High Quality Microgravity Research Articles

Human neural network activity reacts to gravity changes in vitro.

During spaceflight, humans experience a variety of physiological changes due to deviations from familiar earth conditions. Specifically, the lack of gravity is responsible for many effects observed in returning astronauts. These impairments can include structural as well as functional changes of the brain and a decline in cognitive performance. However, the underlying physiological mechanisms remain elusive. Alterations in neuronal activity play a central role in mental disorders and altered neuronal transmission may also lead to diminished human performance in space. Thus, understanding the influence of altered gravity at the cellular and network level is of high importance. Previous electrophysiological experiments using patch clamp techniques and calcium indicators have shown that neuronal activity is influenced by altered gravity. By using multi-electrode array (MEA) technology, we advanced the electrophysiological investigation covering single-cell to network level responses during exposure to decreased (micro-) or increased (hyper-) gravity conditions. We continuously recorded in real-time the spontaneous activity of human induced pluripotent stem cell (hiPSC)-derived neural networks in vitro. The MEA device was integrated into a custom-built environmental chamber to expose the system with neuronal cultures to up to 6 g of hypergravity on the Short-Arm Human Centrifuge at the DLR Cologne, Germany. The flexibility of the experimental hardware set-up facilitated additional MEA electrophysiology experiments under 4.7 s of high-quality microgravity (10-6 to 10-5 g) in the Bremen drop tower, Germany. Hypergravity led to significant changes in activity. During the microgravity phase, the mean action potential frequency across the neural networks was significantly enhanced, whereas different subgroups of neurons showed distinct behaviors, such as increased or decreased firing activity. Our data clearly demonstrate that gravity as an environmental stimulus triggers changes in neuronal activity. Neuronal networks especially reacted to acute changes in mechanical loading (hypergravity) or de-loading (microgravity). The current study clearly shows the gravity-dependent response of neuronal networks endorsing the importance of further investigations of neuronal activity and its adaptive responses to micro- and hypergravity. Our approach provided the basis for the identification of responsible mechanisms and the development of countermeasures with potential implications on manned space missions.

Isolated bubbles growing and detaching within an electric field in microgravity

The experimental outcomes of single bubbles nucleated and growth from a heated surface immersed in an electric field in high-quality microgravity level are presented. Data were obtained between September 2019 and January 2021 from the European experiment known as Reference mUltiscale Boiling Investigation (also multiscale boiling project), in which single bubbles of FC-72 were nucleated on a heated surface, on-board the International Space Station. In the experiments reported here, which are only a part of the complete dataset, an electrostatic field is imposed in the boiling region by means of a washer-shaped electrode, centred above the nucleation site. The experimental apparatus is designed to initiate a single bubble from an artificial nucleation site machined in the surface. Such bubbles are heavily distorted by the electric stresses; in particular, contact angles and contact line length increase with electric field intensity. While in the absence of electric field no detachment occurs, when the electric field is applied the bubbles are continuously and regularly sucked towards the electrode as they are attracted to regions of weaker electric field; a detailed analysis of the electric forces is provided as well. The significant contribution of electro-convection is highlighted by the bubbles growth rate. These experimental observations contribute to the insight of the basics of boiling and the effects of an electric field on the ebullition cycle and show promising opportunities for practical application of electric fields in space.

Life of a single bubble growing within an electric field in microgravity: some preliminary results of the Reference mUltiscale Boiling Investigation

The experimental outcomes of single bubbles nucleated and growth from a heated surface immersed in an electric field in high-quality microgravity level are presented. Data were obtained between September 2019 and January 2021 from the European experiment known as Reference mUltiscale Boiling Investigation (also multiscale boiling project), in which single bubbles of FC-72 were nucleated on a heated surface, on-board the International Space Station. In the experiments reported here, an electrostatic field is imposed in the boiling region by a washer-shaped electrode, centred above the nucleation site. The bubbles are heavily distorted by the electric stresses; in particular, contact angles and contact line length increase with electric field intensity. In the appropriate conditions, bubbles are continuously and regularly sucked towards the electrode, because they are attracted to regions of weaker electric field. The significant contribution of electro-convection is highlighted by the bubbles growth rate. These preliminary results contribute to the insight of the basics of boiling and show promising opportunities for practical application of electric fields in space.

