Journal of Space Science and Technology
Year:2024 | Volume:17 | Issue:1 (پیاپی 60)|Papers Count:7

This article presents a method for enhancing the accuracy of the initial alignment process of inertial navigation systems with a stabilized platform using state feedback control in flight mode. In the proposed method, a state feedback controller is designed utilizing stable platform deviation angles and sensor errors extracted via a Kalman filter. By verifying the system's observability and incorporating suitable flight maneuvers, the navigation error propagation equations are expressed as a time-invariant system, enabling the estimation of sensor angles and errors during the alignment phase. This lays the groundwork for state feedback design. Subsequently, considering the stable platform's motion equations and applying the principle of separation of observer and controller design, a state feedback controller is developed. Finally, simulation results demonstrate that the proposed method improves the accuracy of the alignment process and, consequently, enhances navigation accuracy compared to the conventional output feedback method.

In high-resolution remote sensing satellites, achieving stability and meeting stringent pointing requirements are crucial for mission success. Accurate gyroscopes are employed as primary attitude sensors to ensure this stability. However, gyroscope data must be calibrated at appropriate intervals to maintain high attitude estimation accuracy and prevent drift over time. This research investigates an Extended Kalman Filter (EKF)-based approach for gyro calibration, aiming to enhance the precision and reliability of attitude estimation. Initially, a comprehensive model that includes the main gyro parameters—such as biases, scale factors, and misalignments—is proposed. This model is the foundation for developing an EKF-based algorithm designed to estimate and correct these gyro parameters dynamically. Following this, the study implements a Multiplicative Quaternion Extended Kalman Filter (MQEKF), which utilizes star sensor data as inputs to improve the accuracy of attitude estimation further. A quaternion feedback controller is implemented to evaluate the effectiveness of the proposed gyro calibration method within the attitude control loop. The simulation results demonstrate that the satellite's stability and pointing are maintained with accuracies better than 0.005°/s in angular velocity and 0.15° in angular positioning. These results highlight the method's potential to significantly benefit missions with tight control requirements significantly, providing enhanced performance and reliability in high-precision space applications. This approach offers a robust solution for improving satellite mission outcomes where precise attitude control is essential.

In this paper, we aim to employ the least squares support vector regression (LS-SVR) for the spatio-temporal modeling of the ionospheric total electron content (TEC). This model utilizes simple linear equations to solve the system of equations, thereby reducing the computational complexity and enhancing both the speed of convergence and the accuracy of the results. We utilized observations from 15 GPS stations in north-western Iran from day 193 to day 228 in 2012. The results of the LS-SVR model were compared with those of support vector regression (SVR), artificial neural networks (ANN), adaptive neuro-fuzzy inference system (ANFIS), Kriging model, global ionospheric maps (GIM), and the International Reference Ionosphere 2016 (IRI2016) as well as TEC values obtained from GPS. The accuracy of all models was evaluated and interpreted at interior and exterior control stations. The analyses indicate that the average root mean square error (RMSE) for the ANN, ANFIS, SVR, LS-SVR, Kriging, GIM, and IRI2016 models at two interior control stations are 3.91, 2.73, 1.27, 1.04, 2.70, 3.02, and 6.93 TECU, respectively. Furthermore, the average relative errors of these models at the same control stations were calculated as 15.98%, 9.39%, 7.85%, 6.09%, 11.60%, 12.54%, and 26.56%, respectively. Analysis of the precise point positioning (PPP) method demonstrated an improvement of 50 mm in the coordinate components using the LS-SVR model. The results of this study demonstrate that the LS-SVR model can serve as a viable alternative to global and empirical models of the ionosphere in the studied area. The LS-SVR model provides a high-precision local ionosphere model.

Achieving low ripple, high efficiency, high reliability, and optimal volume and weight are crucial in the power supply of traveling-wave-tube amplifier (TWTA) lamps in satellites. This article focuses on optimizing the efficiency and reliability of high-voltage DC/DC electronic power converters for use in satellite and TWTA systems. The optimization goal, using the multi-objective genetic algorithm NSGA-II, is to minimize the objective function, encompassing both efficiency and reliability. Reliability is assessed through a Markov model, which considers short-circuit and open-circuit failures in circuit switches and diodes, as well as short-circuit failures in passive circuit elements. The optimization process begins with defining the input variables for the algorithm. Sensitivity analysis is utilized to eliminate parameters with low sensitivity whose variations do not significantly impact the objective function. Parameters for the NSGA-II algorithm, including the number of iterations, population size, and probabilities of crossover and mutation, are precisely determined to ensure accurate computation of circuit variables. The results demonstrate that this method achieves high reliability alongside high efficiency through the optimal selection of circuit components, ensuring the converter's effectiveness for application in satellite systems.

