رضا امجدی فرد

The prioritization and verification of space emerging technologies is a multi-step, iterative process that needs to collective intelligence (the participation of all stakeholders), as well as the use of analytical methods to identify requirements. This process begins with identifying specialists who have enough knowledge and experience regarding to each technology, and followed by extracting and evaluating the necessary data, prioritizing technology options, identifying challenging technologies and the essential acquisition strategy, and finally prioritizing them. In this article, we implemented a method to identify and prioritize some space technologies which could be used in the electrical power subsystem (EPS) of a satellite. Based on the results, it would be possible to choose the best method to access the required technology; national development or benefiting of available technology in the market. To evaluate the suggested method, the power subsystem components are divided into three categories: electrical power generation sources, energy storage sources, and power electronic circuits. Applying the proposed method shows that the selected technologies are those is recently used in space. This method can also be applied to other subsystems.

The space environment includes different types of particles originating from both within and without the solar system. They can categorize depending on their origin (cosmic-galactic, solar, and Van Allen belts), and can cause severe damage to electronic components or functional failure of the equipment. Therefore, the radiation environment is an important concern in the system-level design of a satellite. The correct evaluation of radiation effects should occur as early as possible in the design procedure, and be upgraded as necessary throughout the development of project phases. Space-borne technology provides global data set of uniform quality and rapid data acquisition and also, global coverage collected data is updated in every time range. Due to space standards of NASA and ESA, one of the effective factors on degradation of space systems is radiation damages. The space radiation environment varies dramatically with the latitude, longitude, and altitude of the orbit, and also varies significantly with time. Satellite in the geosynchronous transfer orbit (GTO) faces significant amounts of particles including the high-energy electrons and protons trapped in the Van Allen belts (extend from an altitude of about 640km to 580000km). These particles are the source of three kinds of damage to electronic equipment (total ionizing dose (TID), displacement damage (DD), and single event effects (SEE)). In this article, the flux of the different energetic particles in the GTO is obtained by employing SPENVIS web-based software. SPENVIS is developed by a consortium led by the Royal Belgian Institute for space aeronomy for ESA’s space environments and effect section. Results show that the radiation fluxes have very drastic changes during every orbit time due to passing through the Van Allen Belts. The maximum flux of protons and electrons is in the range of 108 p/cm2.s. The sensitive electronic components cannot tolerate the total ionizing dose made by this amount of flux density. Therefore, to reduce the dose below the specified limits by the manufacturer, an aluminum shield must be used. Results show that in order to decrease the dose below the 10krad, the thickness of the shield should be equal to 6mm. This amount of shield is much thicker than those are used in LEO (Low Earth Orbit), and increases the total mass of the satellite. Regarding electric power generated by solar panels of satellite benefiting AZUR SPACE solar cell (3G30) If the thickness of the protective coating (cover-glass) of the cells is considered equal to 100 um, the efficiency loss of. Therefore, to support the subsystems and payloads over the whole mission life, the more solar panel is needed in comparison with satellites in LEO. Besides, the simulations show that with the increase of the thickness of the shielding from 4mm to 6 mm, the overall rate of single event upset (SEU) decreases from 3.7225E-06 /bit to 2.6556E-06 /bit (about 30%).

Reliability assessment of power converters is extremely important due to the degradation of the converter performance under the thermal and electrical stresses. The space environment is one of the stressful environments for electronic components and equipment due to the range and high speed of temperature changes.The normal or abnormal operation of a converter depends on the quality of the manufacturing process and the environmental and operating conditions. The failure indices usually are obtained based on the previous failures data which are calculated using the history of the main parameter of the converter. These indices are strongly influenced by the aging process. In this article, a new real-time indicator is introduced using the monitoring of the main parameters of the converter. The indicators are calculated using Replicator Neural Network (RNN). In fact, these indicators are obtained based on a comparison between a reference model of the converter in normal conditions and the estimation of abnormal operation of the converter in the future. In the proposed method, a normal distribution function is used to find the limits of error signals. The proposed method has several advantages such as considering all the uncertainties during the process of manufacturing the device, no need for the aging test data, and including all the failure types. In the Electrical power subsystem of a spacecraft, the reliability of power converters can be assessed based on the obtained data from the qualification models, benefiting the proposed method.

