Present as well as future challenges of space exploration point to the need for improved thermal control systems. The “Effect of Marangoni Convection on Heat Transfer in Phase Change Materials” experiment, which is approved by ESA for execution on board the International Space Station, aims to contribute directly to current knowledge and basic understanding of heat and mass transport in phase change materials (PCMs) that incorporate a free surface in reduced gravity. The experiment will apply fixed temperatures to opposite ends of PCM samples held in cuboidal and cylindrical containers in order to drive controlled melting and solidification cycles that will be observed by means of optical cameras. The recorded images will be complemented by thermal measurements at key positions along the samples, which will allow different thermocapillary flow regimes to be distinguished according to their temporal dynamics. It is anticipated that thermal Marangoni (thermocapillary) convection will increase the heat transfer rate in these PCM devices by a significant factor (on the order of two or more) compared to melting governed by thermal diffusion (conduction). If the PCM designs prove robust, the experiment results can be expected to lead to substantial improvements in future designs for passive PCM applications in space missions.

A detailed numerical investigation of pattern selection for thermocapillary flow in rectangular containers in microgravity is presented. These dynamics are studied for liquid n-octadecane, an alkane with high Prandtl number (Pr = 52.53), due to its relevance to recent microgravity experiments. Pattern selection is analyzed in terms of the aspect ratio, I', and the applied Marangoni number, Ma. In short containers, the bifurcation picture is characterized by a transition from steady thermocapillary flow to a standing wave (SW) oscillatory mode as Ma is varied. This transition takes the form of a primary subcritical Hopf bifurcation accompanied by a secondary saddle node; these two bifurcations delimit a region of bistability. In large containers, the dynamics is characterized by a supercritical Hopf bifurcation that marks the transition from steady flow to a traveling wave (TW) mode. The critical Ma for this transition increases with I'. In intermediate containers, a complex pattern selection scenario is found, where both steady and oscillatory convection, in the form of either TWs or SWs, can appear depending on I' and Ma. Finally, we apply this bifurcation analysis to help explain recent results on thermocapillary flows during the melting of phase change materials in microgravity [Salgado S??nchez et al., A20 (2021)]. The temporal evolution of the phase change is characterized by an effective I' and Ma in the liquid phase. We find very good agreement between the flow transitions observed during melting and those predicted for the equivalent rectangular containers over the explored range of 1.5 I' 16.

The Thermocapillary Effects in Phase Change Materials in Microgravity (TEPiM) experiment investigated the potential of Marangoni convection for heat transfer enhancement in Phase Change Materials (PCMs) in weightlessness, where the large melting/solidification timescale compromises their performance as thermal control devices. The TEPiM experiment, which was conducted during the 65th ESA Parabolic Flight campaign, represents the first microgravity research of this nature. We present here the main scientific outcome of the experimental campaign by measuring the precise contribution of thermal Marangoni convection to the heat transfer rate of the system. The test cells, holding the experimental PCM and air, were heated to drive controlled solid/liquid phase transitions during the microgravity lapses provided in the flight. Careful observation of the melting front confirms the enhancing effect of thermocapillary convection on heat transport, able to increase the phase change rate by a factor of 1.88. This result strongly supports that, as natural convection is exploited on ground, the thermal Marangoni effect can be used in weightless conditions to improve PCMs performance.

This paper describes the European Space Agency (ESA) experiments devoted to study thermodiffusion of fluid mixtures in microgravity environment, where sedimentation and convection do not affect the mass flow induced by the Soret effect. First, the experiments performed on binary mixtures in the IVIDIL and GRADFLEX experiments are described. Then, further experiments on ternary mixtures and complex fluids performed in DCMIX and planned to be performed in the context of the NEUF-DIX project are presented. Finally, multi-component mixtures studied in the SCCO project are detailed.

The Thermocapillary Effects in Phase Change Materials in Microgravity (TEPiM) experiment aims to analyse the potential of Marangoni convection for heat transfer enhancement in Phase Change Materials (PCMs) in weightlessness, where the slow characteristic time of the phase change process constrains their use as thermal control devices. On ground, natural convection masks the influence of Marangoni flow, which means that quantifying each contribution to the heat transfer rate of the system precisely is not possible. In this sense, the microgravity environment provided by parabolic flights gives an excellent opportunity to execute an experiment on PCMs phase change coupled with thermocapillary convection, and retrieve useful data to validate theoretical and numerical models. We note that such microgravity research has never been performed prior to this project. In this paper, we describe the design, preparation and performance of the TEPiM microgravity experiment, executed during the 65th ESA Parabolic Flight campaign. The experiment cells, filled with solid n-octadecane and a layer of air, were heated to observe the melting process under the microgravity portions provided during the flight. The promising results obtained support the positive impact of thermocapillary effects in PCMs melting, and suggest themselves for further investigation. We also expect that the valuable lessons learned presented here will help the scientific community in developing future microgravity experiments of this nature.

