This paper has some interesting ideas. They want to manufacture really tiny black holes (radii of "a few attometers") and use Hawking radiation (which is invers

This paper has some interesting ideas. They want to manufacture really tiny black holes (radii of "a few attometers") and use Hawking radiation (which is inversely related to mass) to drive the vehicle. The black hole serves as both engine and fuel tank. https://arxiv.org/abs/0908.1803 https://arxiv.org/abs/0908.1803