Reduced Gravity Environment Research Articles

Microgravity effects on nonequilibrium melt processing of neodymium titanate: thermophysical properties, atomic structure, glass formation and crystallization

The relationships between materials processing and structure can vary between terrestrial and reduced gravity environments. As one case study, we compare the nonequilibrium melt processing of a rare-earth titanate, nominally 83TiO2-17Nd2O3, and the structure of its glassy and crystalline products. Density and thermal expansion for the liquid, supercooled liquid, and glass are measured over 300–1850 °C using the Electrostatic Levitation Furnace (ELF) in microgravity, and two replicate density measurements were reproducible to within 0.4%. Cooling rates in ELF are 40–110 °C s−1 lower than those in a terrestrial aerodynamic levitator due to the absence of forced convection. X-ray/neutron total scattering and Raman spectroscopy indicate that glasses processed on Earth and in microgravity exhibit similar atomic structures, with only subtle differences that are consistent with compositional variations of ~2 mol. % Nd2O3. The glass atomic network contains a mixture of corner- and edge-sharing Ti-O polyhedra, and the fraction of edge-sharing arrangements decreases with increasing Nd2O3 content. X-ray tomography and electron microscopy of crystalline products reveal substantial differences in microstructure, grain size, and crystalline phases, which arise from differences in the melt processes.

Granular sample collection simulation via counter rotating wheels sampler for small-sized system at reduced gravity environment

Granular sample collection simulation via counter rotating wheels sampler for small-sized system at reduced gravity environment

Cryogenic flow boiling in microgravity: Effects of reduced gravity on two-phase fluid physics and heat transfer

With the growing interest in space exploration, cryogenic technologies involving two-phase flow and heat transfer are in high demand to successfully procure advanced space applications such as fuel depots and nuclear thermal propulsion (NTP) systems for deep space missions. However, the unique and extreme thermal properties of cryogenic fluids introduce distinct flow boiling fluid physics and energy transport phenomena, which differ significantly from those observed with conventional fluids. Understanding the unique two-phase physics in cryogenic flow boiling remains an ongoing challenge. Furthermore, the lack of readily available microgravity cryogenic steady-state heat transfer data hinders the assessment of gravitational effects on cryogenic flow boiling. This study aims to elucidate the gravitational effects on two-phase fluid physics and heat transfer by conducting the first-ever experimental measurement of cryogenic flow boiling performance using a steady-state heated method in a reduced gravity environment. Parabolic flight experiments were performed to acquire both heat transfer measurements and high-speed video of interfacial behaviors, under varying gravity levels (microgravity, hypergravity, Lunar gravity, and Martian gravity). The experiments involved flow boiling of liquid nitrogen (LN2) with a near-saturated inlet along a circular heated tube of dimensions 8.5-mm inner diameter and 680-mm heated length. The operating parameters varied are mass velocity of 398.3 – 1342.8 kg/m2s, inlet quality of -0.08 to -0.01, and inlet pressure of 413.68 – 689.48 kPa. Captured microgravity flow patterns range from bubbly to annular, all having vapor structures that are larger than those under higher gravity levels. Under microgravity, absence of buoyancy yields symmetrical vapor structures without flow stratification, laying a physical foundation for the distinct two-phase heat transfer trends during LN2 flow boiling in microgravity. Transient data collected during the flight parabolas exhibited decreasing heated wall temperature as the aircraft transitioned from hypergravity to microgravity phases. The temperature variation indicated an enhancement in flow boiling heat transfer with decreasing gravity levels and a reduction with increasing gravity levels. The effect of reduced gravity on cryogenic flow boiling heat transfer coefficient (HTC) is discussed based on steady state heat transfer analysis. Seminal HTC correlations are evaluated against the measured microgravity HTC data, of which one is identified for superior accuracy in predicting microgravity data. Finally, a new HTC correlation is proposed to improve accuracy of microgravity predictions, yet there still exists room for further improvement with future terrestrial flow boiling experiments at different flow orientations relative to Earth gravity.

