نشریه علوم و فناوری فضایی
سال هفدهم شماره 1 (پیاپی 60، بهار 1403)

A method for increasing the accuracy of the initial alignment process of inertial navigation systems with a stable platform is presented through state feedback control in flight mode. In the presented method, the state feedback controller is designed by using the stable plate deviation angles and the sensor error which is extracted with the help of Kalman filter. To do this, while checking the observability of the system, by adding suitable flight maneuvers and expressing the equations of propagation of navigation error, in the form of a fixed piece system with time, it is possible to estimate the angles and errors of the sensors in the align phase. The groundwork is provided for the design of state feedback. Then, taking into account the stable platform motion equations and using the principle of separation of observer and controller design, a state feedback controller is designed. In the end, the simulation results of the proposed method show an increase in the accuracy of the alignment process and, consequently, an increase in the accuracy of the navigation, compared to the conventional output feedback method.

IIn high resolution remote sensing satellites, meeting stability and pointing requirements are very crucial in mission’s success. In this regard, usually, very accurate gyroscopes are utilized as one of the main attitude sensors. In order to avoid decreasing attitude estimation accuracies, gyroscopes data should be calibrated in appropriate time intervals. In this research an Extended Kalman Filter (EKF) based approach is investigated for gyro calibration. Therefore, at first, a model which contains main gyro parameters, namely, biases, scale factors and misalignments is proposed. Then, an EKF based algorithm for gyro parameters estimation is presented. Next, a Multiplicative Quaternion Extended Kalman Filter (MQEKF) which uses star sensor data as measurement is applied for attitude estimation. Finally, in order to evaluate the performance of the proposed gyro calibration method in attitude control loop, a quaternion feedback controller is implemented. The simulation results show that satellite’s stability and pointing are maintained with accuracies better than 0.005 deg/second and 0.15 deg which demonstrate the proposed method will be beneficial for missions with tight control requirements.

In this paper, the aim is to use the least squares support vector regression (LS-SVR) for spatio-temporal modeling of the ionospheric total electron content (TEC). In order to do this, the observations of 15 GPS stations in the north-west of Iran have been used in the period from 193 to 228 at 2012. Comparing the results of the new model with support vector regression (SVR), artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), Kriging model, GIM and international reference ionosphere 2016 (IRI2016) as well as TEC obtained from GPS. The analyzes performed show that the averaged RMSE of ANN, ANFIS, SVR, LS-SVR, Kriging, GIM and IRI2016 models in two interior control stations are 3.91, 2.73, 1.27, 1.04, 2.70, 3.02 and 6.93 TECU, respectively. Also, the averaged relative error of the models in two interior control stations was calculated as 15.98%, 9.39%, 7.85%, 6.09%, 11.60%, 12.54% and 26.56%, respectively. Analysis of the PPP method shows an improvement of 50 mm in the coordinate components using the LS-SVR model. The results of this paper show that the LS-SVR model can be considered as an alternative to global and empirical models of the ionosphere in the study area.

One of the most important issues related to the power supply of TWTA lamps in satellites is to have low ripple, high efficiency, high reliability and optimal volume and weight,. In this article, the efficiency and reliability of high voltage DC/DC electronic-power converter is optimized for use in satellite and TWTA lamps. The goal of optimization using multi-objective genetic algorithm (NSGA-II) in this article is to minimize the objective function, which includes efficiency and reliability. Markov model is used to evaluate reliability, in which short-circuit and open-circuit errors are considered for circuit switches and diodes, and short-circuit errors are considered for passive circuit elements. for optimization, first, the input variables of the algorithm are determined as the input of the objective function, so that with the help of sensitivity analysis, the parameters that have low sensitivity and their changes do not have a major impact on the objective function are eliminated. parameters of NSGA-II algorithm, including the number of iterations, the number of populations, and the probability have been determined for the accurate calculation of circuit variables. the results section this method, in addition to maintaining high efficiency, with the optimal selection of elements, high reliability can be achieved .

In this paper, the models of space technology development in regional countries have been studied first, and the main criteria of each of these models have been classified. In this research, by ignoring the leading countries such as USA, Russia, European Union, China, Japan and India, the prominent countries of the region in the field of space technology have been investigated. These countries include the occupying regime of Al-Quds, South Korea and Turkey in the first degree of importance and the United Arab Emirates, North Korea, Kazakhstan and Pakistan in the second degree of importance. Then, SWOT analysis has been done for the space technology trends in the country, and by considering the requirements of the space technology development models, the proper development model has been introduced with the relevant requirements. According to the obtained results, the indigenous development model is the best space technology development model for the country, and one of the most important infrastructures needed in this model is to have a suborbital laboratory and a minimal mass orbital launch service.

Earth's gravity is one of the forces that constantly affects living organisms. It's changes can affect organisms behavior and performance. Study of such effects can lead to the discovery of new practical methods. Heavy metal toxicity have a lot of risks to human health. They sometimes act as a pseudo element of the body and they may even interfere with metabolic processes. Cadmium as one of the most hazardous heavy metals, cause defects in DNA repair following the induction of oxidative stress, DNA damage and may lead to cancer. Several methods have been introduced to remove heavy metals from drinking water. Bioremoval by probiotic is one of these safe methods. In this study Lactobacillus acidophilus effect on cadmium bioremoval was measured in microgravity and Mars gravity conditions. The results demonstrated that the 24-hour water treatment by L. acidophilus removed 43.77% of the cadmium concentration in the Earth gravity, 54.74% under microgravity and 54.84% in Mars gravity. Statistical analysis showed that L. acidophilus was effective in cadmium bioremoval and this ability was maintained even with gravity changes. Therefore, this bacterium can be used to remove heavy metal pollution during space missions in order to maintain the health of astronauts.

Due to the limited communication time between LEO satellites and the ground station and large volume of satellite image data, it is necessary to establish a high transmission rate connection. Therefore, the use of a high-efficiency satellite antenna is inevitable. In order to use the limited viewing time of the satellite, it must be possible to communicate with the ground station at low angles and change the main beam direction of satellite antenna to the direction of the ground station. The proposed array is composed of 8 antenna elements with a compact microstrip feed network. Low profile structure, circular polarization, high gain and low cost specifications of this proposed antenna array, candidate it for conformal array antenna in satellite applications.