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14 March 2019

Helium-3: Lunar Gold Fever

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In 1986, scientists at the Institute of Fusion Technology at the University of Wisconsin estimated that the lunar “soil”, called the regolith, contains one million tons of helium-3 (3He), a material that could be used as fuel to produce energy by nuclear fusion. According to the study, mining it would be a profitable undertaking: the energy produced by the helium-3 would be 250 times greater than that needed to extract this resource from the Moon and transport it to Earth, where the lunar reserves of helium-3 could supply human needs for centuries.

The analysis of the researchers, based on samples collected by the Apollo missions, triggered a fever for this new lunar gold, which would be worth billions of dollars for those who controlled it. However, more than 30 years later, not a single gram has been collected yet, and there are those who say that it will never happen, because —according them— helium-3 has only served to inflate an enormous balloon of unfounded speculation.

The nuclear fusion of light atoms, such as the hydrogen isotopes deuterium (2H) and tritium (3H), has been seen for decades as the energy source of the future, inexhaustible and much less polluting than the fission of heavy atoms such as uranium. However, the technological development needed for it to be a practical and energy-efficient option still keeps researchers busy, and it is not an entirely clean energy: the fusion of deuterium and tritium produces neutrons, particles that cause radioactive contamination and that cannot be contained with electromagnetic fields, since they lack an electrical charge.

Against this, helium-3 (a non-radioactive isotope of the gas used to inflate balloons) offers remarkable advantages: its fusion with deuterium is more efficient than deuterium-tritium and does not release neutrons but protons, which can be easily contained thanks to their positive charge. In addition, it is possible to capture its energy to produce electricity directly, without the need for a water heating process to move turbines, as in current nuclear fission plants.

Major obstacles

The problem is that helium-3 is extremely scarce on Earth. This isotope comes mostly from the solar wind, but the Earth is protected under the shield of its atmosphere and its magnetic field. In contrast, for billions of years the Moon has accumulated an incredible amount of this material in its surface layer, although at such a low concentrations that it would be necessary to process enormous quantities of regolith to harvest it by heating it at 600 °C. To this would be added the difficulty and the cost of transporting it to Earth.

Aerial drone image of the ITER construction site. Credit: Oak Ridge National Laboratory

Despite the major obstacles, “there may be some chances to use helium-3 as a second-generation fuel,” fusion physicist John Wright of the Massachusetts Institute of Technology tells OpenMind. However, for Wright, vast improvements in fusion technology will still be needed “before we have to worry about mining.”

The main objection to fusion with helium-3 is summed up by Frank Close, a physicist from the University of Oxford. In 2007, Close wrote in the journal Physics World that “deuterium reacts up to 100 times more slowly with helium-3 than it does with tritium,” which would require much higher melting temperatures than in current reactors. In practice, Close pointed out, deuterium would tend to fuse with itself to form tritium, which would then react again with deuterium as in conventional fusion, producing neutrons. In summary, Close labelled the idea of generating electricity from lunar ​​helio-3 as moonshine.

“Helium-3 has no relevance for fusion,” stresses Close to OpenMind; “Nothing has changed in the laws of physics since my 2007 article.” Although the physicist believes it is possible for us to see the development of lunar mining, “there is no point in going to the Moon for helium-3 if your goal is to make fusion.”

New strategies for fusion

However, Close’s objections are based on conventional fusion reactors, such as ITER, an international project under construction in France, which will weigh three times as much as the Eiffel Tower and reach temperatures of 150 million degrees centigrade. A design of the same type for helium fusion would require higher temperatures and even more massive sizes. Therefore, new strategies are needed. “The challenge is managing the amount of tritium that stays in the plasma from those side reactions to minimise deuterium-tritium neutron production,” writes Wright.

And someone has made it possible, although still without a positive energy balance. Gerald Kulcinski, director of the Institute of Fusion Technology at the University of Wisconsin and one of the authors of that pioneering study in 1986, has been developing fusion with helium-3 for decades. “It is correct that the energy required for deuterium-helium-3 fusion is about two to three times higher than for deuterium-tritium,” Kulcinski tells OpenMind.

Gerald Kulcinski has been developing fusion with helium-3 for decades. Credit: University of Wisconsin-Madison

The small reactor developed by the researcher manages to overcome the obstacle, minimising the production of neutrons and reducing their energy. Even more promising, adds Kulcinski, is the helium-3-helium-3 fusion, more complicated but totally neutron-free. “That would be truly a game changer, but I’m not sure I’ll see that in my lifetime,” he concludes. For analyst Thomas Simko of RMIT University in Australia, “helium fusion reactors probably won’t be developed until mid-century at the earliest.”

But even overcoming the stumbling blocks of fusion technology, there would still be that of lunar mining. However, Simko points out that we will probably see the first exploratory steps in the coming years, so that “when helium-3 is needed, it will already be known where it is and how to extract and deliver it.”

First steps for lunar mining

Indeed, it seems that these first steps are already underway. Some national space agencies as well as various private companies have their sights set on lunar mining, to which is added the interest of the emerging powers: the Chinese probe Chang’e 4, perched on the hidden side of the Moon, could include among its targets the preliminary tracking of the presence of helium-3, something that has also been said of the lunar mission Chandrayaan 2 that India will launch in April.

Conceptual design lunar Helium-3 mining. Credit: University of Wisconsin-Madison

For its part, the European Space Agency has signed a contract with several companies in order to study the future exploitation of lunar regolith resources to support an inhabited colony; in this case, helium-3 could be used to power a local reactor, or even as fuel for spacecraft powered by nuclear fusion.

In fact, many experts see this in situ use of resources as a more realistic option. “I don’t think there’s all that much to be gained in mining the Moon and bringing it back to Earth,” planetary geologist Paul Byrne of North Carolina State University tells OpenMind. “I think it’s a much better use of our money, time, and creativity to use lunar resources to support humans living on the Moon, and supporting future robotic and crewed exploration to other parts of the Solar System.” In short, with gold or without it, it seems that lunar fever is showing no signs of abating.

Javier Yanes

@yanes68

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