讲座题目：Modeling of lunar Helium-3 distribution with remote sensing data from Chang’E-1

主讲人: 曾镜涛教授

时  间: 2008.04.02, 16:00-17:00

地  点: E307

摘  要: Sometime around 2050, due to shortage of fossil fuels and their green house effects, human society has to make the transition to other energy sources. Nuclear energy can provide a temporary solution but short of a permanent one because of the limited supply of fissible uranium and the proliferation problem that comes with it. Other forms of alternative energy like solar, wind or biofuels are either too expensive or diffuse in power density that they can only play a supplementary role. The only viable energy source that can assume a dominant role is nuclear fusion, if current international R&D effort in fusion technology is carried out as planned and achieving its goal successfully.[Ref1]

　

Of all fusion fuels that are technologically feasible in the near future, helium-3 is regarded as ideal judging from its high power conversion efficiency, low radioactivity, and its benign proliferation impact. However, terrestrial supply of helium-3 is extremely limited, because it rarely occurs in nature and is produced only as the decayed product of tritium. By one estimate, in year 2000 the total reserve of helium-3 on earth is just about 500 kg. [Ref.2]

 Significant amount of lunar helium-3 is well documented in literature. Helium-3 concentration from Apollo and USSR lunar soil samples are verified by scientific studies. Existing analyses published indicate that there are at least 1,000,000 tons of helium-3 imbedded on the lunar surface. This amount of lunar helium-3 is significant because it is estimated that fusion energy released from 30 tons of helium-3 is enough to satisfy the electric power consumed by USA for a year. There is roughly 10 times more energy contained in the lunar helium-3 than in all the economically recoverable fossil fuels on the Earth. Even at a cost of 1 billion US dollar per ton of helium-3, in terms of energy it is equivalent to oil at US$7 per barrel. No wonder some fusion enthusiasts regarded the noon as the “Persian Gulf” of energy in the 21 Century.[Ref.2]

　

The helium-3 on the lunar surface has its origin from the solar wind. Irradiation of the lunar regolith (the layer of loose, heterogeneous material formed over the last 4.6 billion years by the impact of large and small meteoroids breaking down surface rocks on the moon surface) by the solar wind results in up to 20 ppb (by weight) helium-3 concentration in some lunar soils. The abundance of helium-3 at any location in the lunar regolith depends on the surface maturity (exposure age), the relative amount of solar wind fluence and soil chemistry, in particular the titanium content, because ilmenite (FeTiO3) retain helium-3 much better than other major lunar minerals. [Ref. 3, 4]

　

For the Appolo samples it has been shown [Ref.5,6] that helium3 content is correlated to the product of titanium content and soil maturity. Recent investigations used the Clementine UV/Vis multispectral data to derive the lunar surface optical maturity. Lunar distribution of titanium (TiO2) is derived from Clementine UV data by Lucey et al. [Ref.7] as well. Due to the absence of a measurable lunar magnetic field, solar wind fluence model have been developed just taking into account of the effect of the Earth’s magnetosphere along the lunar orbit by a number of authors [Ref.3,4,8].

　

These three pieces of data/model are first combined together by Johnson et al. [3] to arrive at an estimate of the lunar helium-3 abundance. They concluded that the highest helium-3 concentration tend to occur in the lunar farside maria and the higher TiO2 mare regions on the lunar nearside, ranging from 7 to 17 ppb. It was also found that maturity has less influence on the helium-3 estimates than titanium content and solar wind fluence.

　

The Instruments on Chang’E-1, China's first Lunar satellite, are aimed at collecting data to confirm these model calculations, so that we can have a better estimate of the lunar helium-3 reserve. More detail of the data collected by Chang’E-1 will be discussed.

　

参考文献:

1. J. F. Santarius, “Luna helium-3 and Fusion Power”, presented in IEEE Sectional Meeting 2004.

2. J. F. Santarius, G.L. Kulcinski, G.H. Miley, “A Strategy for D-Helium3 Fusion development”, UWFDM-1291, Fusion technology Institute, University of Wisconsin, presented at the ANS Annual Meeting, June 2006.

3. J. R. Johnson, T.D. Swindle, P.G. Lucey, “Estimated solar wind-implanted helium-3 distribution on the Moon”, Geophys. Res. Lett. 26, 385-388 (1999).

4. Wenzhe Fa and Ya-Qiu Jin, “Quantitative estimation of helium-3 spatial distribution in the lunar regolith layer”, Icarus, Volume 190, Issue 1, September 2007, Pages 15-23.

5. J.L. Jordan, “Prediction of the He3 distribution at the lunar surface”, in Space Mining and Manufacturing, annual Invitational Symposium, p.64-65, NASA Space Engineering Research Center for the Utilization of Local Planetary Resources, Univ. of Arizona, Tucson, 1989.

6. L.A. Taylor, “Helium-3 on the Moon: Model Assumptions and Abundances”, in Engineering, Construction and Operations in Space IV, Proc. Space ’94, Albuquerque,