  Recent studies have shown that the medium-Earth orbit (MEO) region of the
Global Navigation Satellite Systems is permeated by a devious network of
lunisolar secular resonances, which can interact to produce chaotic and
diffusive motions. The precarious state of the four navigation constellations,
perched on the threshold of instability, makes it understandable why all past
efforts to define stable graveyard orbits, especially in the case of Galileo,
were bound to fail; the region is far too complex to allow of an adoption of
the simple geosynchronous disposal strategy. We retrace one such recent
attempt, funded by ESA's General Studies Programme in the frame of the GreenOPS
initiative, that uses a systematic parametric approach and the straightforward
maximum-eccentricity method to identify long-term stable regions, suitable for
graveyards, as well as large-scale excursions in eccentricity, which can be
used for post-mission deorbiting of constellation satellites. We then apply our
new results on the stunningly rich dynamical structure of the MEO region toward
the analysis of these disposal strategies for Galileo, and discuss the
practical implications of resonances and chaos in this regime. We outline how
the identification of the hyperbolic and elliptic fixed points of the
resonances near Galileo can lead to explicit criteria for defining optimal
disposal strategies.

Earth and Planetary Astrophysics