Over the last few years, new Global Navigation Satellite System (GNSS) applications have emerged that go far beyond the original objectives of GNSS which was providing position, velocity and timing (PVT) services for land, maritime, and air applications. Indeed, today, GNSS is used in Low Earth Orbit (LEO) for a wide range of applications such as real-time navigation, formation flying, precise time synchronization, orbit determination and atmospheric profiling. GNSS, in fact, can maximize the autonomy of a spacecraft and reduce the burden and costs of network operations. For this reason, there is a strong interest to also use GNSS for High Earth Orbit or Highly Elliptical Orbit (HEO) missions. However, the use of GNSS for HEO up to Moon altitudes is still new, and terrestrial GNSS receivers have not been designed to cope with the space environment which affects considerably the GNSS receiver performance and the GNSS solution (e.g. navigation solution). The goal of our research is therefore to develop a proof of concept of a spaceborne GNSS receiver for Earth-Moon transfer orbits, assisted by Inertial Navigation System (INS), a Star Tracker and an orbital forces model to increase the navigation accuracy and to achieve the required sensitivity.