Journal of Space Science and Technology
Year:2012 | Volume:5 | Issue:3 (12)|Papers Count:9

Due to high design and launch cost of satellites, their failure probability should be minimized. Single Event Effects (SEUs) are one of the most common error sources in satellite microelectronic. To cope with these unwanted errors, various techniques are used. The reliability analysis of these methods is one of the major acceptance criteria to validate these techniques. In order to evaluate the reliability of satellite subsystems, it is required to determine the SEU rate as a primary factor. A practical method to determine this rate is based on Weibull approach in which the SEU cross section is used as an initialized parameter. In this paper, the SEU rate is calculated based on weibull method for Low Earth Orbit (LEO) satellites, as case study Iranian demonstrated Rasad and Omid satellites. Furthermore, based on the proton density, an accurate time-varying SEU rate model is proposed which determines the rejuvenation time for SEU susceptible subsystems.

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. On the other hand, global positioning system is able to determine its position with an average accuracy around the earth. But the GPS alone isn’t enough for navigation of orbital modules, because it doesn’t have situation of orbital modules. The integrated inertial navigation system with global positioning system is a low cost method of providing an accurate and reliable navigation system in the civilian and military aerospace applications. In this paper, using the extended Kalman filter, we design an algorithm to estimate error of sensors, navigation and GPS. This method can be widely used in the integrated navigation INS / GPS in aerospace applications and provides an accurate navigation.

After setteling the LEO satellite in the given circuit, the ground station needs to communicate with it for the received of information and control of its subsystems. Due to the fact that satellite communication channels are influenced by shadowing conditions, if a line of sight (LOS) signal exists between the receiver and the transmitter, then the radio channels conditions are good and the Additive White Gaussian Noise channel is modeled as Rician distribution. However, under poor conditions and in the lack of LOS, channel model is Rayleigh, and due to the radio link conditions the channel will be switched between these two models. In a proper model, the time varying behavior of the station – satellite radio link should be considered. The importance attached to this issue is due to its considerable effect on the selection of modulation type, design of channel access method, and error control. In this view, the present study has sought to momentarily determine the range of variations in error probability. Through calculations and simulation, the Bit Error Rate received during the satellite trajectory has been obtained for any given moment and its range of variations has been determined.

The NAVSTAR Global Positioning System (GPS) is a satellite-based navigation and positioning system which includes a constellation of 32 satellites, remote control stations and its receivers and can be used for determination the geographical positions of its users. GPS signal simulator needs for test and verification of GPS receiver' s performances in special applications at the Laboratory. For this mission we should simulate the various static and dynamic scenarios for GPS receiver tracks and generate GPS signals for all the satellites. For GPS signals, generation of all its elements like the Navigation messages, C/A codes, frame and subframe structures should be defined and used in this project.

In this paper, in order to separate images in four spectral bands (from blue to near infrared) in multispectral cameras, four-color separation prism advantages are reviewed.Then, while description of ray tracing of four-color separation prism, main design parameters and principles are mentioned. After that, design of a four-color separation prism model that attached to detector (CCD) by using the Zemax software are described, also spot diagrams, ray tracing and aberration graphs are analyzed. Finally, while expression four-color separation prism characteristics that yield from programming with Zemax software, including weight, length of the optical path and thickness of equivalent blade, its specifications in remote sensing satellite multispectral cameras are explained.

Inertial Navigation System (INS) and Global Positioning System (GPS), are used in various navigation and positioning applications. Because each of the INS and GPS technologies has some limitations and advantages, during last two decades, the systems integration has been widely used for accurate and reliable navigation and positioning. In an integrated system, accurate GPS observations are used to estimate the high rate INS errors and state vector (including INS error vector, position, velocity and other optional parameters). A field test results are presented in this paper. The goal of this test is to compare the coordinates of a relatively low cost INS, GPS RTK coordinates, and the integrated GPS/INS results. The decentralized approach has been used for this integration.

Numerical investigation has been made on a linear array of surface wave driven plasma monopole antenna using finite difference time domain simulation. Variations of the excitation power can be used for construction of a dynamically reconfigurable antenna. Plasma elements in the nominal pressure of 0.4 mb are fed through an RF power at 500 MHz using an equal power divider. The results show that while the variations of the excitation power shift the array resonant frequency between 50 MHz to 120 MHz, the array gain and directivity remain approximately unchanged in the new resonant frequency. Since efficiency is critical to communication systems, the total efficiencies of the reconfigurable array were analyzed from the least to the highest excitation power. The highest efficiency belongs to the array which the separation between elements is a quarter of wavelength. Using this cutting edge technology in space application, it will be possible to transmit through an antenna in a multiple frequency avoiding interference between adjacent antennas.

In this paper, specific grains burn back is presented by new geometrical method. The software is developed for Wagon wheel grains and 3D grains. Rapid solid motor ballistic simulation code produces required charts with considered nozzle geometry. Presented method used geometrical introducer point (GIP) to produce the various grains.Limitations and configurations are simply modeled. Thrust, total pressure and temperature are illustrated as web burned changing. The results confirm the performance of the developed algorithm for mentioned grain analysis. Lower time processing and rapid ballistic analysis are the benefits of the presented algorithm. Finally results of the burn back analysis code and the internal ballistic simulation code are evaluated by some other existent codes and real cylindrical grain test.