  Space Vehicle (SV) life span depends on its station keeping capability.
Station keeping is the ability of the vehicle to maintain position and
orientation. Due to external perturbations, the trajectory of the SV derives
from the ideal orbit. Actual positioning systems for satellites are mainly
based on ground equipment, which means heavy infrastructures. Autonomous
positioning and navigation systems using Global Navigation Satellite Systems
(GNSS) can then represent a great reduction in platform design and operating
costs. Studies have been carried out and the first operational systems, based
on GPS receivers, become available. But better availability of service could be
obtained considering a receiver able to process GPS and Galileo signals. Indeed
Galileo system will be compatible with the current and the modernized GPS
system in terms of signals representation and navigation data. The greater
availability obtained with such a receiver would allow significant increase of
the number of point solutions and performance enhancement. For a mid-term
perspective Thales Alenia Space finances a PhD to develop the concept of a
reconfigurable receiver able to deal with both the GPS system and the future
Galileo system. In this context, the aim of this paper is to assess the
performances of a receiver designed for Geosynchronous Earth Orbit (GEO)
applications. It is shown that high improvements are obtained with a receiver
designed to track both GPS and Galileo satellites. The performance assessments
have been used to define the specifications of the future satellite GNSS
receiver.