This paper reviews space technology development models in countries similar to Iran to identify strategic approaches that can be adapted for its national context. Two countries are examined: the first group consists of countries more advanced in space technology, and the second includes those following the former to enhance capabilities. Leading countries like the United States, Russia, China, Japan, India, and the European Union have been excluded from this analysis due to their well-established programs. The countries under investigation are categorized based on technological achievements and aspirations: the first category includes Israel (the occupation regime of Al-Qods), South Korea, and Turkey, which have made substantial progress in developing indigenous space technologies, while the second category includes the United Arab Emirates, North Korea, Kazakhstan, and Pakistan, which are also expanding their space capabilities. A SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis was conducted to evaluate space technology trends and strategic initiatives in these countries. A suitable development model for Iran has been identified, leveraging its unique strengths and opportunities. The results indicate that an indigenous development model is the most suitable strategy for space technology advancement in Iran. This approach emphasizes self-reliance and innovation in developing critical technologies. Key infrastructure for this model includes establishing a suborbital laboratory and a minimal mass orbital launch service, which are essential for fostering technological independence and supporting sustainable growth in Iran’s space sector.

Changes in Earth's gravity can significantly affect the behavior and performance of organisms, leading to the discovery of new practical methods for various applications. Heavy metal toxicity poses substantial risks to human health. Cadmium (Cd), one of the most hazardous heavy metals, causes defects in genome repair following oxidative stress and DNA damage, potentially leading to cancer. Several strategies have been introduced to remove heavy metals from water, including surface adsorption, membrane filtration, ion exchange, chemical precipitation, and nanotechnology treatments. Among these, bioremediation using probiotics has been identified as a cost-effective, safe, and efficient method for heavy metal removal. This study measured the effect of Lactobacillus acidophilus on cadmium bioremoval under simulated microgravity and Mars gravity conditions. For the bioremoval tests, 52.5 μg/L of cadmium was added to bacterial biomass and subjected to microgravity conditions. Similar samples were also placed under Mars's gravity. Control samples were maintained under identical conditions but with Earth's gravity. At the end of the treatment period, the tubes were centrifuged, and the remaining cadmium concentration in the supernatant was measured. The results showed that a 24-hour water treatment by L. acidophilus removed 43.77% of the cadmium concentration under Earth's gravity, 54.74% under microgravity, and 54.84% under Mars's gravity. Statistical analysis demonstrated that L. acidophilus effectively facilitated cadmium bioremoval, and this capability was sustained even under different gravitational conditions. Therefore, this bacterium can mitigate heavy metal pollution during space missions, safeguarding astronauts' health.

High-gain antennas are crucial for ensuring stable communication in imaging and remote sensing satellites due to their ability to support high data transmission rates while compensating for the limitations associated with increasing transmitter power or reducing transmission rates. Various antenna types, including electromechanical pointing structures, planar phased array antennas, and conformal phased array antennas, are employed for high-resolution image transmission and communication with ground stations. In satellite communication systems, small-gain omnidirectional antennas typically exhibit a significant gain of 15 dBi. Among these, the conical structure maximizes effective area, while the polyhedral pyramidal structure is also highly effective. An X-band patch antenna was designed and subjected to full-wave simulation using CST software to enhance performance. The designed antenna achieved a peak gain of 5.64 dBi at 8.45 GHz. The antenna array configuration includes eight patch antennas mounted on each face of a polyhedral array, with power distributed via an 8-way Wilkinson power divider. The resulting array achieved a gain of 14.3 dBi, by array theory principles. The construction of a polyhedral conformal array yielded a maximum gain of 18.3 dBi, with consistent gains exceeding 15 dBi for elevation angles beyond 30°. A high-gain circularly polarized array antenna was specifically engineered for satellite system applications, ensuring a robust and effective design and construction. A triangular planar array facilitates the development of various conformal array configurations, making it well-suited for satellite applications.