Microgravity Research Articles

Unsteady magneto bioconvective Sutterby nanofluid flow: Influence of g-Jitter effect

This study is driven by the potential applications of a microgravity environment in various sectors and fields of engineering, especially in the manufacturing of semiconductors. An electrically conducting bioconvective Sutterby nanofluid flow was considered around an exponentially stretching surface through g-Jitter and nonlinear thermal radiation effects. The dimensional partial differential equations (PDEs) that govern the fluid flow system are changed into nondimensional PDEs through nonsimilar transformations. Once these PDEs have been linearized using Quasilinearization, the implicit finite difference scheme is used to solve them numerically. A MATLAB code was constructed for the numerical calculations and for analysing the results via graphs. These findings indicate that the greater values of amplitude ε1 result in a steep rise in the velocity and surface drag near the sheet's wall for assisting buoyancy. An enhancement of approximately 108 % in the drag coefficient is observed when ε1(the amplitude in g-Jitter) jumps to 1 from 0. The percentile increments in heat transport strength due to the rise of radiation Rd from 1 to 2 is 80 %, and due to the intensification of the temperature difference ratio φw from 1.5 to 2 is about 167 %. Elevating Peclet number Pe led to the depletion of the microbial boundary layer thickness. Oxytactic microbes' presence impacts the enhanced mass transport strength of nanoparticles. The current findings have been validated by comparing them to previously published results, and they have been shown to be in perfect agreement with those results.

Adaptive and intelligent control of a dual-arm space robot for target manipulation during the post-capture phase

Dual-arm space robots provide a promising solution for efficiently and flexibly completing complex on-orbit servicing tasks. However, their effectiveness is often hindered by strong dynamic coupling between the robotic arms and the satellite base in the microgravity environment. In this paper, both robotic arms are used as task arms, and a system model that considers the closed-loop constraint formed after a dual-arm space robot captures a target is established. On this basis, two types of control strategies, namely self-tuning control strategy (STC) and radial basis function neural network control strategy (RBF) are proposed for trajectory tracking of the target transferred or detumbled by the robot arms in the presence of system uncertainty or external disturbances. The control methods are verified and compared against the traditional computed torque control strategy (CTC) in terms of control accuracy and system robustness through simulation. The results demonstrate the excellent robustness of both RBF and STC strategies. RBF outperforms the other strategies in terms of control accuracy, while STC proves to be the most energy-efficient.

1G and microgravity tank self-pressurization: Research on cryogenic fluid thermal stratification

A correlation numerical model was constructed, and relevant experiments were simulated to investigate the influence of gravity level on the self-pressurization process of the cryogenic fluid of liquid nitrogen. The calculated results agreed well with the experimental data. On this basis, the influences of a normal gravity environment and a microgravity environment on the self-pressurization process of liquid nitrogen in the normal-temperature fluid Perfluoro-n-Pentane (PnP, or C5F12) tank of National Aeronautics and Space Administration (NASA) were analyzed. According to the calculation results, an explicit horizontal interface is formed between the gas and liquid phases in the tank during the 1G (G = 9.81 m/s2) self-pressurization process. The ullage pressure increases as time progresses, and obvious thermal stratification phenomena are observed in the ullage along the axial and radial directions. However, the thermal stratification of the liquid zone is not obvious. The ullage near the gas‒liquid interface shifts from counterclockwise movement to clockwise movement, while the liquid changes from clockwise movement to counterclockwise movement. In the process of microgravity self-pressurization, the gas‒liquid interface in the tank presents an irregular shape, and the ullage pressure increases continuously before 400 s and then tends to be stable. The axial thermal stratification of fluid in the tank tends to disappear as time progresses, but obvious radial thermal stratification is observed. The ullage in the tank moves up and down as a response to the Marangoni migration effect. The temperature of the liquid zone in the tank during 1G self-pressurization tends to be consistent more quickly than that during microgravity self-pressurization, and the average temperature is higher. However, the temperature reduction rate of the ullage in the tank during microgravity self-pressurization is higher than that during 1G self-pressurization. Numerical simulation results can provide references to further study the on-orbit pressure control technique of cryogenic liquid tanks.

