نشریه علوم، فناوری و کاربردهای فضایی
سال چهارم شماره 1 (پیاپی 7، بهار و تابستان 1403)

In this article, the synthesis of the two-dimensional radiation pattern of multi-beams in the time-modulated planar antenna array is discussed. With the aim of reducing the time of numerical calculations of multi-beam synthesis and eliminating the traditional and optimization approaches, which are mostly complicated and time-consuming, the convolutional neural network approach has been investigated. In this study, the simultaneous shaping of multiple beams as desired in the time modulated antenna array is presented for the first time. By using the method of switching elements and their time modulation, which is based on the Chabi-Sheff distribution, to use and realize multi-beams such as the fundamental beam and the first and second harmonics with low side lobe level and steering at different spatial angles, create various random data. After that patterns and modulations like them are stored. After that, by presenting and designing a model of the convolutional neural network, learning the model for the relationship between the main beam pattern and the first two harmonic patterns with the time modulation of each element has been done. The presented neural network has been able to learn the relationship between the time modulation parameters of the antenna array elements with the main beam patterns and the first and second harmonics with a mean square error of about 0.03. In order to evaluate this model, a random sample of data has been selected to give its patterns to the input of the network. The output of the network has estimated the time modulation sequence of each element. Finally, the modulation pattern of the estimated elements is compared with the main patterns of the comparison and shows the closeness of the original pattern to the estimated pattern. This method provides a good capability for arbitrary control of multiple beams for applications that require establishing multiple connections.

The design of space operations must be done carefully. Because the smallest mistake in the design and construction of the spacecraft causes heavy financial losses. Electronic boards are one of the most important components of electronic systems in any operation. These boards must continue to operate under the applied loading. Strong levels of random vibrations can cause damage and fracture in electronic boards. The random vibration field applied to the electronic board can be modeled by mixed-mode I/II loading. Solder joints are very sensitive components of satellites. Fracture of electronic packages often occurs due to cracking in the joint between the electronic board and the solder under mixed-mode I/II loading. In this research, a new fracture criterion based on the maximum tangential stress is presented to predict the fracture for the interfacial crack between the electronic board and the solder. Based on the presented criterion, the direction and moment of crack initiation are predicted for the interfacial crack between isotropic and orthotropic materials. In this way, the fracture limit curve can be drawn. By comparing the presented criterion with the available experimental data, it can be concluded that the presented criterion has sufficient validity to evaluate the prediction of fracture in interfacial cracks between isotropic and orthotropic materials.

In this paper, an adaptive fault-tolerant control based on modified nonsingular fast terminal sliding mode control is developed for attitude tracking of a satellite with three magnetorquers and one reaction wheel. The proposed approach is designed to be robust in the presence of actuator faults, external disturbances, and inertia uncertainties and preserve the acceptable performance of system. The adaptive law is designed to estimate the upper bound of uncertain expressions, increase the tracking accuracy, and improve the performance of system. This parameter with a coefficient of sliding surface variable are used in the reaching phase of control law to achieve the chattering-free phenomenon. Stability and finite-time convergence of attitude variables is proved by the extended Lyapunov condition. To increase the tracking accuracy and compensate the required torque, a reaction wheel is used as a redundancy. Also, for increasing the control accuracy, the dynamics of this actuator is considered as well as the constraints of magnetorquers and reaction wheel. The simulations are performed and compared with the similar control method under the mentioned conditions to evaluate the performance of the proposed method. The results show the finite-time convergence, increasing the tracking accuracy, smoothing of satellite attitude changes, and generating the chattering-free control signals.

The layout design of satellite components is a key method to improve the overall performance of the satellite; So that proper placement design has been a common feature in most of the successful satellites. In this research, the layout and configuration design of a remote sensing satellite will be discussed. This design is done using the requirements given to the structural subsystem by other subsystems. The difference between the layout of this satellite and other satellites is that in this satellite the elements are placed on the main structure of the satellite, which includes Honeycomb plates (honeycomb core and an aluminum shell), instead of a layered arrangement. For this purpose, in the first step, the satellite structure along with all the elements of different subsystems will be modeled in Solidworks Software. Next, according to the given requirements, the layout of elements will be done. After that, the results of the center of mass and moments of inertia in two open and closed states of the solar panels are obtained. These results show that the cross moments of inertia are insignificant (close to zero) compared to the moments around the coordinate axes; therefore, it can be stated that the considered coordinate axes are consistent with the main axis of the satellite; This is a proof of a suitable layout and configuration design.

