Subspacecraft-point coverage of typical missions. Panel a: actual subspacecraft points of the five Cassini Grand Finale closest approaches. The global coverage is very limited, and the orbit height from the Saturn surface inherently differs much at different latitudes because of the high orbital eccentricity. Panel b: fairly sparse subspacecraft-point coverage is plotted for the simulated missions of near-circular polar orbits and seven-day POD tracking time. Panels c and d: demonstrate two circumstances under which the targeted tesseral and sectoral gravitational coefficients can be solved from POD simulations. Panel c: plotted mission adopts a 1000 km high, 60° medium-inclination orbit, and the tracking time is three months. Panel d: simulated missions tracked for three months with polar orbits.