Modelled microgravity impacts Vibrio fischeri population structure in a mutualistic association with an animal host.

Perturbations to host-microbe interactions, such as environmental stress, can alter and disrupt homeostasis. In this study, we examined the effects of a stressor, simulated microgravity, on beneficial bacteria behaviours when colonising their host. We studied the bacterium Vibrio fischeri, which establishes a mutualistic association in a symbiosis-specific organ within the bobtail squid, Euprymna scolopes. To elucidate how animal-microbe interactions are affected by the stress of microgravity, squid were inoculated with different bacterial strains exhibiting either a dominant- or sharing-colonisation behaviour in High Aspect Ratio Vessels, which simulate the low-shear environment of microgravity. The colonisation behaviours of the sharing and dominant strains under modelled microgravity conditions were determined by counting light-organ homogenate of squids as well as confocal microscopy to assess the partitioning of different strains within the light organ. The results indicated that although the colonisation behaviours of the strains did not change, the population levels of the sharing strains were at lower relative abundance in single-colonised animals exposed to modelled microgravity compared to unit gravity; in addition, there were shifts in the relative abundance of strains in co-colonised squids. Together these results suggest that the initiation of beneficial interactions between microbes and animals can be altered by environmental stress, such as simulated microgravity.

Additive manufacturing of metallic glass from powder in space

Additive manufacturing of metals – and in particular building with laser-based powder bed fusion – is highly flexible and allows high-resolution features and feedstock savings. Meanwhile, though space stations in low Earth orbit are established, a set of visits to the Moon have been performed, and humankind can send out rovers to explore Venus and Mars, none of these milestone missions is equipped with technology to manufacture functional metallic parts or tools in space. In order to advance space exploration to long-term missions beyond low Earth orbit, it will be crucial to develop and employ technology for in-space manufacturing (ISM) and in-situ resource utilisation (ISRU). To use the advantages of laser-based powder bed fusion in these endeavours, the challenge of powder handling in microgravity must be met. Here we present a device capable of building parts using metallic powders in microgravity. This was proven on several sounding rocket flights, on which occasions Zr-based metallic glass parts produced by additive manufacturing in space were built. The findings of this work demonstrate that building parts using powder feedstock, which is more compact to transport into space than wire, is possible in microgravity environments. This thus significantly advances ISRU and ISM and paves the way for future tests in prolonged microgravity settings.

Gravitational Ischemia in the Brain: How Interfering with Its Release May Predispose to Either Alzheimer’s- or Parkinson’s-like Illness, Treatable with Hyperbaric Oxygen

The physiological mechanisms for releasing and resolving gravitational ischemia in the brain, and their susceptibility to malfunction, may play an important role in a variety of neurological illnesses. An astronaut on a space walk in a micro-gravity environment may be susceptible to neuro-ocular symptoms associated with unopposed gravity-resistance mechanisms for partially preventing gravitational ischemia in the brain, and for attenuating its impact—mechanisms which may be required for normal brain physiology on Earth. Astronauts on the International Space Station typically breathe a mixture of gasses similar in composition to what they breathed on Earth, following the 1967 death of three astronauts, including Ed White, by fire on the Apollo 1 spacecraft, which was carrying 100% oxygen. For the last decade, astronauts have been studied extensively by flight physicians regarding the commonly experienced symptoms of VIIP, or ‘visual impairment and intracranial pressure’ syndrome. In this paper, we compare VIIP syndrome to the neuro-ocular and Parkinson’s-like symptoms which occurred during and after the 1918–1919 influenza pandemic. The common denominator may be gravitational ischemia in the brain, and the mirror-imaging failed mechanisms for its release (in influenza) versus unopposed gravity-resistance mechanisms (in astronauts). Some research has suggested that astronauts may benefit from breathing oxygen concentrations somewhat higher than 20%, and under slightly elevated pressure. These may possibly prevent maladaptive mechanisms leading to Alzheimer’s- or Parkinson’s-like illness by compensating for impaired mechanisms for releasing and resolving gravitational ischemia in the brain.

