Assessing reduced-dynamic parametrizations for GRAIL orbit determination
and the recovery of independent lunar gravity field solutions
Orbit determination of probes orbiting Solar System bodies is currently
the main source of our knowledge about their internal structure,
inferred from the estimate of their gravity field and rotational state.
Non-gravitational forces acting on the spacecraft need to be accurately
included in the dynamical modeling (either explicitly or in the form of
empirical parameters) to not degrade the solution and its geophysical
interpretation. In this work, we present our recovery of NASA GRAIL
orbits and our lunar gravity field solutions up to degree and order 350.
We propose a systematic approach to select an optimal parametrization
with empirical accelerations and pseudo-stochastic pulses, by checking
their impact against orbit overlaps or, in the case of GRAIL, the very
precise inter-satellite link. We discuss how parametrization choices may
differ depending on whether the goal is limited to orbit reconstruction
or if it also includes the solution of gravity field coefficients. We
validate our setup for planetary geodesy by iterating extended lunar
gravity field solutions from pre-GRAIL gravity fields, and we discuss
the impact of empirical parametrization on the interpretation of gravity
solutions and of their error bars.