Helium (4He) is the second most abundant element in the known Universe (after hydrogen) but only makes up 5.2 parts per million (ppm) of the Earth’s atmosphere. Helium-3 (3He) is an isotope of helium with two protons and one neutron. It is not radioactive and very rare on Earth (7 parts per trillion) but exists in recoverable concentrations in the lunar topsoil (in the top 2 -3 m of lunar regolith). It is even more abundant on the gas giants Jupiter, Saturn, Uranus and Neptune.
Lunar soil sample #75501 brought back by Apollo 17 in 1972 revealed the presence of He-3 and since then every country planning moon missions has the vision of mining for 3He on the moon and of vast quantities of energy production by means of a aneutronic fusion process on earth. (For old fogies like me, 1972 was the year of Watergate!)
In fusion reactions neutrons are “nasty”. They are very hard to contain and make other materials radioactive on collision. The first generation fuels of Deuterium and Tritium (reactions 1 and 2 below) produce many neutrons. A second generation with Deuterium and 3He only produces a few. A 3He – 3He reaction would produce none.
Kulcinski: Fusion Energy could provide that new energy source in the middle of the 21st Century. ….. However, …… the DT Tokamak does not appear to be the ultimate answer. The problem lies in both the DT fuel cycle, which emits 80% of its energy in highly damaging and radioisotope producing neutrons, and in the complex design of the Tokamak.
fusion reactions after Kulcinski
But the promise of having 3He available to produce power is immense.
The moon contains 1 – 2 million tonnes of 3He in its topsoil. Using the D-3He reaction, and assuming a conversion efficiency of 60%, one tonne of 3He would generate about 100 TWh of electrical power. The world today consumes about 20,000 TWh per year of electricity. The entire electricity needs of the world could be satisfied by 200 tonnes of 3He per year. If just 10% of the reserves on the moon were recoverable that would still be 100,000 – 200,000 tonnes and sufficient for satisfying 500 – 1000 years of the world’s current electricity consumption. A space shuttle could probably transport around 20 – 30 tonnes of cargo per flight. The logistics do not seem to be beyond the bounds of feasibility.
The production cost of electricity today (large coal fired or nuclear) is around 5 – 6 US¢/kWh. A cargo of – say – 20 tonnes of 3He could thus generate 2,000 TWh which would be worth $120 billion. Assuming that no more than about 25% of the electricity price could be allocated to the fuel cost, $30 billion could be available for the infrastructure and operating cost to mine and transport one shuttle-load of 3He from the moon to the earth every year. Most would be needed for amortising the investment cost of the infrastructure (moon station, mining rovers, soil processing, earth side station ….). One mining rover could perhaps produce 50 – 100 kg of 3He per year. To make up a shuttle load some 200, unmanned, mining rovers could be required. For the sake of argument take this infrastructure amortisation to be as much as 80% of the allowable $30 billion. That would still leave $6 billion available for the operating cost of each shuttle flight. This is speculative but even the economics are not beyond the bounds of do-ability.
Terrestrial fusion research has concentrated on the first two reactions (1st generation) above, both of which produce neutrons. The second generation reaction using Deuterium and 3He does not itself generate neutrons but inevitable D-D reactions will also take place and produce some neutrons. The 3rd generation 3He – 3He reaction produces no neutrons (aneutronic reaction).
fusion power features after Kulcinski
The fusion process is not yet developed and a road map for getting to a working fusion power station has yet to be fully detailed. But in the meantime, a race to establishing mining operations on the moon is beginning. Some “test” mining could well start within 2 decades.
So it might be a little too early to invest in 3He mining on the moon and expect a return in your own lifetime but it might be worthwhile in the name of your grandchildren!
United States: MIT Technology Review
Furthermore, in today’s moon race, unlike the one that took place between the United States and the U.S.S.R. in the 1960s, a full roster of 21st-century global powers, including China and India, are competing.
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.
China: China is devoting considerable resources to the most futuristic and elusive of unconventional energies: nuclear fusion. ……
Helium-3 is a helium isotope that is light and non-radioactive. Nuclear fusion reactors using helium-3 could provide a highly efficient form of nuclear power with virtually no waste and negligible radiation. In the words of Matthew Genge, lecturer at the Faculty of Engineering at the Imperial College in London, “nuclear fusion using helium-3 would be cleaner, as it does not produce any spare neutrons. It should produce vastly more energy than fission reactions without the problem of excessive amounts of radioactive waste.” Unfortunately, helium-3 is almost non-existent on earth.
