نشریه علوم و فناوری فضایی
سال سیزدهم شماره 4 (پیاپی 45، زمستان 1399)

In this paper, a modified proportional navigation (PN) with weighted combination of linear acceleration and line-of-sight (LOS) acceleration feedback is suggested. For this purpose, a comprehensive miss distance analysis is carried out for PN with linear acceletation feedback and PN with LOS acceleration feedback using a fifth-order binomial guidance and control system. The miss distance (MD) due to initial heading error, target acceleration, and seeker noise is separately analysed. As a special case, a modified PN with acceleration feedback using variable gains is suggested based on MD analysis for infra red seekers. The comparison of PN strategies is carried out using an equivalent effective navigation ratio, defined by using LOS rate profile solution. In addition, the first-order optimal guidance law is converted into PN with PD block with variable gains.

This paper presents numerical study on spray characteristics and droplet distribution by using Lagrangian method in the discrete phase model of CFD. A two-fluid Eulerian method and Lagrangian approach is selected for modeling two phases turbulence flow in mixing chamber and atomization at outlet of nozzle while turbulence has been modeled by K-ɛ. In this study, water has been used instead of fuel and Nitrogen instead of atomization gas or oxidizer, while their ratio has been considered 0.32 to provide 26 degrees cone angle and this way, droplet‘s characteristic has been studied and compared with maximum entropy methods. Then droplet‘s diameter has been investigated by changing liquid and gas phase flow rateand based on that, we can optimize atomizer ‘s working condition with maximum efficiency with respect to its cone angle, droplet ‘s diameter and velocity and level of penetration by minimum need of experimental tests.

Several novel control techniques have been created as a result of the diversity of researches which are conducted about the problem of satellite attitude control. There are always uncertainties in the problem of satellite attitude control in the space missions. Therefore, Adaptive control is a method which is taken into consideration. High computational volume is one of the problems of adaptive control technique. In this paper, a control technique which is based on optimization concepts is introduced for the problem of satellite angular velocity and attitude control. Also, it's developed based on the three-dimensional special orthogonal group, and it's not faced by a singularity problem. For comparison, the linear quadratic regulator (LQR) control technique is simulated. Finally, the results of the simulations show that the performance of the presented adaptive control technique is optimal, and this method is robust to inertia changes.

This paper analyses the dynamic behavior of the rigid solar panels deploying mechanism of a spacecraft with flexible hinges. The proposed mechanism, maintaining a proper speed, guarantees the deployment synchronization of solar panels and minimizes the effects of impact and vibration applied during the final stage and after the panels lock-up using torsional springs in the hinges and yoke driven assembly. The equations of the motion of the system are derived using Lagrangian approach and the behavior of the mechanism for constant and variable torque excitation modes is investigated. The simulation results presented along with the dynamic simulations performed by Adams software and conventional mechanisms show the efficiency of the proposed method.

Studying vegetation status is one of the most important environmental issues. Using contemporary and field methods in this regard will cost a lot of time and money. Remote sensing technology and satellite image processing is a solution that can facilitate such difficult processes. In this study, remote sensing technology will be integrated with web geographic services to provide users with adequate analysis of the growth of the plants and their changes based on vegetation indices in the shortest possible time. Important technologies used for this purpose are ENVI IDL, Google Map API, JavaScript, and ASP.NET. The service was successfully implemented and was employed for Landsat satellite images. In order to evaluate the performance of the service at different points and with a different number of images, the timeliness of the NDVI vegetation index was prepared. The processing time evaluation also showed that by increasing the number of satellite images the processing time will increase linearly.

In this numerical study, effect of magnetic field on the convective heat transfer of a magnetic fluid in an enclosure is investigated in the microgravity condition. Two cases of a single magnetic field source under the enclosure and two sources on the top and below the enclosure are considered and the simulations are carried out for different magnetic field intensities and magnetic source distances from the enclosure. Results indicate that the heat transfer in the microgravity is much lower than that of natural condition due to the lack of the flow vortex. Applying the magnetic field and the induced vortex due to the magnetic body force cause a significant improvement of the heat transfer. Results show that the heat transfer rate in the microgravity condition can be increases up to 6.5 times. Moreover, placing two magnetic field sources improves the main vortex and leads to 19.7 times enhancement of the heat transfer rate compared to the case of single source.

The presence of ionizing radiation in the space environment, due to trapped particles, solar particles and cosmic rays can be a serious threat to the proper functioning of electronic components used in satellites and spacecraft. In this work, the leakage current variation of a silicon diode, as the basic element of many electronic components, has been investigated in the exposure of space protons. For this purpose, the GEANT4 Monte Carlo code has been used to calculate the non-ionizing energy loss in the device. The simulation of electrical parameters for irradiation of space protons were also done by SILVACO software. The results show that the leakage current increases by about 1.85 times the amount of it before irradiation, up to about 96.2 nA/μm by the increase in the proton flux up to 2.1×1012 p/cm2. Irradiation of BPW34 photodiodes under 30 MeV protons was performed to validate the results of simulation.

This paper presents a new approach to eliminating noise and disturbances in the corse alignment process for inertial navigation systemsBecause of extreme fluctuations and quasi-static environments, the corse alignment process often involves a lot of errors and noise. Initially, the coarse alignment process for inertial navigation systems is described exhaustively and then, with the assumption of disturbances and noise, we attempt to nudify to improve and initialize the initialization accuracy. Subsequently, introducing the filtering characteristics of the digital filter for the mutation , Due to the deletion of some of the sensor's main data, identifies the missing parameters and estimates the state variables using the Kalman filter matrix based on the variance of the data error. Identifying the missing parameters of the transformation matrix in the coordinate system using the Kalman filter Matrix is the innovation of this paper, which leads to improved note coarse alignment will be inertial navigation systems.