The Impact of Microgravity on Immunological States.

As we explore other planetary bodies, astronauts will face unique environmental and physiological challenges. The human immune system has evolved under Earth's gravitational force. Consequently, in the microgravity environment of space, immune function is altered. This can pose problematic consequences for astronauts on deep space missions where medical intervention will be limited. Studying the unique environment of microgravity has its challenges, yet current research has uncovered immunological states that are probable during exploration missions. As microgravity-induced immune states are uncovered, novel countermeasure developments and personalized mitigation programs can be designed to improve astronaut health. This can also benefit immune-related monitoring programs for disorders on Earth. This is a comprehensive review, including gaps in knowledge, of simulated and spaceflight microgravity studies in human and rodent models.

X-Ray Imaging in the Simulated Microgravity Environment of Parabolic Flight.

INTRODUCTION: The advancement of human spaceflight has made urgent the need to develop medical imaging technology to ensure a high level of in-flight care. To date, only ultrasound has been used in spaceflight. Radiography has multiple advantages over ultrasound, including lower operator dependence, more rapid acquisition, typically higher spatial resolution, and characterization of tissue with acoustic impedance precluding ultrasound. This proof-of-concept work demonstrates for the first time the feasibility of performing human radiographs in microgravity.METHODS: Radiographs of a phantom and human subject's hand, knee, chest, cervical spine, and pelvis were obtained aboard a parabolic flight in microgravity and simulated lunar gravity with various subject and operator positions. Control radiographs were acquired with the same system on the ground. These radiographs were performed with a Food and Drug Administration-approved ultra-portable, wireless, battery-powered, digital x-ray system.RESULTS: The radiographs of the phantom acquired in reduced gravity were qualitatively and quantitatively compared to the ground controls and found to exhibit similar diagnostic adequacy. There was no statistically significant difference in contrast resolution or spatial resolution with a spatial resolution across all imaging environments up to the Nyquist frequency of 3.6 line-pairs/mm and an average contrast-to-noise ratio of 2.44.DISCUSSION: As mass, power, and volume limitations lessen over the coming decades and the miniaturization of imaging equipment continues, in-flight implementation of nonsonographic modalities will become practical. Given the demonstrated ease of use and satisfactory image quality, portable radiography is ready to be the new frontier of space medical imaging.Lerner D, Pohlen M, Wang A, Walter J, Cairnie M, Gifford S. X-ray imaging in the simulated microgravity environment of parabolic flight. Aerosp Med Hum Perform. 2023; 94(10):786-791.

Effects of heating configuration and operating parameters on heat transfer and interfacial physics of microgravity flow boiling with subcooled inlet conditions – Experiments onboard the International Space Station

This study is part of the Flow Boiling and Condensation Experiment (FBCE), a collaborative effort between the Purdue University Boiling and Two-Phase Flow Laboratory (PU-BTPFL) and the NASA Glenn Research Center. The FBCE fitted with the Flow Boiling Module (FBM) was launched to the International Space Station (ISS) in August 2021 and experiments were successfully performed from February to July 2022 to amass a large microgravity-flow-boiling database. This study is focused on heat transfer and flow visualization of microgravity flow boiling of n-Perfluorohexane in a rectangular channel of 5.0 mm height, 2.5 mm width (heated), and 114.6 mm length, with subcooled inlet conditions. High-speed-video photography is utilized to present flow patterns and temporal interfacial behavior. Heat transfer results are presented in the form of flow boiling curves and both parametric curves and streamwise profiles of wall temperature and heat transfer coefficient. Firstly, the parametric effects of mass velocity (199.4 – 3200.0 kg/m2s), inlet subcooling (0.2 – 46.0°C), and inlet pressure (124.2 – 176.7 kPa), on the aforementioned aspects are assessed for double-sided heating to establish them for a microgravity environment. Of these three parameters, mass velocity and inlet subcooling mostly determine the microgravity flow boiling behavior, while inlet pressure plays an insignificant role. Flow patterns for double-sided heating are more complex than those for single-sided heating due to interaction between the two vapor layers. Vapor interaction is minimized at high subcoolings and high mass velocities due to strong condensation offered by the subcooled bulk liquid layer separating them. Despite the different flow patterns, both single- and double-sided heating generally result in similar parametric trends and local heat transfer coefficients for similar operating conditions. Flow instabilities manifest as temporal flow anomalies and temperature oscillations, and their severity increases with increasing boiling number. Secondly, the effects of heating configuration are analyzed by comparing and contrasting several aspects of single- and double-sided heating data. The heat fluxes at which onset of nucleate boiling degradation (ONBD) and critical heat flux (CHF) occur are distinctly different for single- and double-sided heating. There exists a threshold inlet subcooling demarcating the dominance of flow acceleration and condensation effects in vapor removal from the near-wall region and replenishment of fresh liquid for boiling. Above the threshold, condensation from the near-wall region is dominant and single-sided heating yields higher heat fluxes, and below it, acceleration is dominant and double-sided yields higher heat fluxes. At mass velocity in the range of 200 – 2400 kg/m2s, the threshold inlet subcooling lies in the approximate range of 20 – 30°C (corresponding inlet quality of roughly -0.40 – -0.20).

