Determination of optimum STC orientation by GA

Abstract

Optimum orientation of star tracker, which minimizes the precision of georeferencing without ground control points is searched. The study aims to obtain the best orientation of STC that minimizes the uncertainty of georeferencing. Precision of georeferencing is estimated by Differential Sensitivity Analysis (DSA) based on partial derivatives of input parameters which contains certain amount of uncertainty. Uncertainties of interior camera parameters, camera position, image timing and digital elevation model (DEM) are included in the precision estimation procedure of the georeferencing. Uncertainties of these parameters are assumed to be normally distributed and the confidence interval for the input parameters are obtained from the manufacturers and the vendors. Orbit of BilSAT on the 3rd of August 2005 is used for the optimization analysis. Interior camera parameters are assigned in reasonable ranges for a small satellite. Analysis are conducted for the imaging geometry of 0°, 5°, 10°, 15°, and 20° cross-track rotations of the camera with respect to body fixed reference system of the satellite. Sum of the obtained georeferencing precisions is considered as the objective function to be minimized. Optimization procedure searches the optimum solution in the plane of two variables; pitch and yaw angles of the STC with respect to body fixed reference system of the satellite. Genetic Algorithm (GA) is implemented for the search of the optimum solution.