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Crystal Growth Experiment in Space
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ii) Elucidation of crystallization mechanism

Process where crystals emerge from liquid or gas is separated into the “nucleationEfrom the environment phase that is the first stage of crystallization and the “crystal growthEwhere nucleus becomes big. In the past, research focus was on the crystal growth. Since phenomenon of nucleation is difficult to be measured, it is an important research subject in materials science. Recently the microgravity experiment on nucleation was conducted using ISAS’s sounding rocket (Fig. 3). This experiment was intended to reveal crystal creation of cosmic dusts and carbonate. Using the microgravity environment lasting several minutes produced by ballistic flight of the sounding rocket, we observed and measured the aspect of the nucleation to understand its physics. We also obtained the basic data towards the long-duration and repeated experiments to be conducted in Kibo and so on.

Figure 3
Figure 3. Nucleation experiment under microgravity


Elucidation of the complex process of crystal growth, which has not been studied in space experiment so far, can be a new theme. Many complex processes are observed in material creation process in nature. For example, in mineral formation process, not only temperature and pressure but also chemical reaction is involved. It is not rare that multiple constituents with largely different molecular weights take part in crystallization in living organism. Specific research targets in this regard include the repetition of mineral formation involving complex chemical reactions and biomineralogy.

iii) Reproduction of crystallization in outer space

Discussion on the origin and evolution of the solar system has been made based on observation results and analysis of incoming meteorites in the past. Various researches are performed for chondrules of spherical particle seen in many meteorites since they are likely to have much information about the formation era of the solar system. In the past, it was believed that the formation of chondrules takes several thousands to several tens of thousands years. On the other hand, some researchers advocate that chondrules are formed from dusts in the time scale of second or less. This theory suggests that they are produced by heating and melting of the cosmic dusts caused by shock waves and the subsequent process of supercooling coagulation.

At present, advancements are seen in space science and space engineering fields, specifically such as sample return mission by asteroid exploration project represented by HAYABUSA. Along with the progress, a series of the research containing the reproduction of cosmic dust generation and chondrule formation, analysis of samples returned by exploration projects, and comparison with theoretical computation results will become possible by collaboration of the multiple disciplines such as the space environment utilization science and shock energy engineering. One idea of the space experiment themes in this approach is “reproduction experimentEby combination of levitation, supercooling coagulation, and in-situ observation. It may be also possible to conduct the reproduction experiment of cosmic dust using vast outer space outside the ISS.

Conclusion

Following the guide to the space experiment performed mainly by space agencies and emergence of new themes, we are now in the stage where researchers and engineers take initiative to perform space experiments. Needless to say, it is important to assure continuous researches in the future and accumulate the results. Some readers may expect that outcomes of the space experiment performed in orbit contribute directly to our daily lives. Such contribution may be achieved in the long term perspective. But if we expect quick return, it may end with disappointment. Rather, the most important thing is that we steadily pave the way of new disciplines using the specialty provided by the space environment. This approach must be the shortest way to contributing to a wide range of science and industry. Space environment utilization science must open new possibilities for humankind.

(Yuko INATOMI)

Refernces:

Websites introducing ISS experiment
http://iss.jaxa.jp/en/iss/index.html
http://iss.jaxa.jp/en/kibo/

ISAS News
December 2008 issue , May 2009 issue , December 2011 issue , October 2012 issue


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