Functional Meta-Analysis of the Proteomic Responses of Arabidopsis Seedlings to the Spaceflight Environment Reveals Multi-Dimensional Sources of Variability across Spaceflight Experiments.

The human quest for sustainable habitation of extraterrestrial environments necessitates a robust understanding of life's adaptability to the unique conditions of spaceflight. This study provides a comprehensive proteomic dissection of the Arabidopsis plant's responses to the spaceflight environment through a meta-analysis of proteomics data from four separate spaceflight experiments conducted on the International Space Station (ISS) in different hardware configurations. Raw proteomics LC/MS spectra were analyzed for differential expression in MaxQuant and Perseus software. The analysis of dissimilarities among the datasets reveals the multidimensional nature of plant proteomic responses to spaceflight, impacted by variables such as spaceflight hardware, seedling age, lighting conditions, and proteomic quantification techniques. By contrasting datasets that varied in light exposure, we elucidated proteins involved in photomorphogenesis and skotomorphogenesis in plant spaceflight responses. Additionally, with data from an onboard 1 g control experiment, we isolated proteins that specifically respond to the microgravity environment and those that respond to other spaceflight conditions. This study identified proteins and associated metabolic pathways that are consistently impacted across the datasets. Notably, these shared proteins were associated with critical metabolic functions, including carbon metabolism, glycolysis, gluconeogenesis, and amino acid biosynthesis, underscoring their potential significance in Arabidopsis' spaceflight adaptation mechanisms and informing strategies for successful space farming.

BubbleMask: Autonomous visualization of digital flow bubbles for predicting critical heat flux

Flow boiling utilizes the latent heat of the fluid to provide an efficient thermal management solution through bubble-induced advective transport. In microgravity environments, flow boiling becomes even more advantageous as macroscale flow helps efficiently remove bubbles from the heated wall, resulting in enhancing heat transfer as well as critical heat flux (CHF). However, connecting flow boiling physics and bubble information is a challenging task due to the complexity and high dimensionality of bubble dynamics. To overcome this challenge, the advances in computer vision techniques and models such as VISION-iT can be leveraged to autonomously extract physically meaningful features related to spatial statistics, interfacial characteristics, and bubble dynamics by digitalizing flow bubble information. In this study, 30,000 flow boiling images under microgravity conditions are used to compute ten different features of 155,000 individual bubbles. The extracted bubble information is then used to predict CHF by using a classical flow boiling model, the Interfacial Lift-off Model. This vision-based approach suggested here has the potential to revolutionize the study of such thermofluidic topics by providing visual insights that agree well with experimental data.

