  Evaluation of gravity control concepts should be examined with respect to
currently known physical theories. In this work we study the hypothetical
conversion of gravitational potential energy into kinetic energy using the
formalism of general relativity. We show that the energy involved in the
process greatly exceeds the Newtonian estimate, given the nature of general
relativity. We conclude that the impact of any gravity manipulation for
propulsion greatly depends fundamentally on its exact definition.
