WP7: Coordinates and Reference Systems (Research and technological development)

Objectives

This WP aims at determining a shape and gravity model for the Martian satellite Phobos, establishing coordinate systems for Phobos, the Moon and the icy satellites and developing a rotation model for the natural satellites.

Description of work

Task 7.1 : Reference shape and gravity model for Phobos

Realize a reference system for the Martian satellite Phobos by establishing a dense (if possible global) control point network. Measure large numbers of image coordinates for prominent surface features. Solve for the 3D-coordinates of the control points by bundle block adjustments. Spacecraft ephemeris data from WP7 will be used as a basis. Establish a reference shape model as well as a gravity field model assuming a homogenous mass distribution (TUB/DLR).

Task 7.2 : Realization of the Phobos coordinate system

Implement a bundle block adjustment that simultaneously solves for the 3D-coordinates of the surface features and for rotational parameters of Phobos. Measure librational (and possibly precessional) motion of Phobos to define a coordinate system (TUB).

Task 7.3 : Realization of the Lunar coordinate system

The goal of this task is to warrant Lunar maps which are free of distortion and which are correctly tied to Lunar-fixed coordinates and therefore provide an accurate realization of the Lunar reference system. Image and ancillary data from recent international Lunar missions will be cross-compared and verified for correct and consistent instrument alignments, spacecraft orbit and instrument pointing information. Images of the Apollo landing sites (for which Moon-fixed coordinates are precisely known) will provide ground truth and anchor points for Lunar maps. Maps will be fed into the appropriate data distribution channels (WP9).

Task 7.4: Reference shapes of icy satellites

The shapes of satellites are a result of their dynamical states mainly determined by the satellites’ rotation, by tidal interaction with the central planet, and by the rheology of the interiors (e.g., rigidity, viscosity of ice and rock at the respective forcing frequency). The existing shape models for Saturn's icy moons and the Galilean satellites will be updated using limb studies and control-point networks based on imaging data from the Voyager, Galileo and Cassini spacecraft. This study will benefit from updated trajectory data determined in WP7. This WP is an invaluable contribution in preparation of future ESA missions to Europa, Ganymede, and Callisto, currently under study in the Cosmic Vision program.

Task 7.5: Realization of icy satellites coordinate systems

Based on Voyager, Galileo, and Cassini imaging data the realizations of coordinate systems of the outer planet moons shall be improved. Control-point network analysis will be carried out to constraint rotational parameters, e.g., libration amplitudes and frequencies as well as obliquity,nutation and precession constants. Expressions for the time-dependence of the rotational parameters in the newly defined coordinate systems will be derived. The WP will address the Galilean satellites (Io, Europa, Ganymede, and Callisto) and Saturn's satellites (Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Iapetus, possibly Phoebe and Hyperion).

Task 7.6: Theory of the rotation of the natural satellites

The rotational motion of bodies are sensitive to gravitational external couplings and to geophysical internal couplings that depends on the interior properties of the body. The objective of this task is to study the rotation of natural satellites in spin-orbit synchronous resonance and to analyse the differences of each satellites (strong gravitational tidal effects, presence of atmosphere, internal ocean, core-mantle friction...) that might modify the librational response of the body. These signatures are precious to understand and correctly interpret the rotational observations and realization of coordinate