Sex differences in muscle health in simulated micro- and partial-gravity environments in rats

Skeletal muscle size and strength are important for overall health for astronauts. However, how male and female muscle may respond differently to micro- and partial-gravity environments is not fully understood. The purpose of this study was to determine how biological sex and sex steroid hormones influence the progression of muscle atrophy after long term exposure to micro and partial gravity environments in male and female rats. Male and female Fisher rats (n ​= ​120) underwent either castration/ovariectomy or sham surgeries. After two weeks recovery, animals were divided into microgravity (0g), partial-gravity (40% of weight bearing, 0.4g), or full weight bearing (1g) interventions for 28 days. Measurements of muscle size and strength were evaluated prior to and after interventions. At 0g, females lost more dorsiflexion strength, plantar flexion strength, and other metrics of muscle size compared to males; castration/ovariectomy did not influence these differences. Additionally, at 0.4g, females lost more dorsiflexion strength, plantar flexion strength, and other metrics of muscle strength compared to males; castration/ovariectomy did not influence these differences. Females have greater musculoskeletal aberrations during exposure to both microgravity and partial-gravity environments; these differences are not dependent on the presence of sex steroid hormones. Correspondingly, additional interventions may be necessary to mitigate musculoskeletal loss in female astronauts to protect occupational and overall health.

Bioinspired Rigid-Flexible Coupled Adaptive Compliant Motion Control of Robot Gecko for Space Stations.

This paper presents a study on bioinspired rigid-flexible coupling adaptive compliant motion control of a robot gecko with hybrid actuation for space stations. The biomimetic robot gecko is made of a rigid trunk, four motor-driven active legs with dual-degree-of-freedom shoulder joints, and four pneumatic flexible pleated active attachment-detachment feet. The adaptive impedance model consists of four input parameters: the inertia coefficient, stiffness coefficient, damping coefficient, and segmented expected plantar force. The robot gecko is equipped with four force sensors mounted on its four feet, from which the normal force of each foot can be sensed in real-time. Based on the sensor signal, the variable stiffness characteristics of the feet in different states are analyzed. Furthermore, an adaptive active compliance control strategy with whole-body rigidity-flexibility-force feedback coupling is proposed for the robot gecko. Four sets of experiments are presented, including open-loop motion control, static anti-interference experiment, segmented variable stiffness experiment, and adaptative compliant motion control, both in a microgravity environment. The experiment results indicated that the presented control strategy worked well and the robot gecko demonstrates the capability of stable attachment and compliant detachment, thereby normal impact and microgravity instability are avoided. It achieves position tracking and force tracking while exhibiting strong robustness for external disturbances.

Precise measurement method of carrier motion state in microgravity environment

In the field of aerospace and planetary science, precise measurement of the motion state of a moving carrier represents an important part of scientific exploration missions. the paper presents a fusion of the stereo vision and IMU to measure the velocity, angle, and angular velocity of a moving carrier precisely. First, a stereo camera self-calibration model with additional geometric constraints is developed, whichaccuracy of better than 0.379 pixels is achieved. Then, a three-dimensional reconstruction with accuracy of better than 0.727 pixels is achieved. Finally, the spatial relationship between the carrier, the stereo camera, and the IMU is used to determine the absolute pose change of the moving carrier relative to the center of the Earth. The proposed method ensures high measurement accuracy of the velocity, angle, and angular velocity of the moving carrier of better than 0.19 mm/s, 0.09°, and 0.127°/s, respectively, which can provide reliable technical support for the motion state estimation of deep space moving vehicles.

Calibration of the axial stiffness of a single-beam acoustic tweezers.

Single-beam acoustic tweezers have recently been demonstrated to be capable of selective three-dimensional trapping. This new contactless manipulation modality has great potential for many scientific applications. Its development as a scientific tool requires precise calibration of its radiation force, specifically its axial component. The lack of calibration for this force is mainly due to its weak magnitude compared to competing effects such as weight. We investigate an experimental method for the calibration of the axial stiffness of the radiation force by observing the axial oscillations of a trapped bead in a microgravity environment. The stiffness exhibits a linear relationship with the acoustic intensity and is of the mN/m order. Then, a predictive model, loaded with the experimental acoustic field, is compared to the measured stiffness with very good agreement, within a single amplitude coefficient. This study paves the way for the development of calibrated acoustic tweezers.

