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This work evaluates the added benefit of using laser altimeter measurements for orbit reconstruction. As a spacecraft orbits a celestial body, its altimetry swaths progressively cross previous swaths. These locations, known as crossover points, yield valuable information about the orbited body and the spacecraft trajectory. The mathematical expressions for the inclusion of crossover measurements into orbit determination algorithms are presented and evaluated. It is shown that a first-order approximation of these expressions is insufficient and a more detailed expression is developed. To evaluate the impact of altimetry crossover measurements on orbit determination, the planetary mission Jupiter Icy moons Explorer (JUICE) by the European Space Agency (ESA) is used as a case study by means of a covariance analysis. In this initial analysis, the assumption is made that all altimetry measurements are obtained with nadir pointing which limits the direct applicability of our method until pointing is accounted for. • Altitude difference crossover measurements improve orbit determination. • Crossovers reduce position uncertainty marginally due to Doppler precision advancements. • Laser altimetry crossovers with JUICE mission as case study. • Covariance analysis of estimation uncertainty when altimetry crossovers are included. [ABSTRACT FROM AUTHOR]

Abstract We examine the dynamics of energetic magnetospheric ions in the highly perturbed and asymmetric electromagnetic environment of the Jovian moon Callisto. The Alfvénic interaction of the (nearly) corotating magnetospheric plasma with Callisto's ionosphere and induced dipole generates electromagnetic field perturbations near the moon, the structure of which vary as a function of Callisto's orbital position. For this study, these perturbations are obtained from the AIKEF hybrid model (kinetic ions, fluid electrons) which has already been successfully applied to Callisto's local plasma environment (Liuzzo et al., 2015, 2016, 2017). To isolate the influence of Callisto's ionosphere and induced dipole field on energetic ion dynamics, we analyze the trajectories of energetic hydrogen, oxygen, and sulfur ions exposed to various configurations of the locally perturbed electromagnetic fields. We present spatially resolved surface maps that display accessibility of Callisto to these ion populations for select energies from 1 keV to 5000 keV. The Alfvénic plasma interaction with (i) Callisto's induced magnetic field, (ii) Callisto's ionosphere, and (iii) the combination of both, all leave distinct imprints in these accessibility patterns. Draping of the magnetospheric field around Callisto's ionosphere partially shields the moon's trailing (ramside) hemisphere from energetic ion impacts, and the induced field tends to focus energetic ion impacts near Callisto's Jupiter-facing and Jupiter-averted apices. Depending on the nature of Callisto's Alfvénic plasma interaction, the accessibility of its surface to energetic protons may evolve non-monotonically with increasing energy. We also present maps of energetic ion accessibility and the resulting energy deposition onto Callisto at the time of the Galileo C3, C9, and C10 flybys. Our findings show that the shielding of Callisto's surface from energetic ion impacts is most effective during flybys that took place while the moon was located at an intermediate distance to the center of Jupiter's magnetospheric current sheet. In this case, the ionosphere and induced dipole field both make substantial contributions to the electromagnetic field perturbations near Callisto. [ABSTRACT FROM AUTHOR]

The JUpiter ICy moons Explorer mission of the European Space Agency, that will be launched in the year 2022, will study the geodesy and physical characteristics of Jupiter and its icy moons Europa, Callisto and Ganymede. The final phase of this mission, planned for the year 2032, is still under investigation and foresees phases in circular orbit around Ganymede. In this paper two types of science orbits around Ganymede, that optimize the observational performances and the probe life-time, are proposed. While the first type allows, at “zero cost”, the obtaining of repeated observations of a given point of the surface, the second type, with a limited cost, adds to the periodicity of observation, the condition of synchronism with the Sun. This synchronism permits both the achievement of a condition of permanent sunlight for the probe, thus leading to an extension of the mission duration, and a minimization of the variations of spectral signature due to the Sun's position. [ABSTRACT FROM AUTHOR]

