Simulations of a satellite system for co-location in space

Abstract

This thesis work investigates the potential performance of the future co-location satellite mission, GRASP, by presenting the simulations in the MatLab environment. The purpose of GRASP is to assess the potential performance of geodetic techniques combined in space. One of the satellites, acting as a GRASP, of different satellite constellations; like Globalstar, Iridium and Orbcomm, was tested for different orbital height, inclination, eccentricity etc. LAGEOS-1 satellite was also tested for the higher altitude of 6000 km. NORAD's (North American Aerospace Defense Command) TLEs (Two-Line Element Sets), containing the mean orbital elements, were used to generate orbital state vectors of position and velocity for the selected satellites by performing orbit propagation with the SGP4 (Simplified Perturbation Models) as implemented in 'Revisiting Spacetrack Report #3'. The Globalstar, Iridium, Orbcomm and LAGEOS-1 satellites were selected as the co-location satellite and their coordinates were determined by the GPS constellation and also by the VLBI network of ground stations. One day orbital data with time steps of 1 minute and 1 second were generated by the SGP4 propagator and passed to the MatLab code for coordinate determination by GPS and VLBI respectively. The 30 GPS satellites were taken from the GPS constellation for higher visibility of the co-location satellite. A VLBI network of 21 existing stations was chosen such that it is spread throughout the globe to provide maximum visibility and improved coordinate determination for co-location satellite.