Uranus gravity field investigations from an orbiter mission

High-precision radio tracking from a future Uranus orbiter may provide key constraints on Uranus’ internal structure and dynamics, provided suitable instrumentation and an optimized orbital tour. We present the results of radio science simulations to evaluate gravity field recovery performance across different orbital configurations.

We run numerical simulations of the gravity experiment by using NASA/JPL MONTE orbit determination software, assuming the orbiter to be equipped with high-end radio tracking system capable of generating accurate Doppler and range observables at both X- and Ka-band, supporting triple-link plasma calibration. Two representative mission scenarios are analyzed: (i) southern-hemisphere periapses at an altitude of ~7000 km, passing outside the ring system, and (ii) low-altitude periapses at ~1000 km, passing inside the rings. The results show indeed a strong dependence of gravity field recovery on orbital geometry. In the higher-altitude scenario, only the J₂ and J₄ zonal harmonics can be estimated with sufficient accuracy, whereas the lower-altitude configuration enables the reliable determination of J₆.

In parallel, we investigate the effect of Uranus’ normal modes of oscillation on the spacecraft dynamics. The free oscillation spectrum is computed assuming a simplified internal structure model, adapted from approaches developed for the Juno and Cassini missions. Although individual mode frequencies are unlikely to be resolved, their cumulative effect produces time-variable perturbations on the low-degree zonal harmonics that may act as a source of noise in gravity field estimation.

These results highlight the critical role of high-end radio tracking instrumentation and orbital design in maximizing the scientific return of gravity science at Uranus and provide a quantitative framework for evaluating the observability of its interior and dynamical processes.