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Raumfahrt - NASAs EmDrive Leader Has a New Interstellar Project

10.05.2020

Harold White left NASA in December to join a new nonprofit focused on building the technologies to bring humans to the outer solar system and beyond.

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THE SOLAR SYSTEM isn’t big enough for Harold White—but it’s a start. The 54-year-old physicist has devoted his career to researching advanced propulsion concepts that he hopes may carry humans to the outer solar system and eventually into the uncharted wilderness of interstellar space. Conventional rocket engines are too slow to cover these vast distances on human timescales, so White has focused on more exotic solutions like faster-than-light warp drives and quantum vacuum thrusters that get a boost from space-time itself.

White’s research pedigree may sound like it was cribbed from a mad scientist in a pulp sci-fi novel, but most of his work was done as the leader of NASA’s Advanced Propulsion Physics Lab at Johnson Space Center. The lab, which White christened Eagleworks, was founded in 2009 to explore the frontier of physics in search of the next big breakthrough in space power and propulsion. In December, White left the lab he led for a decade to head up R&D at the Limitless Space Institute, a new nonprofit in Houston working to accelerate the human exploration of interstellar space.

“It seemed like a great opportunity to more purposefully pursue advanced power and propulsion with a little more intensity,” says White. “It was a personal choice and the next step for me to take in terms of my pinnacle objective: enabling human exploration of the outer solar system and other stars.”

Limitless Space Institute was founded last year by Kam Ghaffarian, an engineer and entrepreneur who also founded the nuclear energy company X-energy and Stinger Ghaffarian Technologies, one of the largest engineering contractors for NASA. His new organization plans to foster advanced space power and propulsion technologies through a mix of in-house research, grants, and partnerships with other institutions, including NASA’s Eagleworks. Earlier this month, Ghaffarian announced the nonprofit’s first round of Interstellar Initiative Grants, which will award researchers up to $250,000 to work on problems related to interstellar travel.

“The initiative was set up to foster and sponsor other people pursuing theoretical and empirical work that will hopefully help increase the maturity and capability of the interstellar research community,” says White.

Limitless will select its first round of grantees in September, and the institute will give applicants carte blanche to determine what kind of research they want to do. The only stipulation in the call for proposals is that the research should ultimately be about making spacecraft “go incredibly fast.” In the meantime, White says the institute is focusing on a few core research topics related to power and propulsion. Some of these areas include working with known physics and engineering concepts. For example, the institute plans to partner with universities to develop small-scale nuclear reactors that produce no more than 10 megawatts of power. White says these reactors will first be developed for terrestrial applications with an eye toward integrating them with spacecraft later on.

 

White will also be conducting research that grows out of his work at NASA on the EmDrive, a so-called “impossible engine” that produces thrust without propellant by bouncing radio waves around in a metal cone. The EmDrive test device used by White and his colleagues was a copper frustum—a cone with its top lopped off—that was just under a foot long. During tests it was placed in a vacuum chamber, and a device outside the chamber sent microwaves to antennas inside the cone. How those microwaves generate thrust inside the cone is a subject of divisive theoretical debate.

If the EmDrive or something like it works, it would be a huge boon to space exploration. We’d no longer have to haul all our fuel with us, which is a major limitation on how far humans can travel into space. It could also potentially produce way more thrust than a conventional engine. This means human missions to the outer solar system might only take a year or two, rather than a decade. But the real icing on the cake is that an EmDrive—or something like it—would blow open the door to interstellar travel. Our closest stellar neighbor is 4 light years away; it would take thousands of years to reach it with a conventional rocket. If we want to head to the stars, we’re going to need a souped-up engine.

In 2016, White and his team at NASA published the first peer-reviewed experimental evidence that appeared to show the EmDrive actually producing thrust. The results of White’s experiment and the theory behind it remain controversial. No one can agree about whether the device actually produced thrust or how to explain it if it did. But the fact that NASA was even supporting this kind of far-out research was good news for anyone planning a vacation to Alpha Centauri.

At Limitless, White wants to take the research even further, but he won’t be building any engines—at least not yet. Instead, he’ll be probing the fundamental physics that he and others believe may explain how exotic propulsion systems like the EmDrive work. He calls it a dynamic vacuum model, and it cuts to the heart of what we talk about when we talk about “physical reality.”

Most physicists today view the physical world as a soup of subatomic particles like photons, quarks, and neutrinos in which the location of a particle at any given time is a matter of probability. This picture of reality is known as the Copenhagen interpretation of quantum mechanics. It may be the most popular scientific theory of reality, but it’s far from the only one. A competing view, known as pilot wave theory, says the quantum world is deterministic. In this theory, subatomic particles are “piloted” along a definite path like a train on its tracks, and the only reason their location appears nondeterministic is that we don’t understand the deeper quantum field that may ultimately constitute reality.

This quantum field is referred to as the quantum vacuum and can be thought of as the vast, undulating floor upon which the rest of reality is built. If you were to take all the matter out of the universe and bring the temperature down to absolute zero, the quantum vacuum would be what’s left. We’re accustomed to thinking of vacuums as totally empty, but the quantum vacuum is never truly empty. Electromagnetic waves and particles are popping in and out of existence all the time, and it’s these energy fluctuations that give rise to the physical world.

