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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Overexpression of Catalase in Mitochondria Mitigates the Effects of Simulated Microgravity and Social Isolation on Cytokine Expression in Mouse Hippocampus

Space flight missions are becoming longer and more common and evidence points to the physiological toll the missions have on the human body. Aging, sedentary lifestyle, and spaceflight have similar degenerative effects on almost every part of our body; both exposure to the space environment and aging result in cardiovascular deconditioning, bone loss, muscle atrophy, brain changes, and immune response impairment. We hypothesize that exposure to the space environment generates excessive Reactive Oxygen Species (ROS), which results in neuroinflammation and aging-like degenerative symptoms in the brain. We used the hindlimb unloading (HU) model to mimic microgravity with either paired or single housed animals (social isolation). Responses to 30d (30 days) of HU were compared in wildtype or transgenic MCAT (Mitochondrial-targeted CATalase) mice, in which mitochondrial ROS is quenched by over-expression of human catalase. Expression of 4-Hydroxynonenal (4HNE) and Park7 (redox-sensitive chaperone and sensor of oxidative stress) were measured by ELISA (Enzyme-Linked ImmunoSorbent Assay), a protein array quantified from the hippocampal cytokines and 8-hydroxy-2'-deoxyguanosine in serum was measured by ELISA to assess oxidative DNA damage. Preliminary analysis of cage behavior patterns from video collected at the end of the study showed that MCAT HU mice (socially housed) were more active and conducted more exploratory activities compared to NL (Normally Loaded). Our biochemical results showed simulated microgravity and/or social isolation caused changes in levels of cytokines related to immune responses. Two-way ANOVA (Analysis of Variance) revealed significant interaction effects of HU and genotype in expression levels of five cytokines (out of 35) in socially-housed animals. Elevation of these generally pro-inflammatory cytokines by HU in WT (Wild Type) mice was mitigated in MCAT mice, suggesting a role for mitochondrial ROS signaling in inflammatory CNS (Central Nervous System) responses to microgravity. Interestingly, some of these cytokines in the hippocampus displayed strong correlations to the 4HNE levels. We also found substantive cytokine responses to social isolation in the hippocampus; housing and genotype interaction effects were significant (by 2-Factor ANOVA) for 15 cytokines, most of which were mitigated in MCAT mice.Taken together, our results showed that both simulated microgravity and social isolation influenced cytokine levels in the hippocampus and MCAT mice were at least partially protected from these changes. These findings implicate a potentially important role for mitochondrial ROS in CNS responses to the challenges posed by long duration spaceflight.

MCAT↗
NASA NTRS2016

Building a Robust Commercial Microgravity Economy in Earth's Orbit: Economic Readiness Considerations

The reduced gravity environment of space provides a unique opportunity to further our understanding of various materials phenomena involving the molten, fluidic and gaseous states as well as life science applications where, contrary to earlier beliefs, microgravity induces changes in single cells and simple organisms; not only in large organisms with a complex overall response to gravity (or lack thereof). The potential breadth of commercial opportunities in microgravity thus spans over many verticals of the private sector with applications ranging from fiber optics, high-resolution crystals, microencapsulation, 3D organs to perfume and color dyes. Overall, products manufactured in microgravity hold the promise to have key properties surpassing their best terrestrial counterparts. Commercialization, also known as taking a new technology to market, is a journey in itself where the business, economic, market and technological components must align to generate a successful outcome. A business perspective is very different than technology maturation. In order for a technology to be ready for commercialization, it must not only be mature, but it must also have a compelling business case, and the means to scale up production must be identified and practical. Creating a robust economy in Earths orbit (Fig 1) is especially challenging because of the complexity (high risks, lack of standardization) involved in predicting future growth. This complexity can easily overwhelm the fact that many of the products have an attractive touch of space which aids with branding and marketing.This paper reviews the types of added value that can be extracted from space, with an emphasis on the microgravity environment. In addition, lessons learned from past commercialization efforts will be reviewed. While past efforts have yielded some point successes, they have as a whole failed to precipitate a sustainable LEO based market

