Journal of Space Science and Technology
Year:2014 | Volume:7 | Issue:2 |Papers Count:9

In this paper attitude control system of nanosatellite based on Single Gimbal Control Moment Gyroscope (SGCMG) is presented. A LQR/LQG method is developed for stability of satellite and a feedback quaternion strategy is used for maneuvering mode. In the stabilization mode LQR/LQG controllers are designed with linearization of nonlinear dynamic equation of satellite and control moment gyroscope, so that in other reseach didn’t use this controller in the stabilization mode of this system. In the maneuvering mode a feedback quaternion controller applyed for nonlinear system. Numerical simulations are provided to show the efficiency of the proposed controller for a nanosatellite with four single gimbal control moment gyroscope pyramid cluster. Results of simulations shown that LQR/LQG method is more accurate in compared with feedback quaternion controller.

In this study, univariate linear regression model was developed for monitoring secchi depth in the Caspian Sea using level 1b and level 2 data. The in-situ measurements were carried outduring 25 one-day campaigns in the Caspian Sea. In this study, 25 level 1b MERIS images were utilized and then converted to level 2 data using C2R processor. The ability of univariate linear regression for the extraction of secchi depth from level 1b and level 2 wasinvestigated. The results demonstrated that the level 2 data lead to better performance than level 1b data. The level 2 data are able to retrieve the secchi depth in the Caspian Sea with correlation coefficient and percent of absolute error about 0.86 and 28.6%, respectively. Finally, secchi depth map of Caspian Sea was retrieved from MERIS level 2 images using developed univariate empirical model.

According to the importance of knowing aerodynamic parameters of parachutes used as recovery system of a sounding rocket, some launching tests were conducted to achieve the acceptable reliability. A testing rocket which simulated the recovery condition of the sounding rocket was used in these tests. Furthermore, the results of the tests used for validating a simulation code written for investigating the aforementioned two stage recovery system process. Some aerodynamic parameters of parachutes such as drag coefficient, opening force coefficient, and filling time, filling distance and drag area increase during inflation process were estimated from the tests in various conditions. The results show that for the first and second used drogue chutes with large canopy- loading, in contrast to the main parachute with small canopy- loading, the inflation parameters were not dependent on the height or air density. The drag area versus time shows linear variation for the first drogue chute, and shows second and third function for the other two parachutes. The situation of the second drogue chute in front of the main parachute affects the filling time of the main parachute. The distance between the parachutes, the ratio of their canopy areas and the air velocity are some parameters that affect the filling time. The results of this investigation could be worth for the design of a decelerator system, preciously.

In this article the results of research to achieve a comprehensive code of remote sensing satellite conceptual design is presented. In compiling the code with considering the design philosophy of "better, faster, cheaper" has been attempted in caddition to the use of new technologies and the experiences of experts, local constraints such as national launchers limitation also be considered. The main advantage of the proposed code than conventional models, is using accurate simulation methods and newer models in the process of conceptual design of subsystems. view of the practical experience of the past to choose the best design starting point, achieve an operational plan to reduce the risk of costly changes, next steps of design has been achieved.

This study, focuses to simulate separation process in different launchers numerically using fluent software. In present case, an aerodynamic equations coupled with rigid body dynamics, because of resultant aerodynamic forces and gravity, is developed to simulate the detachment motion of strap-on boosters. As can be seen from the results, by changing in booster elongation and changing in operation mach number and the effect of expansion waves from the core rocket and the booster, separation trajectory follows safe separation or collision between core and booster.

Recently, new actuators known as fluidic momentum controllers (FMC) have been proposed for satellite attitude control. This actuator has many advantages such as high applied torque to weight ratio, easiness in assembly, low transmitted vibration and so on respect to the other momentum exchange devices like momentum/reaction wheels or CMGs. However, one of the main problems in implementing such actuators is complexity in mathematic modeling of them. This issue makes many researchers to use a simplified model for control system designing without to consider uncertainty in this simplified model. In this paper for eliminating of this problem, an adaptive sliding mode control (SMC) has been used in this article. This control method is not also robust respect to uncertainties but also can estimate over threshold of them without necessity to use larger and heavier actuators to be sure of satellite stability. According to the results, we can observe that proposed control system is capable to reach satellite to the desire attitude in minimum time and without overshoot.

The aim of the paper is to describe a methodology of damage detection in the liquid propellant engine which is based on artificial neural networks in combination with stochastic analysis. It is assumed that the liquid propellant engine have faulty data collection system. Then a filtering algorithm for elimination perturbation data has been applied. The damage is defined as fuel and oxidizer channels clogging up. The key stone of the method is feed-forward multi layer network with back propagation algorithm. It is impossible to obtain appropriate training set for real engine, therefore stochastic analysis using mathematical model is carried out and dynamic simulation is made to get training set virtually. Engine channels clogging up leads to unwanted variation of pressure, flow rate of oxidizer and fuel and other main parameters of engine. Then variations considered as best input data for damage detection. The methodology was carried out using laboratory test.

Gyrocompass is used to justify and aim (orient) the missiles; it is used in equipment and accuracy of launch position as well to find azimuth in particular points. Observations and reading in this kind of compass are done optically which suffers from low accuracy and optical illusion. In this paper a simple algorithm is suggested by utilizing methods based on processing digital image and neural networks for automatic reading of a trade gyrocompass. In the method at first, by analyzing the difference of sequential images taken from the compass display, the back frame is specified. Then the display region is extracted by edge detection and morphology operation. After that the segmented numbers are recognized one by one through the trained neural networks. Finally, the gyrocompass angle is calculated accompanied by accuracy of arc second by geometric analysis of relative position of scaled board and indicated index. The usage of suggested method in the step of back frame recognition has been evaluated on 6 real test video sequences and the next steps have also been evaluated on more than 300 real images.