Mission Analysis for the Optimization of the GPS Coverage for an Earth Observation Satellite

The goal of this work is to present an advanced study of the GPS coverage capability of a Low Earth Orbit (LEO) satellite. The motivation for this arises in the satellite control environment, during the operations preparation phase, by the need of predicting the time necessary to the on-board GPS receiver to fix the first orbital position, after the on-orbit injection at LEOP (Launch and Early Operational Phase). Once the first acquisition is performed, the satellite will be ready to enter the normal mode. The availability of a proper GPS coverage at LEO altitudes should be evaluated not only during the LEOP - clearly more critical - but also in the entire routine life of the satellite. Different approaches to optimize the GPS coverage, proposed by manufacturers and satellite operators, are considered, showing key strengths and weak points of the selected strategies. Operational and structural constraints must be taken into account when aiming at the proposal of different approaches to the GPS coverage issue, such as occultation of the on-board star trackers and the GPS antennas.