This research focused on investigating additive manufacturing factors using Selective Laser Melting (SLM) with maraging grade 300 steel powder via Taguchi method. The main objectives were to explore the influence of process parameters and achieve optimal levels. Experiments were exactly designed with the assistance of Mini-Tab software. The study specifically targeted scanning speed, hatch distance, layer thickness, and scanning strategy for fabricating tensile samples. Comprehensive characterization using optical and scanning electron microscopes examined mechanical and microstructural properties. The analysis revealed that the optimal levels for achieving desirable results were as follows: scanning speed of 100 mm/s, layer thickness of 20 microns, hatch distance of 0.15 mm, and implementing the Stripe scanning strategy in the XY direction. The output results showed significant findings, with a final tensile strength of 951 MPa, porosity measured at 0.4%, and an impressive relative density of 99.6%. In conclusion, this research provides valuable insights into optimizing the selective laser melting process with maraging grade 300 steel, offering crucial knowledge about effective process parameters for obtaining optimal mechanical and microstructural properties in the additive manufacturing of tensile samples.

In this paper, In the preliminary phase of space mission design, the selection of the spacecraft's trajectory is critical. This study simulates the dynamics of low-thrust orbital transfers within a two-dimensional orbital plane, employing a set of ordinary differential equations to represent the continuum of the spacecraft's orbital elements. These elements are encapsulated by six orbital parameters, manipulated under a defined thrust vector strategy within the action space, adhering to a specified policy framework. An agent, trained via a reinforcement learning algorithm within an actor-critic network architecture, is tasked with executing a low-thrust transfer between Low Earth Orbit (LEO) and Geostationary Orbit (GEO). The algorithm dynamically adjusts the spacecraft's trajectory, informed by initial orbital conditions and mission-specific constraints, to derive an optimal thrust angle trajectory and corresponding adjustments in orbital elements for the maneuver. To validate the algorithm's efficacy and robustness, a comparative analysis is conducted by implementing an alternative transfer mode at a varied orbital altitude. Additionally, the study explores the impact of adjusting the algorithm's degradation coefficient hyperparameter on the learning efficacy. Conclusively, the findings suggest that the agent, once adequately trained within the specified dynamical model, is capable of autonomously executing analogous orbital transfers. This is achieved without necessitating reiteration of the dynamical simulations, contingent solely upon the stipulation of initial and terminal orbital parameters.

In this article, the optimal design of a flying object is discussed with the help of designing the required speed. In this design method, the input information includes the type of fuel composition, payload mass, and maximum flight range, and the purpose of the design is to determine the initial mass and main dimensions of the aircraft. At the beginning of the design, the configuration of the bird is selected, and then with the determination of the fuel composition, the main characteristics of the fuel are determined as the main design inputs in the first step. By going through the design stages and by performing weight and geometric calculations, the initial mass of the flying object, the initial mass of the stages, the amount of fuel and oxidizer of the stages and the amount of thrust of the engines are determined. Then, to ensure the design method, similar flying objects in terms of fuel type, number of stages and also the final range have been used for validation. After performing the classical design, optimizing the mass function is considered, for optimization, the parameters λ_νi (relative initial thrust of the stages), P_ci (internal combustion pressure of the engines) and P_ei (exit pressure of the nozzle of the engines) with three GA methods (genetic evolutionary algorithm), ABC (bee colony evolutionary algorithm) and CA (cultural evolutionary algorithm) have been optimized and the results have been compared with each other. After analysis of the results, it is clear that the minimum mass (objective function) and the most optimal value is related to the cultural optimization method (CA), which reduces the initial mass by bringing the flying object to the final range.

One of the most important parameters in the operation of the diffuser of the vacuum simulator is the ratio of the cross-sectional area of the diffuser inlet to the outlet cross-section of the nozzle. Increasing this parameter increases the expansion length of the supersonic flow and causes instability in the process of starting up the diffuser. In the present study, the effect of the different diffuser inlet to nozzle exit area ratio (Ad/Ae) on the starting performance of a second throat exhaust diffuser has been investigated experimentally. Vacuum simulation tests have been carried out on several conical nozzles with different exit area by a high-pressure air apparatus. Investigations show that at high Ad/Ae before starting the diffuser, oscillations in the pressure of the test chamber are created due to the instability of the flow at the diffuser inlet. By frequency analysis of the vacuum chamber pressure, it is observed that as Ad/Ae increases, the number of oscillatory modes of the vacuum chamber pressure increases and the dominant frequency of the oscillations before starting the diffuser becomes larger. It was also observed that, generally, with the increase of Ad/Ae the amount of motor pressure corresponding to the start of oscillations decreases. In addition, according to the investigations, with the increase of Ad/Ae from 1.27 to 7.81, the minimum starting pressure of second throat exhaust diffuser increases by 20.33 %.