Satellite architecture and preliminary in-orbit experiment of Taiji-1

Taiji-1 is China’s first in-orbit technology validating satellite related to spaceborne gravitational wave (GW) detection. The satellite was launched at 600km sun synchronized orbit on 31 August 2019. It has accomplished its mission goals while all subsystems have validated their key technologies in orbit. The subsystems include optical metrology system (OMS), drag-free attitude control system (DFACS), thermal control subsystem, high-quality microgravity satellite platform and so on. This paper presents system architecture of Taiji-1 analyzing in-orbit experimental results of thermal stability, reaction wheel vibration contributing to the noise of gravitational reference sensor (GRS) measurement noise, and the center-of-mass (CoM) of GRS calibration.

Gravity scaling law of heat transfer in nucleate pool boiling

Boiling phenomenon can realize high performance heat exchange due to latent heat transportation accompanying the liquid-vapor phase change, resulting in its wide applications for high heat flux transfer both in normal gravity on the ground and in space microgravity environment. It is well known that gravity strongly affects boiling phenomenon by creating forces in the systems that drive motions, shape boundaries, and compress fluids. The study of the influence of gravity on boiling heat transfer is of great significance for relevant space applications. Our current knowledge on boiling phenomenon, however, is often composed of a great amount of empirical correlations and semi-mechanistic models for engineering applications, which are mainly depended upon empirical data obtained from elaborately designed experiments on the ground. Although many empirical correlations and semi-mechanistic models include gravity as a parameter, they usually fail when extended beyond the empirical range they were based on. Microgravity experiment offers a unique opportunity to study the complex interactions in boiling phenomenon without gravity, and thus to reveal the mechanism of gravity, or gravity scaling law, underlying boiling phenomenon by comparing microgravity experimental data with those obtained in normal gravity. Review of the up-to-data progress on gravity scaling law of nucleate pool boiling heat transfer is made in the present paper, especially focusing on the RKM (Raj-Kim-McQuillen) gravity scaling law which presents a unified framework for scaling behaviours of nucleate pool boiling heat transfer relevant to gravity based on the quasi-steady state, ground-based short-term reduced gravity experimental results acquired during transition periods of approximately 3–5 s when the acceleration varied continuously from hypergravity to low- g , or vice versa , in parabolic flights. The gravity scaling parameter for heat flux was updated based on high quality microgravity data aboard ISS (the International Space Station), and its robustness in predicting low gravity heat transfer is further demonstrated by predicting many of the trends in the pool boiling literature that cannot be explained by any single model. There are, however, some deficiencies and/or unsolved problems in the RKM gravity scaling law. The definition of the dimensionless temperature involves the temperatures of the boiling incipiency and of the CHF (critical heat flux). It was implicitly assumed that these two characteristic temperatures are constants in different gravity conditions. These assumptions, however, have no theoretical or empirical basis in fact. Moreover, recent numerical studies utilizing the lattice Boltzmann method, as well as some experimental evidences, showed that the temperature of CHF increases with the gravity level. Furthermore, the hypotheses on the asymptotic behaviours near the boiling incipiency and the critical heat flux confused the meaning of different gravity scaling parameters, which are defined clearly in the present paper. An important reason for the deficiencies of the RKM gravity scaling law is the lack of empirical data, especially experimental results in long-term, steady state pool boiling in different levels of reduced gravity. Thus, a variable gravity pool boiling experiment project utilizing CSS (the Chinese Manned Space Station) under construction, as well as systematic numerical simulations, are suggested in order to promote the research in this field.

