Microgravity Science and Technology最新文献

The influence of the forced convection rate on the chemical structure of a polymethyl methacrylate (PMMA) flame in an oxidizer flow under microgravity conditions was studied using numerical modeling. Gas flow around a solid sphere was simulated using the full Navier–Stokes equations for a multicomponent mixture. A multistep chemical kinetic mechanism was considered in the gas phase. The heat transfer and radiation in both the condensed and gas phases were considered in the modeling. On the PMMA surface, the pyrolysis reaction leading to the transformation of fuel from the condensed phase to the gas phase is specified. The forced convection speed varied in the range from 3 to 20 cm/s. Analysis of CO₂ concentration fields near the burning surface under microgravity conditions showed that the maximum CO₂ concentration is observed in the downstream zone. The width of the flame zone and its chemical structure depend on the intensity of forced convection. The width of the flame against the flow decreases, and the maximum CO concentration increases as the forced convection rate increases. Analysis of the rates of fuel consumption reactions showed that at a low convection speed (v_st=3 cm/s), the reaction with the H radical, which has the highest diffusion coefficient, plays a crucial role in MMA oxidation.

For surface tension driven flow, interfacial heat transfer can alter the flow regime and its transition condition. This paper investigates the influence of interfacial heat transfer on critical transition and hydrothermal wave propagation of nanofluid thermocapillary convection for the first time, and three environment temperature conditions is considered, e.g. the cold-end temperature, the average temperature of the hot and cold-end, and a linear temperature distribution. The results indicate that, as nanoparticles volume fraction increases the critical Marangoni number decreases under various ambient temperature conditions, meanwhile, the fundamental frequency of the velocity oscillations exhibits a linear decrease, and the propagation angle and temperature fluctuation range of hydrothermal waves are decreased. Furthermore, for the three ambient temperature scenarios, the linear temperature distribution condition can amplify the propagation angle and temperature fluctuation range of hydrothermal waves. Consequently, the manipulation of both the nanoparticle volume fraction and ambient temperature condition provides a means to control the instability of nanofluid thermocapillary convection.

In this paper, the Electro-elastic instability(EEI) of an Oldroyd-B fluids flow the microchannel with the obstacles and heterogenous surface charged is studied. The changes in fluid flow are presented by considering three different ranges of Weissenberg numbers(Wi), the expansion lengths (textrm{EL}), and the asymmetric potential distributions. Under the combined effects of heterogeneous surface potential and elastic stresses, not only the vortices but also lip vortices are generated near the obstacles. At lower Weissenberg numbers, the stable and symmetric flow field is observed. As Wi increases, it is worth noting that the flow field becomes unstable and chaotic due to the enhanced electro-elastic instability. But the asymmetry of the velocity diminishes as (Wi>10). In addition, the presence of different vortex dynamics is observed as the Wi varies, such as the lip vortices, angular vortices, and oscillating lip vortices. Further, the flow of fluid at different expansion ratios is investigated. With the decrease of expansion lengths (textrm{EL}), the backflow and asymmetry are reduced, the lip vortex disappears and then the angular vortex appears. Finally, by increasing the upper zeta potential ((zeta _{textrm{w}})) of the obstacles, the mixing efficiency is improved. The research results may be helpful to the electrodynamic transport of viscoelastic fluids in porous media and the analysis of micromixers for industrial applications.

Precise formation control is increasingly demanded in high-resolution remote sensing formations, gravitational detection interferometers and distributed space telescopes. One composite formation flying method using disturbance-free payloads was previously proposed to enhance formation accuracy and payload stability. This method divided satellite formation into coarse formation using conventional satellite buses and fine formation using precise payloads. To verify the effectiveness of the proposed formation method and the payload stability performance, this paper develops an experimental system using two air-floating satellite prototypes. First, the experimental design is proposed and the experimental system model is established. Second, the experimental prototype development and system architecture are described in detail. Finally, the composite formation flying effectiveness is further demonstrated by coarse and fine formation control experiments. The experiment results indicate that the composite formation flying method effectively improves the formation accuracy for distributed payloads and isolates microvibrations from satellite buses to enhance payload stability.