Cozmuta, Ioana↗
NASA NTRS2020

The Mitigating Effects of Artificial gravity on Microgravity

The effects of microgravity on the human body can be debilitating however, the use of artificial gravity has the potential to completely mitigate these effects. Developing an artificial gravity habitation spacecraft concept could have positive effects on the astronauts spending long durations in space. Researching the past and upcoming artificial gravity concepts was accomplished using resources provided by my mentors, i.e. NASA Technical Reports Server (NTRS), human research roadmap, and the Aerospace Research Central (ARC) in coordination with other academic sources and research papers. This research has been accomplished over a several week period that looks at past artificial gravity concepts and the implications of instituting them or new designs in the future. Also, the research examines how to improve future artificial gravity concepts by applying what we know about past designs and what we are creating today. The expected outcomes of artificial gravity are that the health risks imposed on astronauts due to not being in Earth’s gravity environment for long duration space missions will decrease. No other microgravity mitigation technique addresses neurological problems such as fluid shift and VIIP syndrome as they only address physical conditions with exercise and supplements Another outcome is that using artificial gravity should reduce the long-term health effects that happen after the astronauts return to Earth because they will not be exposed to microgravity for as long. The real outcomes should be similar, if not the same, as the expected outcomes mentioned above. This process of creating artificial gravity aboard spacecrafts has potential to create a plethora of positive outcomes. The research completed will contribute to NASA’s missions and goals because the information gathered directly relates to the goal of sending humans to Mars and beyond and the research looks at how to solve one of the major problems associated with achieving that goal soon: microgravity. This research will contribute to NASA’s mission of sending astronauts to Mars, with a lower risk assessment, because artificial gravity will potentially mitigate the health risks (VIIP syndrome) associated with long duration in space flight.

Elizabeth Anne Westfall↗
NASA NTRS2021

Review of Vapor Compression Refrigeration in Microgravity Environments

Using a vapor compression cycle for cooling in microgravity environments was already suggested in the 1970s to leverage the high coefficient of performance. Since then, only a few systems have operated in microgravity with scarce documentation of these flights. The lack of measured data and detailed documentation makes identifying the necessary next steps difficult for researchers entering the field of refrigeration in space. This paper provides a review of available literature for vapor compression systems flown in microgravity by outlining the history of vapor compression devices in space and presenting performance data. Moreover, gaps in the literature are highlighted and open questions are posed based on the reviewed material. Next steps of research are suggested to support and ultimately achieve reliable vapor compression refrigeration in space. Calculating equivalent masses for a fair comparison of different microgravity cooling technologies is proposed by capturing both energy consumption and used volume.

Vapor compression↗
NASA NTRSDate not supplied

Simulation-Aided Design and Interpretation of Results of Microgravity-Based Solidification Experiments

The preparation and interpretation of microgravity experiments conducted on the International Space Station (ISS) can be challenging because of the remote location of the equipment. Although a “ground unit” is typically available on Earth, it is not located in the laboratory of the principal investigator. Furthermore, test experiments in the ground unit cannot fully duplicate heat transfer conditions of the weightless environment, and thus be a reliable reference for experiment design. Under such conditions, numerical simulations are a valuable tool both for preparing the experiments and interpreting the results obtained under terrestrial and micro-gravity conditions. In this work, we developed a detailed 3D model of the “SUBSA” furnace located at the ISS, and demonstrate its use in our present investigation which includes melt growth and vapor growth of InI crystals on the ISS. In 2002, the SUBSA furnace was designed and built for the growth of InSb crystals in the Microgravity Science Glovebox (MSG) at the ISS. The SUBSA furnace features a transparent section without heating elements, where the axial temperature gradient is high. In our present investigation, we have used the same furnace to grow four InI crystals from the melt, and two InI crystals from the vapor phase (2018-2021). InI crystals have ~20 times lower thermal conductivity than InSb crystals. As a result, during melt growth, the InI crystals were exposed to extremely high temperature gradients. To reduce the axial temperature gradient, we added external jackets made from high thermal conductivity material to the growth ampoules. The SUBSA furnace could not be modeled as asymmetric because of its rectangular shape and right-angled transparent section, which contains a convoluted geometry. The rectangular shape of the transparent section further complicates modelling of radiative heat transfer, which dominates in the zone. At present, numerical simulations are being conducted to resolve an apparent discrepancy between the readings of the 5 thermocouples located in the SUBSA furnace, and the observed position of the solid and molten material. The 3D simulation will be presented, along with the calibration and growth experiment results conducted in microgravity and in the SUBSA ground unit. The developed model should be useful for upcoming microgravity investigations planned to be conducted in the SUBSA facility.

