Microgravity Science and Technology最新文献

Short-radius centrifugation (SRC) is a promising and economically feasible countermeasure in space flight and applies to gravity therapy in terrestrial medicine. The potential occurrence of undesirable orthostatic and vestibular reactions limits the use of this method. One way to minimize these risks is the ability of a human to adapt to the effects of overload. It is known that artificial gravity training may improve orthostatic tolerance. New data demonstrated that cardio-postural interactions and muscle-pump baroreflex activation are present during short-arm centrifugation. Based on previous studies, we hypothesized that repeated SRC in the interval training mode with angular velocities from 22 to 28 rpm may also improve postural tolerance. Six healthy male volunteers were observed before and immediately after five consecutive SRC sessions. The rest between SRC was at least three days. The SRC mode was an interval and included five 300-second platforms with 1.27 g at the feet and four 300-second platforms with 2.06 g at the feet. We registered the main postural characteristics and ground reaction forces data when the participant kept the center of pressure at a given point in a standing position with biofeedback and without this. After the first SRC session, there was a significant posture decondition. The SRC training effect was already noticeable after the second SRC session and was stable until the end of the experiment. The results demonstrate the development of postural tolerance to artificial gravity exposure in this mode and expand the understanding of sensorimotor adaptation capabilities.

Brazil has a Microgravity Program mainly based mainly on sounding rockets experiments. The Santa Branca Mission, aimed to qualify the Brazilian Suborbital Microgravity Platform (MQ-MSP). The group of the Coordination of Applied Research and Technological Development (COPDT) of the Brazilian Space Research Institute (INPE) participated with an experiment in a fast solidification furnace, capable of producing temperatures up to 900 °C, which was tested with semiconductor and metal alloys. This paper describes the construction and performance of this furnace during the last suborbital flight, the Santa Branca Mission, which took place in 2022. The solidification furnace is now qualified and ready to be used by other institutions for sounding rocket flights.

For small droplets undergoing phase change, gravity is generally considered negligible. In the case of binary droplets evaporation, convective flows can be induced due to various mechanisms, such as continuity, buoyancy and/or selective evaporation of one of the components. Convection can also be induced by surface tension gradients resulting from concentration variations along the interface. This study presents experimental results of evaporation for binary mixture droplets. We concurrently investigate sessile and pendant droplets to assess gravity’s impact on binary droplet evaporation. We examine compositions including, pure butanol, pure methanol, pure water, and 50% per volume mixtures of water-butanol and water-methanol, evaporating in a controlled atmosphere. In the case of water-butanol mixtures, the drops contact line ‘depins’ during the evaporation process whereas the case of water-methanol mixture, the contact line of the drops remains pinned most of the lifetimes. The analysis of the evaporation dynamics reveals differences in the evaporation of these two mixtures and the effect of orientation (gravity). For water-butanol mixtures the evaporation occurs in four stages linked to preferential evaporation of the more volatile component and the ensuing surface tension gradients. In the case of water-methanol mixtures, contact lines tend to be pinned during most of the lifetimes of drops. The evaporation rate of the mixture is found to be between the ones of the pure components, i.e. water and methanol. The case of sessile drops exhibits a slight enhancement in evaporation rate in the case of the sessile configuration compared to the pendant one for pure water and mixture cases, which is explained by density differences and buoyancy driven flows. Solutal Marangoni flows in the case of water-methanol mixtures are deemed weaker compared to water-butanol ones. The use of the two mixtures allowed to have a good comparison between two cases where solutal-Marangoni effect can be strong (water-butanol) and weak (water- methanol) influence. The densities of the two organic liquids also highlighted gravitational effect due to the large difference in vapor densities.

Three-dimensional (3D) particle tracking is a challenging task in dense granular systems. Magnetic particle tracking has been developed in recent years to reconstruct a tracer’s trajectory in granular systems. The method can be low-cost, compact, and flexible. In this work we applied a Hall sensor array method to track the trajectories of a magnetic intruder particle in a 3D granular bed in the centrifuge of the Chinese Space Station (CSS). We present a developed algorithm. By placing sensors in an array in a same plane, our algorithm can exclude the interference of varying external field. The method’s static accuracy can reach 0.02 cm, and the maximum deviation of our measurement from a known path is also checked to be 0.02 cm. On CSS, two independent sensor arrays are used to cross-check the accuracy of the method. The two measured trajectories are well overlapped. This confirms the method’s reliability and robustness of tracking an intruder in a dense granular bed.

The stability of thermocapillary flow in a liquid bridge under a transverse rotating magnetic field (RMF) was numerically investigated by the linear stability analysis using the spectral element method. Three commonly used RMF models, namely, the infinite model, the simplified finite model and the Φ₁-Φ₂ model, are employed to describe the RMF and their results are compared. Additionally, for the Φ₁-Φ₂ model, the uniform and non-uniform RMF were also compared. The numerical results show that with the increase of magnetic Taylor number Ta, the critical Marangoni number (Ma_c) for the three RMF models increases firstly, then decreases sharply to a minimum, finally increases again when the RMF is strong enough to suppress the radial and axial convection induced by thermocapillary force. Two transitions between the wavenumber k=1 and k=2 mode are observed with increasing Ta. The results obtained by the simplified finite model are in good agreement with those of the Φ₁-Φ₂ model, however, the infinite model has a significant deviation compared to the Φ₁-Φ₂ model. Besides, the results indicate that the non-uniform RMF has a relatively weak action compared with the uniform RMF.

