Navigation and geodesy in the solar system: current capabilities and future prospects

Deep space navigation and planetary geodesy have undergone profound developments over the past few decades, driven by advances in radiometric tracking, high-stability timing systems, and fully relativistic dynamical models of the solar system. Spacecraft such as Cassini, Juno, and BepiColombo have demonstrated that Doppler and range measurements at the 10⁻⁵-10⁻⁶ m/s level and centimeter-level ranging can be routinely achieved, enabling detailed investigations of gravity fields, planetary interiors, and precise tests of general relativity and alternative theories of gravity. The synergy between navigation and geodesy is evident: precise spacecraft tracking requires accurate models of planetary gravity and ephemerides, while the tracking data themselves refine those models and test fundamental physics. This paper reviews the physical principles behind the main radiometric observables, namely two-way range, range rate (Doppler), and delta-differential one-way ranging (ΔDOR), and their role in modern dynamical modeling of the solar system and in deep-space navigation. It then presents recent results from BepiColombo’s cruise phase and the Mercury Orbiter Radioscience Experiment (MORE), summarizes major achievements from Cassini and Juno at Saturn and Jupiter, and outlines the scientific opportunities offered by ESA’s JUICE mission in performing a “tomography” of Ganymede. Finally, it discusses future concepts such as advanced interferometric architectures, time-delay mechanical noise cancellation, and compact deep-space atomic clocks, which promise further improvements in accuracy and open new avenues both for planetary science and for tests of relativistic gravity.