نشریه علوم، فناوری و کاربردهای فضایی
سال سوم شماره 2 (پیاپی 6، پاییز و زمستان 1402)

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.

To discuss the potential role of iridium (Ir) nanoparticles loaded under atmospheric conditions, we prepared a series of catalysts with the same active phase but different contents of 10wt%, 15wt%, and 20wt% on gamma-alumina for decomposition of hydrazine. The performance of the catalysts was better with 15wt% and 20wt% of the Ir nanoparticles, and also the selectivity to hydrogen was about 27%. An increase in the reaction rate from 181 h-1 to 218 h−1 was observed in the loading of 15% by weight of iridium particles due to the good dispersion of the active phases by preventing surface agglomeration. As a satisfactory result of this investigation, Ir catalysts with different weight percentage (15wt% and 20wt%) showed the same activity and selectivity, and are suitable substitutes for each other. Using a catalyst with a lower weight percentage of the active phase and high activity is economically acceptable due to its low cost.

The sandwich panel is an important element of the satellite structure which various metal and composite materials are used to make its faces. Anodizing is used as a conversion coating in order to achieve the final properties of the panel surface and stability in the space environment. Anodizing is an electrochemical process in which an oxide layer is formed using electricity. During the anodizing process, concentration polarization is created and the process is stopped when the limiting current resulting from the movement of electrical charges between the surface of the anodic layer and the electrolyte is increased. By stopping the process without spending enough time to obtain a thickness sufficient for colorability, a black anodic layer for use in space coatings is not obtained. In this research, by performing the anodizing process in four container of 250, 500, 2000 and 40000 cm3, the effect of the volume of the electrolyte on the wear and corrosion and optical-thermal properties of the layer obtained in each of the processes was investigated. The results showed that with the increase in the volume of the electrolyte caused by the increase in the volume of the container, the stopping time of the process increases. The evaluation of optical-thermal properties, wear resistance and corrosion resistance was done by infrared emission coefficient and solar absorption test, pin on disk test and salt spray test, respectively. The results of measuring optical-thermal and wear and corrosion properties for three container with volume of 500, 2000 and 40000 cm3 showed that with the increase in the volume of electrolyte and the process completion time of the process, the thickness of the anodic layer increased, which improved the optical-thermal properties, corrosion and wear resistance.

This paper compares spacecraft attitude control in the presence of disturbance torque using an adaptive backstepping controller and an extended state observer-based backstepping controller. Firstly, the adaptive backstepping controller is designed, in which the unknown parameters in a specific disturbance model are estimated using an adaptive law so that the closed-loop system is stable. Afterward, the backstepping control based on the extended state observer is designed. In this approach, the standard backstepping controller is initially designed, and then disturbances with a completely unknown model are estimated by the extended state observer, and the disturbance is rejected by applying the feed-forward law. The simulation results for two different disturbance models show that the backstepping controller based on the extended state observer demonstrates very good results compared to the adaptive backstepping controller when no disturbance information is available. This is for the reason that the extended state observer estimates the uncertainties more accurately.

This article presents a solution for reducing the height of magneto-electric dipole antennas by using an artificial magnetic conductor structure as the antenna's ground plane. Two types of antennas were investigated: a linearly polarized antenna and a right-handed circularly polarized antenna. For the linearly polarized antenna, a 7 x 7 array of artificial magnetic conductor cells (AMCs) was designed at 3.5 GHz and placed on the antenna's ground plane. By adding artificial magnetic conductors, the height of the first antenna was reduced to 0.16 λ. The simulation results show that the impedance bandwidth for values of |S11|<[-10dB] is 1.9 GHz from 2.3 GHz to 4.2 GHz (58.46%), while the measured impedance bandwidth of fabricated prototype is 2.13 GHz from 2.21 GHz to 4.34 GHz (65.03%). The second antenna, which is a right-handed circularly polarized magneto-electric dipole antenna fed by a Y-shaped feed line, has also been improved using an artificial magnetic conductor structure on its ground plane. A 5 x 5 array of AMC cells is used to reduce the height of the antenna to 0.13 λ. The simulation results show an impedance bandwidth of 1.24 GHz from 2.46 GHz to 3.7 GHz (40.25%), while the fabricated prototype has an impedance bandwidth of 1.3 GHz from 2.38 GHz to 3.68 GHz (44.52%).

