Search for: gravity-gradients
0.008 seconds

    Robust integrated orbit and attitude estimation using geophysical data

    , Article Aerospace Science and Technology ; Volume 93 , 2019 ; 12709638 (ISSN) Kiani, M ; Sharif University of Technology
    Elsevier Masson SAS  2019
    Geophysical information such as the Earth geomagnetic field and gravity gradient (GG) data can provide a basis for autonomous concurrent orbit and attitude estimation (COAE) of satellites in low earth orbits (LEO), as magnetometers and gravity gradiometer measurements are in general functions of time, position as well as the vehicle's orientation. While gradiometer has recently been investigated just for orbit estimation (OE), the current study is focused on COAE via only utility of the GG data. To this aim, observability conditions are analyzed, where the sensitivity of the proposed COAE approach with respect to various system and roto-translational elements is also examined. Considering... 

    Simultaneous Attitude and Orbit Determination Using Sensor Fusion Algorithm Based on the Dynamic of Satellite and Star Tracker

    , M.Sc. Thesis Sharif University of Technology Khalesi, Ruhollah (Author) ; Salarieh, Hassan (Supervisor)
    Control and guidance of a vehicle is vital for it to do its mission correctly. Guidance system and decisional algorithms used in it need exact information of instantaneous position, velocity, and attitude of the guided vehicle to determine and issue proper guiding commands.
    Estimation algorithms and navigation sensors are two necessary tools for navigation. In the first section of present study, the satellite equations of motion are derived and a 6-DOF simulation is done for it. In the second section, measurements of star tracker will be simulated using results of the first section. The third section appertains to development of navigation equations, attitude determination using UKF... 

    Fault-tolerant control of flexible satellite with magnetic actuation and reaction wheel

    , Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; 2021 ; 09544100 (ISSN) Hajkarim, M. H ; Assadian, N ; Sharif University of Technology
    SAGE Publications Ltd  2021
    The attitude fault-tolerant control of a flexible satellite actuated by reaction wheels and magnetic torquer bars is investigated in this article. A low earth orbit is considered for moment perturbations such as drag and gravity gradient. Furthermore, the flexible panels attached to a rigid central body are modeled through the assumed mode approach by a finite set of bending modal motion. The ordinary differential equations of their generalized coordinates are found using Lagrange’s equation, and the resulting dynamical model is validated by comparing its simulation results to the NX Siemens software results. Finally, a fault-tolerant controller based on sliding mode control is suggested and...