Experimental proof-of-concept of the effect of inlet geometry on excavation forces and their reduction for small-scale continuous excavators

Future in situ resource utilisation (ISRU) lunar mission concepts will require mechanisms that allow the available feedstock–mainly the lunar regolith–to be extracted from the lunar surface. Such extraction techniques in the reduced gravity environment of the Moon will need to minimise excavation forces, due to mass restrictions for robotic landers/vehicles and the large financial implications of placing cargo onto Earth’s satellite. An investigation of necessary excavation forces, both horizontally as well as vertically, for small-scale continuous lunar excavation systems based on their geometric inlet shapes, cutting angles, and digging depths has been undertaken. The use of vibration to disaggregate lunar soil and to reduce the necessary forces is explored as a proof-of-concept. Tests performed in a large analogue testbed have shown that the optimisation of the cutting geometry is crucial, as it inherently influences the necessary forces or even prevents deeper cuts into the soil. Our experiments indicate that shallow cuts (low digging depth) into soil at shallow angles are beneficial, and that the piling up of large surcharge masses must be avoided. Critically, applying vibration to cutting edges seems highly beneficial, as the achievable force reductions of up to 50% in the tested conditions far outweigh the additional power requirements. To make these implications immediately applicable to a wider audience, an estimation of available traction forces for certain robotic vehicles based on their mass is added for comparison.

Preliminary Design of a Space Habitat Thermally Controlled Using Phase Change Materials

We explore the preliminary design of a space habitat thermally controlled using phase change materials (PCMs). The PCM is used to maintain a suitable, habitable temperature inside the habitat by isolating it from the external solar radiation. The system is studied numerically considering only diffusive heat transport (conduction), a scenario with practical application to microgravity or reduced gravity environments. The system dynamics are explored for a wide range of governing parameters, including the length of the PCM cell L, the thermo-optical properties—absorptivity α and emissivity ε—at the external boundary of the habitat wall exposed to solar radiation, the eclipse (illumination) fraction τe (τi) of the solar cycle, and the PCM used. We find that the thermo-optical properties at the external radiated boundary, characterized by the absorptivity–emissivity ratio (α/ε), play a key role in the system response and largely define the optimal design of the habitat. This optimum balances the heat absorbed and released by the PCM during repeated illumination and eclipse cycles.

CHARACTERIZATION OF A CAPILLARY-DRIVEN FLOW IN MICROGRAVITY BY MEANS OF OPTICAL TECHNIQUE

The motion of a gas-liquid interface along a solid wall is influenced by the capillary forces resulting from the interface's shape and its interaction with the solid, where it forms a dynamic contact angle. Capillary models play a significant role in the management of cryogenic propellants in space, where surface tension dominates the behavior of gas-liquid interfaces. Yet most empirical models have been derived in configurations dominated by viscous forces. In this study, we experimentally investigate the wetting of a low-viscosity, highly wetting fluid in a reduced gravity environment. Our setup consisted of a transparent and diverging U-tube in which capillary forces sustain the liquid motion. Combining particle image velocimetry (PIV) and high-speed backlighting visualization, the experimental campaign allowed for measuring the interface evolution and the velocity field within the liquid under varying gravity levels. This work reports on the preliminary results from the image velocimetry and shows that the velocity profile within the tube is close to parabolic until a short distance from the interface. Nevertheless, classic 1-D models for capillary rise face difficulties reproducing the interface dynamics, suggesting that the treatment of the surface tension in these problems must be reviewed.

-Omics studies of plant biology in spaceflight: A critical review of recent experiments

Researchers have been studying transcriptomic and proteomic responses of plants to ranges of reduced gravitational conditions. These include blue and red light in microgravity, circadian rhythms in microgravity, microgravity in different ecotypes, microgravity on suborbital flights, and they have using a variety of experimental equipment. Recent findings have linked microgravity and transcriptomic changes in genes relating to cell wall synthesis and modification, oxidative stress, abiotic stressors, phytohormones, sugar synthesis and metabolism, ribosomal biogenesis, and plant defense to other organisms. Although we have a better-established profile of the transcriptomic response of plants to reduced gravity, some areas of study have not yet been thoroughly investigated. The initial stages and progression of transcriptional responses to microgravity, the responses of additional plant species, and tissue-specific transcriptional responses to microgravity should all be further investigated in order to better develop our understanding of how plants react to a reduced gravity environment. In the near future, advancing technology, rapidly growing databases, and an increasing number of spaceflight opportunities will allow for more research to be conducted to address these and many other related questions in plant space biology.

