Space-environment utilizing science describes research that uses microgravity, vacuum, solar energy, cosmic rays, etc., inherent in the space environment to solve a variety of scientific issues. In the past, microgravity has been most utilized in this discipline. In a microgravity environment, thermal convection and flotation, sedimentation and convection, which are caused by differences in specific gravity, are greatly suppressed as compared with those on the ground. Benefiting from these features, a number of experiments have been conducted around the world in an attempt to produce homogeneous crystals or alloys that are difficult to produce on the ground. In fact, however, materials with excellent homogeneity as many scientists expected have not been obtained. Studies on the mechanisms causing inhomogeneity clarified that microgravity of at least 2-3 x 10-5g, ideally 10-6g, was required to produce the expected materials. The International Space Station (ISS) now under construction offers one way to realize this level of microgravity easily for long duration. The Japanese Experiment Module “KIBO” on the ISS is planned to be available from 2007. Japan will finally obtain an ideal microgravity environment, which has been long awaited by the science community utilizing the space environment.
Research activities in the fundamental science field
In the past, space experiments have mainly targeted research in materials science and life science fields. Naturally, these sciences will make up most of the experimental themes using “KIBO”. In addition, research in the fundamental science field is increasing lately. The technologies and research related to these three fields are collectively called “space-environment utilizing science.”
The Institute of Space and Astronautical Science (ISAS) of JAXA is responsible for leading space-environment utilizing science in Japan. To this end, the Steering Committee on Space Utilization, an advisory organization to the Executive Director of ISAS, was founded when the three space-related organizations were merged into JAXA in October 2003. Representatives from the science community engaged in space-environment utilizing science joined the committee. The 60 research Working Groups (WG) were selected by the committee in FY2005. Each WG is implementing its research to plan future space experiments. There are 22 WGs for the materials-science field and six for the fundamental-science field. The WG themes for the fundamental-science field as of FY2005 are as follows:
Dusty plasmas refer to a system where fine particles are mixed in plasma. Interplanetary dust, planetary rings and the tails of comets were presumed to be the system. This hypothesis launched research on dusty plasmas. In 1986, Ikezi predicted that the particles could form a regular structure called Coulomb crystal. In 1994, several research laboratories succeeded in forming Coulomb crystals independently but almost simultaneously. What the WG is targeting is this dusty plasmas that involves Coulomb crystal formation.
Since the Coulomb crystal predicted by Ikezi was a crystal formed by repulsive interaction, many researchers believe that the particles must be confined, by using external electrodes for example, in order to form the Coulomb crystals. Some researchers think that attractive interaction also exists in the Coulomb crystal formation. In this context, JAXA has started dusty plasma research to clarify the mechanism of Coulomb crystal formation. We first introduced a theoretical model and investigated the energy change of the whole system against the change of distance between particles. From this model, we found that the energy of the system decreases in specific distances between particles under a certain condition. The energy decrease indicates that there is a possibility that a regular structure may be self-organized.