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NASA NTRSDate not supplied

Secondary Volcanically-Induced Lunar Atmosphere and Lunar Volatiles: 3-D Modeling and Analysis

The fact that the Moon could have a transient secondary atmosphere due to volcanic outgassing has been known for some time, though typically such an atmosphere was believed to be extremely thin (~10-8 bar) [1]. But recent research by Needham and Kring (NK) [2] suggests that during the peak of volcanic activity ~3.5 Ga such a volcanically-outgassed atmosphere could reach ~10-2 bar of surface pressure. In similar research Wilson et al. [3] proposed a more conservative estimate, arguing that the thickness of such an atmosphere would depend on the intervals between major eruptions and may not exceed microbar densities. In either case a collisional atmosphere could be present, which would control transport of outgassed volatiles (such as H2O) and their deposition in polar regions, where they could be preserved until modern day frozen in permanently shadowed regions (PSR) or buried beneath the regolith. Here we study such a hypothetical atmosphere to investigate its stability, meteorological properties and the effect on transport of volatiles. We use the ROCKE-3D planetary 3-D General Circulation Model (GCM)[4]. The insolation and orbital parameters were set to conditions 3.5 Ga. The atmospheric composition, based on the list of outgassed species presented by NK in combination with our estimates for atmospheric escape, condensation and the results from our 1-D chemistry model, was chosen to be either CO-dominated or CO2-dominated (depending on atmospheric temperature). In this study we restricted ourselves to relatively "thick" lunar atmospheres of 1-10 mb, though we believe that our results will scale to thinner atmospheres as well. We present the results for ground and atmospheric temperature for modeled atmospheres over a wide parameter space. In particular we consider different atmospheric compositions (CO or CO2 dominated), a set of atmospheric pressures from 1 mb to 10 mb and a set of obliquities from 0o to 40o. We also present an experiment of a single major eruption [5] and show that in just 3 years ~80% of the outgassed water is deposited in polar regions. This demonstrates the efficiency of such an atmosphere in delivering volatiles. We argue that a secondary lunar atmosphere could play a significant role in forming volatile deposits currently observed in the polar regions of the Moon.

Lunar atmospheres↗
NASA NTRS2019

Manufacturing of Thermoset Polyimide Composites by Laser Sintering

Selective Laser Sintering (SLS) is an additive manufacturing technique that builds 3D models layer by layer using a laser to selectively melt cross sections in powdered polymeric materials, following sequential slices of the computer-aided design (CAD) model. SLS generally uses thermoplastic polymeric powders such as polyamides. The resultant 3D-printed objects are often weaker in their strength compared to traditionally processed materials, due to their higher porosity. This paper described the process development of using melt-processable imide oligomers terminated with reactive 4-phenylethynylphthalic anhydride (4-PEPA) to conduct laser sintering (LS). The first successful 3D-printing of high temperature RTM370 thermoset polyimide carbon fiber composites were further post-cured to promote additional crosslinking for achieving higher temperature (T g = 370°C) capability. Another novel imide oligomer, RTM385-SLS, formulated with a complex melt viscosity [ƞ*] of ~104-105 poise is also suitable for LS. RTM385-SLS resin powder was mixed with 20-25% of hexagonal boron nitride (h-BN) and subjected to LS to print out “Green” specimens which could be further post-cured to afford a thermally conductive but electrically insulating composites with high T g of 385 °C. The cured composite specimens were then subjected to mechanical testing, thermal conductivity and porosity measurements as well as SEM characterization.

