  Gravitational radiation is an elusive form of radiation predicted by general
relativity, it is the subject of intense theoretical and experimental research
at the limit of the sensitivity of today's instrumentation. In spite of the
fact that no direct evidence of this radiation now exist, observed
astrophysical phenomena have given convincing proofs of its existence. Theories
predict that gravitational radiation may also be employed for propulsion,
moreover the nonlinear behaviour of spacetime may permit the generation of
spacetime singularities with colliding beams of gravitational radiation, this
phenomenon could become a form of propellantless propulsion. Both applications
would require gravitational wave generators with high power and appropriate
optical properties. Among the proposed techniques that could be applicable to
the production of gravitational waves, a promising one is the possible emission
of gravitons by quantum systems. A hypothesis describing the production of
gravitons in s-wave/d-wave superconductor junction is presented.