It does, however, exist on the moon. Lacking an atmosphere, the moon has been bombarded for billions of years by solar winds carrying helium-3. As a result, the dust of the lunar surface is saturated with the gas. It has been calculated that there are about 1,100,000 metric tons of helium-3 on the lunar surface down to a depth of a few meters, and that about 40 tons of helium-3 – enough to fill the cargo bays of two space shuttles –could power the U.S. for a year at the current rate of energy consumption. Given the estimated potential energy of a ton of helium-3 (the equivalent of about 50 million barrels of crude oil), helium-3 fuelled fusion could significantly decrease the world’s dependence on fossil fuels, and increase mankind’s productivity by orders of magnitude.
However, supplying the planet with fusion power for centuries requires that we first return to the moon. At present, only China has this in mind, with its Chang’e program, a lunar exploration program that will send astronauts to the moon by the early 2020s. If Beijing wins the second “race for the moon,” and establishes a sustained human outpost conducting helium-3 mining operations, it would establish the same kind of monopoly that in the past created the fortunes of ventures like the East India Company. The ramifications would be significant, to say the least.
China Daily: Helium-3, an isotope of the element Helium, is an ideal fuel for nuclear fusion power, the next generation of nuclear power. Nuclear fusion creates four times as much energy as nuclear fission, the current form of commercialized nuclear power. Nuclear fusion does not produce environmental problems like radioactive nuclear waste.
“Currently nuclear fusion technology is not mature, but once it is commercialized, fuel supply will become a problem,” Ouyang added. It is estimated that reserves of Helium-3 across the Earth amount to just 15 tons, while 100 tons of Helium-3 will be needed each year if nuclear fusion technology is applied to meet global energy demands. The moon on the other hand has reserves estimated at between 1 to 5 million tons.
“Each year three space shuttle missions could bring enough fuel for all human beings across the world,” said Ouyang.
The Indian Space Research Organization’s first lunar probe called Chandrayaan-I, launched on October 22, 2008, was reported to be mapping the Moon’s surface for 3He-containing minerals:
Indian space scientists expect to map the lunar surface for the helium-3 (He-3) mineral to fuel nuclear power plants and frozen water as they make final preparations for India’s mission to the moon, expected to blast off next month. ……
“Probably 10 years from now fusion reactors which can use He-3 will be available. Our second mission to the moon, Chandrayaan-II, will also have a lunar lander and help us collect samples of the mineral. The government has given clearance for Chandrayaan-II and we will start the mission as soon as Chandrayaan-I is completed,” Chandrayaan project chief Mylswamy Annadurai said. Programme director (satellite navigation) Surendra Pal said a couple of tonnes of He-3 would be enough to meet the energy needs of the world.
“In the next 40 years, it will be possible to transport it to the earth,” he said. Besides He-3, India’s first moon mission will also search for important minerals like titanium, uranium- 238 and possibility water. “Chandrayaan will look for large craters which have never been exposed to sun light. They are potential sites for frozen water, which is great subject of interest for humans,” the head of ISRO’s astronomy and instrumentation division Sree Kumar said.
Russian space technology companies are also interested
Scientists believe the moon’s rich resources of helium-3 could be used in futuristic fusion reactors on Earth that would generate electricity without producing nuclear waste. Such fusion technology could also power rockets for deep space travel in the future.
There is so little helium-3 on Earth that the technology hasn’t been studied much. The moon appears to have it in abundance because it lacks the atmosphere and magnetic field that keep helium-3 from raining down on our planet from outer space.
Now private commercial interests are looking at mining operations on the moon and it is those who reach the moon first and establish operations there (and this is likely to happen within 20 years), who will dictate how the surface of the moon gets divided up.
Lunar soil in a hard vacuum will be much harder to “mine” than on Earth. The mining equipment would pose formidable engineering challenges. Harnessing the solar energy to process the minerals and extract 3He will need to be ingenious. Whether to transport the 3He as a liquid or a compressed gas will affect the design of the moon station and of the transport vehicle. But while getting there and starting the mining and recovery of 3He and transporting it back to the earth now looks doable that may not be the real barrier. The 3He has to be used on Earth to generate energy and that process is not ready yet. So far, controlled nuclear fusion is yet to be achieved. Thermo-nuclear warheads have been successfully tested but that is -by definition – an uncontrolled, singular event with a limited amount of fuel. To go from that to a continuous, controlled process with a regular supply of fuel and a continuous evacuation of electrical energy is easier said than done. Bringing back 3He from the moon may be easy in comparison.
