Juno was inserted into a highly elliptic, polar, orbit about Jupiter on July 4th 2016. Juno’s magnetic field investigation acquires vector measurements of the Jovian magnetic field using a flux gate magnetometer co-located with attitude-sensing star cameras on an optical bench. The optical bench is placed on a boom at the outer extremity of one of Juno’s three solar arrays. The Magnetic Field investigation (MAG) uses measurements of the optical bench inertial attitude provided by the micro Advanced Stellar Compass (µASC) to render accurate vector measurements of the planetary magnetic field. During periJoves, MAG orientation is determined using the spacecraft (SC) attitude combined with transformations between SC and MAG. Substantial pre-launch efforts were expended to maximize the thermal and mechanical stability of the Juno solar arrays and MAG boom. Nevertheless, flight experience demonstrated that the transformation between SC and MAG reference frames varied significantly in response to spacecraft thermal excursions associated with large attitude maneuvers and proximate encounters with Jupiter. This response is monitored by comparing attitudes provided by the MAG investigation’s four CHU’s and the spacecraft attitude. These attitude disturbances are caused by the thermo-elastic flexure of the Juno solar array in response to temperature excursions associated with maneuvers and heating during close passages of Jupiter. In this paper, we investigate these thermal effects and propose a model for compensation of the MAG boom flexure effect.

The micro Advanced Stellar Compass (µASC), an attitude reference for the Juno Magnetic Field investigation, also continuously monitors high energy particle fluxes in Jupiter’s magnetosphere. The µASC camera head unit (CHU) shielding is sufficient to stop electrons with energy <15MeV. By recording the number of particles that penetrate µASC CHU shielding and deposit energy in the CCD sensor, the µASC functions as an energetic particle sensor with a detection threshold well above that of the Juno Energetic Particle Detector Instrument (JEDI) flown for that purpose. Radiation data gathered by the µASC is used to monitor the radiation environment of Jupiter and mapping of the trapped high energy particles. Comparison of the particle population around Jupiter with individual perijove particle observations reveals disturbances when Juno is traversing Ganymede’s M-shell. We present highly energetic electrons interaction with Ganymede’s magnetic field, magnitude and extend of the particle depletion associated with the Ganymede interaction.