Sharif Digital Repository

The problem of spacecraft attitude determination (AD) using thermal data is investigated. Given the Solar space environment, the key dominant mechanism of heat transfer will be radiation, in which the Sun and Earth are the major contributing heat sources that affect the satellite external surface temperatures. In this sense, the net heat fluxes (NHF) of a satellite surface that is insulated against any internal heat communication will only be related to these main radiating sources. In order to utilize the satellite temperature data for AD, a heat attitude model (HAM) that relates the satellite surfaces NHF to its attitude is developed using three orthogonal satellite surfaces. Assuming... 

The estimation of attitude and deformation of a flexible satellite using magnetometer and sun sensor data are studied in this thesis. To this end, the dynamical differential equations of the flexible satellite have been derived using Lagrange’s equation. These equations of motion are then utilized for the purpose of simulation and verification. After introducing the measurements equations, the observability of the satellite with flexible panels has been evaluated. Afterward, the attitude of the satellite body and deformation of the flexible panels have been estimated by EKF (Extended Kalman Filter) as well as UKF (Unscented Kalman Filter). The results show that the estimations using UKF are... 

This study presents the best layout with optimal number of sensors for an arbitrary monitoring area based on reference free damage detection and localization. In recent years, damage detection approaches with the concept of instantaneous baseline measurements in Structural Health Monitoring (SHM) with lamb wave propagation are being developed. An array of spars transducers is obligatory in SHM with lamb wave propagation, so that designing the best one is a concern for many researchers. To obtain the best sensors layout, damage localization process should be done for all definable sensors layouts in many different crack positions. Obviously, doing this seems not practical as wave propagation... 

Application of composite patches in repair of damaged/aged aircraft structures is one of the most popular repairing methods in aerospace engineering and because of its advantages the use of this type of repair is increasing today. However, to use these patches in life extension of aged aircraft, the added weight to the structure should be strictly controlled. This could be best done if achieving the optimum and smart design by using optimization and structural health monitoring methods. These two concept about pre-designed of composite patch repair are investigated in this thesis. The simulation by Abaqus software and experimental results and tests will be used for this purpose. In first... 

This paper presents a novel method for satellite attitude determination, using Electrostatically Suspended gyroscope (ESG). In this method, two superconducting rings rotated around a spherical rotor, which causes a variable flux in rings. So according to faraday’s law of induction, a voltage will be induced in the rings. Using this voltage and a kalman filter, attitude of satellite will be determined. ESG works precisely, when the rotor is maintain at the center of gyroscope cavity, between three pairs of circular electrode, so a backstepping control algorithm will be designed In order to this purpose. The performance of attitude determination using this ESG and designed control algorithm is... 

In this Thesis, attitude and orbit of a satellite is estimated using a star sensor and an earth sensor. An algorithm has been developed to estimate satellite attitude and orbit that can be implement on a satellite as strap-down hardware. This system has an uncomplicated implementation compared with platform based systems. That mentioned algorithm estimates satellite orbit by using identified star vectors via star sensor and identified earth vector via earth sensor simultaneously. It also knows the stars vectors according to Star Catalog. Attitude estimation is also executed using both star and earth sensor. It has to be said that an Unscented Kalman Filter synthesize both sensors output data... 

The problem of attitude determination (AD) has always been a challenging issue for space missions that is of importance either independently or for attitude control purposes. The problem of AD is generally focused from two aspects: measurement mechanisms (sensoring) and determination algorithms. From the former point of view, there exists a variety of measuring systems such as the Sun sensors, magnetometers, gyroscopes, star and horizon sensors that have been separately or collaboratively utilized for AD. Integrative usage of sensors not only can bring about added advantages in terms of accuracy, but also provides for estimates of attitude during special times such as the Sun eclipse. The... 

Acoustic excitation frequency effect on NACA 0012 airfoil boundary layer and on its wake development was investigated experimentally in two wind tunnels. Airfoils chord lentgh were 100 and 152 mm. Flow Reynolds numbers was 60000 and 160000 in the first wind tunnel and 100000 and 250000 in the second one. Excitation frequency range was chosen between 300 and 2400 Hz. Airfoil flow and sound characteristics was measured using a 1-D hot-wire sensor and two microphones, one mounted on the wind tunnel wall and the other flash mounted on the model at 10 percent of chord length, respectively. Airfoil angle of attack was set at zero degree in the first wind tunnel and at three angles of zero, five... 

Structural health monitoring (SHM) has been motivated in aircraft and civil industries over the two last decades. Ultrasonic guided wave propagation technique is one of the best damage detection methods in airplane thin wall structures because of their large distance traveling and low attenuation.
In fact by efficient design of sensors pattern one can effectively pick up the changes that happen in propagated signals due to presence of any kind of structural damage. This could be effectively achieved by numerical simulation techniques like finite element modeling. To obtain a damage detection algorithm based on instantaneous baseline data, here, finite element technique is employed for... 

Rapid growth of space traffic and small satellite systems for current and future space missions have generated new enhanced performance requirements for navigation subsystem. As such, the navigation subsystem is considered as a vital part of all active satellite systems that effectively influences their successful missions. In this regard, the present work is dedicated on the subject of autonomous satellite navigation utilizing nonlinear filters, for which some laboratory experimentations have also been implemented. Generally, advanced orbit and attitude estimation algorithms can effectively compensate for the effect of low cost hardware and sensor packs utilized in microsatellites. In... 