We report on thermodiffusion experiments conducted on the International Space Station ISS during fall 2016. These experiments are part of the DCMIX (Diffusion and thermodiffusion Coefficients Measurements in ternary Mixtures) project, which aims at establishing a reliable data base of non-isothermal transport coefficients for selected ternary liquid mixtures. The third campaign, DCMIX3, focuses on aqueous systems with water/ethanol/triethylene glycol as an example, where sign changes of the Soret coefficient have already been reported for certain binary subsystems. Investigations have been carried out with the SODI (Selectable Optical Diagnostics Instrument) instrument, a Mach-Zehnder interferometer set up inside the Microgravity Science Glovebox in the Destiny Module of the ISS. Concentration changes within the liquids have been monitored in response to an external temperature gradient using phase-stepping interferometry. The complete data set has been made available in spring 2017. Due to additionally available measurement time, it was possible to collect a complete data set at 30∘C and an almost complete data set at 25∘C, which significantly exceeds the originally envisaged measurements at a single temperature only. All samples could be measured successfully. The SODI instrument and the DCMIX experiments have proven reliable and robust, allowing to extract meaningful data even in case of unforeseen laser instabilities. First assessments of the data quality have revealed six out of 31 runs with some problems in image contrast and/or phase step stability that will require more sophisticated algorithms. This publication documents all relevant parameters of the conducted experiments and also events that might have an influence on the final results. The compiled information is intended to serve as a starting point for all following data evaluations.

A comparative analysis of the vibratory environment of the DCMIX2/3 thermodiffusion experiments is presented here by using acceleration signals coming from different sensors placed in the Destiny, Columbus and Kibo modules. The es03 sensor nearest to the experimental device and located inside the Glovebox (Destiny module) has been defined as reference. Data were downloaded from the NASA PIMS website paying special attention to the runs coinciding with disturbances such as dockings or extravehicular activities (EVAs) as they could particularly affect the International Space Station (ISS) microgravity levels. The analyses have been made minute by minute for the three acceleration components by using the Frequency Factor Index (FFI), Spectral Entropy (SEN) and Root Mean Square (RMS) values evaluated over one-third-octave frequency bands. Spearman’s rank correlation coefficient and the coherence function have been used to investigate the degree of linear correlation between the reference signal and the other ones. SEN evolution showed different patterns compared to the reference. Also, RMS values surpassing the ISS microgravity limits were detected in all sensors, mainly at low frequency bands (< 10 Hz) and prevailing on z A direction. However the sensors located in the Destiny module better accomplished the ISS vibratory limits requirements. Finally, some degree of linear correlation at structural frequencies (< 3 Hz) has also been detected. Overall, the sensors placed in the Destiny, Columbus and Kibo modules presented different vibratory characteristics and, despite they offer valuable information of the whole environment, may not be sufficient to properly characterize DCMIX2/3 experiments.

In this work, a random statistical analysis has been used to compare the behavior of a classical PID and a Fuzzy controller for the attitude control of a nanosatellite. Both controllers were designed in a previous work. Here, their performance and robustness have been analyzed in a wide range of configurations and scenarios. This allows us to test and compare the accuracy, efficiency and robustness of both controllers, and in addition, to extrapolate the results from a particular satellite configuration to different satellite configurations, which facilitates the use of these algorithms in a wide range of missions.

Vibroequilibria theory, based on minimizing an averaged energy functional, predicts the quasi-equilibrium shape that a fluid volume will take when subjected to high-frequency vibrations. Here we present a detailed comparison of the predictions of vibroequilibria theory with the results of direct numerical simulations in horizontally vibrated rectangular containers, finding very good agreement over a range of parameters. The calculations also reveal an important difference in the behavior between small and large fluid volumes. With dimensionless volume larger than about 0.36, the symmetric vibroequilibria solution suffers a saddle-node instability prior to contact with the container bottom. This saddle-node bifurcation is analyzed using a simplified family of surfaces and shown to persist when gravity is included. Finally, an investigation of dynamic effects is presented, where a strong correlation is found between modulated subharmonic surface waves and the first odd sloshing mode. At large enough amplitude, this sloshing destroys the underlying vibroequilibria state and thus represents a possible instability for vibroequilibria in low viscosity fluids.

The dynamics of two weakly coupled parametric oscillators are studied in the neighborhood of the primary subharmonic instability. The nature of both primary and secondary instabilities depends in a critical way on the permutation symmetries, if any, that remain after coupling is considered, and this depends on the relative phases of the parametric forcing terms. Detailed bifurcation sets, revealing a complex series of transitions organized in part by Bogdanov-Takens points, are calculated for representative sets of parameters. In the particular case of out-of-phase forcing the predictions of the coupled oscillator model are compared with direct numerical simulations and with recent experiments on modulated cross waves. Both the initial Hopf bifurcation and the subsequent saddle-node heteroclinic bifurcation are confirmed.

