"For every action, there is a reaction: that is the principle on which all space rockets operate, blasting propellant in one direction to travel in the other. But one NASA engineer believes he could take us to the stars without any propellant at all.

Designed by David Burns at NASA’s Marshall Space Flight Center in Alabama, the “helical engine” exploits mass-altering effects known to occur at near-light speed. Burns has posted a paper describing the concept to NASA’s technical reports server.

It has been met with scepticism from some quarters, but Burns believes his concept is worth pursuing. “I’m comfortable with throwing it out there,” he says. “If someone says it doesn’t work, I’ll be the first to say, it was worth a shot.”

To get to grips with the principle of Burns’s engine, picture a box on a frictionless surface. Inside that box is a rod, along which a ring can slide. If a spring inside the box gives the ring a push, the ring will slide along the rod one way while the box will recoil in the other. When the ring reaches the end of the box, it will bounce backwards, and the box’s recoil direction will switch too. This is action-reaction – also known as Newton’s third law of motion – and in normal circumstances, it restricts the box to wiggling back and forth (see video below)..."

https://www.newscientist.com/article/2218685-nasa-engineers-helical-engine-may-violate-the-laws-of-physics/