SIMULATED MICROGRAVITY CHANGES THE NUMBER OF MECHANICALLY GATED AND MECHANOSENSITIVE ION CHANNELS GENES TRANSCRIPTS IN RAT VENTRICULAR CARDIOMYOCYTES

The mechanoelectrical feedback in the heart is based on the work of mechanically gated (MGCs) and mechanosensitive (MSCs) channels. Since microgravity alters the heart’s morphological and physiological properties, we hypothesized that the expression of both MGCs and MSCs would be affected. We employed RNA transcriptome sequencing to investigate changes in the gene transcript levels of MGCs and MSCs in isolated rat ventricular cardiomyocytes under control conditions and in a simulated microgravity environment. For the first time, our findings demonstrated that simulated microgravity induces alterations in the gene transcript levels of specific MGCs, such as TRPM7, TRPV2, TRPP1, TRPP2, Piezo1, TMEM63A, TMEM36B, and known MSCs, including K2P2.1, K2P3.1, Kir6.1, Kir6.2, NaV1.5, CaV1.2, KV7.1. However, other voltage-gated channels and channels lacking a voltage sensor remained unaffected. These findings suggest that the altered expression of MGCs and MSCs could lead to changes in the net currents across the membrane, ultimately impacting the heart’s function.

Synergistic Microfluidic and Optical Performance Enhancements of Photoelectrodes for Space Applications

The realisation of long-term space missions as well as lunar habitats require reliable and efficient oxygen and chemical producing devices e.g., for life support, fuel generation and in-situ resource utilisation (ISRU). We have recently demonstrated that integrated semiconductor-electrocatalyst systems can be operated in microgravity environments generated for 9.2 s at the Bremen Drop Tower (Center of Applied Space Technology and Microgravity, ZARM) at terrestrial efficiencies, thus opening the possibility of utilising these photoelectrochemical (PEC) devices for chemical synthesis in space. 1,2 , 3 Our findings reveal that by altering the electrocatalyst surface morphology through nanostructuring, we can introduce catalytic hot-spots on the photoelectrode which - through their hydrophilic nature - can also enhance gas bubble detachment in microgravity and thus circumvent the near-absence of buoyancy.1,3 We have found that the surface hydrophilicity and electrocatalyst loading require however careful balancing as the most effective nanostructures for gas bubble desorption can also result in less catalyst material on the photoelectrode surface, which in turn leads to a non-optimal PEC device performance.Here, we present a combined theoretical and experimental microfluidic, optical and photoelectrocatalytic performance analysis of photoelectrodes with integrated, nanostructured electrocatalysts, aiming at providing a guideline for an optimal design for microgravity applications. Focusing on the hydrogen evolution reaction (HER) and a well-investigated photoabsorber for this reaction, p-type InP, we firstly built an optoelectronic model in COMSOL Multiphysics in pursuit of quantifying the optical performance enhancements of Rh and Pt electrocatalyst nanostructures such as nanopyramids, nanowires and sub-wavelength aperture holes.4 We then developed a microfluidic model using the same nanostructure geometries to predict the hydrophilicity of the device surface and subsequently, the gas bubble contact angle. The best-performing nanostructured photoelectrodes predicted in our models where then manufactured, photoelectrochemically tested and fully optically and spectroscopically characterised. Predicted local electric field enhancements through catalytic hotspot formation were moreover experimentally validated using scanning electrochemical cell microscopy (SECCM). Our findings indicate that our developed optoelectronic and microfluidic models can be utilised to design a theoretical framework for identifying ideal electrocatalyst nanostructures for microgravity applications.References Brinkert K, et al. Efficient solar hydrogen generation in microgravity environment. Nature Communications 9, (2018). Brinkert K, Mandin P. Fundamentals and future applications of electrochemical energy conversion in space. npj Microgravity 8, (2022). Akay Ö, et al. Releasing the Bubbles: Nanotopographical Electrocatalyst Design for Efficient Photoelectrochemical Hydrogen Production in Microgravity Environment. Advanced Science 9, 2105380 (2022). Tembhurne S, Haussener S. Integrated Photo-Electrochemical Solar Fuel Generators under Concentrated Irradiation. Journal of The Electrochemical Society 163, H988 (2016). Pan Y, Huang S, Li F, Zhao X, Wang W. Coexistence of superhydrophilicity and superoleophobicity: theory, experiments and applications in oil/water separation. Journal of Materials Chemistry A 6, 15057-15063 (2018).

