On the BepiColombo and Juno Radio Science Experiments: precise models and critical estimates

Radio Science Experiments (RSEs)
 use radio
 links between 
spacecraft
 and Earth to look for 
changes
 in
 the
 frequency as 
well as
 round‐trip
 light time
 of signals 
to 
investigate geophysical
 phenomena
 and
 for tests 
of 
fundamental
 physics. BepiColombo and Juno are two space missions that will perform RSEs, thanks to a very accurate tracking: to extract the desired information, it is not sufficient to improve the precision of observations, we need also to develop accurate mathematical models making smaller the residuals, defined as the observed observables minus the computed observables. However, sometimes, even highly accurate mathematical models are not sufficient for the determination of a given parameter with the required accuracy. In this paper, after a brief summary of the mathematical models needed for top accuracy RSEs, we will present two critical cases from the simulations of the BepiColombo and Juno where also these accurate models may not be sufficient to determine some quantities with the desired accuracy.