Propellantless engine for interstellar travel -- but is it revolutionary or illusory?

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https://www.wired.com/story/mach-effect-...ar-travel/

EXCERPT: . . . As the pandemic raged across the globe, Jim Woodward and Hal Fearn met regularly in the pancake house parking lot to keep their experiments going. Funded by a grant from a NASA program that also supports research on far-out concepts such as inflatable telescopes and exoplanet photography, the duo has been developing what they call a Mach-effect gravitational assist (MEGA) drive, a propulsion system designed to produce thrust without propellant.

Every spacecraft that has ever left Earth has relied on some type of propellant to get it to its destination. Typically a spacecraft moves by igniting its fuel in a combustion chamber and expelling hot gases. (Even more exotic forms of propulsion, such as ion thrusters, still require propellant.) That’s why humans have remained stuck so close to home. A spacecraft can only accelerate as long as it has fuel to burn or a planet to loop around for a gravitational assist. Those methods can’t even carry a vehicle all the way to Alpha Centauri, our closest neighbor, in any reasonable amount of time. The fastest spacecraft ever built, the Parker Solar Probe, which will hit speeds over 400,000 miles per hour, would take thousands of years to get there.

Woodward’s MEGA drive is different. Instead of propellant, it relies on electricity, which in space would come from solar panels or a nuclear reactor. His insight was to use a stack of piezoelectric crystals and some controversial—but he believes plausible—physics to generate thrust. The stack of crystals, which store tiny amounts of energy, vibrates tens of thousands of times per second when zapped with electric current. Some of the vibrational frequencies harmonize as they roll through the device, and when the oscillations sync up in just the right way, the small drive lurches forward.

This might not sound like the secret to interstellar travel, but if that small lurch can be sustained, a spacecraft could theoretically produce thrust for as long as it had electric power. It wouldn’t accelerate quickly, but it could accelerate for a long time, gradually gaining in velocity until it was whipping its way across the galaxy. An onboard nuclear reactor could supply it with electric power for decades, long enough for an array of MEGA drives to reach velocities approaching the speed of light. If Woodward’s device works, it’d be the first propulsion system that could conceivably reach another solar system within the lifespan of an astronaut. How does it work? Ask Woodward and he’ll tell you his gizmo has merely tapped into the fabric of the universe and hitched a ride on gravity itself.

Sound impossible? A lot of theoretical physicists think so too. In fact, Woodward is certain most theoretical physicists think his propellantless thruster is nonsense. But in June, after two decades of halting progress, Woodward and Fearn made a minor change to the configuration of the thruster. Suddenly, the MEGA drive leapt to life. For the first time, Woodward seemed to have undeniable evidence that his impossible engine really worked. Then the pandemic hit... (MORE - details)


https://www.youtube.com/watch?v=_INqXPFdJM8
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