Abstract
Normal 0 21 false false false TR X-NONE X-NONE In this study, an Unscented Kalman Filter (UKF) algorithm is designed for estimating the attitude of a picosatellite and the in-orbit external disturbance torques.The estimation vector is formed by the satellite’s attitude, angular rates, and the unknown constant components of the external disturbance torques acting on the satellite. The gravity gradient torque, residual magnetic moment, sun radiation pressure and aerodynamic drag are all included in the estimated external disturbance torque vector.The satellite has magnetometers and gyros onboard as the attitude sensors. Because of the inherent nonlinear dynamics and the nonlinear measurement model, the UKF, which is a nonlinear version of the Kalman Filter, is selected as the filter algorithm. Performance of the proposed algorithm is demonstrated via simulations for a cube pico pico-satellite and the results are analyzed for different scenarios. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Normal Tablo"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"MS Mincho"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}
Highlights
There are numerous researches on cubesats, and this number is increasing day by day, the investigations are still far from being concluded
An Unscented Kalman Filter (UKF) algorithm is designed for estimating a pico-satellite’s attitude and the in-orbit external disturbance torques acting on the pico-satellite
Gravity-gradient torque, sun pressure, aerodynamic drag and residual magnetic moment are included in the estimated disturbance torque vector
Summary
There are numerous researches on cubesats, and this number is increasing day by day, the investigations are still far from being concluded. An UKF algorithm is designed for estimating a pico-satellite’s attitude and the in-orbit external disturbance torques acting on the pico-satellite. The Euler angles representing the attitude of the satellite (φ is the roll angle about x axis; θ is the pitch angle about y axis; ψ is the yaw angle about z axis), the body angular rates with respect to the inertial axis frame and the constant components of the external disturbance torques form the state vector:. The dynamic equations of the satellite can be derived by the use of the angular momentum conservation law (Wertz, 1998): THE MAGNETOMETER MEASUREMENT MODEL The Earth magnetic field vector components can be modeled in the orbit frame as a function of time (Sekhavat et al, 2007):. For an n dimensional state vector, these sigma points are obtained by: THE GYRO MEASUREMENT MODEL As aforementioned, the other attitude sensor onboard the satellite is the gyro. The inertia matrix of the satellite is J=diag(2.1x10-3,2.0x10-3,1.9x10-3)kg.m2, which corresponds to a 10cm cubic satellite with an approximate mass of 1.2kg, as mentioned
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