Changing Juno's orbital period and its effect on gravity science at Jupiter

NASA’s Juno spacecraft successfully completed its prime mission in 2021 by performing 33 close encounters with Jupiter, and it is presently in its extended phase. These encounters, known as perijoves, occurred every 53 days at altitudes of about 4,000 kilometers above the planet's 1-bar surface and were specifically designed to study Jupiter's magnetosphere, atmosphere, and gravity field. During the nominal mission, Juno’s gravity science experiment achieved an unparalleled level of accuracy in resolving the planet’s low- and high-degree zonal gravity field. By employing precise Doppler-tracking techniques via X- and Ka-band radio links, scientists were able to estimate Jupiter’s gravity moments and rotational parameters, offering insights into its internal structure and deep atmospheric dynamics.

Prior to the initial science perijove in 2016, there were plans to reduce the Juno orbital period from 53 days to 14 days, marking the beginning of science operations. However, a potential anomaly in the propulsion system led to the decision to keep Juno in its 53-day orbit, lengthening the duration of the prime mission by roughly a factor of four. This had far-reaching implications, impacting both science operations and mission management. Nevertheless, the Juno team adeptly adapted to these unforeseen circumstances by promptly laying out a new mission plan. The change in the orbital period also held significant consequences from a scientific point of view: for instance, the ability to carry out Jupiter's radio occultations during the extended mission is directly related to this event. Here we explore in detail the repercussions from a radio science operations and gravity science point of view and discuss the impact of orbital period changes on reaching the experiment’s prime mission objectives.

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