Microgravity environment provides a new experimental frontier for fundamental physics research. It is very useful not only for exploration of fundamental physics laws but also for educational program in physics study. Preservation of symmetry is one of the most effective merits of microgravity utilization in fundamental physics. The first edition of ``Microgravity Physics Research Scenario'' will be established on the basis of discussions in the Working Group on Microgravity Physics. It is expected that this scenario arouses interest of Japanese researchers and promotes space utilization in the discipline of fundamental physics.
In recent years the accurate diffusion coefficient of the semiconductor melts is indispensable for the optimization of the growth process of the single crystal. The crystal growth simulation requires the accuracy of the diffusion coefficient over 95％. If we perform the diｆｆusion experiment such an accuracy, we need a few hours at high temperature condition. It is difficult to keep liquid samples at such high temperatures on the ground for such a long time without the thermal convection. It is recognized that the diｆｆusion coefficient can be measured in an error of less than 1％ under microgravity. Nevertheless, it is the fact that there are limited opportunities of microgravity experiments. Therefore, it is deeply desired to establish the reliable model of diffusion in the liquid states, by which we can estimate the diffusion coefficient of the melts of semiconductors reliably. As is well known that the liquid is characterized by the particular feature of the short range order. Therefore, it is extremely important for the establishment of model of diffusion to study the structure
of liquids in detail.
Highly pure Si was undercooled by an electromagnetic levitator combined with a laser heating unit. The crystal
growth velocity was measured as a function of undercooling and the appearance of the solid-liquid interface was observed by a high-speed camera. The result was compared with the predicted value based on the dendrite growth theory. The growth behaviors of Si were found to be classiˆed into three categories of disk-like growth, isolated dendrite growth, and closer dendrite growth at low, moderate, and high undercooling values, respectively. The transition undercoolings for the classifications were 100 and 210 K.
The resupply technology of cryogenic liquid propellants under microgravity condition is a key to construct an infrastructure of future space transportation system. This paper presents an overview of Cryogenic Fluid Management (CFM) under microgravity, which is the base of this technology. In addition, some experiments on forced convective boiling of the cryogenic fluid, which was conducted by the author's group, is described. Through this experiments, some points to which we should pay attention for drop experiments, such as pressure limit, flow rate measurement and experimental time limit, are also described. Outline of experimental project, which will be conducted by the author's group, is presented.
Measurement for the liquid volume in a closed volume under micro-gravity condition is one of important space technologies, for example, in order to know how much water or fuel is left in a container. However, it is difficult to measure the liquid volume in such a situation because liquid and gas system are not clearly separated, rather mixed up. In order to establish an effective and low cost measurement technique, a Helmholtz resonance is applied in the present study. We successfully detected the Helmholtz resonance frequency and its higher order harmonics for a closed container system under micro-gravity condition. The detection of the higher harmonics is indispensable to apply this technique to a large-scale container because the Helmholtz resonance frequency becomes low as increasing the volume of container. The accuracy of this measurement technique is also investigated here. We report the results of micro-gravity experiment and discuss the effectiveness of this measurement technique.
Axisymmetric mode oscillations of a magnetic fluid column supported by a magnetic field are examined experimentally in the presence of gravity. A magnetic fluid column, height 9.78 mm, is formed vertically in a magnetic field generated by Helmholtz like coils fastened on an electrodynamic exciter, and vibrated vertically to produce axisymmetric oscillations. Nonlinear jumping phenomena, transition from the (0, 1) mode standing wave to the progressive wave and mode coupling are observed at larger amplitude oscillations. One-half subharmonic oscillations such as the (3, 1), (4, 1) and (5, 1) modes arise beyond some threshold values of the excitation amplitude. These new phenomena are useful to discuss the liquid column oscillations in a microgravity environment in the Floating Zone Technique.
