Hypothetical Gravity Control and Possible Influence on Space Propulsion
  In nearly all concepts invoked or proposed to change or shield gravity it is intuitively assumed that manipulation of gravity automatically leads to a breakthrough for propulsion. In this study it is shown, that even if gravity could be hypothetically controlled along the manipulation schemes outlined, the gains in terms of propulsion would be modest and lead to no breakthrough. Although the manipulation schemes presented are not exhaustive, they include the most straightforward ones from the current physics point of view. 
M. Tajmar, O. Bertolami