## 2 Moon Raw Material Surveying Strategy
### Helium-3 Inventory  
Another very valuable raw material found on the Moon is the helium-3 isotope. It is called the fuel of the future because it will be used in future generations of fusion power plants using aneutronic reactions, i.e., reactions that do not generate neutrons that destroy reactor shields and cause the formation of secondary radioactive elements as would be the case when using tritium. Thermonuclear reactors built to operate on the basis of \({}^{3}\)He fuel will be small, compact, ecological, highly effective, and highly competitive with classic nuclear energy. A detailed discussion on the advantages of D + \({}^{3}\)He fuel over D + T fuel can be found in the publication [21]. Helium-3 also has other important applications, e.g., cryogenics, quantum computers, and the detection of fissile materials through its use in neutron detectors. Unfortunately, on Earth, the helium-3 isotope is extremely rare and extremely valuable. It occurs in much larger quantities on the Moon. \(\alpha\) particles, i.e., the nuclei of the helium atom, are a component of the solar wind with the \({}^{4}\)He/\({}^{3}\)He isotope ratio of 2500:1. The Earth's magnetic field protects it from the influence of the solar wind. In the case of the Moon, for billions of years it has been deprived of a strong magnetic field that would protect it from the effects of the solar wind, and only has residual local magnetic fields. The Moon also has no atmosphere. As a result, solar wind particles reach the lunar ground and can be intercepted by it. For billions of years, the solar wind carried helium atoms, creating a huge inventory of helium (including helium-3) on the Moon. The resources of helium-3 on the Moon [22; 23] were estimated at 6.50 \(\times\) 10\({}^{8}\) kg. This is a resource that can be classified as renewable because the solar wind constantly deposits nuclei of helium atoms (including the helium-3 isotope). However, the given estimates of the resources of helium-3 on the Moon [22; 23], it may be underestimated, because scientists currently believe that the Moon may have lost its magnetic field earlier than expected in previous analyses, and therefore the period of helium accumulation (including helium-3) on the moon could have lasted longer. The average [24] concentration of \({}^{3}\)He in the lunar regolith does not exceed 20 ppb. This means that with a \({}^{3}\)He concentration of 20 ppb, 150 tons of regolith would have to be processed to obtain 1 g of \({}^{3}\)He. Scientists believe that there may be areas of higher concentration of Helium-3 on the Moon. The results [25; 26] of the Change-1 probe indicate that there may be regions with \({}^{3}\)He concentrations of 80 ppb/m\({}^{2}\) or higher on the Moon most of all in lunar maria. When looking for high concentrations of helium-3, attention should be paid to the presence of titanium and iron, and specifically the mineral ilmenite (FeTiO\({}_{3}\)). Ilmenite can store up to 10 to 100 times more helium than other minerals in the regolith. Helium atoms are dissolved in the ilmenite crystal lattice, the structure of which allows helium atoms to penetrate and store in it. However, to extract helium (including helium-3) from ilmenite, it is necessary to heat it. In work [22], tests were carried out on the thermal release of helium from ilmenite. The optimal heating temperature for helium-3 was found to be around 1000 K, giving a cumulative release rate of 74% [27]. For an optimal heating temperature of 1000 K, the heat release time of helium-3 is approximately 1 s. At lower temperatures, helium-3 is also released from ilmenite, but the process is less efficient, mainly helium-3 is released from the shallower layers and the amount of helium-3 released is smaller. This means that obtaining helium-3 from ilmenite using thermal methods will be energetically expensive. Therefore, the discovery [28] made by the Chinese Chang E-5 probe that in the glassy surface layer of ilmenite helium is stored in gas bubbles is extremely important.