Opposed flame spreading over polyethylene insulated wire in low air flow velocity has been investigated under
microgravity environment. The experiments were performed at Japan Microgravity Center ( JAMIC) 10 s dropshaft. Four samples of different insulation thickness, 0.075, 0.15, 0.3 and 0.5 mm, with the same inner core diameter, 0.5 mm, were used. Experiments were performed with changing O2 concentration, 21-50％, and external air flow velocity, 0 (quiescent)－20 cm/s. The results show that flame shape changes strongly depending on air ｆｌow velocity and oxygen concentration. The flame spread rate is affected by air flow velocity, and the effect is much stronger in high oxygen concentration. According to the results, flame spread phenomenon of wire insulation is classified into four different regimes based on air flow velocity, namely, (1) oxygen supply control regime, (2) geometrical effect regime, (3) thermal regime and (4) chemical kinetic control regime. In low ‰ow velocity region such as ventilation air in spacecraft, maximum flame spread rate appears in between the regime (1) and (2). The regime (2) is the one special for the wire insulation, firstly pointed out in the present paper, where the flame spread rate increases with decrease in external ‰ow velocity under strong wire geometrical effect, i.e. wire thickness and surface curvature.
Oscillatory thermocapillary flow is investigated experimentally in liquid bridges of high Prandtl number fluids. The
effect of heat transfer from the liquid free surface on the onset of oscillations is investigated. The heat transfer is mainly due to conduction as well as the natural convection of air around the liquid bridge. The airflow in the present work is varied by varying the temperatures of the cold wall and the ambient air. It is found that when the free surface is nearly flat, the critical Marangoni number (Macr) varies substantially when the temperature of the cold wall or the ambient air is varied, but when the surface is highly concave, Macr is not affected appreciably. The present work shows that it is important to know the surrounding air condition when one compares various data for the onset of oscillations for liquid bridges with nearly flat free surfaces.
``Microgravity Science Research International Announcement of Opportunity 2000'' (hereinafter ``IAO'') is a solicitation of microgravity researches which plan to use the ``International Space Station'' (hereinafter ``ISS''). The IAO released in September 2000 and the proposal due was in January 2001. 115 proposals including 19 Japanese ones were applied to the IAO and have undergone three step evaluations; science, technical preliminary and program reviews. The authors have been involved in this selection process as the planning and management staffs of the space agencies and have found various issues. This report summarizes the theme selection process of the IAO and points out the issues that they found.
The effect of micorgravity on the growth of colloidal crystals were studied using TR-IA #5 sounding rocket launched in 1996. This was the first flight experiments on colloidal materials in Japanese microgravity programs. Polystyrene latex were carefully deionized using ion-exchange resin. Major difficulties encountered in executing micorgravity experiments were maintaing ionic concentration at very low level during the preparation of flight. The importance of selection of cell materials and suitable operations that realize the expected purity of deionized water is mentioned.
An electro-magnetic levitation furnace for use in parabolic flight was developed, which consists of a furnace chamber, an evacuation pump, two sorts of RF power supplies, and the cooling system. A graphite suscepter was used for semiconducting materials, such as silicon, to be heated so as that the electrical conductivity is enlarged enough for the sample to be levitated only by RF electromagnetic force. The parabolic fright experiment was carried out by using GULFSTREAM-II of Diamond Air Service, where the sample of non-doped silicon was successfully levitated.
In November 1998, the world's first HDTV pictures from space were successfully taken aboard the space shuttle that carried the American hero, Senator John Glenn, and Japanese astronaut, Chiaki Mukai. Various special measures were required to prepare the HDTV camera, with its built-in VCR (HDCAM), for use in the space environment of the shuttle, in order to satisfy all of the safety standards set by NASA. The HDTV pictures taken from the orbit show clear and detailed images of clouds and geographical features of the earth and have been widely acclaimed for their high scientific value. The achievement has expanded the proven possibilities of HDTV as a part of the visual infrastructure of the 21st century space age. We introduce the HDTV images taken from the orbit and also present some technological topics related to this achievement.
Bonner Ball Neutron Detector (BBND) was developed to measure neutron radiation in the international space station (ISS), as a part of the NASA Human Research Facility (HRF) project. It was launched on March 2001 and has been operating normally on orbit. The BBND is composed of detector unit, control unit and hard drives. The measurement data is stored in the hard drive and is transmitted to ground via HRF workstation. This experiment will be continued for up to 8 months. The BBND is the first Japanese experiment hardware for the ISS.