  Despite numerous successful missions to small celestial bodies, the gravity
field of such targets has been poorly characterized so far. Gravity estimates
can be used to infer the internal structure and composition of small bodies
and, as such, have strong implications in the fields of planetary science,
planetary defense, and in-situ resource utilization. Current gravimetry
techniques at small bodies mostly rely on tracking the spacecraft orbital
motion, where the gravity observability is low. To date, only lower-degree and
order spherical harmonics of small-body gravity fields could be resolved. In
this paper, we evaluate gravimetry performance for a novel mission architecture
where artificial probes repeatedly hop across the surface of the small body and
perform low-altitude, suborbital arcs. Such probes are tracked using optical
measurements from the mothership's onboard camera and orbit determination is
performed to estimate the probe trajectories, the small body's rotational
kinematics, and the gravity field. The suborbital motion of the probes provides
dense observations at low altitude, where the gravity signal is stronger. We
assess the impact of observation parameters and mission duration on gravity
observability. Results suggest that the gravitational spherical harmonics of a
small body with the same mass as the asteroid Bennu, can be observed at least
up to degree 40 within months of observations. Measurement precision and
frequency are key to achieve high-performance gravimetry.

Instrumentation and Methods for Astrophysics;Earth and Planetary Astrophysics;Robotics