نشریه علوم، فناوری و کاربردهای فضایی
سال چهارم شماره 2 (پیاپی 8، پاییز و زمستان 1403)

This article investigates the enhancement of the control performance of flexible spacecraft by addressing actuator faults, input saturations, and internal and external disturbances (including flexible solar panel vibrations) during attitude maneuvers. First, the proposed disturbance observer, which can estimate the angular velocity and lumped disturbances of the system, is developed. Hereinafter, a fault-tolerant control algorithm is proposed using an integral sliding mode with adaptive gain to accurately estimate the upper bound of actuator faults with input saturation considering the rigid-flexible body interaction effects. On the other hand, fault-tolerant control, which proposes adaptive gain in the structure of the sliding surface, has the potential to eliminate the undesirable phenomenon of chatter in the system. The global stability of the nonlinear system is proven using Lyapunov theory. Additionally, during the attitude maneuver, active vibration control, also referred to as strain rate feedback control, using piezoelectric sensor/actuator patches is simultaneously implemented to reduce residual vibrations caused by rigid-flexible body dynamic interactions and the effect of actuator faults. The simulations in the form of a comparative study with conventional approaches show the validity and capability of the proposed approach in reducing the effect of external and internal disturbances for flexible spacecraft with actuator faults.

In this paper, using a developed software, the combustion process inside the cryogenic engine is simulated one-dimensionally and using the equilibrium solution. The propellants are kerosene_LOx. In this regard, models for combustion and nozzle analysis have been used. By using this software, initially, the behavior of the cryogenic motor at the design point is simulated. Then the sensitivity analysis has been done on the film cooling flow percentage. The results of the analysis at the design point show the accuracy of the engine performance. The results of the sensitivity analysis show that the temperature of the combustion chamber has an increasing-decreasing behavior based on the percentage of flow rate, because the fuel-to-air ratio of the combustion chamber approaches the stoichiometric number for some flow rates and then falls away, but the molar mass of the gases has changed and as a result of the impact The specific and characteristic speed of the behavior has a decreasing behavior in terms of the increase in flow rate, so that increasing the cooling percentage up to 20% reduces the specific impact by 7 seconds.

In this research, firstly, the importance of accurate calculation of satellite speed losses and the factors affecting them were discussed. The input data of 15 satellite launchers built by different countries around the world with variations in the number of stages, orbital height and payload mass were collected and by means of accurate path simulation software, their optimal turn angle program was extracted as well as speed losses due to earth's gravity, propulsion and the drag is calculated and presented. In the following, by using the non-linear regression method, three analytical relations with acceptable error have been extracted and introduced to estimate speed losses, which can replace the use of route simulation code in the conceptual design phase of carriers. These relationships have been evaluated by the information of two satellites outside the statistical data used in the regression, including Safir and Epsilon, and the accuracy of the algorithm has been confirmed with a maximum error of 12% and an average error of less than 6%.

Studying the parameters that influence additive manufacturing and determining the optimal conditions for part production is a complex challenge. Research is actively focused on understanding how process conditions affect the evolution of microstructure and the resulting mechanical properties of fabricated components. A study was conducted to investigate the effect of selective laser melting additive manufacturing process parameters on the mechanical properties of Maraging 300 steel samples. The mechanical properties were determined using 2D digital image correlation on flat tensile samples (in accordance with the ASTM E8 standard). Laser scanning speed (70, 100 mm/s), hatch distance (100, 150, 200 μm), and layer thickness (20, 40 μm) were evaluated for their effects on mechanical properties. The desired mechanical properties were extracted using the digital image correlation test, a non-contact optical method for measuring mechanical properties. According to the results of the study, the laser scanning speed significantly influences the mechanical properties of samples more than other additive manufacturing parameters according to the relationship between the selected parameters and the laser energy density and their effect on the molten pool. Based on the results, the optimal sample is made with a scanning speed of 70 mm/s, a hatch distance of 200 μm, and a layer thickness of 20 μm. This sample has a yield strength of 1785 MPa, an ultimate strength of 1816 MPa, an elongation of 17.4%, and a Poisson ratio of 0.34.

