نشریه علوم و فناوری فضایی
سال سیزدهم شماره 3 (پیاپی 44، پاییز 1399)

Orbital transfer blocks has the task of transferring satellites to objective orbits from parking orbit. In this paper, Attention will be given to multidisciplinary optimal design of the propulsion system of two liquid component which is one of the most important subsystems of Orbital transfer blocks. Designing with multi objective bipropellant system, based on minimum total mass and maximum Isp, and at the end mentioned to costs and compared. For combinations of NTO as Oxidizer and fuels which are: UDMH, MMH, Hydrazine and RP-1 then for usual structures that utilized in this systems, design and optimization occurred by multi objective hybrid Particle Swarm Optimization (PSO) algorithms.

in this paper, design, implementation and test of 24 bit acoustic DAQ subsystem for bio-capsule of Pajohesh explorer is presented. the proposed structure has been used B&K 4942 microphone as input sensing element. the proposed DAQ, has 48Ksps speed, 24 bit resolution, 113dB dynamic range and 23 KHz BW. we used a ARM Cortex M3 for signal handling and processing. the acquiescing data have been sending to Bio- capsule FC and also recorded in a Micro-SD card. power consumption of the proposed DAQ is obtained 2.8W. the proposed DAQ take a place with dimentions of 40*40*100 mm3 inside of bio-capsule stand.

Halo orbits are of importance for observation and study of the space due to their specific characteristics including the orbital position and the periodic motion. In this regards, present paper has focused on optimal trajectory planning to transfer to halo orbits. To this aim, homotopy approach has been adopted for optimal trajectory design. This approach has improved the convergence rate and insensitivity of the problem to initial guess. The designed trajectory transfers a spacecraft orbiting the Earth to a Halo orbit around Lagrangian point L1 of the Earth-moon restricted three-body system. The propulsion system has been assumed to be low thrust with constant specific impulse. Homotopy approach has a broad domain of applicability and methods in which continuation method has been employed here among them. The optimal designed trajectory minimizes the fuel consumption via transforming solution of the minimum energy problem utilizing the homotopy approach. This approach simplifies solution of the complex problem of minimum fuel indeed.

In this paper, WNN with PSO training algorithm is used to modeling and prediction of time-dependent ionosphere total electron content (TEC) variations. 2 different combinations of input observations are evaluated. The number of stations used to train of WNN with PSO algorithm selected 20 and 10. In all testing mode, 3 GPS stations with proper distribution are considered as a testing stations. Statistical indicators relative error, dVTEC and correlation coefficient were used to assess the wavelet neural network model. The results of proposed model compared with GPS-TEC and international reference ionosphere 2012 (IRI-2012) TEC. Average relative error computed in 3 test stations are 5.43% with 20 training station and 9.05% with 10 training station. Also the correlation coefficient calculated in 3 test stations are 0.954 with 20 training station and 0.907 with 10 training station. The results of this study show that the WNN with PSO algorithm is a reliable model to predict the temporal variations in the ionosphere.

This paper presents design, analysis and performance verification test of student microsatellite Attitude Determination and Control Subsystem (ADCS) . ADCS design and implementation procedure contains several various steps. There are four main test levels during simulation called “Model-in-the-Loop”, “Software-in-the-Loop”, “Processor-in-the-Loop” and “Hardware-in-the-Loop”. This paper is a result of scientific and practical research during two years, on the student microsatellite, which is an eight-nation collaboration project among Asia-Pacific universities. In what follows, “Model-in-the-Loop” and “Processor-in-the-Loop” test and simulation will be discussed. The aim of this paper is to illustrate the result of these two tests and validate the ADCS design. In the end, it is demonstrated that designed control algorithms are precise enough to meet the student microsatellite ADCS requirements and they can be used in the next level of microsatellite development.

In this paper, an anti-jamming GPS array antenna with seven antenna elements on the conformal structure is proposed for GPS applications by switching on/off the antenna ports. In this proposed antenna, when the received power is high, the antenna feeds are switched off to create null in the direction of jammer to reduce the jammer effect. This structure composed of seven patch elements where each element placed on special face of the structure. Whatever antennas be more directive, we can create deeper nulls. These specifications introduce this antenna as a good candidate for GPS applications to mitigate the jammer effects.

In this paper a new structure for the inertia measurement unit is presented; the proposed structure consists of three rotary discs around the three main axes in the body, and an accelerometer is mounted on each disc. It is shown in this paper that the proposed structure reduces the effect of disturbing accelerometer parameters, such as constant and variable bias, as well as noise depletion. Due to the proposed rotational structure, it is necessary to continuously sample the accelerometers. In order to use the sampled data, calculations should be performed in discrete mode. In this paper, a method for combining this information is presented. By examining the proposed equations, the successful performance of this method is shown in the reduction of the effect of three constant bias parameters and the bias of the accelerometer and the measured noise. As well as the efficiency of the proposed method for measuring the acceleration of the device using Numerical representation is shown.

In this paper, an accurate computational method is proposed to measure the relative accuracy of the star sensor, which does not require complex laboratory instruments. The proposed method uses the direct observation of the night sky along with the exact equations of motions of the Earth and stars to measure the accuracy of the star sensors in the order of 1 arcsecond. The Classical Laboratory Measurement Procedures of the star sensor’s accuracy requires at least a sky simulator along with some auxiliary tools such as a collimator, an accurate 3 DOF Rotary table, an exact alignment instruments, and so on. The classical procedure, in addition of being complex and time-consuming, is costly, and the auxiliary tools also increase the measurement error by themselves. Identifying and eliminating these errors are more difficult process. The proposed procedure is more accurate and more reliable because the sensor is tested in its actual operating environment, i.e., the sky, rather than the simulated laboratory environment.