The dynamics of solar system bodies provides an ideal natural laboratory for measuring their interior properties, and understanding their formation and evolution
This theme studies the various techniques to measure the dynamics of planetary spacecraft and natural solar system bodies, with a focus on creating novel analysis tools, tracking methods and data fusion techniques. The developments we make will allow current and future missions to provide improved estimates of geodetic parameters of planetary bodies, such as gravity field coefficients, rotational variations and tidal parameters, as well as natural satellite ephemerides.
We are at present involved in developments for the JUICE missions, with a leading role for the PRIDE experiment, and a supporting role on GALA, to which a number of our students have contributed. This themes bridges the gap between astrodynamics and planetary exploration: it uses observations of dynamics to improve estimates of physical properties of solar system bodies. This provides a natural link with the theme of ‘Planet and moon interiors’.
Ephemerides and dissipation – unveiling a system’s evolution
A current focus in this area is developing models and techniques for the improved determination of ephemerides of solar system natural satellites, in particular concerning data processing from future missions. Ephemerides provide an ideal means to study the orbital evolution of the satellites, through the determination of tidal dissipation parameters in the system. Dissipation is, in turn, a driving force behind a systems, and a satellite’s, long-term evolution. Data analyses over the past ~15 years, mostly from optical astrometry, have yielded the first such determinations of dissipation parameters from ephemerides for Martian, Jovian and Saturnian. The latest analyses of the Saturnian satellites’ orbital evolution (Lainey et al., 2020) indicates that the Saturnian interior dissipation follows a completely different behaviour than what has heretofore been assumed. In particular, it appears that dissipation is much stronger than has thus far been assumed, and well in line with the novel ‘resonance locking’ paradigm described by Fuller et al. (2016). In Delft, we are working on analyzing how future missions can provide improved estimates of these dissipation parameters, in particular for the Jovian system.
Above: Artist impression of JUICE in its future Jovian ecosystem during the mission. Credits: ESA
The JUICE mission – ESA’s flagship mission to study icy moons
The data from the JUICE mission will be a game changer for the determination of Jovian system ephemerides. The unique combination of flybys of three Galilean satellites, and the Ganymede orbit phase, with radio science coverage throughout, will provide data of extraordinary accuracy to improve our estimates of the ephemerides. However, various challenges will need to be overcome for this to be realized. Firstly, the determination of the four Galilean satellites’ dynamics from the JUICE tracking data will lead to an ill-posed estimation problem, due to the fact that there is no data at Io, limited data at Europa (two flybys), and exceptional data at Ganymede (orbit phase). Means to mitigate this issue include combination with upcoming Europa Clipper data, radar ranging data as well as fusion with past and future optical data, including mutual events, stellar occultations and mutual approximations, (see Fayolle et al., 2021). We are currently in the process of investigating strategies of merging these data sets. Additionally, getting a consistent dynamical solution of the spacecraft dynamics, and moon dynamics, over the course of the JUICE mission, will require a re-evaluation of dynamical modelling techniques, to ensure that the data is exploited to its fundamental precision.
The PRIDE experiment – supporting planetary tracking with radio astronomical techniques
For the JUICE mission, the PRIDE experiment will provide high-accuracy VLBI data points of spacecraft right ascension/declination w.r.t. radio astronomical background sources. These data will be instrumental in determining the out-of-plane components of the ephemerides of the moons, as well as of Jupiter itself (Dirkx et al., 2017). In addition, PRIDE will provide ad hoc three-way Doppler data for each receiving telescope, which may provide opportunities to improve effective data qualities under certain conditions. We are in the process of analyzing this in the context of the ExoMars-LaRa mission.