Interplanetary navigation during ESA's bepicolombo mission to Mercury

Presently, the use of Solar Electric Propulsion (SEP) as the principal propulsion and navigation system for interplanetary missions is reaching its maturity level after decades of consideration only on the design boards. NASA's Deep Space 1 successfully demonstrated the use of its ion propulsion system, while ESA is about to launch its SMART-1 mission to the Moon based on the use of a Hall thruster. Among other low-thrust missions, ESA is also planning to send a probe to Mercury using a SEP system supported by a series of flybys at Venus and Mercury. The navigation based on a low-thrust propulsion system prior to the flybys at Venus and Mercury is the subject of the present paper. This includes the orbit determination accuracy assessment of the interplanetary trajectory during coast and thrust arcs, as well as the performance of the propulsion system and the ranging devices. The cases studied in the paper demonstrate the observability of the low-thrust vector components, especially its out-of-plane component. A brief description is given of the software tool SEPNAV that was developed for the analysis of low-thrust navigation.