Thermophysical Property Measurements of Refractory Oxide Melts With an Electrostatic Levitation Furnace in the International Space Station

Due to their high melting temperatures and the risk of contamination from the crucibles, molten oxides which melting temperatures are above 2000 °C can hardly be processed using conventional methods. This explains that their thermophysical properties are very scarce. Containerless methods with gas flows have been developed and several thermophysical properties such as density, surface tension, and viscosity have been reported. However, the gas flow has detrimental side effects such as deformation of the sample and induction of internal flows in the molten sample, which affect the accuracy of the measurements. The electrostatic levitation furnace onboard the International Space Station (ISS-ELF), which utilizes the Coulomb force to levitate and melt samples in microgravity, has several advantages for thermophysical property measurements of refractory oxide melts. Levitation without a gas flow coupled to a reduced gravity environment minimizes the required levitation (positioning) force and reduces the deformation as well as the internal flow. This report briefly introduces the ISS-ELF facility and the thermophysical property measurement methods. The measured density, surface tension, and viscosity of molten Al2O3 are then presented and compared with the ones obtained by other methods. Finally, the measured data of refractory oxides whose melting temperatures are above 2,400 °C are summarized.

Effects of walking, running, and skipping under simulated reduced gravity using the NASA Active Response Gravity Offload System (ARGOS)

Past research efforts have focused on the energy difference between altered locomotion methods in reduced gravity at different speeds, suggesting that skipping is energetically more efficient than walking and running in these environments. While skipping may be more beneficial from an energy standpoint, the full range of reasons behind the gait transition and locomotion selection have not been researched. This includes damage to the leg muscles, which is partially prevented by a transition from walking to running locomotion methods known as the walk-run transition. In a space environment, these factors will play a role in astronaut health and injury prevention. Participants walked, ran, and skipped on a treadmill for this study while being supported by an analog for activity on other planets called the Active Response Gravity Offload System (ARGOS). These intervals were performed under 1g, then under simulated 0.38g, and 0.17g conditions to simulate gravity conditions on Mars and the Moon. Electromyography was used to monitor muscle activation, along with the Vicon motion capture system for 3D motion analysis. Results show that there are significant changes (p <0.05) in activation of the TA and MG under simulated Martian and Lunar gravity conditions, as well as significant changes (p <0.05) in dorsiflexion and plantar flexion under several conditions. These findings suggest that there are fundamental changes in the way humans move in these reduced gravity environments and that the effect these changes have on the body should be included in the development of astronaut training regimen and equipment development. These changes may affect safety issues associated with locomotion, including increased trip and fall risks. Additionally, the reduction of energy expenditure demonstrated in this study, as well as detrimental effects from gait asymmetry on muscle growth, may prove to be counterproductive to efforts meant to reduce muscle and bone degradation in reduced gravity environments. The efficacy of running or skipping as preferred methods of locomotion in reduced gravity environments are yet to be sufficiently supported by gait analysis.

Effect of Water Depth on Heart Rate and Core Temperature During Underwater Treadmill Walking

Exercising using an underwater treadmill (UTM) has become a popular modality; however, few studies have focused on the physiological demands of UTM walking at varying water depths. Thus, the objective of this study was to investigate changes in heart rate (HR) and core temperature (CT) values in college-aged males and females while exercising at different water immersion depths using an UTM. Twenty participants (age = 21.50 ± 2.19 years; height = 169.04 ± 10.85cm; weight = 75.56 ± 22.28kg) walked at water depths of 10cm below the xiphoid process and at the level of the superior iliac crest (I.C.). Each UTM session lasted 15 minutes, consisting of 5-minute bouts at 1, 2, and 3 mph. Polar HR monitors and ingestible thermoregulatory pills were used to measure HR and CT. Results indicated that HR at 1 (p = .305) and 2 mph (p = .864) were not significantly different between water depths. Heart rate was significantly higher at 3 mph (p = .003) at the I.C. water level. No significant differences were found in CT at 1 (p = .919), 2 (p = .392), or 3 mph (p = .310) during either immersion depth. As a result, higher immersion depths resulted in a lower average HR during higher intensity exercise due to the increased buoyancy effects and the reduced gravity environment of the water. Thus, exercising in higher immersion depths allows participants to exercise at a higher intensity with less overall stress placed on the lower extremities.