Magnetically-Induced Buoyancy for Efficient Electrochemical Oxygen Production in Microgravity

The realization of long-term space travels and the establishment of a lunar research platform are challenged by the lack of technological device architectures for efficient, stable and continuous oxygen production. One obstacle is that the near-absence of buoyancy in microgravity results in hindered gas bubble desorption at the electrode-electrolyte interface, causing lower efficiencies for electrolyser systems when operating in space.1,2 The significantly reduced buoyancy force also has severe complications for phase separation, which is a crucial process for a variety of space technologies also including heat transfer, fuel production and removal of carbon dioxide from cabin air. Multiple approaches have been studied in the past to induce phase separation such as creating centrifugal force fields. These approaches lack however efficiency, stability and robustness.3,4 In our recent work, we demonstrate the use of magnetic polarisation to artificially induce buoyancy in the electrolytic oxygen evolution half-cell reaction and thus significantly increasing the overall half-cell efficiency. This was carried out in a series of experiments at the Bremen Drop Tower, Center of Space Technology and Microgravity (ZARM, Germany), where short-term microgravity conditions of 9.2 s were achieved.5,6. Chronoamperometric and cyclic voltammetry measurements on high-activity RuOx electrocatalyst structures on a Ti substrate were undertaken with and without a magnet in close proximity to the electrode to closely monitor the electrochemical performance in a three-electrode potentiostatic arrangement and to demonstrate the magnetic effect on gas bubble desorption during free fall. It was observed that current densities for the electrodes at a potential of +1.49 V vs RHE were significantly higher in the presence of a magnet. We conclude that magnetic phase separation can be utilised in electrolytic systems in reduced gravitational environments to efficiently detach oxygen bubbles from the electrode surface and operate the devices at higher efficiencies, providing a key advancement for future oxygen production in space missions.2,3,5 References Cheng, W.-H.; Richter, M. H.; May, M. M.; Ohlmann, J.; Lackner, D.; Dimroth, F.; Hannappel, T.; Atwater, H. A.; Lewerenz, H.-J. (2018). Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Lett., 3, 1795−1800.Saravanabavan, S.; Coulthard, C. T.; Kaur, M.; Brinkert, K. (2022). Catalysis in Space Environments. doi.org/10.1002/9783527830909.ch7 In: Hessel V., Stoudemire J., H. Miyamoto & I. D. Fisk (Eds.). In Space Manufacturing and Resources.Wiley-VCH. ISBN: 978-3-527-83091-6Romero-Calvo, Á.; Akay, Ö.; Schaub, H.; Brinkert, K. (2022). Magnetic phase separation in microgravity. npj Microgravity 8 (32). doi.org/10.1038/s41526-022-00212-9.Harvey, A.; Ramshaw, C.; Reay, D. A. Process Intensification: Engineering for Efficiency. Sustainability and Flexibility. 2nd edition. Butterworth- Heinemann; 201Brinkert, K.; Richter, M. H.; Akay, Ö.; Liedtke, J.; Giersig, M.; Fountaine, K. T.; Lewerenz, H. J. (2018). Efficient solar hydrogen production in microgravity environment. Commun. 9(2527). doi: 10.1038/s41467-018-04844-yhttps://www.zarm.uni-bremen.de/fileadmin/user_upload/drop_tower/Users_Manual_0412.pdf

