based positioning systems are made and control by Developed countries and their precise location services are rarely available to civilians and other countries. Also, the signals of the satellite systems are fallible and low-power, and are not suitable for closed locations. The use of a local positioning system along with global positioning is one of the programs that governments are urging in the future to enhance the reliability of the positioning, increase coverage of users and reduce the system error. In this research, after introducing local positioning system and its most important applications, its indicators will be compared with international positioning standards and its market in Iran will be analyzed.
Space subsystems design: (navigation, control, structure and…)
Seyyed Rashad Rouholamini; Mohammad Ali Amirifar; Alireza Rajabi; Nooredin Ghadiri Massoom
Volume 15, Issue 3 , September 2022, , Pages 33-47
Abstract
In this paper, by creating and developing a code based on thermodynamics and gas dynamics equations, the performance characteristics of a 1N hydrazine monopropellant thruster such as thrust force, specific impulse, characteristic exhaust velocity, and propellant mass flow rate have been studied theoretically ...
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In this paper, by creating and developing a code based on thermodynamics and gas dynamics equations, the performance characteristics of a 1N hydrazine monopropellant thruster such as thrust force, specific impulse, characteristic exhaust velocity, and propellant mass flow rate have been studied theoretically in terms of reaction chamber temperature. In this regard, by taking into account the adiabatic assumption, the reaction chamber temperature of monopropellant thruster has been analyzed zero-dimensionally using the ammonia dissociation rate as an independent variable under equilibrium and non-equilibrium conditions and it has been analyzed one-dimensionally using the hydrazine and ammonia homogeneous and heterogeneous reaction rate constants. Also, the effect of nozzle throat thermal expansion on reaction chamber pressure, thrust force, and propellant mass flow rate and the effect of reaction chamber pressure on ammonia dissociation rate and consequently on reaction chamber adiabatic temperature under thermodynamic equilibrium conditions have been studied.
Z. Mehrafroz; S. Radpour
Volume 2, Issue 1 , April 2009, , Pages 35-42
Abstract
In this paper, reliability growth concepts and modeling methods have been studied and a reliability growth model for launch vehicles has been proposed. Numerical example shows how we can obtain the model parameters. A method for calculating the initial launch vehicle reliability is suggested, also a ...
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In this paper, reliability growth concepts and modeling methods have been studied and a reliability growth model for launch vehicles has been proposed. Numerical example shows how we can obtain the model parameters. A method for calculating the initial launch vehicle reliability is suggested, also a method for estimating and validating of launch vehicle reliability in various number of launches with number of successes based on binomial distribution has been proposed. Results show after 10 successful launches we can conclude that launch vehicle reliability is between 0.741 and 1.
H. Karami Mazraeshahi; S. A. R Jalali-Chimeh; M. Naderi-Tabrizi
Volume 4, Issue 2 , January 2012, , Pages 35-46
Abstract
In this paper the apparent velocity regulation system has been studied and simulated. The objective of this system is to adjust the missile’s fight velocity with the predetermined value, in specified time steps. In fact the apparent velocity regulation system calculates and changes the thrust of ...
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In this paper the apparent velocity regulation system has been studied and simulated. The objective of this system is to adjust the missile’s fight velocity with the predetermined value, in specified time steps. In fact the apparent velocity regulation system calculates and changes the thrust of the engine (pressure of the combustion chamber) in order to accomplish the desired fight velocity. For this purpose, a dynamic simulation for the propulsion system and also the missile’s flight has been developed. After analyzing the results, it is revealed that using the apparent velocity regulation system; the flight’s range accuracy will be improved dramatically. Comparing two similar missiles, with a same disturbance; one equipped with the apparent velocity regulation system and the other not, revealed that using such a controlling system will keep the accuracy of the target hitting within 200 meters while in the absence of it, the error would be more than 1.5 kilometers
H. Kazemi; A.A. Golroo
Volume 5, Issue 2 , July 2012, , Pages 35-48
Abstract
The international system proposed the liability convention 1972 for compensating damages occurred while utilizing space. However, certain key principles of liability such as some rules of conflict law and jurisdictions have been neglected there. This convention failed to provide a unified regime like ...
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The international system proposed the liability convention 1972 for compensating damages occurred while utilizing space. However, certain key principles of liability such as some rules of conflict law and jurisdictions have been neglected there. This convention failed to provide a unified regime like that of established by the Warsaw system for air carrier liability against passengers and cargo. Because of this failure and due to the international nature of space activities, during the past two decades, states inclined toward bilateral and multilateral space agreements for determining liability and compensating probable damages. In this paper it is argued that international law system is capable of finding common points in the said agreements and taking a new step toward uniformity of international regulations of space liability by modifying the convention 1972
A. Saghari; M. Mirshams; A. Jafarsalehi
Volume 7, Issue 2 , July 2014, , Pages 35-47
Abstract
In this article the results of research to achieve a comprehensive code of remote sensing satellite conceptual design is presented. In compiling the code with considering the design philosophy of "better, faster, cheaper" has been attempted in caddition to the use of new technologies and the experiences ...
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In this article the results of research to achieve a comprehensive code of remote sensing satellite conceptual design is presented. In compiling the code with considering the design philosophy of "better, faster, cheaper" has been attempted in caddition to the use of new technologies and the experiences of experts, local constraints such as national launchers limitation also be considered.The main advantage of the proposed code than conventional models, is using accurate simulation methods and newer models in the process of conceptual design of subsystems. view of the practical experience of the past to choose the best design starting point, achieve an operational plan to reduce the risk of costly changes, next steps of design has been achieved.
Leyla Mohammadi; Shervin Amiri; Gholamreza Mohammadkhani
Volume 9, Issue 2 , September 2016, , Pages 35-46
Abstract
One of the main challenges of the Open-Loop Signal Tracking method in GPS-RO space receivers, is Doppler prediction. Almost in all satellite communication systems, accurate carrier phase tracking under difficult conditions is depend on Doppler prediction accuracy. Obviously, there are several methods ...
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One of the main challenges of the Open-Loop Signal Tracking method in GPS-RO space receivers, is Doppler prediction. Almost in all satellite communication systems, accurate carrier phase tracking under difficult conditions is depend on Doppler prediction accuracy. Obviously, there are several methods for producing a predicted Doppler model, and one of the earliest is Sokolovskiy. In this paper, we are analyzing the typical and operational atmospheric Doppler prediction models for the Open-Loop Signal Tracking of radio occultation, in satellite communications. A summary and comparison between these methods will be concluded in the end of this paper. finally we propose a prediction method can be used in national GPS-RO payloads for predicting atmospheric doppler based on combination of Sokolovsky and C.O. Ao methods.
