Even travelling at the maximum speed the Universe allows, it would take us years to reach our nearest neighbouring star. NASA engineer David Burns has produced an engine concept that could theoretically accelerate to 99 percent of the speed of light – all without using propellant.
It works by exploiting the way mass can change at relativistic speeds – those close to the speed of light in a vacuum. It has not yet been reviewed by an expert.
Even some headlines claiming the engine could ‘violate the laws of physics’, it’s definitely not going to break physics anytime soon.
Burns describes a box with a weight inside, threaded on a line, with a spring at each end bouncing the weight back and forth. In a vacuum – such as space – the effect of this would be to wiggle the entire box, with the weight seeming to stand still, like a gif stabilized around the weight.
Overall, the box would stay wiggling in the same spot – but if the mass of the weight were to increase in only one direction, it would generate a greater push in that direction, and therefore thrust.
According to the principle of the conservation of momentum – in which the momentum of a system remains constant in the absence of any external forces – this should be not completely possible.
Special relativity loophole
According to special relativity, objects gain mass as they approach light speed. So, if you replace the weight with ions and the box with a loop, you can theoretically have the ions moving faster at one end of the loop, and slower at the other.
But Burns’ drive isn’t a single closed loop. It’s helical, like a stretched out spring – hence “helical engine”.
“The engine accelerates ions confined in a loop to moderate relativistic speeds, and then varies their velocity to make slight changes to their mass. The engine then moves ions back and forth along the direction of travel to produce thrust,” he wrote in his abstract.
According to New Scientist, the helical chamber would have to be pretty large. Around 200 metres (656 feet) long and 12 metres (40 feet) in diameter, to be precise.
And it would need to generate 165 megawatts of energy to produce 1 newton of thrust. So a lot of input for a teeny tiny output. It is horribly inefficient.
“The engine itself would be able to get to 99 per cent the speed of light if you had enough time and power,” Burns told New Scientist.