  The force exerted by the gravitational field on a Casimir cavity in terms of
Archimedes force of vacuum is discussed, the force that can be tested against
observation is identified, and it is shown that the present technology makes it
possible to perform the first experimental tests. The use of suitable high-Tc
superconductors as modulators of Archimedes force is motivated. The possibility
is analyzed of using gravitational wave interferometers as detectors of the
force, transported through an optical spring from the Archimedes vacuum force
apparatus to the gravitational interferometer test masses to maintain the two
systems well separated. The use of balances to actuate and detect the force is
also analyzed, the different solutions are compared, and the most important
experimental issues are discussed.
