To obtain the detailed heat transfer data and the data concerning directly to the heat transfer mechanisms, i.e. the liquid film thickness underneath attached bubbles, a structure of transparent heating surface was investigated for the TR-IA No. 5 rocket experiment conducted in September, 1996. The sequence of various combinations of system pressure and supplied heat flux level was developed to ensure the boiling initiation, the establishment of experimental conditions for succeeding subdivided phases and the removal of accumulated bubbles. Based on the experimental results and analysis, the summary and comments about the experimental hardware, the sequence of system parameters varied, the structure of coalesced bubble are presented as the first report for the purpose of the improvement of further studies in the same research field.
The self-diffusion coefficient of liquid germanium, which shows semiconductor properties in the solid crystalline state, was measured by the long capillary method under microgravity due to the launch of the fifth TR-IA rocket. The obtained self-diffusion coefficients are smaller than the previous data on the ground. Only in the low temperature range, a good agreement was obtained between experimental values and calculated ones based on the hard sphere model with low packing fractions. The experimental values were compared also with previous MD simulations. The chaotic circumstance, that is various predicted values of self-diffusion coefficient in the wide range, indicates that studies must be performed further and further with the particular relation to liquid structures.
In order to clarify the solidification mechanisms of Al-Ti and Al-Ti-B system alloys under microgravity conditions, experiments were performed using Sounding Rocket TR-lA No. 6. Different compositions of six samples were melted and solidified in the two isothermal furnaces on board the rocket. In the higher temperature furnace (1400°C), observation of the peritectic composition of Al-1.3%Ti alloy revealed that the primary TiAl3 crystals distributed in the melt act as nucleation sites and then form granular crystals. A study of the hypoperitectic alloy revealed that the TiAl3 and TiB2 crystals in the Al-Ti and Al-Ti-B master alloys melted completely then large crystals formed. In the lower temperature furnace (800°C), TiAl3 and TiB2 crystals in the master alloy remained and nucleated the granular crystals as if a peritectic reaction had occurred.
Marangoni convection in a silicon melt was investigated from viewpoint of a heat and mass transfer for a low Prandtl number liquid. Temperature measurement and flow visualization in a half-zone bridge of molten silicon were carried out in a microgravity condition using the NASDA TR-IA-6 rocket. Fourier-transformation analysis of temperature fluctuations showed several peak frequencies for the microgravity condition when a Marangoni number Ma was 1900. On the other hand, a single peak was seen when Ma= 1315 in the 1-G reference experiment. It suggests that the transition from non-periodic to periodic flow of the silicon Marangoni convection in a half-zone liquid bridge system exists between these conditions. With using the x-ray radiography, tracer motions in the azimuthal directions were observed near the molten silicon surface. This observation indicated that the tracer motions were driven by the temperature fluctuations in the azimuthal direction.
In order to determine accurately the diffusion coefficient of silver ion in the eutectic LiCl KCl melt, a chronopotentiometry has been done under microgravity so as to avoid the natur al convection. The experiment was done as a part of MSL-1 mission. The relative importance of the sources of errors have been evaluated to elucidate the accuracy of the measurements, and the accurate diffusion coefficccients of silver ion in the eutectic LiCl-KCl melt have been derived over the temperature range of 640 and 860 K. By the use of the microgravity, the disturbance due to natural convection has been well suppressed and diffusion coefficients have been determined with the accuracy of 9.6%. Temperature dependence of the diffusion coefficient of silver ion was correlated by the Arrhenius type equation and compared with the results of 10 experiment as follows:
D/ (m2s- 1 )= 2.794x 10- 1 exp (-28899/(RT)) for µG,
D/ (m2s- 1)= 6.91 x 10- 8 exp (-20402/(RT)) for 1 G,
where T is in Kand R is the gas constant, 8.3145 J K- 1•
Shear cell technology for high precise diffusion coefficient measurements was developed by using microgravity condition in MSL- 1. Two diffusion experiments with Sn and PbSnTe specimens were done in the mission. Excellent concentration profile was obtained in self-diffusion experiments of Sn by the shear cell technology developed for these experiments, whereas the PbSnTe experiment results were scattered. The reason for the scattering was ascribed to the facts that steeper temperature gradient was formed in the cartridge under microgravity compared to that on ground. This steeper thermal gradient would enhance the transpiration of the vapor from the center to outer of the cartridge. Temperature dependence of diffusion in Sn was obtained with the data by Frohberg. The dependence was a little different from that obtained by Frohberg.
