Hera represents the European Space Agency's inaugural planetary defence space
mission, and plays a pivotal role in the Asteroid Impact and Deflection
Assessment international collaboration with NASA DART mission that performed
the first asteroid deflection experiment using the kinetic impactor techniques.
With the primary objective of conducting a detailed post-impact survey of the
Didymos binary asteroid following the DART impact on its small moon called
Dimorphos, Hera aims to comprehensively assess and characterize the feasibility
of the kinetic impactor technique in asteroid deflection while conducting
in-depth investigation of the asteroid binary, including its physical and
compositional properties as well as the effect of the impact on the surface
and/or shape of Dimorphos. In this work we describe the Hera radio science
experiment, which will allow us to precisely estimate key parameters, including
the mass, which is required to determine the momentum enhancement resulting
from the DART impact, mass distribution, rotational states, relative orbits,
and dynamics of the asteroids Didymos and Dimorphos. Through a multi-arc
covariance analysis we present the achievable accuracy for these parameters,
which consider the full expected asteroid phase and are based on ground
radiometric, Hera optical images, and Hera to CubeSats InterSatellite Link
radiometric measurements. The expected formal uncertainties for Didymos and
Dimorphos GM are better than 0.01% and 0.1%, respectively, while their J2
formal uncertainties are better than 0.1% and 10%, respectively. Regarding
their rotational state, the absolute spin pole orientations of the bodies can
be recovered to better than 1 degree, and Dimorphos spin rate to better than
10^-3%. Dimorphos reconstructed relative orbit can be estimated at the sub-m
level [...