  An E\"otv\"os experiment to test the weak equivalence principle (WEP) for
zero-point vacuum energy is proposed using a satellite. Following the
suggestion of Ross for a terrestrial experiment of this type, the acceleration
of a spherical test mass of aluminum would be compared with that of a similar
test mass made from another material. The estimated ratio of the zero-point
vacuum energy density inside the aluminum sphere to the rest mass energy
density is ~ 1.6 X 10^{-14}, which would allow a 1% resolution of a potential
WEP violation observed in a satellite mission test that had a baseline
sensitivity to WEP violations of ~ 10^{-16}. An observed violation of the WEP
for vacuum energy density would constitute a significant clue as to the origin
of the cosmological constant and the source of dark energy, and test a recently
proposed resolution of the cosmological constant problem, based on a model of
nonlocal quantum gravity and quantum field theory.