A model to predict the oscillation frequency for drops pinned on a vertical planar surface

Accurate prediction of the natural frequency for the lateral oscillation of a liquid drop pinned on a vertical planar surface is important to many drop applications. The natural oscillation frequency, normalized by the capillary frequency, is mainly a function of the equilibrium contact angle and the Bond number ( $Bo$ ), when the contact lines remain pinned. Parametric numerical and experimental studies have been performed to establish a comprehensive understanding of the oscillation dynamics. An inviscid model has been developed to predict the oscillation frequency for wide ranges of $Bo$ and the contact angle. The model reveals the scaling relation between the normalized frequency and $Bo$ , which is validated by the numerical simulation results. For a given equilibrium contact angle, the lateral oscillation frequency decreases with $Bo$ , implying that resonance frequencies will be magnified if the drop oscillations occur in a reduced gravity environment.

Characterization of simultaneous heat, oxygen, and carbon dioxide transfer across a nonporous polydimethylsiloxane (PDMS) hollow fiber membrane

The provision of atmospheric oxygen, removal of carbon dioxide and heat is essential to sustain crew health during human spaceflight missions. Microgravity and reduced gravity environments (such as a planetary surface) limit the use of bubble-forming technologies, since surface tension and inertial or viscous forces may dominate buoyancy, creating an adverse effect in the system. Gas-to-liquid contacting membranes would allow for non-bubbling mass transfer through solution-diffusion, with the potential for simultaneous heat transfer, as done in membrane distillation operations. Previously published work, with similar applications, have focused on characterizing microporous membranes. In this study, a commercially available, nonporous polydimethylsiloxane (PDMS) hollow fiber membrane separated carbon dioxide from an ambient gas stream (296 K) while deoxygenating a cooling-water feed (274 K). Control experiments were conducted with gas and water at ambient temperatures (296 K and 292 K, respectively). Results show that increasing water feed rate (0.5 to 1.5 LPM) reduced the percentage of oxygen transferred from the water to the gas stream (approximately 25% less). Also, a reduction in water temperature significantly reduced percent oxygen transferred (approximately 35% reduction). System heat transfer and carbon dioxide transfer rates were positively correlated to gas flow rates, showing gas-phase dependence. Coefficients derived from the experimental results were used to form semi-empirical mass transport models. Results of this study developed two findings, that a nonporous PDMS membrane could be used for simultaneous heat and mass transfer which could also be described from first-order principles.

From Spaceflight to Mars g-Levels: Adaptive Response of A. Thaliana Seedlings in a Reduced Gravity Environment Is Enhanced by Red-Light Photostimulation.

The response of plants to the spaceflight environment and microgravity is still not well understood, although research has increased in this area. Even less is known about plants’ response to partial or reduced gravity levels. In the absence of the directional cues provided by the gravity vector, the plant is especially perceptive to other cues such as light. Here, we investigate the response of Arabidopsis thaliana 6-day-old seedlings to microgravity and the Mars partial gravity level during spaceflight, as well as the effects of red-light photostimulation by determining meristematic cell growth and proliferation. These experiments involve microscopic techniques together with transcriptomic studies. We demonstrate that microgravity and partial gravity trigger differential responses. The microgravity environment activates hormonal routes responsible for proliferation/growth and upregulates plastid/mitochondrial-encoded transcripts, even in the dark. In contrast, the Mars gravity level inhibits these routes and activates responses to stress factors to restore cell growth parameters only when red photostimulation is provided. This response is accompanied by upregulation of numerous transcription factors such as the environmental acclimation-related WRKY-domain family. In the long term, these discoveries can be applied in the design of bioregenerative life support systems and space farming.

Test Data Analysis of the Vented Chill, No-Vent Fill Liquid Nitrogen CRYOTE-2 Experiments

NASA is interested in developing efficient methods with which to transfer cryogenic propellants to enable future in-space cryogenic propellant vehicles, particularly the cryogenic fuel depot. The process of transferring cryogenic propellants between two vessels in a reduced gravity environment is complicated by the low normal boiling point of cryogens, high propensity for boiling during tank chilldown, and the fact that liquid cannot be transferred with the receiver tank vent valve open to space. This paper presents test data analysis of the liquid nitrogen vented chill, no-vent fill (NVF) experiments on the CRYOTE-2 tank. 53 tests were conducted, and while not originally intended, were performed in a somewhat parametric fashion. Performance between three different injectors are compared, as well as the effect of initial receiver tank wall temperature, receiver tank fluid initial condition, supply pressure, mass flow rate, and trigger point on the NVF process. From in-depth test data analysis, the highest performing injector based on maximizing evaporation heat and mass transfer between droplets and ullage as well as condensation heat transfer at the liquid/vapor interface, was the 3-spray injector.