additive Manufacturing↗
NASA NTRSDate not supplied

Study of Martian Polar Caps with GISS ROCKE-3D GCM

Martian polar caps consist of both H 2 O and CO 2 ice. While H 2 O ice is mainly passive on modern Mars, it may have not been the case in recent Martian history, when its obliquity was higher, or when it was changing rapidly. The distribution of ice species in the snowpack affects its physical and thermodynamic properties. In the upper layers, it determines its albedo and thermal emissivity. Thus understanding the mutual effect between these ices and their interaction with the atmosphere is crucial for understanding the evolution of Martian polar regions. In this study, we employ a newly-developed Exotic Ices snow model coupled to the NASA Goddard Institute for Space Studies (GISS) ROCKE-3D planetary General Circulation Model (GCM) [1] to study the behavior of Martian polar caps. ROCKE-3D is a planetary GCM developed at NASA GISS as an extension of its Earth climate model, modelE [2]. It has been extensively used to simulate climate of various planets, including Mars (e.g. [3,4]). The Exotic Ices snow model was specially developed for planetary applications which involve more than one condensable in the atmosphere, in which case snow can contain multiple species of ice (CO2 and H 2 O in the Mars case). For each species of ice, the model uses their proper physical properties and phase diagram, but otherwise it treats all species of ice on an equal footing. The combined effects on albedo, thermal inertia and mutual insulation are treated accordingly. The snowpack interacts with the atmospheric dust cycle, and can accumulate a prognostic amount of dust, though the effect of dust on snow properties is not currently treated explicitly, and is prescribed. In this study, we first validate our model against the modern Martial climate, for which we use mission results from Mars Climate Sounder (atmospheric temperature and dust optical depth), SPICAM on Mars Express (atmospheric water), and Viking 2 (surface pressure). We investigate the effect of snow radiative properties on CO 2 and water cycles and the ability of our model to accurately reproduce those with minimal model tuning. We then perform simulations for several obliquities from a recent Martian past, and investigate the behavior of the Martian polar caps in such conditions.

Mars↗
NASA NTRS2008

Modeling of the Ablation of Fibrous Materials in the Knudsen Regime

During atmospheric entry of planetary probes, the thermal protection system (TPS) of the probe is exposed to high temperatures under low pressures. In these conditions, carbonous TPS materials undergo gasification in the Knudsen regime leading to mass loss and wall recession called ablation. This work aims to improve the understanding of materiaVenvironment interactions through a study of the coupling between carbon dioxide transport in the Knudsen regime, heterogeneous oxidation of carbon, and sutface recession. A 3D Monte-Carlo simulation tool is used for this study. The fibrous architecture of the materiils, consisting of high porosity random array of carbon fibers, is numerically reproduced on a 3D Cartesian grid. Mass transport in the Knudsen regime from the boundary layer to the surface, and inside this porous material is simulated by random walk. A reaction probability is used to simulate the heterogeneous oxidation reaction. The surface recession is followed by front tracking using a simplified marching cube approach. The output data of the simulations are ablation velocity and dynamic evolution of the material porosity. A parametric study is carried out to analyze the material behavior as a function of Knudsen number for the porous media (length of the mean free path compared to the mean pore diameter) and the intrinsic reactivity of the carbon fibers. The results enable extrapolation of laboratory experimental data to actual entry conditions.

Lachaud, J.↗
NASA NTRS2015

Low Cost Upper Stage-Class Propulsion (LCUSP)

NASA is making space exploration more affordable and viable by developing and utilizing innovative manufacturing technologies. Technology development efforts at NASA in propulsion are committed to continuous innovation of design and manufacturing technologies for rocket engines in order to reduce the cost of NASA's journey to Mars. The Low Cost Upper Stage-Class Propulsion (LCUSP) effort will develop and utilize emerging Additive Manufacturing (AM) to significantly reduce the development time and cost for complex rocket propulsion hardware. Benefit of Additive Manufacturing (3-D Printing) Current rocket propulsion manufacturing techniques are costly and have lengthy development times. In order to fabricate rocket engines, numerous complex parts made of different materials are assembled in a way that allow the propellant to collect heat at the right places to drive the turbopump and simultaneously keep the thrust chamber from melting. The heat conditioned fuel and oxidizer come together and burn inside the combustion chamber to provide thrust. The efforts to make multiple parts precisely fit together and not leak after experiencing cryogenic temperatures on one-side and combustion temperatures on the other is quite challenging. Additive manufacturing has the potential to significantly reduce the time and cost of making rocket parts like the copper liner and Nickel-alloy jackets found in rocket combustion chambers where super-cold cryogenic propellants are heated and mixed to the extreme temperatures needed to propel rockets in space. The Selective Laser Melting (SLM) machine fuses 8,255 layers of copper powder to make a section of the chamber in 10 days. Machining an equivalent part and assembling it with welding and brazing techniques could take months to accomplish with potential failures or leaks that could require fixes. The design process is also enhanced since it does not require the 3D model to be converted to 2-D drawings. The design and fabrication process can be sped up and improved with fewer errors to be accomplished in weeks instead of months.