V Riabov↗
NASA NTRS2022

Microgravity Electrical Capacitance Tomography Data Set

Propellants mass gauging technologies designed to work in an accelerated environment, where the propellant remains settled at one end of the propellant tank, do not work well in a microgravity environment because the propellant is not necessarily settled. While some microgravity mass gauging technologies exist at various TRLs, most of them have major disadvantages. Improvements in microgravity propellant mass gauging will result in improvements to many areas of propellant management, which influences performance and mission assurance. Electrical Capacitance Tomography (ECT) is a sensing technology that has been used in the oil/gas industry for decades to measure multi-phase flow rate in pipes. ECT, when installed in a tank, is able to reconstruct the liquid distribution inside of the tank, which can then be integrated to obtain mass. ECT mass gauging recently achieved high accuracy in laboratory testing on the ground, and while ECT mass gauging will theoretically work during all phases of flight, it had not yet been tested in microgravity. The NASA KSC Launch Services Program, with support from the Flight Opportunities Program, successfully flew an ECT tank liquid mass gauging system experiment on a Zero-G parabolic flight aircraft. The experiment hardware was rented from a company; NASA LSP did no technology development work for this project. This STRIVES entry is for the entire raw data set, which consists of approximately 25GB of csv files of capacitance and motion data from the ground and flight tests of the experiment. The data set will be available on the NASA LSP Electronic Slosh Data Catalog (ESDC), and the public may request the data set from the authors (POC: Jed Storey, jedediah.m.nasa.gov).

mass gauging↗
NASA NTRSDate not supplied

Flow Boiling and Condensation Experiment: Flow Boiling in a Rectangular Channel with Subcooled Inlet Conditions in Microgravity

Two-phase thermal management subsystems that take advantage of both the sensible and latent heat of a working fluid can potentially yield significant enhancements in overall performance by adopting heat transfer processes that are based on phase transition like boiling and condensation. Performance of terrestrial two-phase flow systems may be predictable because the hydrodynamic and body forces are understood, however, in microgravity, which is predominant during planetary space travel, forces that are masked by the strong body force on Earth (gravitational or buoyancy force) reappear with different magnitude and influence. The need arose for a facility that provides for two-phase flow with phase transition testing in microgravity. The Flow Boiling and Condensation Experiment (FBCE) is a facility that was launched to the International Space Station in August of 2021 and is in operation since February of 2022. This facility enables investigators to perform two-phase flow and phase transition research in flow boiling and condensation. Along with the test module that is experiment specific, the FBCE system consists of the fluid, avionics, and software subsystems. Currently two test modules, namely, the Flow Boiling Module (FBM) and the Condensation Module for Heat Transfer (CM-HT) are available. A third module, the Transfer Line test Module (TL) is being developed. The fluid subsystem conditions and delivers the fluid at the desired thermodynamic state to the test module. It consists of two fluid modules and a heater module that are connected by flex hoses for fluid circulation and by data and electrical cables for control and data acquisition. Two avionics modules acquire pressure and temperature data from various sensors in the flow loop. For FBM, a high-speed camera is available to acquire images of the boiling process. Experiments are operated autonomously by software and are based on an Experiment Parameters Master Table (EPMT) that is uploaded to ISS and is executed by the FBCE flight software. This presentation briefly introduces the objectives of FBCE and provides a system description of the experiment onboard of the ISS/Fluid Integrated Rack (FIR). Results of the test campaign carried out using the FBM are presented. Specifically, microgravity flow boiling of n-perfluorohexane (test fluid) is discussed with subcooled inlet conditions in a single-side-heated rectangular channel of dimensions 114.6-mm heated length, 2.5-mm heated width, and 5.0-mm height. Key operating parameters investigated are mass velocity (199.90 – 3200.13 kg/m2s), inlet subcooling (0.10 – 45.76°C), and inlet pressure (113.30 – 164.29 kPa). Image sequences acquired via high-speed-video are shown to elucidate the interfacial flow physics. The effects of various parameters on flow boiling heat transfer in microgravity, from the onset of boiling to the critical heat flux are discussed. Heat transfer results are presented in terms of flow boiling curves, streamwise profiles of wall temperature and heat transfer coefficient, and parametric trends of local and averaged heat transfer coefficient, and the critical heat flux.