One of the main issues in the arrangement of equipment in multi-layered satellites includes placing the equipment in each layer separately. In the arrangement of equipment on surfaces, the non-overlap constraint has always been a challenge, especially for parts that do not have a circular cross-section. This paper presents a robust flexible programming model (RFPM) for placing equipment in different layers and considering uncertainty for placement of cubic equipment. Comparing the output of the proposed model with previous studies in this field shows that the efficiency of the model has increased significantly to meet the limitations of non-overlapping between equipment. Eventually, it is expected that this research can cover the existing gaps in this field and by observing other limitations such as stability and thermal limitations, moments of inertia and center of gravity, it will reduce the design time in the conceptual and preliminary phase and ultimately reduce the overall dimensions of the satellite, which has always been one of the main goals of designers.

The gyroscope system is an attractive nonlinear system that is used in various industries such as the military, aerospace, navigation, etc. Considering the importance and applications of the non-linear system of the gyroscope, the design of the control system for the operation of the gyroscope system is indispensable. Most systems in the real world have nonlinear dynamics, and it is inevitable to avoid the destructive effects of noise and unpredictable external disturbances. Nonlinear uncertainties in gyroscope dynamics, noise, and unpredictable external disturbances are major challenges in controller design. The model-free control is developed for this system. Particularly, the sliding mode controller is widely used in the control of non-linear systems due to its robustness to system dynamic uncertainties and system disturbances. In this paper, the dynamic behavior of the nonlinear gyroscope system is analyzed then a sliding mode controller based on the neural network is used to control the gyroscope system. The stability of the nonlinear gyroscope system is proved using Lyapunov's theory. The nonlinear model of the gyroscope is simulated in Simulink MATLAB to investigate the behavior of the proposed control method and compare it with other controller's methods, so the efficiency of the proposed control method in the control of the nonlinear gyroscope system is investigated

In this article, a new closed-loop algorithm is presented to generate an optimal angular trajectory for a given satellite to reach the desired final point. Using the capabilities of artificial neural networks, this algorithm can find the best trajectory to reach the final setpoints based on the dynamic behavior of the system and the preset controller capability by using the desired final values of the trajectory and the values of the system state variables at each simulation time. In the presence of external disturbances, this closed-loop intelligent trajectory generation algorithm shows advanced adaptive performance, which allows it to develop the best alternative trajectory to achieve the final setpoint and return the system to the main trajectory. Despite the fact that this algorithm is able to restore the main trajectory, it is also capable of preventing unreasonable control efforts by considering the control properties of the system. This intelligent algorithm of angular path generation shows high accuracy and effective performance after simulations are performed in the MATLAB software environment with predefined external disturbances.

In this article, a fault tolerant control based on a virtual actuator is used for the maneuvering of low earth orbit satellites that are subject to the loss of the effectiveness and additive actuator faults as well as natural disturbances such as atmospheric drag, earth's gravity, solar radiation and third body. In the approach used, there is no need for a separate unit to detect, isolate and identify the error. The main feature of this approach is to provide the same performance for the nominal system and the faulty system since the actuator faults and disturbances are hide from the nominal controller due to placing a virtual actuator between the faulty plant and the nominal controller.For the purpose of satellite maneuvering, using Kepler's orbital dynamics, which is affected only by the Earth's gravity, the desired second orbit parameters are calculated. In addition, orbital dynamics based on six modified orbital elements have been used, which avoids singularities. Then, using the desired orbit parameters, the relative motion elements are calculated and used in the control laws. To demonstrate the effectiveness of the control method, a maneuvering scenario of a satellite with Kepler's orbital dynamics that affected by natural disturbances and the actuator faults, is simulated for 42 days. The satellite has an effective cross-sectional area of 0.56 m2, and an actuator fault is occurred since the 32nd day. The results show higher performances the proposed method compared with conventional controllers like LQR.

