Ricerc@Sapienza

Since the beginning of the space exploration age, the navigation of deep-space probes has been carried out through ground-based measurements of their relative distance and velocity with respect to the Earth's stations. The interplanetary spacecraft host sophisticated radio systems which enable the tracking from ground stations, allowing to acquire the navigation data. The data are collected in batches and then processed by the navigation team to provide the updated trajectory of the spacecraft. Therefore, the navigation of planetary probes completely relies on the ground-based tracking and processing. An alternative technique developed during the last decades is based on inter-satellite radio tracking. Multiple spacecraft equipped with radio subsystems establish the inter-satellite radio links that enable the acquisition of relative distance and velocity measurements. Initially conceived to perform gravity science, it has been successfully employed to obtain extremely accurate mapping of the Earth's and Moon's gravity fields by the missions GRACE and GRAIL, respectively. Besides the gravity field recovery, this configuration has another significant advantage compared to traditional tracking methods, because the inter-satellite measurements can be processed onboard the spacecraft by autonomous navigations systems. However, the processing of these data alone cannot provide the absolute position and velocity of the spacecraft. The purpose of this proposal is to simulate and assess the performances of an autonomous navigation system based on inter-satellite tracking and altimetry. The processing of simultaneously collected altitude and inter-satellite radio measurements would allow to solve the intrinsic deficiency of this latter data type, allowing to obtain the absolute position and velocity of the spacecraft. The successful combination of these two instruments would greatly enhance the capability of deep-space probes to operate autonomously.