The purpose of image registration is to align two or more images taken from the same scene at different times and/or from different perspectives and/or using different devices. In recent years, with the continuous improvement of human ability to observe the earth, the accuracy and quality of remote sensing images have increased. Therefore, the need for new image registration models that can perform high calculations of these images and also have good accuracy is observed. In this thesis, we have used a new method to solve these problems. The proposed solution includes the use of regions of interest in order to reduce the search area and increase the accuracy. For this purpose, first, the areas that are the same between two images are identified, and then, the image is registered according to the similar areas. To find the region of interest, a deep transformer neural network model is used. The proposed deep neural network of the transformer includes several layers of inner-attention and cross-attention, which has the task of learning the importance of different positions within an image and between two images. The proposed model is a self-supervised method that generate training data using the segment swapping. The training data was collected from Google Earth images and annotated by us. After training the model and obtaining the similar regions, we use the common SIFT model to obtain the image registration. For testing, we have used Sentinel-2 aerial images. To quantitatively evaluate the result, we use the root mean square error. Quantitative and qualitative results show a significant performance gap in cost and accuracy, compared to conventional methods of capturing aerial images.

The studied society is the policy documents related to the aerospace field by the policy-making organizations of different countries in all parts of the world. In total, 21 documents from 13 countries have been reviewed in order to deduce the trends and core issues of the space industry. By analyzing the full text of the documents, which was more than 1200 pages, 229 codes were extracted by separating each unit of analysis and were used as input data sets in thematic analysis. The scope of the research is England, China, the United States of America, India, France, Sweden, South Africa, the Netherlands, Brazil, the European Union region, the United Arab Emirates, the Philippines, and Australia. Descriptive analysis method and MAXQDA software were used to interpret and analyze the data.Surveys show that different countries have written strategic documents in order to draw visions, goals and technology roadmaps in order to keep up with the drivers of the development of the space industry. These documents provide valuable insight into the priorities, investments, and collaborative efforts that are shaping the future direction of the space industry. The analysis of these strategic documents can lead to the understanding of scientific and technological trends in the space industry. The content analysis of the documents has led to the identification of 20 technological areas in 5 core areas, autonomous space, advanced space systems, complex space operations, space sustainability and space digitization.The identification of 20 key technology areas in five general axes shows the multifaceted nature of the space industry and emphasizes the strategic priorities of different countries around the world. The analysis of the strategic documents of different countries shows that there are many opportunities and challenges for both newcomers and veteran actors with the expansion of the space market in the coming years. The analyzes performed are an important decision-making tool in technology planning and technology strategy formulation, it is of great importance in terms of determining the direction and priorities in the development of the space industry and can help to formulate effective strategies and plans in the future.

Phase orbital maneuvers with the goal of rendezvous are a series of orbital adjustments made by a spacecraft to align its orbit with another object, such as another spacecraft or space station. These maneuvers usually involve adjusting the speed and trajectory of the spacecraft to gradually decrease the distance and match the target orbit at a certain time. If the orbital phase adjustment is without regard to specific time (non-orbital rendezvous), the problem is greatly simplified, but in the case of specific time (phase change in a specific period of time), the problem becomes complicated and can be analyzed by two objectives including, fuel consumption and elapsed time. In this research, the influence of the location of performing the phase change maneuver in a circular orbit has been investigated by various true anomalies. Based on the results, from 0 to 10 degree true anomaly, the duration of the maneuver increases with a very large slope, and after that, the duration of the maneuver decreases until the anomaly of 270 degrees.

In the depths of space, inherent challenges arising from long distances and harsh environmental conditions require advanced technologies to overcome these obstacles and enhance space communications. This paper presents an innovative method for designing reflector antennas using the deployable mesh reflector mechanism, which operates in the X and Ka bands. By leveraging the advantages of a dynamic network structure, this approach provides unparalleled flexibility in adapting to various dimensions of space structures. The proposed mesh reflector antenna is collapsible in three-dimensional space (3U), significantly easing its transportation. After releasing of satellite into orbit and by utilizing the specified mechanisms, the antenna expands up to 1 meter, thereby offering a broader coverage area for information exchange. Precise dynamic analyses demonstrate that the designed mechanism, without the use of stepper motors and with the incorporation of dampers and springs, enables controlled antenna deployment with suitable speed and torque. This, in turn, minimizes vibrations and disturbances to the satellite, enhancing stability during operations. The innovative method holds significant potential for improving the quality and efficiency of information transmission in deep space and can substantially contribute to advancements in space technology. Its applications span a wide range of space domains, including communication satellites, navigation, and remote sensing, heralding remarkable developments in this field

