Sharif Digital Repository

Orbit perturbations are most important environmental factors that affecting performance of satellites. These effects mainly in two ways affect the satellite. Through the first, perturbing acceleration, change the orbital elements and the second, moments due to perturbations, couple the dynamics and attitude equations. Various studies regarding how the resources of major perturbations such as direct solar radiation, atmosphere and the third body attractions have been done. However, effects a significant number of other perturbations, such as solar, rotation of the atmosphere, reflected solar radiations, earth oblateness with high order of earth harmonics consideration and small forces (such... 

Pyroshock Test is one of important environment tests in satellite design process.pyroshock or pyrotechnic shock is one of loads that exerted on spacecraft and it's subsystems during launch process. pyroshock can cause failure in some subsystems like sensitive electronic parts, solar cells and so on. For this reason it's necessary to make sure about strength of component under pyroshock which can be done by pyroshock simulator.The purpose of this research is to design a pyroshock simulator that can simulate a pyroshock with given SRS (Shock Response Spectrum) for satellite components.Requirements and constraints for design have been defined such as test item dimensions,weight range and also... 

Pyrotechnic devices are widely used by the aerospace and defense industries and consist of a broad family ofsophisticated devices using self-contained energy sourcessuch as explosives and/or pyrotechnic compositions.Pyrotechnic shock, or pyroshock, is the transient oscillatoryresponse of a structure to loading (high frequency, highmagnitude stress waves) induced by the detonation ofpyrotechnic devices incorporated into or attached to thestructure.Pyroshock Test is one of importantenvironmental tests in satellite design process. Pyroshock is one of loads that exerted on spacecraft and it's subsystems during launch process. Pyroshock can cause failure in some subsystems like sensitive... 

Control of line of sight (LOS) orientation is a fundamental prerequisite for virtually all dynamic applications in which an optical sensor is used to obtain images. In this research, a 3 DOF parallel mechanism is utilized to build a stable platform for high precision satellite photography. The platform may be designed based on the Stewart platform concept. The stability is obtained by controlling the roll, pitch and yaw of the mechanism. To apply linear control techniques and to use roll-pitch and yaw rates and also their absolute values, an active stable platform is designed. Line Of Sight (LOS) is a position vector from origin of a topocentric-horizontal system to the satellite of... 

The huge capability of high resolution satellite imageries (HRSI), that includes spatial, spectral, temporal and radiometric resolutions as well as stereoscopic vision introduces them as a powerful new source for the Photogrammetric,Remote Sensing and GIS communities. High resolution data increases the need for higher accuracy of data modeling.The satellite orbit, position, attitude angles and interior orientation parameters have to be adjusted in the geometrical model to achieve optimal accuracy with the use of a minimum number of Ground Control Points (GCPs). In order to obtain high resolution and definition imaging for many applications including surveillance, target tracking, and... 

In synthetic aperture radar (SAR) satellites, the nadir echo is defined as the backscattered signal from the point directly below the satellite on the earth surface. If the timing of the radar is such that the nadir echo arrives at the receiver while the receiver is turned on for receiving the desired signal, it could damage the receiver or disrupt the resulting SAR image, unless it is suppressed enough by proper design of antenna radiation pattern. In current SAR satellites, ”avoiding” this phenomenon is associated with two problems: 1) limiting the swath width, 2) imposing stringent restrictions on the selection of pulse repeatition frequency (PRF). Therefore, ”suppressing” the nadir echo,... 

Modeling and Controlling of a satellites fuel slosh is considered a vital problem in the field of satellite attitude control. In this paper modeling and control of the attitude of a satellite carrying a partially filled spherical fuel tank, which uses the diaphragm as a propellant management device (PMD), has been studied. The fuel slosh dynamics is modeled using a spherical pendulum with two degrees of freedom and a rigid arm, which represents the first mode of sloshing. The effects of the diaphragm that surround the fuel surface, are considered as torsional springs and dampers attached to the satellite body. The combined dynamics equations of the satellite rigid motion and the fuel slosh...