Could starships use cold fusion propulsion?

Voyager 1 is now leavingsolar system, making it the first manmade probe to enter interstellar space. That's quite an achievement, and it only took 30+ years. But if we're going to get serious about boldly going where no man has gone before, and send humans beyond the solar system, we're gonna need a cheap and plentiful energy source to help us get there.

Exactly how much energy are we talking about? Well, back in January, a paper appeared on thearXiv by Marc Millis, a former head of NASA's Breakthrough Propulsion Physics Project, calculating the costs -- in terms of energy -- of a truly interstellar manned space mission. And it wasn't good news.

For one scenario, he assumed a 500-person space ship on a one-way trip to establish a human colony on some distant exoplanet. That would require an exajoule of energy, or 1018 J, i.e., just about the same amount of energy consumed by everyone on Earth in one year.

An unmanned mission to Alpha Centauri would be even more of an energy hog, because of the need for more complicated maneuvers (deceleration, etc). That would require 1018 J. Millis figures we won't have the ability to generate that kind of energy until 2200 for the passenger ship, and 2500 for the unmanned probe.

Scientists are mulling all kinds of options, of course, including harnessing the power of thestars, i.e., nuclear fusion (as opposed to the nuclear fission underlying nuclear power plants). As Carl Sagan once noted, "Every time you look up at the sky, every one of those points of light is a reminder that fusion power is extractable from hydrogen and other light elements, and it is an everyday reality throughout the Milky Way Galaxy."

One Small Problem ...

There's just one problem. We can achieve hotnuclear fusion, but recreating the intense temperatures and pressures that exist inside stars currently requires more energy than it gives back, so it's economically unfeasible, and pretty much an energysinkholefor the time being.

If only we could achieve fusion at room temperatures! That's the claim of proponents of so-called "cold fusion," a field that has languished on the fringe since its alleged discovery almost 20 years ago. Back in 2000,TIMEmagazine listed cold fusion as one of the "worst ideas" of the 20th century.

Prevailing scientific opinion is still that the vast majority of cold fusion research falls under the rubric of "pathological science": the results are always on the verge of a stunning validation. Whenever said validation fails (again) to materialize, there is always a handy rationale for why it isn't really a definitive failure -- and why the naysayers are just closed-minded tools of the scientific establishment, conspiring to keep these unsung geniuses down.

Running Hot and Cold

It all started in 1989, when two chemists at the University of Utah named Stanley Pons and Martin Fleischmann believed they had succeeded in producing nuclear fusion in a jar. Hundreds of researchers all over the world scurried to reproduce the experiments, and failed.

By the end of that year, a panel of experts had conducted a Department of Energy (DOE) review and concluded there was no basis for the claims.

Fifteen years later, the DOE decided to take another look at the accumulated evidence over the last 15 years and re-evaluate the cold fusion controversy. They still didn't find the evidence sufficiently convincing to launch a federally-funded research program.

But they felt that funding agencies should consider proposed projects on a case-by-case basis, provided those proposals met "accepted scientific standards and undergo the rigors of peer review." Heck, sometimes long shots pay off, so why not throw some funding scraps into the hat? That's why there are a couple of research programs looking into cold fusion, most notably one with the US Navy's Space and Naval Warfare Systems (SPAWAR).

In 2009, SPAWAR claimed to have detected a cold fusion reaction, and there have a been few other promising glimmers here and there over the years. But robust reproducibility remains elusive, adding credence to criticisms from physicists that the much-touted results are likely to be due to experimental error (either in the set-up, or the measurements).

So, while physicists are willing to concede there might be something of marginal interest going on, most remain unconvinced that this is bona fide cold fusion. Hardly anyone holds out any hope of it becoming a viable energy source in the foreseeable future.

Oh, and we don't call it "cold fusion" anymore. The current preferred terminology is Low Energy Nuclear Reactions (LENR), thank you very much.

Abra-ca-dabra!

The latest cold fusion claims are coming out of Italy from a physicist named Andrea Rossi, who has invented a cold fusion device known as thee-cat, or energy catalyzer.

罗西声称正在融合丰富镍with hydrogen nuclei to create copper, and release large amounts of energy -- using simple tabletopelectrochemistryinstead of huge machines that recreate stellar-scale temperatures and pressures.

Sounds pretty frickin' awesome, doesn't it? The e-cat would be just the ticket for powering an interstellar mission.

罗西已经展出几半公开的装置demonstrations, most recently on October 28. The purported "success'" of this latest demonstration has been met with enthusiasm by cold fusion acolytes and the occasionalgullible journalist.

So why aren't physicists (and morelevel-headed journalists) all over the world jumping up and down with excitement over Rossi's spectacular breakthrough?Ethan Siegel of Starts With a Banghandily lays it all out for you:

Rossi has never published a peer-reviewed paper on how his device works, either theoretically or experimentally.
here are only very rough schematics publicly available, and they are all from theJournal of Nuclear Physics, which is Andrea Rossi's own private journal. But doesn'tJournal of Nuclear Physicssound reputable? Not quite: it was founded just last year, in 2010. Don't confuse it with the real journal, which is simplyNuclear Physics.
Andrea Rossi had a company in the 1980s, Petroldragon, which claimed to turn garbage into oil. Sound too-good-to-be-true? Andrea Rossi went to jail for this scam, although hegives his own versionof the events.
The first reactor, scheduled to be built for Defkalion in Greece, was mysteriouslycancelled at the last minute by Rossi....
No one observing these tests has ever been allowed to "look inside the Turk," so to speak. In other words, no one -- other than Rossi himself -- has any idea what the internal design and mechanism that result in the claimed nuclear fusion (and energy production) actually is.

Ethan followed up with asecond post第二天,与布鲁克海文国家Lab's Peter Thieberger, explaining in careful detail the specific physics of why Rossi's claims of cold fusion are highly suspect. Go read that, and if you still want to invest in Rossi's technology -- well, I've got a bridge in Brooklyn you might be interested in buying, too.

They Want to Believe

Alas,cold fusionacolytes have responded to the criticism by (once again) shrilly decrying their critics as being closed-minded, misinformed, not willing to give cold fusion a fair shake, and so forth. There is little evidence to back up such claims. As Iwrote back in 2007:

The scientific community as a whole has not unfairly dismissed the claims: it simply remains unconvinced by the erratic evidence that has been presented to it. Should cold fusion advocates one day beat the odds and provide truly reproducible, compelling evidence for low-energy nuclear reactions, the stodgy old scientific establishment might grumble a bit, but ultimately it will accept those findings and alter its theories accordingly. Because that's what the scientific method is all about.

The late Scottish physicist Douglas Morrison was one of the rare skeptical attendees of the annual cold fusion conferences until his death in 2001. Each year, he would listen to the extravagant claims of "excess heat," then stand and make a simple request: "Please can I have a cup of tea?"

Granted, it was a bit cheeky of him, but he made his point: cold fusion talks a good game, yet even the simplest applied energy task remains well beyond its reach.

It takes 4.18joules to raise a gram of water's temperatureby 1 degee Celsius, and it needs to be 100 degrees Celsius to make Morrison's cup of tea. Remember, per Millis' calculations, we'd need an exajoule to sendhumans into interstellar space. So if you're hoping cold fusion will be the answer to powering an interstellar mission, you're in for a very long wait.