https://www.theregister.co.uk/2018/05/25/boffins_unveil_a_rocket_that_will_eat_itself/

Scottish boffins, along with colleagues in Ukraine, have developed a "self-eating" rocket engine that could affordably fling a cubesat into orbit.

The solid-fuel rocket does away with heavy tanks, with the propellant itself forming much of the launcher's structure. As the engine burns its way through that structure, the rocket itself becomes correspondingly lighter, meaning more payload can be carried. An additional benefit is a reduction in debris left in orbit.