Abstract: The JUpiter ICy moons Explorer (JUICE) is an ESA L-class mission concept designed to explore the Galilean satellites of the Jovian system. Although the current mission science goals do not include any astrophysical observations, we find that the planned period of the JUICE mission is optimal for in situ measurements of Interstellar Dust (ISD), due to highly increased flux levels at that time. In case that JUICE carries a dust detector, this could lead to in situ high-resolution mass spectra of ISD grains. Such compositional information on the ISD grains is important for understanding the origins of solar/planetary systems, and therefore could represent a valuable addition to the core JUICE mission science. [Copyright &y& Elsevier]

The JUpiter Icy moons Explorer (JUICE) will investigate Ganymede's and Callisto's surfaces and subsurfaces from orbit to explore the geologic processes that have shaped and altered their surfaces by impact, tectonics, possible cryovolcanism, space weathering due to micrometeorites, radiation and charged particles as well as explore the structure and properties of the icy crust and liquid shell (Grasset et al., 2013). The best possible synergy of the JUICE instruments is required to answer the major science objective of this mission and to fully exploit the potential of the JUICE mission. Therefore, the JUICE team is aiming to define high priority targets on both Ganymede's and Callisto's surfaces to support the coordination of the planning activities by the individual instrument teams. Based on the science objectives of the JUICE mission and the most recent knowledge of Ganymede's and Callisto's geologic evolution we propose a collection of Regions of Interest (RoIs), which characterize surface features and terrain types representing important traces of geologic processes, from past and/or present cryovolcanic and tectonic activity to space weathering processes, which are crucial to understand the geologic evolution of Ganymede and Callisto. The proposed evaluation of RoIs is based on their scientific importance as well as on the opportunities and conditions to observe them during the currently discussed mission profile. • We propose a selection of Regions of Interest (RoIs) on Ganymede and Callisto's surface. • The RoIs represent surface features crucial to understand the evolution of these bodies. • The list helps to fully exploit the potential of the JUICE mission. • The list supports the observation planning and the synergy of the JUICE instruments. [ABSTRACT FROM AUTHOR]

We examine the dynamics of energetic magnetospheric electrons exposed to the highly perturbed and asymmetric plasma environment of Jupiter's moon Callisto. The interaction of the (nearly) corotating magnetospheric plasma with Callisto's ionosphere and induced dipole locally generates intense electromagnetic pileup and draping signatures which vary as a function of the moon's distance to the center of Jupiter's magnetospheric current sheet. In our study, these field perturbations are represented using output from the AIKEF hybrid (kinetic ions, fluid electrons) model of Callisto's interaction with the corotating plasma. In order to constrain the influence of Callisto's variable electromagnetic environment on the dynamics of energetic electrons, we trace the trajectories of more than 6.7 million test particles as they travel through a distinct configuration of the locally perturbed fields. We present spatially resolved maps that display the accessibility of Callisto to electrons at energies E between 10 1 keV ≤ E ≤ 10 5 keV for multiple sets of these perturbed fields, corresponding to select distances of the moon to the center of the Jovian current sheet. The electromagnetic field perturbations near Callisto play a crucial role in generating inhomogeneous precipitation of energetic electrons onto the top of the moon's atmosphere. In particular, Callisto's Jupiter-facing and Jupiter-averted hemispheres are partially protected from energetic electron precipitation: when located far above or below the center of Jupiter's current sheet, Callisto's induced dipole shields the apices of these hemispheres, whereas near the center of the sheet, strong field line draping protects these regions. In contrast to this, the apex of Callisto's trailing hemisphere is exposed to intense energetic electron precipitation at any distance to the center of the Jovian current sheet. We also present maps of energetic electron accessibility during the Galileo C3, C9, and C10 flybys, and calculate the intensity of energetic electron flux onto multiple locations at the top of Callisto's atmosphere. These non-uniform electron fluxes likely cause inhomogeneous ionization of Callisto's atmosphere and may even contribute to irregular erosion of the surface. This paper is a companion to Liuzzo et al. (2019), who studied the dynamics of energetic ions near Callisto. • Callisto's perturbed electromagnetic environment strongly affects energetic electron dynamics. • Induced fields and Alfvén wings partially shield Callisto from impinging magnetospheric electrons. • Energetic electron precipitation onto Callisto's atmosphere is highly inhomogeneous. • Electrons may leave Callisto's local environment, bounce, and then return, causing asymmetric precipitation patterns. [ABSTRACT FROM AUTHOR]