An experimental study of combustion behavior of polyethylene insulated wires in quiescent atmosphere has been performed in microgravity to obtain fundamental data of burning characteristics of wire insulation for fire safety in space. Four samples with different insulation thickness, 0.075-0.5 mm, and the same wire diameter, 0.5 mm, were investigated. The effects of ambient oxygen concentration, wire initial temperature, insulation thickness, and type of diluents, including He, Ar, N2, and CO2, were examined in the microgravity experiments. The results show that flame configuration and flame spread rate in microgravity change strongly depending on ambient oxygen concentration . It was indicated that flame spread rate decreases with increase in insulation thickness. In addition, decrease rate of flame spread rates as a function of wire insulation thickness appears to be smaller with larger insulation thickness. Flame goes out at highest oxygen concentration with He diluted
atmosphere among the four dilution gases under microgravity. Also, it was observed that CO2 diluted atmosphere increases flammability of polyethylene insulated wires in microgravity compared with normal gravity.
Natural convection effect on transient short-hot-wire method is studied experimentally, by comparing the wire temperature variations obtained for various liquids under normal gravity with those under microgravity conditions. The critical time corresponding to the onset of natural convection effect is determined and non-dimensionalized as the critical Fourier number Foe. A correlation equation for Foe is proposed as functions of Rayleigh number Ra and aspect ratio L. The equation is found to agree well with the previous results obtained for the cases of large aspect ratio. It can be used generally to estimate the critical times for various cases of transient hot-wire method which is widely used to measure the thermal conductivity and thermal diffusivity of fluids.
Large grain bulk RE-Ba-Cu--0 (RE: rare earth elements) superconductors can be used for various applications such as magnetic bearing, load transport and field trapping magnet. The magnetic field generated by bulk RE-Ba-Cu-O is proportional to its radius, however, it is very difficult to grow a large grain bulk on the ground due to the contamination from the substrate or the crucible. Such a problem can be solved by growing large RE-Ba-Cu--0 in microgravity environment, in which the bulk can be supported by a seed crystal alone during the crystal growth. Such experiments will be conducted in the USERS (Unmanned Space Experiment Recovery system) project. In this paper, the experiment plan and the present status of the system development will be reported.
In order to conduct the advanced mobile satellite communication/broadcasting experiments, the ETS-VIII will be launched in 2002. In these experiments, the 13 m aperture cable-mesh/truss antenna reflectors are employed for transmission and receiving antennas. To construct such an antenna, we have developed modular mesh deployment antenna. Fourteen 4.8 m modules would construct a 19.2 m X 16.7 m (13 m aperture) antenna reflector. Deployment tests and surface measurements for one of the 14 modules were performed using Airbus A300. The antenna reflector module successfully deployed and the analytical model was precisely correlated to resultant deployment characteristics. Surface shape in micro-gravity environment was also measured and the accuracy of a shape forming process on ground was evaluated.
Levitation experiments were carried out in microgravity condition during parabolic flights were carried out using a newly developed electromagnetic levitation furnace with 1 kW power supply. The main objectives of the experiments were to confirm the levitation stability for solid and molten alloy samples. We also examined the performance and adaptability of the levitation furnace during the parabolic flight. Using a symmetric coil spherical nickel samples were stably hold within a second after the microgravity condition was attained . Spherical lead samples were also stable hold under microgravity. The experiments were successfully performed and the results showed that the technical bases for the containerless process under microgravity conditions were established.
Inside the Space Shuttle and the International Space Station, it is not completely weightless. The difference from the weightlessness is called - g-jitter- In a lot of space experiments, the influence of the g-jitter on their results has been adversely reported. To extend our understanding on the g-jitter systematically, a working group has been organized under the JASMA. The working group already held a few research meetings. Some presentations made at the meetings are briefly introduced.
A micro-gravity working group (MGWG) was established at the Japan-US Science, Technology & Space Application Program (JUSTSAP) Workshop in 1997. In order to achieve the identification and promotion of our greater cooperation in micro-gravity research, the MGWG has sponsored a micro-gravity experiment performed on board the flight of the Space Shuttle, STS-95. Preliminary results of the experiment were presented to the MGWG during the 8th JUSTSAP Workshop in Kapolei Hawaii, Nov. 9-13, 1998. The STS-95 has received a great deal of attention due to the presence of Senator John Glenn and Doctor Chiaki Mukai as its crew members. The MGWG experiment title was Japan-US Thermal Science Acceleration Project (JUSTSAP). The experiment was built in the US with the results being provided for the Japanese investigators after the flight. The JUSTSAP experiment represents a good example of the true spirit of cooperation be tween Japan and the U.S. in space technology development being promoted by the JUSTSAP. Our mutual activities through this project can promptly proceed our steps to our goals toward the effective and valuable utilization of the International Space Station, which should lead to the benefit of our coming generations.