Two-phase flow and phase transition↗
NASA NTRSDate not supplied

Role of PIEZO1 in T Cell Activation Under Simulated Microgravity

True and simulated microgravity conditions have been well documented to cause the inhibition of T cell activation by mitogens. Although several studies aimed at exploring the mechanisms for such a phenomenon have been published, how this is occurring remains unresolved. PIEZO1 is a known mechanosensing gene and has been shown to be critically involved in human T cell activation. In our analysis of transcriptomics changes in peripheral mononuclear cells (PBMC) collected from the ISS crewmembers in space, the expression of PIEZO1 was downregulated. To investigate the role of the PIEZO1 gene in T cell activation in microgravity, we used rotating wall vessels (RWV), which simulate microgravity on the ground and are known to inhibit T cell activation. In this pilot study, PBMC cultured in RWV and in the static 1g condition were stimulated with Human T-Activator CD3/CD28 beads. The cells were also treated with and without Yoda1, a chemical agonist that activates PIEZO1 independent of mechanical cues or any other cellular component. After culturing for 24 hours, the cells were stained for activation markers and the PIEZO1 antibody, then were analyzed by flow cytometry. Our results indicate reduced T cell activation with mitogen under simulated microgravity, but no changes of the PIEZO1 signals were detected. In addition, the reduced activation was not restored in cells cultured with Yoda1. Taken together, our results suggest that PIEZO1 may play a minimal role in the inhibition of T cell activation in space.

Honglu Wu↗
NASA NTRSDate not supplied

Moss Tolerance of Deep Space-Like Ionizing Radiation, Singular or Combined With Spaceflight Microgravity-Preparation for the BRIC-27 Experiment to the ISS

Understanding how terrestrial life perceives and tolerates deep space environments is essential to advancing human space exploration missions and searching for life beyond our solar system. Throughout evolution moss adapted to living in extreme environments from the edge of habitability. Moss inhabits areas with high UVB/UVC photon levels such as polar regions subject to ozone holes, high elevation mountain environments, and sites with elevated ionizing particle levels such as those found at nuclear plant accident sites, atomic bomb test sites or radioactive element-rich regions. We investigate if moss tolerance of ionizing radiation encounter terrestrially extends to resistance to deep space ionizing radiation. We exposed moss to high energy ion beams simulating Galactic Cosmic Ray (GCRSim) and Solar Particle Event (SPESim) (NSRL, BNL) that permeate deep space, and moss was unharmed. We also exposed moss to high doses of gamma rays as released in astrophysical events, and moss survived absorption of extremely high doses. Next, we ask if moss tolerance of deep space-like ionizing radiation observed terrestrially differs from that in other deep space environments. In the upcoming BRIC-27 spaceflight experiment we will sequentially expose Antarctic moss C.purpureus to GCRSim and SPESim followed by exposure to spaceflight microgravity and compare gene expression profiles in deep space-like ionizing radiation, singular or combined with spaceflight microgravity. Additionally, we will compare gene expression profiles in spaceflight microgravity, singular or combined with deep space-like ionizing radiation. Hence, BRIC-27 will advance our understanding of the combined effects of both deep space ionizing radiation and microgravity, which may have different and more profound effects on plant physiology and performance than each condition separately.