Protection of astronauts and electronic components in satellites and spacecraft against space rays is one of the most important primary requirements in space missions. In this work, the effect of three materials, aluminum, as the most common material, polyethylene and a graded-z structure, in the protection of space radiations has been evaluated. The calculations of the dose caused by these radiations on the human body and a silicon piece have been carried out by MCNPX Monte Carlo code,. The dose caused by cosmic rays has been calculated after applying shields of aluminum, graded-z structure and polyethylene. The results showed that by using polyethylene and about 4.4% increase in weight compared to the aluminum shield, it is possible to reduce the dose caused by photons by more than 50% in the human body and 30% in silicon parts, and the dose caused by protons by about 30%. It cut both for astronauts and electronic components. Graded-z shielding performed very well in the dose attenuation caused by photons, but appeared ineffective in the dose attenuation caused by protons.

This paper investigates solar activities and its phenomena from the perspective of risks on the functioning of urban infrastructures, industrial systems and economic structure affected by such phenomena. Also, according to the existing analyzes and results, basic requirements have been introduced to prevent the severity of the resulting injuries. Space weather events can cause disruptions in the power grid, telecommunications and radio communications, airlines, railways, and in addition cause damage to pipelines, oil and mining industry. Also, these phenomena can cause damage and dysfunction in satellites that are used for global positioning, communication and weather forecasting. Considering the importance of the items mentioned in this article, an attempt has been made to investigate the research done in some other countries regarding the impact of space weather phenomena on socio-economic systems and to study the disruptions and failures caused by this impacts in the industries and socio-economic infrastructures of the society. This studies can help in the formation of the necessary fields and preventive actions in facing the dangers of space weather in order to lead the scientific community to investigate similar cases in the country in order to create related management and technological measures.

In this paper, the feasibility and performance of using solar arrays equipped with sun concentrators, along with other conventional solar array structures, in CubeSats, is investigated for the first time. For this purpose, seven different structures of solar arrays have been defined and implemented for more than 24 different CubeSat configurations from 0.25U to 27U. Then, by calculating important system-level parameters such as power generation density, power generation cost, reliability of solar arrays, and also a newly proposed parameter, called shape fit factor, the performance of these structures for the introduced configurations are evaluated and compared. To this end, and by considering rational coefficients, a cost function consisting of the four above-mentioned parameters is defined as the degree of merit of different solar array structures used in each CubeSat configuration. The results show that alongside the use of deployable solar arrays, using concentrating solar arrays can provide new capabilities for CubeSats to overcome the challenge of generating sufficient power.

The space environment can cause severe problems for electronic circuits. The plasma, radiation, debris, and no thermal convection are some space environment-specific conditions. Space radiations are the source of several damages, such as total ionizing dose (TID). During a satellite’s mission life, the TID gradually degrades the quality of the electronic components. Designing reliable equipment requires enough information about the mission environment. Some part of this information could be obtained employing dosimetry. There are several dosimeters based on the type and intensity of radiation sources. In the present work, a dosimeter has been introduced that could measure the TID for a satellite in a low earth orbit. This dosimeter uses a RadFET to measure the TID. The simulation results and implemented version of the dosimeter verify the accuracy and quality of the proposed dosimeter. The low power consumption, fast data recording, and thermal stability are some of the features of the proposed dosimeter

Resonant converter due to implementation of zero voltage switching (ZVS) or zero current switching (ZCS), are very interested. Although using these techniques, increases the efficiency and also decreases the generated EMI noise, obtaining the small-signal model of these converters is very complicated. The state-space variables mostly change as a sinusoid curve, so the average of these variables is equal to zero. Therefore the traditional method such as state-space averaging is not applicable in order to obtaining the state space equation of the converter. In this article, the state space equation is obtained by using the extended describing functions. To verify the obtained equation, the Middlebrook method is suggested. By means of this method, the bode-plot of the open-loop transfer function could be obtained based on the existing hardware. So an isolated series resonant converter is implemented and the required signals are measured in order to draw the bode-plot of the open-loop transfer function based on Middlebrook method. Verification is performed by comparing the experimental results with simulation results.

