Bubbles in the pipe flow cause flow unsteadiness, noise and vibration. Common bubble removal technique makes use of the buoyant force. However, under microgravity condition, the buoyant force doesn't act on the bubbles. In this paper, we performed a basic research for a novel bubble removal technique using a branching pipe with a pressure difference. The microgravity experiment was performed in the underground microgravity experiment center ( JAMIC) in Kamisunagawa-cho, Hokkaido. Bubble behavior in a branching pipe under a microgravity condition was investigated by an air-water loop system installed in a free fall capsule. As a result of the experiments, the number of bubbles ‰owed into the branching pipe increased as the bubble diameter increased. When the mean diameter of bubble was over 3.0 mm, 80 of the bubbles were able to ‰ow into the branching pipe. This is because a bubble with a large diameter experiences the large body force caused by the pressure difference between the main and the branching pipe. This pressure difference was generated by the flow separation, which occurred in the entrance of the branching pipe. This tendency was more intensified under a normal gravity condition.
The behavior of chemical wave on the interface between an organic liquid phase and a water phase was investigated under the microgravity of JAMIC in Kamisunagawa, Hokkaido in Japan. On the ground the traveling chemical wave appeared on the interface between the water phase (upper layer) and the organic liquid phase (lower layer) (mode A). Under the microgravity, two new modes appeared; one is the chemical wave with the opposite configuration (mode B: organic liquid phase in the upper layer and the water phase in the lower layer) and the other is the rotation of the semi circular column of organic liquid phase (mode C). The new mode C was reproduced on the ground by the experimental simulation of the microgravity condition in which the density difference was taken to be zero between the organic liquid phase and the water phase. The origin of this new mode C was discussed qualitatively. The tapered cylindrical container upwardly was effective for the realization of the mode C, which is a convenient form for the utilization of the dynamic energy due to the chemical reaction. Finally, the chemical wave in the narrow gap between two cylindrical containers changed into a dynamical labyrinth under microgravity.
The feasibility study has been investigated to build a small satellite (so called `nano-satellite'), which has 3-kg mass
and less than 30-W power, since October in 1998. The experimental 3-axes attitude control of the nano-satellite under micro-gravity field is conducted at in Japan Micro-gravity Center ( JAMIC) in 2002. The small reaction wheel is used as an actuator for the attitude control and enables compensate the small residual deviation of the presume error. This project investigates the validity of the feedback control with the eventual sliding mode control because of the correspondence for the non-linearity of the control system and the excellence for robustness.
The liquid droplet radiator (LDR) is an important candidate to resolve an technical issue that is how to reject of large quantities of waste heat from large structures in space, which handle high power (from megawatts to gigawatts). The performance of LDR elements under microgravity condition has been investigated. It has been clarified that (1) the diameters of droplets and spacing between droplets generated under microgravity can be formulated by the equations based on the law of conservation of mass in the process of generating droplets, (2) the uniform droplet stream is captured under microgravity without splashes, (3) the pumping performance of the working fluid of the centrifugal droplet collector under microgravity can be predicted by the sum of velocity head and pressure head generated in the gyrostatic flow, (4) the gear pump can also function normally under microgravity.
We conducted microgravity experiments to verify fundamental grasping function of a small docking mechanism for mothership-daughtership nano-satellite using the facility of Japan Micro Gravity Center ( JAMIC). The mechanism was designed to grasp a daughtership nano-satellite while compensating for position and attitude control error and to release it stably under speed control in-orbit. The experiment sequences are as the followings: (1) we transmit a drop command to start dropping the rack, (2) a control program starts when note PC detects the drop command, (3) the docking mechanism starts close motion after the daughtership is released from a electro-magnet release mechanism, and (4) the docking mechanism grasps the daughtership under microgravity less than 10 s. Each drop experiment was monitored with three CCD cameras, and the position, attitude, angular velocity of the daughtership, and electric currents, close motion speed and guiding speed of the docking mechanism were measured. In the paper, we explain the experimental system including the docking mechanism, the control system, the daughtership system and the release mechanism, and describe results of microgravity experiments in JAMIC.
Biomedical experiments under microgravity using 10 seconds' dropping capsule at JAMIC has started on January 19 of 2000. The first experiment was to examine the neuro-cardiological response of rats upon sudden exposure to the microgravity conditions 1). Secondary, gene expression analysis on human lymphocytes was conducted using newly developed equipment for 8 secondes microgravity. The resulting data showed several up-and down-regulated genes, some of which corresponding to those identfied for the astronauts' specimen during their flight 2). Thirdly, delayed immunereaction was shown using 8 seconds' microgravity. Becasuse of newly developed instrument in this study, various kind of Biomedical experiments under microgravity became more accessible than before, expanding the dream of the biochemists to outer Space 3). In parallel with these experimental studies, Field Medicine was opened in Urausu which is very close to Kamisunagawa ( JAMIC). Field Medicine is a newly built preventive-, health-promoting Medicine for the elderly 4,5,7). We believe this Field Medicine will prove very productive for creating Space Medicine.
In order to investigate the directional behavior of the g-jitter, a new method for three-dimensional g-jitter analysis has been developed. Both the conventional method and the new one are applied to accelerations measured during STS-65 and STS-95 Space Shuttle flights. From the FFT analysis for the low frequency band, several peaks around 5 Hz considered as the structural vibrations are observed in both results of STS-65 and STS-95. From the FFT result for higher frequency band of STS-65, strong and clear vibration peaks produced from machinery are observed. A vibration composed of single frequency component is mathematically analyzed to understand the fundamental characteristics of the behavior. The analytical result shows that any vibration composed of only one frequency can be transformed to a combination of a linear motion and a circular one on an appropriate coordinate system. In the lower frequency band, the directional motions of the structural vibrations are almost perfectly linear. On the other hand, a vibration in higher frequency band from machinery is a combination of these two motions. These results indicate that the behavior of the g-jitter can be described using a simple model with corresponding to the frequency bands.
In on-orbit experiments of the thermal-fluid phenomena, the dynamic behavior of the fluid is affected by a fluctuation of the gravity level called as the g-jitter. In this research, the natural convection in a closed cylindrical cavity subjected to the g-jitter during the parabolic flight was studied experimentally and numerically. The cavity was filled by the water as test fluid. The wall of the cavity was cooled by the cooling water. Two thin metal films were evaporated on a rod installed along a cylinder axis. The films were kept at a constant temperature electrically. Thus the variation of the surface heat flux was able to be measured through the change of the electric current. The related numerical analyses are also performed. When a g-jitter of a relatively high frequency is applied, the phase difference arises between the gravity and the heat flux variations. The phase shift found in the present numerical analysis agrees with the one obtained from the experiment.
In performing microgravity experiments, g-jitter is unavoidable in space stations, air planes and even in drop shafts. This acceleration affects convective motion in the experiments. A novel non-linear passive damper for microgravity experiments has been developed. The damper is small and does not consume electrical power. The performance of the damper in the Space Station has been estimated. They also measured diffusion coefficient of aqueous solution under microgravity and reduced g-jitter. The diffusion coefficient under the reduced g-jitter shows smaller value than that under normal gravity or with g-jitter. This tendency is similar to the anomalous diffusion decrease of water performed in the Mir Station. Crystal growth in microgravity experiments was measured under reduced g-jitter. The growth rate and surface super saturation were measured accurately using optical measurement system and numerical simulations. A comprehensive growth model applicable in micrograviy and normal gravity was developed.