Nowadays, regarding the advancement of unmanned aerial vehicles and low cost sensors, the idea of utilizing a group of aerial vehicles to perform risky and complicated missions has attracted the attentions of researchers. One of the main subjects in aerial missions is target search and localization. Cooperative target search by the use of multiple aerial vehicles equipped with sensors, could construct a sensor network that makes the system more robust against failures and reduce noises and uncertainties. In addition, the observability and quality of sensor signals could increase if the motion and positions of the vehicles are intelligently optimized.In this research, establishing an... 

In this thesis, the orbit determination of Low Earth Orbits (LEO) using the integrated magnetometer and horizon sensor data has been investigated. Orbit determination is an essential part of a space mission. Not only the modeling, guidance, navigation and control errors may results in error in injecting the satellite into its nominal orbit, the environmental disturbances deviate the satellite from its predicted orbit and from an operational perspective most satellites need continuous orbit determination. Traditionally, ground based orbit determination is used which are non-autonomous and expensive and just can be used for specific times which the satellite can be observed from the ground... 

Cost-effective and reliable damage detection is critical for utilization of composite materials. This research investigates a wavelet-based approach for SHM and detection of through-thickness crack in different lengths and angles in [0/45/-45/90]s CF/EP composite plate utilizing ANSYS finite element method (FEM) software and digital signal processing technique utilizing MATLAB software. To this end, a dual-PZT actuation scheme is applied, aimed at generating the S0 mode at a square composite plate. This study contributes to the damage detection by developing an improved wavelet-based signal processing technique that enhances the visibility and interpretation of the Lamb wave signals related... 

Structural Health Monitoring (SHM) is a multidisciplinary emerging research field. SHM assesses the health state of the structure through processing and interpreting of signals and can predict remain life of the structure. Damage detection with Piezoelectric Wafer Active Sensors (PWAS) is one of the effective and emerging methods of SHM. One of the most critical parts of aerial structures is lap joints in which SHM could be very effective. In this research, damage detection of lap joints using lamb wave propagation has been studied. A 3D model of an aluminum lap joint presented. The PWAS are modeled separately and bonded to the host structure and coupled electromechanically with the... 

Damage detection by Piezoelectric Wafer Active Sensors is one of the emerging efficient and dominant Structural Health Monitoring (SHM) methods. These sensors assess the health state of the structure due two strategies: a) near-field damage detection, b) far-field damage detection. The far-field damage detection is based on the high frequency Lamb wave propagation. As wave travels in a damaged structure, phase and amplitude of the wave will be changed. So comparison of the received signal from the pristine structure with damaged structure can give useful information about the health state of the structure. As PWAS is the essential part of this method, simulation and modeling of this sensors... 

In this research, it has been trying to implement Virtual Structure method for formation flight of multiple spacecraft. In this method, a virtual solid frame with virtual center of mass is considered and agents are arranged in a formation with respect to the virtual center. In this work, a formation keeping control system is implemented in which a feedback from formation to virtual structure and vice versa is considered. The method is implemented firstly in a nongradient field and then developed into a circular orbit in order to investigate the in-orbital effects. An algorithm for collision avoidance, based on relative distances and relative velocities, was also developed. The algorithm was... 

Measurements of magnitude and direction of thrust generated by a propulsion engine is important for verification of design, fabrication, assembely and or repare procedure used for a engine. Due to possible simplification in design calculations, human and machine errors in manufacturing process, the resulted thrust generated may be different from those values expected. Also, It is important to determine the dependency of magnitude and direction of thrust forces relative to tolerances and manufacturing processes. It is necessary to have thrust measuring stand with high accuracy with capability to measure the forces in different directions. A new digital engine test stand has been designed,... 

Examining and improving driving behavior leads to a reduction in road accidents. Driver behavior is generally divided into two categories: aggressive and safe. Driving culture can be enhanced by identifying aggressive behavior and informing drivers directly. This information is used to assign safe drivers to the missions of transport fleet management companies and organizations. Also, this information is used by insurance companies or traffic police to apply discounts or fines. In any case, the detection and notification of aggressive behaviors would reduce accidents and improve the lives and mental safety of passengers and drivers. The detection of driving events is an introduction to the... 

In image processing applications, sensors (Camera, LiDAR and Stereo) are essential for scene perception and Deep learning methods outperform most of the image processing tasks like 3D and 2D object detection and semantic segmentation. Different sensors are used in image processing tasks. Sensor fusion is using multiple sensors data to get better performance. Each sensor captures different data (e.g, color, texture, and depth). Some of them are distorted in inclement weather, intense illuminance changes, and dark environments which multi-sensor data fusion is used to overcome sensor weaknesses. One of the most important fields that sensor fusion used is Auto Driving cars (AD). Different... 

The use of MANETs in many areas is rapidly spreading. Due to dynamic nature,and limited energy of this networks, they are vulnerable to some attacks including blackhole attack. Blackhole attack can disrupt the commiunication between hosts and cause denial of service. One of countermeasures to this attack which has been recently proposed is the ActiveTrust. ActiveTrust is a routing protocol which relys on malicious node detection using trust calculations; this scheme has been proposed for WSNs. In this work we adopt the ActiveTrust’s idea and try to apply it into MANETs. Then we simulate the resulting proposal in NS-3 and compare the results