The present work attempts to characterize the accelerometric environment of the DSC-DCMIX1 thermodiffusion experiment carried out in the International Space Station, from November 7th 2011 until January 16th 2012. Quasi-steady and vibrational/transient data coming from MAMS and SAMS2 sensors have been downloaded from the database of the PIMS NASA website. To be as exhaustive as possible, simultaneous digital signals coming from different SAMS2 sensors located in the Destiny and Columbus modules have also been considered. In order to detect orbital adjustments, dockings, undockings, as well as, quiescent periods, when the experiment runs were active, we have used the quasi-steady eight hours averaged (XA, YA and ZA) acceleration functions as well as the eight hours RMS ones. To determine the spectral contents of the different signals the Thomson multitaper and Welch methods have been used. On the other hand, to suppress the high levels of noise always existing in the raw SAMS2 signals, denoising techniques have been preferred for comparative reboostings considerations. Finally, the RMS values for specific 1/3 octave frequency bands showed that the International Space Station vibratory limit requirements have not been totally accomplished during both quiescent periods and strong disturbances, specially in the low frequency range.

This paper introduces the GeoFlow missions that were performed under microgravity conditions on board the Columbus Laboratory in the International Space Station (ISS) from the scientific operations standpoint. A brief introduction to the three GeoFlow experiments: GeoFlow, GeoFlow-2 and GeoFlow-2b is given, being their main purpose to capture some essential features of the Earth mantle convection. The major scientific requirements of each of the experiments are presented as an introduction for the scientific operations preparation and concept development description. Then, the activities performed in order to execute each of the experiments are presented in detail, focusing on the resolution of the several issues encountered during the mission. The outcomes and lessons learned from such long and complex missions close this paper.

An experiment in microgravity conditions aboard the TEXUS-23 mission was performed to obtain the deformation up to breakage of a cylindrical liquid column in isorotation around an eccentric axis. In previous work, breakage rotation speed was predicted by a numerical method. This method was validated by comparison with analytical and experimental results. The non-symmetric breakage of the liquid column observed in the experiment, however, was not explained by the combined effect of rotation and eccentricity.In this work we use an extension of that method that includes an axial gravitational field. Thus the combined effect of rotation, eccentricity and axial gravity in the stability threshold and in the shape of the liquid bridge is analyzed. In particular, this analysis has allowed us to understand the non-symmetric breakage of the liquid column in the experiment. (C) 2013 COSPAR. Published by Elsevier Ltd. All rights reserved.

Cross-wave descriptions based on a boundary forced nonlinear Schrodinger equation, which have been widely used since Jones [J. Fluid Mech. 138, 53–74 (1984)], rely on the assumption that modulations occur on a slow lengthscale compared with the extent of the forcing. This assumption does not hold for recent higher frequency (large aspect ratio) experiments. We extend the established theory of modulated cross-waves in horizontally vibrated containers by including surface tension and, most importantly, a spatially extended forcing term. The resulting amplitude equations provide predictions for onset values, spatial profiles, and temporal modulations that are compared with previous theory and with experimental measurements. The appearance of temporally modulated solutions, confirmed experimentally, is interpreted as the result of weak symmetry-breaking related to the interaction of waves generated at opposite ends.

We investigate pattern selection at onset in a parametrically and inhomogeneously forced partial differential equation obtained by generalizing Mathieu's equation to include spatial interactions. No separation of scales is assumed. The proposed model is directly relevant to the case of parametrically forced surface waves, such as cross-waves, excited by the horizontal vibration of a fluid, where the forcing is localized to a finite region near the endwall or wavemaker. The availability of analytical solutions in the limit of piecewise constant forcing allows us investigate in detail the dependence of selected eigenfunctions on spatial detuning, forcing width, damping, boundary conditions, and container size. A wide range of onset patterns are located and described, many of which are rotated, modulated, or both, and deviate far from simple crosswise oriented standing waves. The linear selection mechanisms governing this multiplicity of potential onset patterns are discussed.

We present results of an experimental and numerical investigation of the patterns realized by surface waves within an open rectangular container subjected to horizontal vibrations at frequencies of 40–100 Hz. The first instability exhibited by the primary harmonic wave field is subharmonic, and may be identified with the cross-wave instability often seen in wave tank experiments. We show that, contrary to common theoretical and experimental assumptions, and despite their name, these subharmonic waves are not oriented crosswise, but at an intermediate angle with respect to the axis of vibration. Hence, the pattern selection problem for horizontally forced Faraday waves is more complex than has previously been assumed. We establish the robustness of this obliquely oriented surface wave pattern by varying the forcing frequency and amplitude, the fluid viscosity, the fluid depth, and the boundary conditions. Previous work on cross-waves is reviewed and discussed in relation to the current results. Finally, numerical simulations using a reduced model with an appropriate forcing term are used to support the generality of the experimental observations.