  The anomalous time depending blueshift, the so-called "Pioneer anomaly", that
was detected in the radio-metric data from Pioneer 10/11, Ulysses and Galileo
spacecraft may not result from a real change of velocity. Rather, the Pioneer
anomaly may be understood within the framework of general relativity as a time
depending gravitational frequency shift accounting for the time dependence of
the density of the dark energy when the latter is identified with quintessence.
Thus, instead of being in conflict with Einstein equivalence principle, the
main Pioneer anomaly appears merely as a new validation of general relativity
in the weak field and low velocity limit.