Agata Klaudia Zupanska↗
NASA NTRSDate not supplied

Role of PIEZO1 in T Cell Activation Under Simulated Microgravity

True and simulated microgravity conditions have been well documented to cause the inhibition of T cell activation by mitogens. Although several studies aimed at exploring the mechanisms for such a phenomenon have been published, how this is occurring remains unresolved. PIEZO1 is a known mechanosensing gene and has been shown to be critically involved in human T cell activation. In our analysis of transcriptomics changes in peripheral mononuclear cells (PBMC) collected from the ISS crewmembers in space, the expression of PIEZO1 was downregulated. To investigate the role of the PIEZO1 gene in T cell activation in microgravity, we used rotating wall vessels (RWV), which simulate microgravity on the ground and are known to inhibit T cell activation. In this pilot study, PBMC cultured in RWV and in the static 1g condition were stimulated with Human T-Activator CD3/CD28 beads. The cells were also treated with and without Yoda1, a chemical agonist that activates PIEZO1 independent of mechanical cues or any other cellular component. After culturing for 24 hours, the cells were stained for activation markers and the PIEZO1 antibody, then were analyzed by flow cytometry. Our results indicate reduced T cell activation with mitogen under simulated microgravity, but no changes of the PIEZO1 signals were detected. In addition, the reduced activation was not restored in cells cultured with Yoda1. Taken together, our results suggest that PIEZO1 may play a minimal role in the inhibition of T cell activation in space.

Honglu Wu↗
NASA NTRSDate not supplied

Predicting the Microgravity Performance of Terrestrial Portable Fire Extinguishers

Portable fire extinguishers (PFEs) are a key component of spacecraft emergency response systems. The International Space Station uses custom PFEs to meet the unique microgravity and enclosed space requirements of the vehicle. For future crewed missions to Low Earth Orbit and Deep Space destinations, terrestrial commercial off-the-shelf (COTS) PFEs may offer more economical solutions for the destination as well as the visiting vehicle. However, depending on the design of both the spacecraft and the PFE, the reduced gravity environment is likely to impact PFE performance, especially when multiphase microgravity liquid transport processes are present. Additionally, many terrestrial PFEs now use halocarbons as the suppressant. While studies show these are effective in certain terrestrial fires, some data suggest that low concentrations may actually exacerbate a fire, a phenomenon that would prove particularly concerning in spacecraft. To better characterize the potential of employing COTS hardware, two terrestrial PFEs, one charged with HFC-227ea and Nitrogen pressurant and one charged with carbon dioxide, were modeled to predict performance in both 1-g and microgravity environments. Testing was conducted in 1-g to validate the model. Testing was also conducted to evaluate the effect of sub-extinguishment HFC-227ea concentrations on burn rate in controlled samples. Here we provide a detailed description of the model, report the methods and results of PFE testing, discuss the predicted effects of microgravity on PFE performance, and report the results of material burn rates at sub-extinguishment levels of HFC-227ea.

Morgan B Abney↗
NASA NTRSDate not supplied

Role of PIEZO1 in T Cell Activation Under Simulated Microgravity

True and simulated microgravity conditions have been well documented to cause the inhibition of T cell activation by mitogens. Although several studies aimed at exploring the mechanisms for such a phenomenon have been published, how this is occurring remains unresolved. PIEZO1 is a known mechanosensing gene and has been shown to be critically involved in human T cell activation. In our analysis of transcriptomics changes in peripheral mononuclear cells (PBMC) collected from the ISS crewmembers in space, the expression of PIEZO1 was downregulated. To investigate the role of the PIEZO1 gene in T cell activation in microgravity, we used rotating wall vessels (RWV), which simulate microgravity on the ground and are known to inhibit T cell activation. In this pilot study, PBMC cultured in RWV and in the static 1g condition were stimulated with Human T-Activator CD3/CD28 beads. The cells were also treated with and without Yoda1, a chemical agonist that activates PIEZO1 independent of mechanical cues or any other cellular component. After culturing for 24 hours, the cells were stained for activation markers and the PIEZO1 antibody, then were analyzed by flow cytometry. Our results indicate reduced T cell activation with mitogen under simulated microgravity, but no changes of the PIEZO1 signals were detected. In addition, the reduced activation was not restored in cells cultured with Yoda1. Taken together, our results suggest that PIEZO1 may play a minimal role in the inhibition of T cell activation in space.

