Io plasma torus and Europa Clipper: Modeling, calibration, and trajectory reconstruction capability

Precise trajectory reconstruction of deep space probes is a fundamental task for all scientific investigations that require highly accurate knowledge of the spacecraft position and velocity. A classic example consists in the gravity science investigations, where an incorrect knowledge of the probe trajectory may have an impact on the determination of the gravitational accelerations. Typical orbit determination (OD) techniques are based on the radio tracking link established between the probe and the ground stations. For a precise and accurate solution of the probe trajectory all the dominant error sources need to be modeled and calibrated. Planetary and interplanetary plasma constitutes one of the main error sources in deep space as, while the radio signal traverses media with changing refraction indexes, its phase is strongly modified. For spacecraft operating in the Jovian environment, the Io plasma torus (IPT), which is a toroidal region surrounding Io's orbit and the main source of plasma in Jupiter's magnetosphere, represents one of the principal sources of perturbation and requires a thorough calibration process. NASA's Juno, currently in the Jupiter system, was designed to mitigate the influence of the charged particle environment by employing multi-frequency links, enabling the calibrations of the radiometric data and the simultaneous investigation of the distribution and dynamics of the ions. Conversely, NASA's Europa Clipper OD will rely on a single-frequency link (X-band), thus excluding the possibility of intrinsic radiometric data calibration. In this work, we investigate the effect of the IPT on the Clipper radio tracking data, specifically focusing on its effect on orbit reconstruction performance. After a detailed survey of available IPT models and their applicability to the Clipper mission geometry, we develop and test both model-based and empirical calibration methods to mitigate its effect and maximize the mission scientific output.