The dynamics of a droplet on a liquid substrate in the case of an inhomogeneous heating from below has been investigated. The problem is studied numerically in the framework of the slender droplet approximation and the precursor model. The change of the stationary droplet’s shape and the rupture of the substrate layer induced by a floating droplet are investigated. The influence of the gravity force on the shape of the droplet is studied.

Fluid manipulation and control is crucial for space exploration. Motivated by the “Thermocapillary-based control of a free surface in microgravity" (ThermoSlosh) experiment (Salgado Sánchez et al. in Acta Astronautica 205:57–67, 2023), we conduct here a detailed numerical analysis of interfacial dynamics in a two-dimensional cylindrical cell, half-filled with different silicone oils or a fluorinert, and subjected to thermal forcing and vibrations. The effect on the free surface dynamics of the applied temperature difference, vibrational amplitude, fluid viscosity, and contact angle is analyzed; both static and dynamic contact angle models are considered. Results strongly suggest that thermocapillary flows can be used to control the interface orientation within the cell, while supplemental vibrations can be added to increase the system responsiveness. This control can be further improved by using classical proportional-integral-derivative feedback to adjust the cell boundary temperatures in real-time. The proportional and derivative gains of the controller can be selected to optimize the stabilization time and/or energy cost, while the integral contribution is effective in reducing the steady-state error. Overall, the present analysis highlights the potential of using the thermocapillary effect for fluid management in reduced gravity, and evaluates different types of experimental tests that can be executed in the frame of the ThermoSlosh microgravity project.

Friction is a primary failure mode in micro-nano electromechanical systems due to the high surface-to-volume ratio. Microgravity further complicates this issue in journal-bearing-like conformal contacts by promoting irregular disturbances. This paper aims to gain insights into the anti-friction design of journal-bearing-like devices through molecular dynamics simulation. A molecular dynamics model was proposed and the calculation method of the friction force was derived. In the absence of disturbance, the proposed model was compared with a non-conformal model which unfolded the bearing as a plane, and the influence of initial radial clearance and axis inclination on the friction force was investigated. The results showed that the proposed model could present more accurate friction forces than the non-conformal model. The friction force was inversely proportional to the initial clearance, and the axis inclination could reduce the friction force. Regarding disturbances as the superposition of two vibrations perpendicular to each other, in which case the trajectory of the journal was a Lissajous curve, the effects of frequency, stiffness coefficient, amplitude ratio, and frequency ratio were investigated. The results showed that the average friction force increased with the rising frequency in the range of 0.8 ~ 4.8 GHz, then decreased with the further increase of frequency. The average friction force was lowered when the stiffness coefficient increased from 100N/m to 1000N/m. For two representative frequencies, the average friction force exhibited different trends with the amplitude ratio. Except for the case of 1.25, increasing the frequency ratio could reduce the friction force. It seemed that applying a well-designed Lissajous route was a promising way to reduce friction.

Nowadays a propellant residual gauging method based on the thermal response of the tanks’ wall is developed. And the liquid distribution and meniscus height have great effects on the thermal response. Profiles of liquid free surfaces in revolved containers under microgravity are studied through theoretical analysis and numerical simulation in this paper. The analytical formula for the static profile of the liquid surface in the spherical tank is established. It shows that the profile is a section of a circle cut off by the tank wall. For given the geometry of the tank, liquid volume and contact angle, the profile of the free surfaces under microgravity can be obtained by using the Shooting method based on the theoretical model. Numerical simulation is carried out with the Volume of Fluid method, and it is verified that the static profiles at different contact angles and liquid filling rates fit the theoretical descriptions. It is concluded that the meniscus height increases slowly as the filling rate increases, and the smaller the contact angle, the more obvious this trend. Then the theory is extended to the tanks of arbitrary shapes, and the critical position of the profile is derived. Below the critical position the propellant may accumulate in some corners or pits, which makes it unable to be fully utilized. The critical position is related to the shape of the tank and the contact angle. This research is of great value for the prediction of the static profiles of liquid surfaces in tanks and the propellant residual gauging.

The problem of stability of one-dimensional filtration flow in a rectangular domain of porous medium is solved. The flow occurs when a portion of impurity is transported through the region against gravity. It is shown that the instability has an absolute character. A Rayleigh-Taylor instability is observed at the backward front of the concentration pulse. In this case, the observation time is always less than the passage time of the pulse through the domain. A theoretical model is proposed to describe this phenomenon taking into account immobilization and clogging. The influence of the problem parameters on the characteristic time of instability onset is investigated. Comparison of computational results with experimental data has shown the appropriateness of the chosen model. The ways of increasing this time are analyzed. It is shown that only one way to increase the instability time is to significantly reduce the buoyancy force impact. The latter force can be diminish by alteration of the gravity force.