An architecture for a Lunar Navigation system: Orbit Determination and Time Synchronization

This paper shows the architecture of a Lunar Radio Navigation System (LRNS) constituted by a small constellation of satellites supported from Earth by a dedicated network of small dish antennas, capable of establishing Multiple Spacecraft Per Aperture (MSPA) tracking at K band and of implementing the novel Same Beam Interferometry (SBI) technique. SBI will complement standard Doppler and ranging measurements thanks to Code Division Multiplexing with Majority voting (CDM-M) method, where the uplink signal is sent to multiple satellites with a single carrier and onboard transponders will implement Code Division Multiple Access (CDMA), sharing the same bandwidth in downlink. Time synchronization across the constellation will be performed by measuring the desynchronization of each satellite with terrestrial time and compensating accordingly the drift of onboard clocks within the navigation message. The proposed architecture has been validated with numerical simulations showing that orbital accuracies at meter level are achievable for the positioning of lunar orbiters.