Radiation damages have destructive effects on the electronic components of satellites. Due to financial reasons and the presence of different restrictions, the utilize of commercial components ended up common in short-term and low-altitude missions. The most effective method of protection against radiation is the use of shields. The results of calculations obtained from PSTAR and ESTAR software show that in case heavier metals are utilized, the energy range of particles to stop increases. The result of SHIELDOSE, MULASSIS, PSTAR, and ESTAR software calculations is that the amount of thickness of different materials for the radiation tolerance of commercial parts does not differ much in terms of condensation thickness. Also, there is no need for complex protection and it can be used the usual protections. The maximum thickness required for the radiation tolerance of commercial parts is 0.5 mm from the combination of Aluminum and Tantalum. In order to achieve the best result considering the mass budget, it is better to use polyethylene material. From the results of the calculations to change the permutations of the aluminum and polyethylene shields, it can be concluded that it is better to have the first layer of polyethylene and the next layer of Aluminum.

A one-dimensional code was developed to simulate the performance of hybrid rocket engines. In this code, the conservation equations of mass, momentum and energy are solved in one-dimensional and inviscid form. To validate the code and conduct further experimental studies, an experimental setup was designed and manufactured. The stand had various components, including an experimental-scale motor, an oxidizer feeding system, thrust stand, data acquisition and recording equipment. The repeatability of the results has been proven in it. The simulation results, including the combustion chamber pressure and thrust, were compared with the experimental date and good agreement was achieved. By using the code, flow parameters including speed, pressure, density and mass flow rate ratio (O/F) along the combustion chamber were obtained. The regression rate of the fuel surface in different time periods showed that the fuel regression was not uniform, so that at the beginning of the grain there is a minimal regression, but at a distance of about 0.12 m from the beginning, there is a continuous increase in regression reaching the highest amount, and then decreasing towards the nozzle. This code is a useful tool for analyzing and design of hybrid engines.

Tube flow forming is one of the most economical production methods for simple cylindrical tubes with external and internal protrusions with or without flanges. The purpose of flow forming operation for body production is to use more raw materials and increase mechanical properties due to hard work on the part instead of raw machining of tubes. Due to the high strength of these tubes, it is one of the most important methods of manufacturing cylindrical bodies in the aerospace industry. In this research, the formability of high-strength maragining steel has been experimentally investigated by the three-roller flow forming process and finite element analysis. The effect of changes in flow forming process parameters such as mandrel rotation speed, feed rate, and angle of attack on dimensional and geometric accuracy as well as surface quality of the produced product was investigated experimentally and numerically. The results showed that the surface roughness of the final product increases up to 62% as the feed rate increases. Increasing the feed rate also leads to the reduction of out-of-roundness by more than 50%, thus improving the geometric quality of the final part. Increasing the rotation speed of the mandrel leads to a decrease in the surface roughness up to 30%. Also, increasing the rotation speed leads to an increase in the non-rotation of the product. Increasing the angle of attack of the roller from 15 to 30 degrees leads to an increase of about 30% in surface roughness and a decrease in non-roundness and a decrease in diameter growth.

Previous studies have proven the relationship between comfort, health and productivity in typical work spaces. In certain workspaces, such as industrial cleanrooms, resilience becomes more difficult for employees, as strict standards restrict access, movement, and severe interactive and visual limitations. The aim of this research is to find a way to compensate for such shortcomings in the mentioned spaces. The current research is exploratory in terms of purpose and practical in terms of use, and qualitative in terms of data collection techniques. First, documentary studies were conducted in the field of key concepts, quality of space, dimensions of resilience and theoretical foundations of the subject, in order to extract the components affecting the space and its qualitative goals. Then, in order to collect field data, in-depth interviews with experts in the relevant fields, the focus group method was used. Based on this, visual comfort and sound comfort respectively have the highest impact in environmental compatibility to provide spatial desirability; Ergonomic compatibility and sensory-emotional compatibility were evaluated with moderate impact and lower priority in this regard. The result is that the provision of visual and acoustic comfort is the leader in shaping the qualitative model of the desirability of special spaces such as industrial clean rooms. The results of the research were conducted to the form of a comprehensive model as "integrated human-centered model in the interaction between the resilience of the architectural space and the factors of the desirability of the space". According to the field findings and extracted content propositions, visual comfort has the greatest impact on spatial resilience. The results of the research, compared to previous researches, show that, the factor “success” is strongly influenced by the factor “visual comfort”. Finally, the research proposes a multifaceted model for spatial resilience in the architecture of high-constraint work-spaces.