Photoelectrochemical Devices for Oxygen and Fuel Production on Moon and Mars

Human space exploration and the realisation of a green energy economy on Earth are confronted with the same challenge: both require efficient, stable and reliable renewable energy systems.1 Currently existing solutions such as the water electrolyzer in operation on the International Space Station (ISS) for oxygen and hydrogen production are not feasible in future lunar and Martian habitats as they are too bulky and heavy to transport and they lack the required reliability and efficiency2. Photoelectrochemical (PEC) devices not only meet the weight and volume constraints imposed onto devices for space applications by utilising a monolithic design for light absorption, charge separation and catalysis,3 they can also directly be coupled to solar concentrators in order to harvest the abundant solar energy available in space. Despite the advantages, PEC devices are nearly exclusively researched and developed for terrestrial applications and only a very few examples explore the possibility of utilizing the integrated semiconductor-electrocatalyst systems for space applications.4 Here, we present an unprecedented theoretical analysis of the applicability of PEC devices for lunar solar water-splitting and Martian CO2 reduction. These target reactions are in line with roadmaps of international space organisations aiming at a habitat establishment on the lunar South Pole, where water ice is assumed to be present in the Shackleton Crater. Furthermore, the atmosphere on Mars is composed of about 96% gaseous CO2, motivating our choice to investigate Martian CO2 to CO and CH4 conversion.5 Both reaction products could be used as propulsion additives or as precursors for the synthesis of hydrocarbon-based molecules in analogy to terrestrial applications. Firstly, we calculated a refined Martian solar irradiance spectrum and established the theoretical framework to describe PEC devices on Moon and Mars before calculating device limiting efficiencies and expected product rates for realistic devices at different solar irradiance scenarios. Our findings emphasise that PEC devices are indeed applicable on Moon and Mars, particularly when coupled to solar concentrators. In addition, it is evident that gas diffusion electrodes (GDEs), which mark a significant part of CO2 reduction devices investigated terrestrially, are surprisingly not necessarily viable in situations of limited solar irradiance such as present on Mars.References Ross B, Haussener S, Brinkert K. Photoelectrochemical devices for oxygen and fuel production on Moon and Mars. In review. Brinkert K, Mandin P. Fundamentals and future applications of electrochemical energy conversion in space. npj Microgravity 8, (2022).Cheng W-H, et al. Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Letters 3, 1795-1800 (2018). Brinkert K, et al. Efficient solar hydrogen generation in microgravity environment. Nature Communications 9, (2018). Yoshizaki T, McDonough WF. The composition of Mars. Geochimica et Cosmochimica Acta 273, 137-162 (2020).

(Keynote) Releasing the Bubbles: Efficient Phase Separation in (Photo-)Electrochemical Devices in Microgravity Environment

One of the major challenges human space exploration faces is the absence of buoyancy forces in orbit. Consequently, phase separation is severely hindered which impacts a large variety of space technologies including propellant management devices, heat transfer and life support systems e.g., during the production of oxygen and the recycling of carbon dioxide. Of particular interest are hereby (photo-)electrochemical (PEC) devices as they can produce essential chemicals such as oxygen and hydrogen in two set-ups: either, by coupling the electrochemical cell to external photovoltaic cells as currently utilized on the International Space Station or by direct utilization of sunlight in a monolithic device, where integrated semiconductor-electrocatalyst systems carry out the processes of light absorption, charge separation and catalysis in analogy to natural photosynthesis in one system. The latter device is particularly interesting for space applications due to present mass and volume constraints. Here, we discuss two combined approaches to overcome phase separation challenges in (photo-)electrolyzer systems in reduced gravitational environments: using the hydrogen evolution reaction (HER) as a model reaction, we combine nanostructured, hydrophilic electrocatalyst surfaces for efficient gas bubble desorption with magnetically-induced buoyancy to direct the produced hydrogen gas bubbles on specific trajectories away from the (photo-)electrode surface. (Photo-)current-voltage (J-V) profiles obtained in microgravity environments generated for 9.2 s at the Bremen Drop Tower show that our systems can operate with our two-fold approach near terrestrial efficiencies. Simulations of gas bubble trajectories accompany our experimental observations, allowing us to attribute the achieved phase separation in the PEC cells to the increased electrode wettability as well as the systematic use of diamagnetic and Lorentz forces.