A new kind of flame: Observation of the discrete flame propagation regime in iron particle suspensions in microgravity

The rate of flame propagation is generally understood to directly reflect the burning rate of a combustible mixture, as it is proportional to the square root of the overall reaction rate in the flame. However, in the case of heterogeneous mixtures composed of spatially separated discrete heat sources, such as suspensions of solid-fuel particles, theory suggests that the flame propagation speed may become insensitive to the reaction rate. Such a flame propagation regime, known as the “discrete flame” in the literature, is predicted to occur in suspensions of fast-burning metal particles and (or) low-conductivity gas media where the flame propagation becomes dominated by the heat transfer between fast-burning heat sources. In an attempt to experimentally confirm the existence of the discrete flame regime, flame fronts propagating in transparent glass tubes through iron particle (d32=33 µm) suspensions in low-thermal-diffusivity oxygen/xenon mixtures were studied in a high-quality microgravity environment. The experiment was performed on board the European Space Agency MAXUS-9 sounding rocket that lifted off from the Esrange Space Center (Sweden) on April 7, 2017. In total, 41 combustion runs were completed in suspensions with 20% and 40% of oxygen content during the 12 min of microgravity. While the experimentally determined combustion time of a single iron particle differs by a factor of more than three in mixtures with 20% and 40% oxygen content, the flames in these mixtures were found to propagate with practically equal speed in accordance with the predictions of the discrete flame theory.

The 2.5 s Microgravity Drop Tower at National Centre for Combustion Research and Development (NCCRD), Indian Institute of Technology Madras

Space missions involving humans require a better understanding of various phenomena happening in space environments. A number of experiments need to be conducted in microgravity for addressing various issues encompassing safety (primarily fire) and better understanding of fluid and material behaviour. Of the various methods used for obtaining microgravity conditions, drop towers offer ground based microgravity platform. They provide a cost effective platform for doing short duration, repeatable, high quality microgravity experiments. This paper describes key factors that influence the design of a drop tower. The salient features of 2.5 s microgravity tower set up at National Centre for Combustion Research and Development (NCCRD), IIT Madras (IITM) are discussed. Primary features of the three critical elements, namely the drop capsule, the release unit and the decelerator unit are described along with review of these elements in existing drop towers. The IITM drop tower operates in ambient atmospheric conditions to minimise the cost of operation. In order to achieve good quality microgravity levels, a dual capsule configuration is adopted. The shape of the outer capsule is arrived at by detailed transient computational fluid dynamic analysis of the drag shield under free fall condition over the drop height. A pneumatic mechanism is used for capsule release and brought to rest at the end of fall in a carefully designed decelerator unit. The decelerator unit consists of an airbag with controlled air outflow for smooth deceleration.

Design, experiments and multidisciplinary optimization of 2 degrees-of-freedom electromagnetic actuator for application in space vibration isolation

Considering space environmental requirements, a multidisciplinary optimization of a 2 degrees-of-freedom micro linear actuator is carried out to improve the overall performance of a nested flying vehicle in this article. To achieve high-quality microgravity environment, a nested flying vehicle is designed that can be operated inside the Space Station. The electromagnetic actuators are utilized to control the position and posture of the experiment device while the exterior structure is following the movement of the inner system. Each actuator is designed to generate vertical and horizontal forces at the same time. The actuator is composed of two permanent magnets, a 2 degrees-of-freedom coil on a printed circuit board and a steel back yoke. Due to the complexity of structure parameters modification, the geometry, the structural model, electromagnetism model, and multidisciplinary analysis process are integrated based on ModelCenter framework. In this case, the structural model is established using ANSYS/APDL. The electromagnetic analysis is performed by the magnetics postprocessing. The OPTLIB Gradient Optimizer, non-dominated sorting genetic algorithm II, and Design Explorer for multidisciplinary optimization with constraints are utilized for validation mutually. In view of the optimization results, compared with the prototype design based on experience, the width of the back yoke, the weight of actuator, and the residual force have been reduced by 23%, 50%, and 62% while the output forces resulted in an acceptable range.

