Resting Study of Tracer Experiment on Catalytic Wet Oxidation Reactor under Micro-gravity and Earth Gravity Conditions

The International Space Station（ISS） employs catalytic wet oxidation carried out in a Volatile Reactor Assembly （VRA） for water recycling. Previous earth gravity experiments show that the VRA is very effective at removing polar, low molecular weight organics. To compare the reactor performance under micro-gravity and Earth gravity conditions, a tracer study was performed on a space shuttle in 1999 by using 0.2% potassium carbonate as the chemical tracer. In this paper, the experimental data were analyzed and it is indicated that the reactor can be considered as a plug flow one under both micro-gravity and earth gravity experimental conditions. It has also been proved that dispersion is not important in the VRA reactor under the experimental conditions. Tracer retardation was observed in the experiments and it is most likely caused by catalyst adsorption. It is concluded that the following reasons may also have influence on the retardation of mean residence time ： （1） the liquid can be held by appurtenances, which will retard the mean residence time; （2） the pores can hold the tracer, which can also retard the mean residence time.

Neural adaptive control for a ground experiment of the space proximity operation in a six-degree-of freedom micro-gravity simulation system

In this study,a neural adaptive controller is developed for a ground experiment with a spacecraft proximity operation.As the water resistance in the experiment is highly nonlinear and can significantly affect the fidelity of the ground experiment,the water resistance must be estimated accurately and compensated using an active force online.For this problem,a novel control algorithm combined with Chebyshev Neural Networks(CNN)and an Active Disturbance Rejection Control(ADRC)is proposed.Specifically,the CNN algorithm is used to estimate the water resistance.The advantage of the CNN estimation is that the coefficients of the approximation can be adaptively changed to minimize the estimation error.Combined with the ADRC algorithm,the total disturbance is compensated in the experiment to improve the fidelity.The dynamic model of the spacecraft proximity maneuver in the experiment is established.The ground experiment of the proximity maneuver that considers an obstacle is provided to verify the efficiency of the proposed controller.The results demonstrate that the proposed method outperforms the pure ADRC method and can achieve close-to-real-time performance for the spacecraft proximity maneuver.

InSb CRYSTAL GROWTH UNDER MICRO-GRAVITY CONDITION

I.INTRODUCTION In the past several years, people are interested in material processing in space. On August 5, 1987 material processing experiments, including directional solidification of InSb crystal, were carried out for the first time on the 'Recoverable Satellite' in China. In these experi-

Automated Burris gravity meter for single and continuous observation

The Burris Gravity MeterTM manufactured by ZLS Corporation, Austin/Texas, USA, is based on the in- vention of L^R （L. LaCoste and A. Romberg）： The ZLS （zero-length spring）. A digital feedback system （range of about 50 mGal） is used to null the beam. Now, more than 120 gravity meters of this make exist worldwide and are used successfully in exploration, volcanology, geodetic work and surveying. The sensor is made of the well-known （L＆R） metal-alloy zero-length spring providing a low drift characteristic. The drifts observed are comparable to L＆R gravimeters and are less than 0.3 mGal per month, which is much lower than the drifts known for the fused quartz sensors. The dial is calibrated every 50 regal over the entire 7000 mGal meter range. Since the gravity value is determined at these points, there are no periodic errors. By a fourth heater circuit temperature effects are totally avoided. The gravity meter is controlled via Bluetoothce either to a handheld computer （tablet） or a notebook computer. The feedback responds with high stability and accuracy. The hulling of the beam is controlled by the UltraGravTM control system which incorporates an inherently linear PWM （pulse-width modulated） electrostatic feedback system. In order to improve the handling of the gravimeter we have developed two Windows based programs： AGESfield for single measurements and AGEScont for continuous readings.

Dual-manipulator Coordinate Motion Planning Scheme for Robot Satellite

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Growth of Czochralski silicon under magnetic field

Growth of Czochralski (CZ) silicon crystals under the magnetic field induced by a cusp-shaped permanent magnet of NdFeB has been investigated. It is found that the mass transport in silicon melt was controlled by its diffusion while the magnetic intensity at the edge of a crucible was over 0.15 T. In comparison with the growth of conventional CZ silicon without magnetic field, the resistivity homogeneity of the CZ silicon under the magnetic field was improved. Furthermore, the Marangoni convection which has a significant influence on the control of oxygen concentration was observed on the surface of silicon melt. It is suggested that the crystal growth mechanism in magnetic field was similar to that in micro-gravity if a critical value was reached, named the growth of equivalent micro-gravity. The relationship of the equivalent micro-gravity and the magnetic intensity was derived as g=(v0/veff)g0. Finally, the orders of the equivalent micro-gravity corresponding to two crucibles with characteristic sizes were calculated.

EXCITATION MECHANISM OF THERMOCAPILLARY OSCILLATORY CONVECTION

It is suggested that the oscillation of thermocapillary convection may be excited by the buoyancy instability. By means of numerical simulation of the finite-element method, the temperature distributions in the liquid bridge are qualitatively analyzed. The temperature gradient in a certain flow region of liquid bridge may turn to be parallel to the direction of gravity when the temperature difference △T between two boundary rods of liquid bridge is larger than the critical value. The buoyancy instability may be excited, and then the thermocapillary oscillatory convection appears, as the temperature difference increases further. The distribution of the critical Marangoni number in the micro-gravity environment is derived from the data on the ground experiments. The results show that the onset of thermocapillary oscillatory convection is delayed in the case of smaller typical scale of liquid bridge and lower gravity environment.