نشریه علوم و فناوری فضایی
سال ششم شماره 2 (پیاپی 15، تابستان 1392)

Being a very powerful method, Positron Annihilation Spectroscopy (PAS) has been widely used for investigation of defects type and concentration in materials in recent years. In this paper, we first report characteristics of a Positron Annihilation Lifetime Spectroscopy (PALS) system which has been made in an Iranian nuclear spectroscopy instrument company with corporation of Sistan and Baluchestan University for the first time. The system is working with a resolution better than 350ps and can be used for materials such as ceramics, glasses and insulator materials. Next, we report designing and development of the first slow positron beam in Iran and we explain its advantages for exploring defects in materials. Positron Source, moderator and vacuum chamber including positron beam tube and sample chamber, has been designed and prepared. Designing of extraction lenses and magnetic fields has been made using CST STUDIO software in order to optimum focusing and transition of beam.

When the electronic components are exposed to neutron irradiation, electrical properties change by interaction of neutrons in these parts such as capacitance, reverse bias current, the minority carrier lifetime, etc. These changes are very important, so that may impair the performance of the device and disable it. So the measurement of the damage by neutrons in these parts is necessary. One of the most important parameters for expressing the damage to electronic components is a constant,  that is the inverse current of the damage.The constant () is the slope of the reverse current curve versusthe radiation flux. The aim of this work is measurement of the damage reverse current of constant  for diodes 1N4007, BYV27 and BYV95 in various voltages and temperatures.These diodes have been irradiated at the Tehran Research Reactor by fission neutron spectrum.The results are in good agreement with the theoretical relations.

In this paper GPS radio occultation has been introduced as a way to extract the electron density of the ionosphere. A GPS radio occultation occurs when a receiver on-board a LEO spacecraft tracks a GPS satellite as it sets or rises through the earth’s atmosphere. The recorded occulted signal phase and amplitude of the tracked satellite can then be analyzed to derive atmospheric electron density.TEC Monitoring has been studied tocorrect the error caused by the ionospher electron density in the telecommunication satellite global positioning system are briefly introduced as a tool for this method. One occultation event studied near one of the brazilion oson destations and the electron density curves obtained from the data reported Brazil Ionosonde are compared with radio methods.

In this article by analyzing the TLE data of Navid satellite from Iran University of Science and Technology the effects of these data on tracking operation of ground station has been studied. Then the prediction accuracy of satellite position, the error rate of antenna ground station, the error rate of satellite rise time and the sensitivity survey of these toward the variation of drag term (􀜤∗) of TLE data has been investigated. The results show that the accuracy of TLE data, the intervals of updating them and the time elapsed the epoch related to TLE data directly effected on accuracy prediction of the satellite position and tracking operation. In some cases such as the limitation of ground antenna beam, tracking satellite is not succeeded. Therefore it has been suggested that tracking operation of satellite is done by ground station and independent of the TLE data and using TLE data as a reserve state has been considered. In this case TLE data must be updated daily.

Cosmic rays in the atmosphere can cause leukemia and other diseases in the astronauts. Changing in microgravity weight make some unwanted effects on cells of the immune system and hematopoiesis. However, the activity of the body organisms is random in different people, but it can be simulate by special models. There are many different models of hematopoiesis that are simulated the effect of microgravity in the bone marrow. In this study, a self-developed code is used for investigation of absorbed dose effects on declining health of the tissue, blood and lymph, due to cosmic rays in space. The simulation was implemented for different kinds of input dose to body with different time duration. This phenomenon is surveyed for two cases: with considering to effect of production and reproduction of the cells and microgravity and without considering them. The results show effect of production and reproduction of the cell and microgravity can be improve or damage of normal cell about centesimal percent. Also, it can be initiate the anemia and the leukemia on the human at long time.

Aerospace Launch Vehicles (ALV) are generally designed with high reliability to operate in complete security through fault avoidance practices. However, in spite of fault avoidance, fault occurring is inevitable. Hence there is a requirement for on-board fault detection and isolation (FDI) without significant degradation in the ALV performance. The robust observers are widely used in FDI due to reduction of the effect of disturbances in the FDI process. In this paper, the robust fault diagnosis observer is designed for an ALV subject to uncertainties. The linear sliding mode technique is used to design the observer for a linear time varying model of an ALV. The parameter estimation from the sliding mode scheme is compared with those generated by a nonlinear simulation and are found to provide good correlation. Then, a proposed linear sliding mode observer is employed to generate the residual as an indicator of predefined gyroscope faults.

Flight dynamic equations have an effective role in aerospace technologies. It can be as cheap and efficient means for correcting errors in the spatial position and velocity in inertial navigation systems. The Inertial navigation system is an ideal solution for motion detection with high accuracy with fast dynamics, but the precise location and status of the system output can be significantly reduced over time. In this paper, inertial navigation system integrated with a navigation aided system based on online solving of flight dynamic equations. For this purpose, the proposed use of the Lagrangian of Kepler equations and three degrees of freedom of Newton's equations of transfer flights dynamic has been studied. Using this method, online high accuracy to be achieved by flight computer. Kalman filter algorithm is used for integrating inertial navigation and flight dynamic equations. Finally, The simulation results including position and velocity errors with regard to fly a prototype space module, for the proposed two conditions were compared and the advantages and disadvantages of each method are presented

This paper deals with the estimation of gyro model parameters and GEO satellite moment of inertia at the same time in transfer orbit phase. In order to fuse information of attitude determination subsystem sensors, an extended Kalman Filter has been employed. The estimation variables are including: quaternion, angular velocity, moments of inertia, and gyro sensor model parameters which are bias and scale factor vectors. The satellite motion equations along with gyro sensor and quaternion measurements have been used to design an Extended Kalman Filter in order to estimate the desired states. The disturbance torque effect on moment of inertia identification has been also considered. Estimation results via some case studies demonstrate the numerical simulation section exhibit robustness and efficiency of Kalman Fillter.