In JUSTSAP project, it has been reported that it is possible for not only quasi-steady accelerations but also oscillatory g-jitter to make thermal convection, if the direction of the g-jitter is adequate. In order to investigate directional behavior of g-jitter, a new method of 3-dimensional g-jitter analysis is developed and it is applied to accelerations measured during IML-2 mission. Its result shows that oscillatory background accelerations are usually multi-directional. However, when g-jitter is induced by a strong source like a pump, the g-jitter becomes uni-directional and will have larger influence on fluid phenomena.
Recent experimental measurements of various microgravity experiments have been taken on the Mir and Space Shuttle under conditions of microgravity having isolation, non-isolation and forced-g modes using the Microgravity-vibration Isolation Mount (MIM). The results to date show a clear difference between the experimental measurements taken during non-isolated g-levels and isolated g-levels. Importantly, for experiments to be performed on the International Space Station (ISS), it is believed that the microgravity levels of the non-
isolated Mir and Space Shuttle are still better than the level given for the ISS isolation requirement curve and much better than the prediction for non-isolated racks of ISS. This raises concerns for those experiments being performed in experimental facilities not having isolation.
The motion and deformation of a large gas bubble in a liquid-filled cell were experimental ly investigated under microgravity and forced vibration conditions. The experiment was con ducted aboard the Space Shuttle during the STS-85 mission, using a vibration isolation platform (MIM) to either isolate the cell from g-jitter or to impose controlled vibrations of specified frequency and amplitude. The experiments were conducted using two shallow, cylindrical fluid cells (97.3 mm I.D. x 16.8 mm thickness), each containing a mixture of air/mineral oil (cell #1) and air /water-surfactant solution (cell #2). In microgravity, a large air bubble formed in the middle of the cell, and the motion of the bubble and gas-liquid interface was recorded by a video camera under different test conditions. In the isolation mode, high frequency g-jitter above MIM's cutoff frequency of 2 Hz was significantly attenuated, but the low frequency vibrations were transmitted and found to influence the bubble interface. In the forced vibration tests, the large bubble responded to periodic vibrations of low frequency and large amplitude, rather than high frequency and high acceleration level. Bubble movement and non-linear shape oscillation data were obtained and analyzed.
Buoyancy convection induced in a semiconductor solution by gravity fluctuations is studied numerically. Buoyancy forces based on the temperature and concentration differences are taken into ac count. The residual gravity is 0 G and 10-4 G and the amplitude of gravity fluctuation is 10- 4 G and 10- 3 G. The frequency of gravity fluctuation is changed from 10- 3 Hz to 10 Hz. The effect of the amplitude and frequency of gravity fluctuation on the velocity, temperature and concentration fields is investigated and the bifurcation diagrams are produced. Through this analysis, the following results were obtained; (1) The amplitudes of velocity, temperature and concentration fluctuations are small when the frequency of gravity fluctuation is high but they become large when the frequency of gravity fluctuation is lower than 0.01 Hz. (2) The fluctuations of velocity, temperature and concentration deviate from sinusoidal curves and bifurcations occur as the frequency of gravity fluctuation decreases. (3) The amplitude of concentration fluctuations becomes smaller under residual gravity than in the absence of residual gravity. (4) The fluctuations can be reduced by applying magnetic field.
Microgravity environments in the space shuttle and in the international space station are summarized. Effects of g-jitter on microgravity experiments such as crystal growth, diffusion, and fluid flow experiments are discussed and some countermeasures for g-jitter effects are introduced.
Non-Linear Passive Dampers (NLPDs) have been developed for micorgravity experiment. The LNPD is comprised of flexible membranes and connecting rods, and the damping is performed under microgravity utilizing the non-linear elasticity of flexible membranes. The damper is small and simple in construction and it does not consume any electric power. A prototype damper and improved one have been developed and the performances are verified by microgravity experiments using an airplane. The performance of the damper is investigated for utilizing in the Space Station.
It is important to know the microgravity environment during the experiment on ISS. For that reason, recent results of microgravity environment analysis are shown in this paper. Quasi-steady environment and vibroacoustic analysis are included in this result.
In the International Space Station, which will be operational around 2003, a variety of microgravity science experiments will be conducted. The National Space Development Agency of Japan (NASDA) is now developing a series of the multi-user facilities and experiment cartridges to accommodate the experiments into the Japanese Experiment Module (JEM). This article briefly introduces the multi-user facilities and development status of experiment cartridges and experiments which will be onboard around 2003.
Wettability of molten In 0.8Gao.2As on various substrates such as graphite, BN, SiO2, pBN, AIN, SiC, Al2O3, SiN and surface tension of molten In 0_8Gao.2As were measured using the sessile drop method to determine a possible crucible materials for crystal growth. The magnitude of contact angle between the melt and substrates was in the following order: pBN, BN, graphite }} AIN } SiN ] SiO2 } A}2O3, SiC. The surface tension of In 0.8Gao.2As was 441-449 mN/m (at 1100-1300°C). The scattering of the measured surface tension was less than 10%. The effect of roughness of SiO2 container surface was also investigated. The roughness was varied from 0.1 to 4 µm. As a result, the wetting behavior was related to the roughness of the container.
Containerless solidification experiments of NdasFe1s and Nd 90Fe10 alloys during parabolic flights were carried out using an electromagnetic levitation furnace with 1 kW power supply. The temperature of the sample during melting and solidification processes was precisely measured with an optical pyrometer. The forced cooling by helium gas was also tried to attain the lager cooling rate of the sample. The same ferromagnetic metastable phase as that obtained by levitation experiments under gravity condition was obtained. The cooling rate for the formation of the metastable phase under microgravity was small and about one seventh of that under gravity condition. The results showed the microgravity condition was effective for the metastable phase formation of hard magnetic materials.
In order to maximize the science outputs from the International Space Station in Life Science Research, the system of the International Research Announcement of Opportunity has been started. In this announcement, the investigators can propose to use the facilities which the foreign space agencies developed. This allows us to optimize the experiment protocol and increases the science outputs.