Appendix: He-3 availability and recovery
Helium (4He) is the second most abundant element in the known Universe (after hydrogen) but only makes up 5.2 parts per million (ppm) of the Earth’s atmosphere. He-4 is not radioactive and most helium on Earth is a result of radioactive decay mainly from tritium. For every million parts of 4He there is only 1.4 parts of 3He (a concentration of 7 parts per trillion of the Earth’s atmosphere). In the Earth’s mantle up to 200 parts per million of 4He can be 3He.
Production: Current US industrial consumption of helium-3 is approximately 60,000 liters (approximately 8 kg) per year; cost at auction has typically been approximately $100/liter although increasing demand has raised prices to as much as $2,000/liter in recent years. Helium-3 is naturally present in small quantities due to radioactive decay, but virtually all helium-3 used in industry is manufactured. Helium-3 is a product of tritium decay, and tritium can be produced through neutron bombardment of deuterium, lithium, boron, or nitrogen targets. Production of tritium in significant quantities requires the high neutron flux of a nuclear reactor; breeding tritium with lithium-6 consumes the neutron, while breeding with lithium-7 produces a low energy neutron as a replacement for the consumed fast neutron.
The Apollo 17 sample analysis and now confirmed by other samples indicates that the surface top-soil on the moon could contain around 20 – 30 ppm of 4He but with much higher ratios of 3He/4He than on Earth. This gives 3He concentrations of between 1 and 20 parts per billion in sunlit areas (the highlands) and upto 50 ppb in permanently shady areas (lunar seas). A large part (perhaps 50%) of the 3He could be in the 20% of the lunar surface covered by the seas (mare). However the highlands can have a greater depth of regolith (5 m). There is therefore an estimated 1.1 – 2.0 million tonnes of 3He contained in the top 3 m of lunar soil.
Extracting 3He from large quantities of lunar soil is more of an exercise in logistics and engineering and does not need any great theoretical breakthroughs (even if the technology required would place some unique and formidable challenges). Heating lunar soil to about 600ºC would be sufficient to release all the volatiles including all the Helium. There is sufficient solar energy available on the moon to achieve such heating (though some some rather large parabolic mirrors would be needed).
HARVESTING HELIUM-3 FROM THE MOON
The researchers introduced the idea of an automated mobile lunar machine that would excavate the regolith to a depth of 3 meters. It would collect the excavated regolith and separate particles 50 micrometers in size electrostatically because these particles contain the highest helium content. The remaining soil is dumped back on the lunar surface. These particles would be heated to 600-700 degrees Celsius to boil off the trapped gases, which are collected and compressed into cylinders. The cooled particles are also dumped back on the surface. The heat required to heat the particles is sourced from the sun using ‘solar disks’ about 110 meters in size, which concentrate the heat in an oven.
The collected and compressed gases are sent from the mobile miner to a condensing station by automated ground service vehicles. The gases, consisting of hydrogen, nitrogen, oxygen, carbon dioxide and helium, are cooled to about 55 degrees Kelvin in radiators and collected in liquid form. The helium is further cooled in a ‘cryogenerator’ to about 1.5 degrees Kelvin to separate the He-3 isotope from the He-4 isotope. This condensation would allow the He-3 to be extracted as it drains off separately. Also, the ‘waste’ products of this condensation, like oxygen, nitrogen, water, methane and hydrogen, are crucial for life support purposes on the lunar base that would exist.
A possible design for a rover to extract helium-3 from the lunar soil. The robot would capture sunlight, reflected from a gathering dish, to bake the soil. image UWisconsin
……. Keeping the soil properties in mind, a mining method needs to be developed that minimizes friction. Some mining techniques investigated by the Bureau of Mines are using gaseous lubricants, blasting techniques designed for lunar surfaces and using electrothermal (lasers) techniques to break rock. A combination of these techniques would be the ideal approach to lunar soil mining. …..
There are two options for transport: to liquefy He-3 and carry it in liquid form or to transport it as a gas.The first is advantageous in terms of volume and hence the size of the boosters; however, the higher costs of liquefying and the complexity of the spacecraft needed to maintain the products in liquid form will most certainly offset the higher cost of bigger equipment for transporting it as a gas.
Tags: Fusion, Helium-3, lunar mining
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