Two-phase pumped cooling systems are applied when it is required to maintain a very stable temperature for heat dissipation in a system. A novel additively manufactured evaporator for two-phase thermal control was developed at NASA Jet Propulsion Laboratory (JPL). The Two-Phase Mechanically Pumped Loop (2PMPL) allows to manage the heat transfer with much wider breadth of control authority compared to capillary-based systems, while alleviating the system's sensitivity to pressure drops. The focus of this work is the understanding and capturing the micro-scale evaporation occurring in the porous structure of the evaporator. The Boiling and Phase Change Heat Transfer Laboratory at the University of California, Los Angeles (UCLA) developed an all-encompassing numerical simulation tool to predict the operational thermal behavior of the evaporator considering the effect of the liquid-vapor interface at the wick-to-vapor boundary. The numerical model incorporated the behaviour of the liquid-vapor meniscus at particle level located along the evaporative boundary between the wick structure and the vapor chamber. The numerical model allowed to study the effect of different parameters, such as boundary conditions, geometry, wick and fluid properties. An experimental setup was built at UCLA in order to characterize the heat transfer within an additively manufactured porous sample fabricated at JPL and in particular its evaporative heat load under certain heat inputs. The experimental efforts served as validation for the numerical results and aided in the characterization of the transient phenomena, such as dry-out.

The enclosed space environment demands sustainable environmental control systems. Space stations and interstellar missions, both need reliable environmental control and life support systems for crewed flights and long-term habitation. These long-duration space missions require monitoring for potential pathogens and microbial contamination, which is crucial for astronaut health and the reliable operation of space equipment. To meet this critical need, the China Space Station (CSS) is equipped with the Microbial Online Monitoring Module (MOMM), which integrates two methods for microbial detection, the first method involves cultivating microorganisms in culture dishes for observation, while the second method uses isothermal nucleic acid amplification and detection technology based on Loop-mediated Isothermal Amplification(LAMP). This equipment is applied in the microgravity environment of the space station to achieve rapid detection of microbial species and abundance in orbit. Hardware function validation tests and validation experiments of the sensitivity and shelf life of the reagents were conducted on the ground, and several full-process microbial detection experiments were carried out to ensure the function and feasibility of the MOMM. Subsequently, an experimental process of microbial cultivation and observation was successfully carried out on the CSS using air samples from the space station. The MOMM allows for early detection of microbes in orbit, contributing to implementing targeted biosecurity and maintenance measures.

High Frequency Impulse for Microgravity (HIFIm) is an exercise countermeasure that is designed to minimize force and vibration transmission to the spacecraft during exercise without the need for an additional VIS. The purpose of this study was to evaluate the effectiveness of HIFIm in mitigating force transmission in microgravity during parabolic flight. Force between HIFIm and the aircraft was measured using a custom-made arrangement of load cells during repeated jumping by two participants. Mean peak force transmission to the aircraft was 4.79 ± 0.68 N.kg^− 1. In addition, the frequency spectra for the upper and lower fixations to the aircraft were within the envelope of what is permissible for an exercise countermeasure on Gateway. These data support the design concept of HIFIm and suggest that HIFIm could be installed in a space habitat with no, or minimal, additional VIS. Measuring the force and vibration transmission of exercise countermeasures in microgravity during parabolic flight is highly challenging due to the safety constraints of the experimental platform and the extreme changes in acceleration (from 0 to 1.8 g). The fact that this performance can be directly measured for HIFIm is a key advantage. The results presented here add to the mounting evidence that HIFIm is the future of exercise countermeasures.

Astronauts are exposed to microgravity-induced health problems in spaceflight missions. Countermeasures and physical exercises have received increasing attention and its current research trends and landscapes warranted investigation. We conducted a comprehensive bibliometric analysis on astronaut training/countermeasures using the available data from the Web of Science Core Collection database from 1992 to 2022 to summarize the research trends and identify future directions. A total of 1,520 relevant articles were identified. Annual publications of the field have been increased over the years with the emergence of new and effective countermeasures. ‘Microgravity’ was the centered hotspot surrounded by the topics included ‘spaceflight’, ‘hind leg hanging’, ‘simulated microgravity’, and ‘simulated weightlessness’. The top countries that produced the most publications included United States (726 articles), Germany (129 articles), and France (84 articles). The United States played a dominant role in the collaboration network with other countries. Meanwhile, NASA from the United States led the global collaborations and dominated the literature. Future research trend might lie on the design of physical training exercises to tackle the potential health problems on osteoporosis, muscle atrophy, and abnormality on the nervous and cardiovascular system; and artificial/simulated gravity with interdisciplinary sports countermeasure research on physiology, brain science, biomechanics, and aerospace medicine.

Propellant tanks provide non-entrained propellant for thrusters of satellites, which plays an important role in space mission. And the fluid transfer efficiency of tanks is the key to supply non-entrained propellant. An experiment cabin containing two different scaled tank models are designed and experiments of liquid reorientation under microgravity are carried out in the Chinese Space Station. Experiment results present the high liquid transportation efficiency of the two kinds of propellant management devices. Finite element models of the two tank models are established and verified by simulation matching with experiments. Furthermore, methylhydrazine is adopted to carry out more simulation analysis by considering different liquid contact angles and surface tension, and numerical results show smaller liquid contact angle and bigger surface tension can increase liquid flow speed. This research can provide theory and data support for the design of plate type tanks.