Estimating atmospheric density profiles using orbit determination with a focus on JUICE and Cassini

Orbit determination allows us to determine a spacecraft’s position, velocity, and dynamical model parameters that directly affect a spacecraft’s trajectory, such as gravity field coefficients, which relate to the interior structure of a planetary body, and tidal forces. In addition, when a spacecraft experiences substantial drag in the presence of an exosphere/atmosphere, the density profile may be estimated. This work presents an analysis of two cases where atmospheric drag has effects on the orbit and gravity measurements in planetary missions: Cassini, the mission to Saturn’s system which ended with a plunge into the planet in 2017, and JUICE, the future mission to Jupiter’s icy moons which will include an insertion into a circular, polar orbit around Ganymede. For Saturn, we have estimated a vertical atmospheric density profile which we have compared with in-situ measurements taken by Cassini’s INMS (Ion and Neutral Mass Spectrometer). For Ganymede, we find that the exosphere may be dense enough to affect JUICE’s trajectory around the moon.