Reverse Gravitational Frequency?
If we had 1/10,000 the control over the gravitational force that we do over the electromagnetic force, we’d probably have a massless drive.
Getting to that point will probably require a functional Theory of Everything, which seems to get farther away all the time.
Personally, I suspect much of the mass of the universe that we detect is hidden away in other dimensions we cannot perceive more directly. Figuring out how this works might not only give us antigravity but also the ability to take shortcuts thru other dimensions.
Wildly speculative, of course. But all the talk about dark energy and dark matter indicates to me there’s something missing at the very core of our understanding of physics.