I was reading
Modanese, Giovanni; A. Robertson, Glen, eds. (2012). Gravity-Superconductors Interactions: Theory and Experiment. Bentham Science Publishers. doi:10.2174/97816080539951120101. ISBN
978-1-60805-400-8.
It sounds like a more practical destination for our Italian's $24 million of crowd-funding money - still not all that practical, but slightly less off-the-wall.
A black-hole merger seems to have generated enough momentum to kick the fused black hole produced out of the core of the galaxy that had formed around its progenitors. It's not a reactionless drive - gravity waves have energy and momentum - but the example is an attention getting.