Neutrophil-to-Lymphocyte Ratio: A Biomarker to Monitor the Immune Status of Astronauts.

A comprehensive understanding of spaceflight factors involved in immune dysfunction and the evaluation of biomarkers to assess in-flight astronaut health are essential goals for NASA. An elevated neutrophil-to-lymphocyte ratio (NLR) is a potential biomarker candidate, as leukocyte differentials are altered during spaceflight. In the reduced gravity environment of space, rodents and astronauts displayed elevated NLR and granulocyte-to-lymphocyte ratios (GLR), respectively. To simulate microgravity using two well-established ground-based models, we cultured human whole blood-leukocytes in high-aspect rotating wall vessels (HARV-RWV) and used hindlimb unloaded (HU) mice. Both HARV-RWV simulation of leukocytes and HU-exposed mice showed elevated NLR profiles comparable to spaceflight exposed samples. To assess mechanisms involved, we found the simulated microgravity HARV-RWV model resulted in an imbalance of redox processes and activation of myeloperoxidase-producing inflammatory neutrophils, while antioxidant treatment reversed these effects. In the simulated microgravity HU model, mitochondrial catalase-transgenic mice that have reduced oxidative stress responses showed reduced neutrophil counts, NLR, and a dampened release of selective inflammatory cytokines compared to wildtype HU mice, suggesting simulated microgravity induced oxidative stress responses that triggered inflammation. In brief, both spaceflight and simulated microgravity models caused elevated NLR, indicating this as a potential biomarker for future in-flight immune health monitoring.

Aquatic invertebrate protein sources for long-duration space travel

During the summer of 2020, NASA returned to launching astronauts to the International Space Station (ISS) from American soil. By 2024, NASA's mission is to return to the Moon, and by 2028 create a sustainable presence. Long duration missions come with obstacles, especially when trying to create a sustainable environment in a location where “living off the land” is impossible. Some resources on the Moon can be recovered or resupplied; however, many resources such as those needed for sustaining life must be recycled or grown to support humans. To achieve sustainability, food and water must be grown and recycled using elements found within the habitat. NASA's current work focuses on food resupply and growing plants as supplemental nutrient content. This paper examines the possibility for using aquaculture systems to purify water while growing nutrient-rich species as food sources, which aquatic food sources would be ideal for a habitat environment, and which species might provide an ideal test case for future studies aboard ISS. The aquatic species should be rapidly grown with high protein content and low launch mass requirements. Although there are numerous challenges and unknown technology gaps for maintaining aquaculture systems in reduced gravity environments, the benefit of employing such systems would be of great advantage towards creating a sustainable presence beyond Earth's orbit for sustainable aquaculture.

Nanopore sequencing at Mars, Europa, and microgravity conditions

Nanopore sequencing, as represented by Oxford Nanopore Technologies’ MinION, is a promising technology for in situ life detection and for microbial monitoring including in support of human space exploration, due to its small size, low mass (~100 g) and low power (~1 W). Now ubiquitous on Earth and previously demonstrated on the International Space Station (ISS), nanopore sequencing involves translocation of DNA through a biological nanopore on timescales of milliseconds per base. Nanopore sequencing is now being done in both controlled lab settings as well as in diverse environments that include ground, air, and space vehicles. Future space missions may also utilize nanopore sequencing in reduced gravity environments, such as in the search for life on Mars (Earth-relative gravito-inertial acceleration (GIA) g = 0.378), or at icy moons such as Europa (g = 0.134) or Enceladus (g = 0.012). We confirm the ability to sequence at Mars as well as near Europa or Lunar (g = 0.166) and lower g levels, demonstrate the functionality of updated chemistry and sequencing protocols under parabolic flight, and reveal consistent performance across g level, during dynamic accelerations, and despite vibrations with significant power at translocation-relevant frequencies. Our work strengthens the use case for nanopore sequencing in dynamic environments on Earth and in space, including as part of the search for nucleic-acid based life beyond Earth.