A Fast and Self-Acting Release-Caging-Mechanism for Actively Driven Drop Tower Systems

Today’s and future scientific research programs ask for high quality microgravity conditions of 10−6 g on ground combined with high repetition rates of 100 flights per day or more. Accordingly, a new type of drop tower, the GraviTower Bremen, (GTB), has been suggested and is currently under development. As a first stage of development, a GTB-Prototype (GTB-Pro) has been designed which uses an active rope drive to accelerate a slider/drag shield and an experiment therein on a vertical parabola. During the free fall phase, the experiment is decoupled from the slider by a self-acting Release-Caging-Mechanism (RCM). Our prototype will provide 2.5 s of microgravity for experiments of up to 500 kg for at least 100 times per day. In this article, the final concept of the engineering of the active rope drive and the RCM are presented in detail. Based on extensive simulations aiming at an optimization of the whole system we developed a hydraulic rope drive system with minimized vibrational amplitude and low number of eigenfrequencies. The RCM achieves a very fast (≤ 0.1 s) self-acting release of the experiment from the slider by making use of the dynamics of the hydraulic rope drive. Furthermore, passive hydraulic stop dampers in the RCM build a passive and self-acting recoupling mechanism. This system is optimized for a fast decoupling to compensate for the time limitation posed by the chosen drive technology. The simulations included a comparison of different drive technologies, physical effects like the Coriolis force, and the dynamics of the RCM system itself.

Aerodynamic and engineering design of a 1.5 s high quality microgravity drop tower facility

Microgravity experiments are essential for research in space science, biology, fluid mechanics, combustion, and material sciences. One way to conduct microgravity experiments on Earth is by using drop tower facilities. These facilities combine a high quality of microgravity, adequate payload masses and have the advantage of virtually unlimited repeatability under same experimental conditions, at a low cost.In a collaboration between the Institute of Space Systems (IRS) at the University of Stuttgart and Baylor University (BU) in Waco, Texas, a new drop tower is currently under development at the Center for Astrophysics, Space Physics and Engineering Research (CASPER). The design parameters of the drop tower ask for at least 1.5s in free fall duration while providing a quality of at least 10−5g. Previously, this quality has only been achieved in vacuum drop tower facilities where the capsule experiences virtually zero aerodynamic drag during its free fall. Since this design comes at high costs, a different drop tower design concept, which does not require an evacuated drop shaft, was chosen. It features a dual-capsule system in which the experiment capsule is shielded from aerodynamic forces by surrounding it with a drag shield during the drop. As no other dual-capsule drop tower has been able to achieve a quality as good as or better than 10−5g previous work optimized the design with an aerodynamic perspective by using computational fluid dynamics (CFD) simulations to determine the ideal shape and size of the outer capsule and to specify the aerodynamically crucial dimensions for the overall system. Experiments later demonstrated that the required quality of microgravity can be met with the proposed design.The main focus of this paper is the mechanical realization of the capsule as well as the development and layout of the surrounding components, such as the release mechanism, the deceleration device and the drop shaft. Because the drop tower facility is a complex system with many interdependencies between all of the components, several engineering challenges had to be addressed. For example, initial disturbances that are caused by the release mechanism are a common issue that arises at drop tower facilities. These vibrations may decrease the quality of microgravity during the initial segment of free fall. Because this would reduce the free fall time experiencing high quality microgravity, a mechanism has been developed to provide a soft release. Challenges and proposed solutions for all components are highlighted in this paper.

