ATLAS: Orbit Determination and Time Transfer for a Lunar Radio Navigation System

The ATLAS consortium1 has proposed a novel architecture to implement a lunar radio navigation system capable of providing position, navigation, and timing services to several lunar users. The system consists of a small constellation of four satellites in elliptical lunar frozen orbits, with the aposelene above the southern hemisphere. The architecture envisages a ground station network of small dish antennas to establish tracking via multiple spacecraft per aperture at the K-band using a scheme based on code division multiple access. Such a configuration implements the same-beam interferometry technique with spread-spectrum ranging and Doppler measurements. We describe the orbit determination and time synchronization of the satellite constellation, validating the concept in multiple scenarios and establishing the system performance. Numerical simulations show an orbital accuracy ranging from a few centimeters to 10 m, while the signal-in-space error degrades, reaching up to 20 m after 10 h (95th percentile) or 6 h (99th percentile).