  We consider the contribution to our understanding of vacuum-exchange
processes to be made by investigations at the proposed electron-proton collider
THERA. Recent results have highlighted the value of such studies for testing
quantum chromodynamical descriptions of both long-range and short-range strong
interactions. Stringent quantitative constraints have been provided by
exploiting the opportunity to correlate scaling behaviour with helicity
selection in exclusive and semi-exclusive vector-meson production. After
reviewing the progress achieved by the measurement programs presently being
carried out by the H1 and ZEUS collaborations at HERA, we discuss the
performance criteria imposed by such investigations on the THERA accelerator
complex and on the detector design. We conclude that the study of vector-meson
production will form an essential component of the THERA physics program
beginning with the early turn-on stage of the machine and continuing throughout
the achievement of its full high-luminosity potential.
