Sentinel Exclusive: NASA wants to send astronauts beyond the moon

Lab experiments suggest that future fusion reactors could use helium-3 gathered from the moon.
By Mark Williams

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Even more surprising is that one reason for much of the interest appears to be plans to mine helium-3--purportedly an ideal fuel for fusion reactors but almost unavailable on Earth--from the moon's surface. NASA's Vision for Space Exploration has U.S. astronauts scheduled to be back on the moon in 2020 and permanently staffing a base there by 2024. While the U.S. space agency has neither announced nor denied any desire to mine helium-3, it has nevertheless placed advocates of mining He3 in influential positions. For its part, Russia claims that the aim of any lunar program of its own--for what it's worth, the rocket corporation Energia recently started blustering, Soviet-style, that it will build a permanent moon base by 2015-2020--will be extracting He3.

That 1 million metric tonnes of He3, reacted with deuterium, would generate about 20,000 terrawatt-years of thermal energy. The units alone are awesome: a terrawatt-year is one trillion (10 to 12th power) watt-years. To put this into perspective, one 100-watt light bulb will use 100 watt-years of energy in one year.

That's about 10 times the energy we could get from mining all the fossil fuels on Earth, without the smog and acid rain. If we torched all our uranium in liquid metal fast breeder reactors, we could generate about half this much energy, and have some interesting times storing the waste.

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About 25 tonnes of He3 would power the United States for 1 year at our current rate of energy consumption. To put it in perspective: that's about the weight of a fully loaded railroad box car, or a maximum Space Shuttle payload.

To assign an economic value, suppose we assume He3 would replace the fuels the United States currently buys to generate electricity. We still have all those power generating plants and distribution network, so we can't use how much we pay for electricity. As a replacement for that fuel, that 25-tonne load of He3 would worth on the order of $75 billion today, or $3 billion per tonne.

2. SECOND GENERATION: While useful for studying fusion, reactors operating with deuterium-tritium fuel are impractical for commercial use. Among other things, the reaction produces large amounts of radiation in the form of neutrons. Substituting helium-3 for tritium significantly reduces neutron production, making it safe to locate fusion plants nearer to where power is needed the most, large cities. This summer, researchers at the University of Wisconsin Fusion Technology Institute in Madison reported having successfully initiated and maintained a fusion reaction using deuterium and helium-3 fuel.

3. THIRD GENERATION: First-generation fusion reactors were never intended to produce power. And, even if they are perfected, they would still produce electricity in much the same way as it is created today. That is, the reactors would function as heat sources. Steam would then be used to spin a massive generator, just as in a coal- or oil-fired plant. Perhaps the most promising idea is to fuel a third-generation reactor solely with helium-3, which can directly yield an electric current--no generator required. As much as 70 percent of the energy in the fuels could be captured and put directly to work.--Stefano Coledan

Nestled among the agency's 200-point mission goals is a proposal to mine the moon for fuel used in fusion reactors -- futuristic power plants that have been demonstrated in proof-of-concept but are likely decades away from commercial deployment.
Helium-3 is considered a safe, environmentally friendly fuel candidate for these generators, and while it is scarce on Earth it is plentiful on the moon.
As a result, scientists have begun to consider the practicality of mining lunar Helium-3 as a replacement for fossil fuels.