Papers by Keyword: Satellite

Abstract: Satellites with passive thermal control system use thermal coatings, secondary and first surface mirrors and paints to maintain the temperatures of their electronic equipment within operating temperatures. Satellite coatings are exposed to harsh space environments like ultraviolet radiation (UV) and atomic oxygen (AO) that cause thermal degradation. As nature of the space environment, degradation of the surface paints and coatings cause increase in temperatures of the equipment in time. Thermal designer must consider the thermal degradation of the coatings and paints and optimize the radiator sizes of the satellite at Beginning of Life (BOL) and End of Life (EOL) of the satellite in order to maintain the temperatures of equipment within their safe operation limits. For this analysis, a micro-class satellite using passive thermal control with surface paints and interface conductance within each equipment has been studied. The satellite top surface (+Z) faces the earth and bottom surface (-Z) faces deep space. The lateral sides of the satellite are covered with honeycomb solar panels and top and bottom surfaces are covered with white paint which act as satellite radiator. The satellite orbit has been considered as 700 km Sun-Synchronous Low Earth Orbit. In this analysis BOL and EOL thermo optical properties have been used to predict the satellite temperatures before and after degradation of paints. Thermal analysis have been performed and predicted temperatures obtained by using THERMICA thermal analysis software.

Abstract: This paper deals with the objective of controlling a satellite by driving a six-state discrete Kalman Filter to estimate angular rates of satellite base on control sensor noisy data. A typical satellite is assumed in a special orbit and orbital angular velocity and orbital angular acceleration are established. For completion of simulation linear dynamics model of satellites and environment disturbances model such as solar pressure and gravity gradient torque is derived as well. The simulation is progressed at discrete ten second which assumed as data updating rate from sensor. The noisy measurements are produced by sensor and these data is sent to the discrete Kalman Filter part to estimate the attitude and attitude rate. A right balance for Plant noise covariance matrix is determined and also results show that the rate estimates are appropriate for space missions.

Abstract: In this study lightweight carbon fiber and multiwalled carbon nanotubes filled hybrid nanocomposite was fabricated for electromagnetic interference (EMI) shielding in spacecraft. Electrical conductivity was conducted to assess the affect of MWCNT addition on composite. EMI shielding effectiveness (SE) was tested in the frequency range of 1-18 GHz. Comparison of SE was also made with AA6061-T6 sheet. Dispersion of nanotubes in the matrix was examined through microscopy. Results indicated that the conductivity was increased with increasing MWCNTs up to 0.25 wt%. Higher loading level of MWCNTs has resulted in decrease in conductivity due to agglomeration in cured samples. Hybrid nanocomposite exhibited improved SE than AA6061-T6 in 1-8 GHz frequency range. Best SE and electrical conductivity was witnessed in 0.25 wt% MWCNT sample. EMI SE in range of-20 dB to-40 dB can be easily achieved in our developed material.

Abstract: Skylight polarization pattern is used as an important navigation clue for desert ant and bees. The paper will present a new solar direction extracting method based on the polarization degree measurement. Two kinds of solar direction calculation model will be derived, one is by the polarization degree measurement of two observation directions, the other one is by the polarization degree and polarization E-vector direction measurement of the same observation direction.

Abstract: In order to avoid vacuum discharge, it is necessary for the satellite to have real-time monitoring by the vacuum degree of the electrical components that are sensitive to vacuum degree in the process of the thermal vacuum test. This paper introduces two methods of measuring vacuum degree inside the satellite, makes an analysis of failure mechanism of ionization gauge method, and offers suggestions for improvement.

Abstract: Orbit determination by using GPS measurements of a launch vehicle is an important option for the initial orbit determination of the vehicle's payload, and its accuracy is higher than the results generated by radar measurements. However, only broadcast GPS ephemeris and clock products are used in the current GPS measurements processing method, and Klobuchar model is directly used. The paper proposes to use precise ephemeris and clock products, and adopts an improved ionospheric model based on altitude factor for GPS measurements processing. The dynamic smoothing method is further used. The numerical results show that the proposed method can improve the early orbit satellites orbit segment to determine accuracy.

Abstract: The solar direction is an important clue for satellite autonomous navigation. A new method for obtaining the solar direction from skylight polarization for satellite navigation is discussed. The new method is using two E-vector polarization sensors to get solar direction, and the view field of the polarization sensor is discussed.

Abstract: In resent years, due to advances in science technology, space satellites have made progress. So, the presence of space debris has become problem in the world because they may collide each other. In our study, we have developed Spherical Ultrasonic Motor (SUSM) for space use with 3 DOF to drive the satellite thruster and resolve it. We aim that the satellites enter the atmosphere when the satellites reached the end of life, and SUSM controls thrusters when they inject for the directional control. We have made experiments of measuring torque, durability and lifetime. It shows that the torque and lifetime meets target value. But durability does not meet target value. To resolve it, we have applied stator lining materials and shifted frequency with 0.4 kHz from resonant frequency and we have shown that it meets durability-required specifications.

Abstract: Traditional optimization algorithms can only optimize parameters in control laws. Machine learning method can optimize parameters and evolve satellite attitude control law automatically under certain criterion. Single axis satellite attitude simulation system with noise was built up, which included satellite attitude dynamic model, sensors and actuators model. The control laws inputs were attitude error, attitude errors integral and angular velocity error, and outputs were actuators control instructions. Control laws fitness function was an attitude errors statistical function. With suitable function set selected for genetic programming (GP) and parse tree used to represent a control law expression, GP was used to evolve control law expression automatically. Simulation result shows that this method can evolve control law with uncertainties noise better. The evolved control law response and control precision are better than PID, and it can be used in satellite attitude control.

Abstract: The interaction of water hyacinth area with growth is known to be strongly influenced by area size, but little is known about the interdependent role that size and time have on dynamic estimation of water hyacinth area. We report on the fusion of specially designed, satellite and GPS sensor data into area growth model as a function of area and time. We employ a multi-sensor fusion technique that is able to generate uniform data of fitting area growth model with complete control of area and time. Evidence of an overall Goodness of Fit Index of 0.9753 was obtained by using conventional statistic analysis. These findings suggest that the multi-sensor fusion technique readily supports area growth model development with highly resolution. Moreover, it was found that area growth model enjoy an appreciable advantage when it comes to harvesting water hyacinth.