Honglu Wu↗
NASA NTRSDate not supplied

Life Finds A Way, the Dynamics of E. Coli Evolution in Microgravity

Investigating the evolutionary dynamics of Escherichia coli in microgravity offers a unique opportunity to understand microbial adaptation to extreme environments. Here, we explored the effects of simulated microgravity (SµG) on gene expression and genome evolution of Escherichia coli REL606, a strain continuously evolved and documented terrestrially for 35 years. We used transcriptomic profiling over a 24-hour growth cycle to examine how short-term exposure to SµG under glucose-limiting and glucose-replete conditions may influence the genetic adaptations in microbial populations. Pathway analyses of differentially expressed genes suggest that SµG may alter cell membrane structure and function across all conditions, while changes to protein synthesis machinery were uniquely observed in glucose-replete samples. Furthermore, altered expression of several prophage genes across conditions in SµG samples and upregulation of general stress response factors hints at the potential for stress-induced mutagenesis in response to microgravity. We further investigated the impact of long-term exposure to SµG on genome evolution and observed a more rapid accumulation of base substitutions and deletions in SµG sample genomes across time. Specifically, mutations in the mraZ and elyC genes suggest a mechanism for increased production of peptidoglycan in the cell membrane. These findings offer insights into bacterial adaptations in long-term microgravity environments and pave the way for further detailed investigations.

Brittney Lozzi↗
DOE OSTI2020

Utah FORGE: Phase 3 Microgravity Data

A 4D microgravity survey began in early 2019 in order to benchmark surface and subsurface elevations prior to Phase 3 drilling and stimulation campaigns. Microgravity stations are collocated with GPS deformation benchmarks and use the same location survey data. Surveys are undertaken on a quarterly basis. The focus of current activities is comparative analysis of GPS survey results and InSAR analysis (see GDR Submission 1251) to check seasonal variance and to evaluate possible changes in the groundwater elevation. The attached zip file contains a text file and an Excel spreadsheet containing Utah FORGE Phase 3 processed "final" microgravity data through time. The data are identical in both files. The spreadsheet is only supplied for convenience. There is also a ReadMe.txt file that describes the field headings.

15 GEOTHERMAL ENERGY↗
NASA NTRS2021

Developing a Sustainable, User-Friendly Literature Database to Support the Microgravity Simulation Support Facility (MSSF) at NASA's Kennedy Space Center (KSC)

Established in 2017, the Microgravity Simulation Support Facility (MSSF) at NASA’s Kennedy Space Center is the only centralized, dedicated facility supporting ground microgravity research in the United States. The MSSF offers the research community the ability to conduct simulated microgravity research with experimental conditions functionally resembling those aboard the International Space Station (ISS) and in other flight-based experimental environments. Since its inception, the MSSF has supported numerous studies and has since collected an extensive library of relevant and pertinent literature. The goal of our research was to develop and implement a sustainable, user-friendly literature database to better house this literature at the MSSF. To achieve this, our team focused on sorting, optimizing, and analyzing preexisting literature libraries to determine a best suitable and sustainable platform for the MSSF. After establishing initial database platforms, the team worked to develop descriptive and structural metadata categories to best sort the literature, which was followed by rigorous testing and optimization of the database as it was implemented. The MSSF has now been outfitted with a reliable, accessible database that effectively houses literature and provides diverse analysis to the user. Our team is continuing to test and update our platform and parameters as we aim for the formal implementation, expansion, and evolution of our database to better sustain future research ventures at the MSSF and beyond.

Database Development↗
DOE OSTI2022

Elucidating the challenges in extracting ultra-slow flame speeds in a closed vessel - A CH 2 F 2 microgravity case study using optical and pressure-rise data

Refrigerants with a low global warming potential (GWP) possess mild flammability. Hence, a fundamental understanding of their combustion characteristics is required to assess their fire-hazardous potential. The laminar burning velocity is one fundamental property to describe these under safety evaluation aspects. However, measuring laminar burning velocities for slow-burning components, such as low-GWP alternatives, is challenging. This is due to influencing effects such as buoyant flame deformation, stretch, radiation, and confinement, especially at the flammability limits. Here, in the present study, we investigated near-limit flames of the representative refrigerant difluoromethane (CH 2 F 2 ) with nitrogen-enriched oxidizer mixtures to elucidate the potentials and limitations at ultra-slow flame speeds of two widely used flame speed measurement methods in the closed vessel configuration: the optical flame speed measurement in the early quasi-isobaric regime and the flame speed determination from the pressure-rise during the later phase of the isochoric combustion process. Experiments were performed under terrestrial- and microgravity, conducted in a specially designed setup suitable for drop tower applications, using both methods in parallel. Recommendations for the extraction of flame speed data are derived from the non-buoyant reference investigations under microgravity and transferred to ultra-slow flames at terrestrial gravity. Near-limit flames under microgravity were found to be significantly affected by stretch effects for the optical method so that flame speed extrapolations to unstretched conditions are prone to errors. Stretch also affects the pressure method’s lower evaluation limit, and errors can be estimated by combining flame speed data from the pressure method and Markstein lengths from optical experiments.

