  We consider the impact of some known extensions of General Relativity in
observables that will be available with the Galileo positioning systems, and
draw conclusions as to the possibility of measuring them. We specifically
address the effects of the presence of a cosmological constant, a Yukawa-like
addition to the Newtonian potential, and the existence of an extra, constant
acceleration. We also consider the phenomenological impact of a broad class of
metric theories, which can be classified through the parameterized
Post-Newtonian formalism.