The position of the cathode concerning the magnetic field map inside the discharge channel affects the performance and lifetime of the Hall effect thruster. The neutralizer cathode has two important functions in the Hall effect thruster. Almost %18 cathode electrons enter the discharge channel of the Hall thruster and provide the necessary electrons for ionization. The rest of the electrons neutralize the ions coming out from the thruster and the spacecraft remains neutral regarding electric charge. In this article, the map of the magnetic field and separatrix lines inside the thruster are simulated with FEMM software. According to the position of the magnetic field separatrix lines, the neutralizer cathode is placed in three different positions, and the Hall effect thruster performance is simulated using the XOOPIC code and the PIC-MCC method. Shifting the position of the cathode relative to the magnetic field lines and the field separatrix line, significant changes were observed in the parameters of the cathode voltage, the thrust force, and the thruster's specific impact, which improves the thruster's performance. The results of this research show that the performance parameters of the thruster are optimized due to increasing the lifetime of the cathode when the cathode is placed between the first and second separatrix lines.

Seed germination and seedling establishment are considered an essential growth stage and the first stage of plant adaptation in extraterrestrial environments. This project aimed to investigate the rocket launch-induced stress and the space conditions during a short-term space flight on the seed germination indicators and its components for the seeds of two plant species. The dry seeds were placed in a pre-designed metal structure and embedded in the Kavus bio-space capsule. The dry seeds were embedded in a pre-designed metal structure inside the Kavus bio-space capsule. After the successful launch and recovery of the capsule, relevant tests were performed on the seeds. The results were completely different depending on the chosen species. Quinoa seeds showed a positive response to the conditions of launch stress in the form of increased germination indices and radicle length. Eruca seeds showed a completely negative reaction to the stressful conditions of the launch and the space environment, which showed that this decrease reduced the germination index and its related Obviously, collecting sufficient evidence on the subject to prove the results of the present study requires designing more experiments on the seeds of these two species in future launches in Iran.

Studying the microgravity effect on biological samples requires biological experiments using flight facilities such as space shuttle, biological satellites, and the International Space Station, but biological studies in space are expensive and rare, and requires simulation techniques on the ground. Therefore, ground facilities such as two-dimensional clinostat, random position machine, and magnetic levitation are used to create simulated microgravity. The biological sample is suspended under a high gradient magnetic field and simulated microgravity is applied. Using this method, environments with low or high gravity can be created and the effect of magnetic field and microgravity can be investigated on biological samples. This technique has many advantages compared to other methods for achieving microgravity, including unlimited testing time and fast achievement of microgravity. Also, by changing the intensity of magnetic field, it is possible to simulate gravity on the surface of the moon or Mars. In this research, different types of magnetic levitation using electromagnetic field and magnet and the challenges of designing biological experiments will be investigated. Also, the gene and proteomic responses under magnetic levitation and the mechanism of cell growth through different phases of the cell cycle will be studied.

In this article, the optimal path for the soft landing on the lunar surface is generated. Path planning is defined as an optimization problem that aims to achieve the optimal control function for the spacecraft. The thrust value of the device is fixed and the thrust angle is considered as a control variable. The objective function is to minimize the landing time and actually maximize the mass of the device at the moment of landing. The speed constraints related to the soft landing of the vehicle are also included in the objective function in the form of a cost function. Due to the unstructured and infinite search space, a new meta-heuristic algorithm called Particle Swarm Programming is used to find the optimal controller function. This algorithm is based on the Particle Swarm Optimization algorithm and has a favorable performance in the simultaneous optimization of the structure and parameters. The design of the controller was done in two types: open-loop, time-dependent, and closed-loop, time-independent, and in both types, it was able to find the optimal solution for the controller function. The resulting numerical results show a very high agreement of the controller function with the response of other optimization methods. Finally, to make the simulation more realistic, the turbulence conditions are applied to the spacecraft thrust force and the results prove the superiority of the closed-loop, time-independent controller.