Hi @Manny
That’s an interesting challenge 
You can find a discussion on this topic here: Orbit determination for interplanetary missions
To summarize, I think that Orekit needs some additional improvements to be able to perform orbit determination for interplanetary missions.
For orbit propagation, everything is OK. But for orbit determination we need further developments that are summarized in the topic above.
In addition, if remember well, I think the NewtonianAttraction is added automatically to the NumericalPropagatorBuilder. So we need to be able to avoid it for orbit determination of interplanetary missions.
An easy hack is to remove the acceleration of the Newtonian attraction by adding a ForceModel performimg the inverse acceleration. That’s ugly, but needed with the current status of the orbit determination.
I’m very interested on that topic!
Best regards,
Bryan