Combination of the radio occultation method plus change in the orbital plan in order to observe new target (the volcanic outgassing from Io satellite) by passing though the magnetosphere of Jupiter. It poses a challenge in the sensitivity of the electronics. Maybe it is accepted if the risk is low. Idea for the next GTOC challenge maybe? Optimising the cost on the electronics vs the frequency of passages?
At a meeting of the American Geophysical Union in San Francisco in December, he reported an average figure that was between 0.005 and 0.008 per cent greater than the value for Earth's mass established by the International Astronomical Union. A disc of dark matter around the equator 191 kilometres thick and 70,000 km across can explain this, he says. Harris has yet to account for perturbations to the satellites' orbits due to relativity, and the gravitational pull of the sun and moon.
Maybe relativistic GPS could improve this even further? As a side note however, the Juno spacecraft flyby showed an gravity acceleration which matched the calculations, casting doubts on the earlier calculations.