Planning and Execution of Juno Radio Occultation Experiments at Jupiter

Since entering orbit around Jupiter in July 2016, the Juno spacecraft has made unprecedented strides in understanding Jupiter’s atmosphere, magnetosphere, and interior structure. In June 2021, Juno completed its Prime Mission and entered the Extended Mission phase to continue exploring the Jovian system. Juno is equipped with an X-band telecommunications link and a Ka-band radio science link which allow precision measurements of the Doppler shift between the spacecraft and NASA’s Deep Space Network with the primary purpose of determining Jupiter’s gravitational field. In Juno’s Extended Mission, the scope will expand beyond gravity field studies. Radio occultations to measure the ionosphere properties of Ganymede and Europa were executed in June 2021 and September 2022, respectively. Radio occultations of Jupiter’s ionosphere and atmosphere are planned later in the mission, beginning in 2023. Although the radio science instrument was originally designed to measure the gravity field, the instrument is fully capable of making measurements for radio occultations. Challenges in collecting radio occultation data include Juno’s pointing capability due to spin-stabilization, lack of an onboard highly stable frequency reference, and compensation from refraction of Jupiter’s atmosphere on the radio frequency. This paper describes how the Juno Ganymede and Europa radio occultation experiments were planned and executed, along with the necessary preparation work required to plan and execute radio occultations of Jupiter’s intense ionosphere and dense atmosphere.