Assessing the impact of perturbations on the motion of Rosetta spacecraft near Comet 67P/Churyumov-Gerasimenko

Next year marks the tenth anniversary of the conclusion of the Rosetta mission at the Jupiter-family comet 67P/Churyumov-Gerasimenko. The spacecraft-lander duo was the first to perform an extended, close rendezvous with, as well as landed exploration on, a comet during its perihelion passage [1]. The suite of instruments onboard has acquired a unique dataset of remote-sensing and in situ observations of the active nucleus and the ambient comae.

 

    The motion of the spacecraft platform is influenced by various dynamical effects, especially in the immediate vicinity of the nucleus [2]. The gravitational influence of the low-density, kilometre-sized body is weak, however, its bilobed shape (and therefore the mass distribution) gives rise to a significant non-central gravitational component [3,4,5]. The complex rotation state of the nucleus adds to the variability of such perturbation on the spacecraft [6,7]. In this dynamical environment, the role of non-conservative forces will be particularly prominent, and their accurate modelling especially important. Unlike gravitation, which attenuates away from the nucleus, the intensity of solar radiation changes only perceptibly with heliocentric distance. Meanwhile, coma densities are typically larger near the nucleus, and the activity of the comet generally increases as it approaches perihelion. Moreover, the irregular shape of the nucleus and its unevenly distributed surface activity may induce significant spatial and temporal variabilities of the coma structures [8,9]. Both solar radiation pressure and coma drag depend on the configuration, attitude and surface properties of the spacecraft, however. For the coma drag, typical models of flow density and relative velocity may have high uncertainties, leading to potentially substantial mismodeling.

 

   In our work, we investigate the perturbations on Rosetta and their impact on spacecraft motion around 67P in detail.  We utilise (and where necessary extend) the open-source TU Delft Astrodynamics Toolbox (Tudat), taking advantage of its versatility and modularity in dynamical- and observation-model settings, as the generic interface [10]. A focus here is on the incorporation of state-of-the-art physical models that had been developed and validated by Rosetta measurements to capture the intricate behaviour of the rarefied comae [11].  We evaluate model implementation strategies aimed at efficiently quantifying spacecraft perturbations.  The outcome from this (line of) investigation is expected to provide more insight into the optimisation of dynamic models for spacecraft orbit determination. In the subsequent steps of our work, we will reanalyse the spacecraft tracking data to use our improved dynamical model to generate a more robust determination of the comet’s gravity field.

 

 

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