Design of a 1.5 Seconds High Quality Microgravity Drop Tower Facility

Design of a 1.5 Seconds High Quality Microgravity Drop Tower Facility

Hydrothermal Wave Instability in a High-Aspect-Ratio Liquid Bridge of Pr > 200

The long-duration fluid physics experiments on a thermocapillary-driven flow have been carried out on the Japanese Experiment Module ‘Kibo’ aboard the International Space Station (ISS) since 2008. In these experiments, various aspects of thermocapillary convection in a half-zone (HZ) liquid bridge of high Prandtl number fluid have been examined under the advantages of the long-duration high-quality microgravity environment. In 2010, the authors succeeded to realize nonlinear convective fields in the HZ liquid bridge of rather high aspect ratio. Special attention was paid on to the complex convective fields, especially on the behaviors of the hydrothermal wave (HTW) over the free surface visualized by an infrared camera. In order to evaluate the characteristics of the nonlinear convective behaviors and their transition processes, the authors indicate the images taken by the infrared camera describing the time evolution of HTW, the spatio-temporal diagram, the Fourier analysis, and the pseudo-phase space, reconstructed from the time series of the scalar information of the liquid bridge, that is, surface temperature variation. In this paper, the authors introduce the signature of complex HTW behaviors observed at the long-duration on-orbit experiments, and make comparisons with some previous terrestrial and microgravity experiments.

Pool Boiling Heat Transfer on the International Space Station: Experimental Results and Model Verification

The relatively poor understanding of gravity effects on pool boiling heat transfer can be attributed to the lack of long duration high-quality microgravity data, g-jitter associated with ground-based low gravity facilities, little data at intermediate gravity levels, and a poor understanding of the effect of important parameters even at earth gravity conditions. The results of over 200 pool boiling experiments with n-perfluorohexane as the test fluid performed aboard the International Space Station (ISS) are presented in this paper. A flat, transparent, constant temperature microheater array was used to perform experiments over a wide range of temperatures (55 °C < Tw < 107.5 °C), pressures (0.58 atm < P < 1.86 atm), subcoolings (1 °C ≤ ΔTsub ≤ 26 °C), and heater sizes (4.2 mm ≤ Lh ≤ 7.0 mm). The boiling process was visualized from the side and bottom. Based on this high quality microgravity data (a/g<10−6), the recently reported gravity scaling parameter for heat flux, which was primarily based on parabolic flight experiments, was modified to account for these new results. The updated model accurately predicts the experimental microgravity data to within ±20%. The robustness of this framework in predicting low gravity heat transfer is further demonstrated by predicting many of the trends in the pool boiling literature that cannot be explained by any single model.

Swimming behaviour of the upside-down swimming catfish ( Synodontis nigriventris) at high-quality microgravity – A drop-tower experiment

The catfish Synodontis nigriventris often shows a unique swimming behaviour in being oriented upside-down. When swimming near a (e.g., vertical) substrate, however, the animals orient themselves with their ventral side towards this substrate. This tendency is called ventral substrate response (VSR). The VSR does not only override the upside-down swimming behaviour but also the dorsal light response and the ventral light response. In the course of an earlier drop-tower experiment performed at ZARM (Bremen, Germany) using cichlid fish ( Oreochromis mossambicus), we had observed that about 90% of the animals revealed sensorimotor disorders (kinetotic swimming) due to the almost complete lack of gravity as a cue for orientation. In order to further assess the importance of the VSR for postural control in S. nigriventris when being located near a substrate, we subjected catfish in relatively small chambers to drop-tower flights. In contrast to our results regarding cichlid fish, S. nigriventris showed no kinetotic behaviour. This clearly suggests that the VSR overrides even vestibular input and possibly represents the most important single behavioural response in this species.

Otolith asymmetry and kinetotic behaviour of fish at high-quality microgravity: A drop-tower experiment

