  This study provides a continuous ephemeris reconstruction for comet
67P/Churyumov-Gerasimenko by reanalyzing Rosetta radiometric measurements and
Earth-based astrometry. Given the comet-to-spacecraft relative trajectory
provided by the navigation team, these measurements were used to estimate the
comet state and some critical physical parameters, most notably the
non-gravitational accelerations induced by the outgassing of surface volatiles,
for which different models were tested and compared. The reference
reconstructed ephemeris, which uses a stochastic acceleration model, has
position uncertainties below 10 km, 30 km, and 80 km in the orbital radial,
tangential, and normal directions for the whole duration of the Rosetta
proximity phase (from July 2014 to October 2016). Furthermore, the solution can
fit ground-based astrometry between March 2010 and July 2018, covering a
complete heliocentric orbit of 67P. The estimated comet non-gravitational
accelerations are dominated by the orbital radial and normal components,
reaching peak values of $(1.28 \pm 0.17) \times 10^{-8} \, \text{m/s}^2$ and
$(0.52 \pm 0.20) \times 10^{-8} \, \text{m/s}^2$, respectively 15 days and 24
days after perihelion. Furthermore, the acceleration magnitude is shown to have
a steep dependence on the comet heliocentric distance $\text{NGA} \sim
r_\odot^{-6}$ and shows asymmetries in the pre- and post-perihelion activities.
The estimated acceleration components, agnostic due to the limited physical
assumptions, could be used as a constraint for future investigations involving
high-fidelity thermophysical models of the comet surface.