It’s pretty heady stuff, but if physicists can get a better understanding of the quantum vacuum—assuming it exists—they could, in principle, tap its energy to power a spacecraft. Indeed, this is a potential theoretical explanation White and his colleagues at NASA offered for how an engine like the EmDrive might be able to produce thrust. It’s hardly the only explanation—arguably the most convincing one is that the observed thrust was actually just a measurement error.

“Harold tried to come up with a theory to explain the EmDrive by calling it a quantum vacuum thruster,” says Martin Tajmar, a physicist at Dresden University of Technology who studies advanced propulsion systems. “His intuition is good, but the concepts he uses and cites are controversial. Only the experiment counts—no accepted theory has been put on the table that predicts any of this.”

 

It’s one thing to have a theory about why an EmDrive should work, and quite another to have experimental evidence of it in action. White and his colleagues at NASA appeared to have both, but so far no one has been able to replicate their results. Tajmar runs the SpaceDrive program at Dresden where he builds ultrasensitive devices capable of detecting almost imperceptible amounts of thrust. He uses these devices to try to replicate the results of EmDrive studies that appeared to produce thrust like the one conducted by White and his colleagues at NASA.

Tajmar hasn’t seen anything yet, but he says that doesn’t mean that probing the physics with experiments isn’t worthwhile. He compared it to high-temperature superconductivity, a physical phenomenon that may revolutionize electromagnetic technologies, but that wasn’t predicted in theory. “We need to be lucky, have a good intuition, and just try things that were never tested,” Tajmar says. “We were lucky to find high-temperature superconductivity by continuously trying, and hopefully the same thing will happen with breakthrough propulsion.”

At Limitless, White says he’s focused on the considerable task of demystifying and experimentally describing the fundamental physics of the dynamic vacuum model, rather than microwaving metal cones and hoping they produce enough thrust to send humans to the stars. In the last paper White and his colleagues published before he left NASA, they modeled the quantum vacuum around the nucleus of a single hydrogen atom. That’s a long way from an interstellar engine, but White sees it as a critical step on that path.

“There are several threads you have to pull on in the process of marching toward that goal,” he says. “Some of it will include practical steps that leverage known physics and engineering. But you still have to focus on stuff at the frontiers of physics to try to figure out if there are potential new approaches that you can use to meet the performance requirements to accomplish these goals.”

At Limitless, White plans to continue with his research on the quantum vacuum. He says the institute is manufacturing custom Casimir cavities—an experimental setup with two plates placed close together—to study the predicted characteristics and structure of the quantum vacuum believed to exist between the plates. “These things are not necessarily technology, they’re just physics experiments,” says White. “They may lead to things we could put together as a technology, but right now we’re just doing the science first.”

Not everyone is convinced White is headed in the right direction. Jim Woodward, a physicist at California State University, Fullerton, has devoted his career to advanced propulsion. He has an alternative theory explaining the EmDrive that doesn’t invoke quantum vacuums. Instead, he thinks, the thrust is produced by so-called “Mach effects,” which are derived from general relativity rather than quantum mechanics. In this theory, the EmDrive can produce thrust by harnessing the fluctuations in energy produced by the electromagnetic field in the EmDrive interacting with the gravitational field of everything else in the universe.

Woodward says most people working on advanced propulsion are “quantum vacuumers” like White, but he argues that their theories can’t explain why the EmDrive or other advanced propulsion systems would work without bringing gravity into the picture. “The world and its physics is the way it is, not as we would have it be,” says Woodward. “This is not a business for wishful thinkers. I predict that Limitless will have a very hard time finding anything worth funding, and such that they do will not pan out.”

Woodward isn’t just throwing rocks. He has made his own prototype propulsion system called the Mach Effect Gravity Assist drive, or MEGA. It doesn’t look like much—it’s a stack of ceramic disks placed between two small blocks—but it has scored $750,000 in NASA research grants. More importantly, Woodward and his colleagues have evidence that the MEGA drive produces thrust.

 

When an electric voltage is applied to the ceramic disks, it causes them to expand and push on one of the blocks. The theory of mach effects says that when an object accelerates—in this case, the block that is being pushed—it loses a little mass. When the ceramic disks in the middle contract, it gains that mass back. This means the block on the other side of the disks gets pulled forward more than the block with the changing mass gets pulled back. By doing this over and over, Woodward's data suggests the device accelerates forward. Woodward and two other groups have produced data that appear to show the MEGA device producing thrust, but follow-up tests by Tajmar at his lab in Dresden suggest that these may all turn out to be measurement errors too.

It’s not hard to see why most research organizations might shy away from the types of projects that Limitless plans to fund. They’re the very definition of high risk, high reward. They might also seem a little idealistic at a time when NASA is struggling just to put people back on the moon. But White says pursuing this research will also benefit those of us stuck on terra firma.

“In trying to achieve great things, we can realize new technologies that help us in the here and now,” White says. “The long-term application may be interstellar travel, but exploring these things motivates us to push the boundary of what’s possible. And in the process, we can potentially make life better for everybody at home.”

Quelle: WIRED

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