42 ENGINEERING↗
NASA NTRS2013

Thickness and Fuel Preheating Effects on Material Flammability in Microgravity from the BASS Experiment

The Burning and Suppression of Solids (BASS) experiment was performed on the International Space Station. Microgravity combustion tests burning thin and thick flat samples, acrylic spheres, and candles were conducted. The samples were mounted inside a small wind tunnel which could impose air flow speeds up to 40 cms. The wind tunnel was installed in the Microgravity Science Glovebox which supplied power, imaging, and a level of containment. The effects of air flow speed, fuel thickness, fuel preheating, and nitrogen dilution on flame appearance, flame growth, and spread rates were determined in both the opposed and concurrent flow configuration. In some cases, a jet of nitrogen was introduced to attempt to extinguish the flame. Microgravity flames were found to be especially sensitive to air flow speed in the range 0 to 5 cms. The gas phase response is much faster compared to the solid and so as the flow speed is changed, the flame responds with almost no delay. At the lowest speeds examined (less than 1 cms) all the flames tended to become dim blue and very stable. However, heat loss at these very low convective rates is small so the flames can burn for a long time. At moderate flow speeds (between about 1 and 5 cms) the flame continually heats the solid fuel resulting in an increasing fuel temperature, higher rate of fuel vaporization, and a stronger, more luminous flame as time progresses. Only the smallest flames burning acrylic slabs appeared to be adversely influenced by solid conductive heat loss, but even these burned for over 5 minutes before self-extinguishing. This has implications for spacecraft fire safety since a tiny flame might be undetected for a long time. While the small flame is not particularly hazardous if it remains small, the danger is that it might flare up if the air convection is suddenly increased or if the flame spreads into another fuel source.

Combustion↗
NASA NTRS2015

Microgravity Flammability of PMMA Rods in Concurrent Flow

Microgravity experiments burning cast PMMA cylindrical rods in axial flow have been conducted aboard the International Space Station in the Microgravity Science Glovebox (MSG) facility using the Burning and Suppression of Solids (BASS) flow duct, as part of the BASS-II experiment. Twenty-four concurrent-flow tests were performed, focusing on finding flammability limits as a function of oxygen and flow speed. The oxygen was varied by using gaseous nitrogen to vitiate the working volume of the MSG. The speed of the flow parallel to the rod was varied using a fan at the entrance to the duct. Both blowoff and quenching limits were obtained at several oxygen concentrations. Each experiment ignited the rod at the initially hemispherical stagnation tip of the rod, and allowed the flame to develop and heat the rod at a sufficient flow to sustain burning. For blowoff limit tests, the astronaut quickly turned up the flow to obtain extinction. Complementary 5.18-second Zero Gravity Facility drop tests were conducted to compare blowoff limits in short and long duration microgravity. For quenching tests, the flow was incrementally turned down and the flame allowed to stabilize at the new flow condition for at least the solid-phase response time before changing it again. Quenching was observed when the flow became sufficiently weak that the flame could no longer provide adequate heat flux to compensate for the heat losses (conduction into the rod and radiation). A surface energy balance is presented that shows the surface radiative loss exceeds the conductive loss into the rod near the limit. The flammability boundary is shown to represent a critical Damkohler number, expressed in terms of the reaction rate divided by the stretch rate. For the blowoff branch, the boundary exhibits a linear dependence on oxygen concentration and stretch rate, indicating that the temperature at blowoff must be fairly constant. For the quenching branch, the dominance of the exponential nature of the Arrhenius kinetics reaction rate indicates that the temperature is critical.

flammability↗