  We consider a supersymmetric model with a single matter supermultiplet in a
five-dimensional space-time with orbifold compactification along the fifth
dimension. The boundary conditions on the two orbifold planes are chosen in
such a way that supersymmetry remains unbroken on the boundaries. We calculate
the vacuum energy-momentum tensor in a configuration in which the boundary
branes are moving with constant velocity. The results show that the
contribution from fermions cancels that of bosons only in the static limit, but
in general a velocity-dependent Casimir energy arises between the branes. We
relate this effect to the particle production due to the branes motion and
finally we discuss some cosmological consequences.
