Nowadays, global navigation satellite systems (GNSSs) are used for many new applications that go further than the original goal of providing position, velocity and timing for land, maritime and air applications. In particular, GNSS receivers have been adopted as main navigation system for several low Earth orbits (LEOs) missions, increasing the autonomy of the hosting spacecraft, reducing the networking operation costs. Accordingly, they result in an attractive solution even for higher Earth orbits. However, although many studies have shown that GNSS observations can also be obtained at altitudes above the GNSS constellations by using high sensitivity receivers, the use of these signals is still challenging because of their very weak power and the poor relative geometry between the receiver and the transmitters. In this paper, we describe the implementation of an orbital filter specifically designed for moon missions, which aims to improve the navigation performance achievable when using GNSS observations.