Burns said his helical engine would work by accelerating ions confined in a loop. By changing their mass slightly, the engine would then move the ions back and forth along the direction of travel to produce thrust. New Scientist notes that the helical engine would need to be 650 feet long and 40 feet wide in order to work.

This mass changing isn’t prohibited by physics. Einstein’s theory of special relativity says that objects gain mass as they are driven towards the speed of light, an effect that must be accounted for in particle accelerators. In fact, a simplistic implementation of Burns’s concept would be to replace the ring with a circular particle accelerator, in which ions are swiftly accelerated to relativistic speed during one stroke, and decelerated during the other.

But Burns thinks it would make more sense to ditch the box and rod and employ the particle accelerator for the lateral as well as the circular movement – in which case, the accelerator would need to be shaped like a helix.