Space environment radiation affects the operation and life-time of optical and electronic devices on satellites payloads. LIDAR payloads include electro-optical components such as laser section. LIDAR payloads are usually setup on various platforms. Space-borne remote sensing technology provides global data set of uniform quality and rapid data acquisition and also specially provides key information for evaluating the local, regional of aerosol irradiative forcing in global climate system, cloud properties and precipitation, Air pollution and hydrologic cycle. Also, global coverage collected data is updated in every time range. On the other hand, high expenditures of design, manufacture and using advanced technology are caused an increase in design and manufacture of high reliability LIDAR payloads, the mission duration and its quality in space. Due to space standards of NASA and ESA, one of the effective factors on degradation of space systems is radiation damages. In this research, effect of Total Ionizing Dose (TID) radiation on the operation of LIDAR subsystem orbiting 500 km altitude orbit with a 3-year mission is simulated. Radiation simulations on gain medium (Nd:YAG) and pump (laser diode) are performed by GEANT4 and C programming.
Laser subsystem in LIDAR payload includes 3 different parts. These parts are Nd:YAG, mirrors and laser diodes pump. Space radiation sources are classified in three types: Van Allen radiation belts, Galactic cosmic rays (GCR), periodic gradual activities of sun. The sun emits neutralized plasma (almost protons and electrons) to the space. Some energetic particles originated from solar winds and GCRs are trapped in Earth magnetic field. These belts are expanded from 1000km to 65000 km and consist of electrons up to 7Mev and protons up to 300Mev. GCR particles are mainly protons with very high speed originated from out of the galaxy. The most populated particles in 500km altitude are electrons and protons. In order to simulate the radiation effects, Input data such as average flux number of incident particles, total number of particles passing through the sensitive volume are needed. These input data will be entered in GEANT4 toolkit by C. Most important input data are flux, total number of incident particles during the mission, Energy range, geometry, materials definition and their properties, sensitive volume definition are needed physics and initial position of particles. The most important radiation damages related to lasers and solid state optical devices are total ionizing dose and displacement damage. TID is resulted from passing charged particles through matter, while displacement damage is due to collision of passing particles with atoms of matter. TID effects depend on two factors. The first factor is generation of electron-hole pairs in dielectric layers (such as oxides). The second factor is trapping sites (oxide and interface). This damage results in degradation and possible failure, such as threshold voltage shift, decrease in drive current, switching frequencies, leakage current, noises, etc. In bipolar transistors, hfe degradation, leakage current, offset voltage, changes in offset current, bias current and gain degradation in analog devices are possible effect. In other devices, frequency shift in crystals, mechanical degradations and changes in dielectric parameters are considered.
The results demonstrated that the absorbed dose from different space radiation sources for Nd:YAG and laser diode are important. Also, differences between the absorbed doses in 2 cases were simulated. The first case was absorbed dose with no shield against space radiation and the second one was calculating the absorbed dose with 2 mm Al7075 shielding the sensitive volumes against incoming particles. GEANT4 simulations determined that the absorbed dose in Nd:YAG when no shield was used to protect the laser parts against space radiation, was reached 1951 rad. In order to decrease the absorbed dose, the shield was used and it made considerable changes. The absorbed dose was reduced to 275 rad. Calculation showed that approximately 7×1012 protons would pass through the Nd:YAG, during the mission period. The number of passing particles through the sensitive volume depends on particle flux rate, sensitive volume sizes, mission duration. This value for GCR particles was 4×108 particles in each square centimeter. Results related to simulation of inner Van Allen radiation belt particles effect on Nd:YAG showed that the absorbed doses from the inner belt electrons and protons were about 68 rad and 187.5 rad respectively while these values for GCR protons and alpha particles were about 11 rad and 8.5 rad respectively. These values were about 481 rad, 128.5 rad, 7.5 rad and 6 rad for laser diode respectively. The total values for Nd:YAG and laser diode reached 275 rad and 623 rad. It is estimated that absorbed doses for radiation sensitive parts will be increased about 15 percent and according to the threshold current, the optical power versus threshold current curve will be changed.

The Space Environment consists of various radiations sources which emit different types of particle. Due to their high energy and high speed, these space particles can affect materials which they impact, in different ways. One of the most important damages which affect electronic instruments is Total Ionizing Dose (TID).In this article, modeling of these effects is performed by GEANT4 toolkit and Monte Carlo method. This toolkit performs simulations by using C programming language. Total Ionizing Dose effects are simulated for an operational satellite. Regards to considered conditions, failure or success probability in worst case has been analyzed. Based on ECSS, results satisfy standard and mission requirements.