Generally, the determination methods of the satellite orientation are known as attitude determination and attitude estimation. The attitude determination solution of the satellite leads to the Wahba problem. Therefore, at least two independent measurement vectors and two corresponding reference vectors are needed to apply the Wahba problem. These input vectors aren't accurate due to sensor noises, misalignment, and low-order approximations. However, these uncertainties aren't considered in the classic Wahba problem directly. In this case, the estimation error of the Wahba problem depends on the input vectors' accuracy. Hence, modeling error and measurement noise are modeled using Interval analysis. Then, the attitude determination problem is transformed from a single-objective problem to a multi-objective robust optimization problem. Since solving the multi-objective problem with heuristic solvers such as NSGA II is time-consuming, the multi-objective problem was solved using the min-max optimization algorithm. The attitude determination error with the proposed method is reduced (7 times) compared to the quaternion method, and its dependence on the accuracy of the input vectors is reduced (200 times). In fact, while reducing the mean attitude error, the algorithm robustness has increased compared to the uncertainties in the input vectors. Using the min-max algorithm has reduced the execution time of the algorithm (about 600 times) compared to the NSGA II algorithm and is suitable for real-time applications. Based on the results, the proposed method has narrower bounds, so that the mean square error (RMS) is decreased by more than 50% over the q-method.

Paying attention to the increasing use of metal-polymer composites in aerial and space structures and their economic efficiency, it is possible to achieve a more economical and high-quality connection by determining the appropriate parameters. The purpose of this article is to calculate the optimal parameters for the friction stir welding (FSW) process to properly join aluminum to polymer. Polycarbonate sheets and aluminum alloy sheets, widely used materials in the aerospace industry, were employed for FSW. Initially, a traditional FSW was conducted without additional material. Subsequently, for two samples, a layer of epoxy glue was placed between the two sheets, followed by FSW. On the second sample, a restorative FSW was performed with a 10 mm comb stirrer head. The results indicated that the most optimal condition was a spindle speed of 1400 r/min and a welding speed of 50 mm/min, particularly for the sample with epoxy glue and repair welding. Traditional FSW showed flaws, while FSW with adhesive displayed fewer defects. Repair welding significantly influenced the FSW joint, enhancing the cleanliness of the macroscopic appearance of the weld surface. In the tensile test, it was observed that the tensile strength of the repair weld exceeded that of the joint welded by two traditional methods and with glue. Microscopic results revealed more holes in FSW with two traditional methods and with glue, gradually reducing defects during repair welding.

Ion mobility spectroscopy (IMS), as one of the detection methods based on the ionization of mineral, organic, and chemical substances, has been used efficiently for many years in manned and robotic space missions. The space applications of these instruments include environmental monitoring of spacecraft and identification of organic and mineral substances in samples collected from space. In this method, warm-up is required for the cleanup and transport of ions in the drift area of the detector cell. Considering the need to miniaturize and optimize the necessary power of space detectors, the experimental investigation of the thermal gradient and factors affecting warm-up time is essential. For conducting the experimental thermal analysis of the IMS cell, micropumps, desorber, and temperature recording equipment such as a temperature control system, data logger, thermocouple sensors, monitoring system, and resistance temperature detector have been used. In this research, by experimentally investigating the warm-up time and thermal gradient in the IMS cell in different modes and several target temperatures, the main factors have been determined. The results showed that the oscillating air flow inside the IMS cell can reduce the warm-up time and the temperature gradient. Finally, several suggestions for better thermal efficiency are presented.