Validating N-body code chrono for granular DEM simulations in reduced-gravity environments

ABSTRACT The Discrete Element Method (DEM) is frequently used to model complex granular systems and to augment the knowledge that we obtain through theory, experimentation, and real-world observations. Numerical simulations are a particularly powerful tool for studying the regolith-covered surfaces of asteroids, comets, and small moons, where reduced-gravity environments produce ill-defined flow behaviours. In this work, we present a method for validating soft-sphere DEM codes for both terrestrial and small-body granular environments. The open-source code chrono is modified and evaluated first with a series of simple two-body-collision tests, and then, with a set of piling and tumbler tests. In the piling tests, we vary the coefficient of rolling friction to calibrate the simulations against experiments with 1 mm glass beads. Then, we use the friction coefficient to model the flow of 1 mm glass beads in a rotating drum, using a drum configuration from a previous experimental study. We measure the dynamic angle of repose, the flowing layer thickness, and the flowing layer velocity for tests with different particle sizes, contact force models, coefficients of rolling friction, cohesion levels, drum rotation speeds, and gravity levels. The tests show that the same flow patterns can be observed at the Earth and reduced-gravity levels if the drum rotation speed and the gravity level are set according to the dimensionless parameter known as the Froude number. chrono is successfully validated against known flow behaviours at different gravity and cohesion levels, and will be used to study small-body regolith dynamics in future works.

Discrete element modelling for wheel-soil interaction and the analysis of the effect of gravity

The discrete element method (DEM) is widely seen as one of the more accurate, albeit more computationally demanding approaches for terramechanics modelling. Part of its appeal is its explicit consideration of gravity in the formulation, making it easily applicable to the study of soil in reduced gravity environments. The parallel particles (P2) approach to terramechanics modelling is an alternate approach to traditional DEM that is computationally more efficient at the cost of some assumptions. Thus far, this method has mostly been applied to soil excavation maneuvers. The goal of this work is to implement and validate the P2 approach on a single wheel driving over soil in order to evaluate the applicability of the method to the study of wheel-soil interaction. In particular, the work studies how well the method captures the effect of gravity on wheel-soil behaviour. This was done by building a model and first tuning numerical simulation parameters to determine the critical simulation frequency required for stable simulation behaviour and then tuning the physical simulation parameters to obtain physically accurate results. The former were tuned via the convergence of particle settling energy plots for various frequencies. The latter were tuned via comparison to drawbar pull and wheel sinkage data collected from experiments carried out on a single wheel testbed with a martian soil simulant in a reduced gravity environment. Sensitivity of the simulation to model parameters was also analyzed. Simulations produced promising data when compared to experiments as far as predicting experimentally observable trends in drawbar pull and sinkage, but also showed limitations in predicting the exact numerical values of the measured forces.

Development of a mechanistic model of leaf surface gas exchange coupling mass and energy balances for life-support systems applications

Growing plants in space during long-duration missions will be crucial to ensure functions such as food production, air revitalization, and water purification, and requires an in-depth understanding of plant growth and development processes in reduced gravity. In particular, gas exchange at the leaf surface is considerably reduced because of lack or reduction of buoyancy-driven convection, which can translate into reduced biomass production in the long run. To quantify this impaired gas exchange and biomass production, this study formulates a mechanistic model of these variables in low gravity following a chemical engineering approach. The emphasis here is set on short-term physical response of gas exchange at the leaf surface to gravity and airspeed. A mass balance with stoichiometric limitations enables the computation of mass exchange fluxes, and an energy balance relates them to heat transfer fluxes. Leaf surface temperature and biomass production in the form of dry mass and free water mass are then subsequently computed. The validation of this model on sets of independent data from published parabolic flight experiments is presented and a sensitivity study to different parameters highlights the existence of threshold values for gravity, ventilation, light, and stomatal conductance, which dictate the magnitude of changes in leaf surface temperature and photosynthesis rate. These results show that a mechanistic modeling approach coupled to a dedicated experimental approach are key to identify adequate growth conditions for plants in reduced gravity environments.