It has been repeatedly shown earlier that some fish of a given batch reveal motion sickness (a kinetosis) at the transition from hypergravity to (low quality) microgravity in the course of parabolic aircraft flight (PF) experiments. Since it is unknown, whether this behaviour is exclusively induced by microgravity or rather by changing accelerations as they occur during PFs, larval cichlid fish ( Oreochromis mossambicus) were subjected to high-quality microgravity (ca. 4.7 s) in the drop-tower at ZARM, Bremen (Germany). The percentual ratios of the various types of behaviour (normal swimming and kinetotic swimming; kinetotic specimens revealed looping responses/LR or spinning movements/SM) highly differed from those observed in the course of PFs. Whereas kinetoses were exhibited by some 90% of the individuals who had experienced flights at ZARM (SM: 22%; LR: 69%; n = 156 animals), only a rather small proportion of all animals had shown a kinetotic behaviour during PFs (SM: 14%; LR: 10%; n = 71 animals; Hilbig, R., Anken, R., Rahmann, H. On the origin of susceptibility to kinetotic swimming behaviour in fish: a parabolic aircraft flight study. J. Vestib. Res. 12, 185–189, 2003). Thus, the percentual ratio of spinning animals is in a roughly comparable range both during PF and drop-tower microgravity, whereas looping responses are extremely frequently exhibited during exposure to the drop-tower microgravity environment. Since the release of the drop-capsule (total mass of the capsule used: 491 kg) will inevitably lead to a brisk longitudinal compression of the entire setup, many animals will have been provoked to perform a C-start escape response, which – during microgravity – was not discontinued and thus resulted in loop-swimming (like the looping observed during STS-89; Anken, R., Hilbig, R., Ibsch, M., Rahmann, H. Readaptation of fish to 1G after long-term microgravity: behavioural results from the STS 89 mission. Adv. Space Res. 25, 2019–2023, 2000). In striking contrast to the results gained using PF specimens, according to which otolith asymmetry (differences in the size of the inner ear stones between the left and right side of the body) was significantly higher in kinetotic specimens as compared to normally swimming fish, asymmetry did not differ between the SM, LR and normally swimming drop-tower samples. This finding is discussed on the basis of the especially low gravity environment in the drop-tower experiment.

Thermophoretic measurements in presence of thermal stress convection in aerosols in microgravity conditions of drop tower

The aim of the work is getting reference data on thermophoretic motion eliminating gravity-induced perturbation, developing new instrumentation and procedures. A series of experiments on measuring phoretic velocities was performed in the Bremen drop tower providing 4.7 s of high quality microgravity conditions, which allowed making negligible particle sedimentation and buoyancy driven convection. Motion of aerosol particles was observed simultaneously at low resolution to control nongravity convective motion in the cell and at high resolution by the digital holographic velocimeter in order to register particle three-dimensional trajectories. By choosing appropriate cell size and experimental procedures the heat and mass transfer relaxation processes were reduced to less than 0.3 s thus allowing measurements of particle velocities during more than 4 s. Side-wall temperature creep created convective motion in the cell. Its influence was suppressed by choosing sufficiently flat cell geometry. The values of the measured thermophoretic velocities for Knudsen number in the range 0.047–0.89 were found to be between predictions of the classical models of Talbot et al [1] on one hand and Yamamoto and Ishiara [2] on the other hand. Particles of different thermal conductivities (paraffin and NaCl) had about the same velocities. No negative thermophoresis was observed at these conditions for NaCl.

テザー宇宙ロボットの姿勢制御に関する微小重力実験

A tethered space robot, which is connected to a mother spacecraft through a peace of tether, is a new space system proposed in the previous work. The tethered subsystem is envisioned to be a multi-body system for a robot, whose attitude can be controlled under tether tension by its own link motion. This paper discusses about microgravity experiment for a tethered space robot. Design and mechanism of the experimental device, required for the proposed attitude control, were explained. Also, link motion control algorithm was designed for the experimental device. Characteristics of the proposed attitude control were confirmed by microgravity experiment using a drop shaft, which can provide high quality microgravity condition during 4.5s.

Vibration control in space

Most people are aware that the Space Shuttle is used to launch satellites, and occasionally to retrieve them, but far less prominence is given to the scientific programme. Some of the experiments conducted in Earth orbit are very sensitive to even the residual accelerations which exist on the Shuttle which are caused by vibration in mechanical subsystems and crew movement. This article describes some of the techniques which are being proposed to control vibration aboard spacecraft in order to secure a high-quality microgravity environment.