Vickers, John↗
NASA NTRSDate not supplied

3D Climate Simulations of Earth-Like Planets with A Range of Atmospheric Composition, Radiative Transfer, Ocean, And Resolution Configurations, Using the New Version of ROCKE-3D

Understanding the climate of terrestrial planetary atmospheres has been increasingly the focus of research worldwide, in light of the increasing amount of rocky planet discoveries orbiting other stars in or near their habitable zone. Here we present simulations with the new version of the 3D climate model ROCKE-3D, whose version 2.0 will soon become publicly available. A wide range of configurations will be supported, compared to a handful ones in its predecessor, version 1.0 (Way et al., 2017). These include two model resolutions (4x5 and 2x2.5), two radiation schemes (GISS and SOCRATES), three atmospheric configurations (Earth-like, Earth-like without O3 and aerosols, and N2-dominated), and three ocean setups (prescribed sea-surface temperatures and ice cover, q-flux, and dynamic). Simulations of all different configuration combinations have been performed and will become available for use by the community. Key results will be presented across those configurations, together of the role of the structural uncertainty in model setup in the resulting climate calculated by the model.

climate simulations of Earth-like planets↗
NASA NTRS1992

Approaches to ionospheric modelling, simulation and prediction

The ionosphere is a complex, multispecies, anisotropic medium that exhibits a significant variation with time, space, season, solar cycle, and geomagnetic activity. In recent years, a wide range of models have been developed in an effort to describe ionospheric behavior. The modeling efforts include: (1) empirical models based on extensive worldwide data sets; (2) simple analytical models for a restricted number of ionospheric parameters; (3) comprehensive, 3D, time-dependent models that require supercomputers; (4) spherical harmonic models based on fits to output obtained from comprehensive numerical models; and (5) ionospheric models driven by real-time magnetospheric inputs. In an effort to achieve simplicity, some of the models have been restricted to certain altitude or latitude domains, while others have been restricted to certain ionospheric parameters, such as the F-region peak density, the auroral conductivity, and the plasma temperatures. The current status of the modeling efforts is reviewed.

Schunk, R. W.↗
NASA NTRS1992

Fracture mechanics; Proceedings of the 22nd National Symposium, Atlanta, GA, June 26-28, 1990. Vols. 1 & 2

Current research on fracture mechanics is reviewed, focusing on ductile fracture; high-temperature and time-dependent fracture; 3D problems; interface fracture; microstructural aspects of fatigue and fracture; and fracture predictions and applications. Particular attention is given to the determination and comparison of crack resistance curves from wide plates and fracture mechanics specimens; a relationship between R-curves in contained and uncontained yield; the creep crack growth behavior of titanium alloy Ti-6242; a crack growth response in three heat resistant materials at elevated temperature; a crack-surface-contact model for determining effective-stress-intensity factors; interfacial dislocations in anisotropic bimaterials; an effect of intergranular crack branching on fracture toughness evaluation; the fracture toughness behavior of exservice chromium-molybdenum steels; the application of fracture mechanics to assess the significance of proof loading; and a load ratio method for estimating crack extension.

Ernst, Hugo A.↗
NASA NTRS2013

NASA Tech Briefs, Februrary 2013

Topics covered include: Measurements of Ultra-Stable Oscillator (USO) Allan Deviations in Space; Gaseous Nitrogen Orifice Mass Flow Calculator; Validation of Proposed Metrics for Two-Body Abrasion Scratch Test Analysis Standards; Rover Low Gain Antenna Qualification for Deep Space Thermal Environments; Automated, Ultra-Sterile Solid Sample Handling and Analysis on a Chip; Measuring and Estimating Normalized Contrast in Infrared Flash Thermography; Spectrally and Radiometrically Stable, Wideband, Onboard Calibration Source; High-Reliability Waveguide Vacuum/Pressure Window; Methods of Fabricating Scintillators With Radioisotopes for Beta Battery Applications; Magnetic Shield for Adiabatic Demagnetization Refrigerators (ADR); CMOS-Compatible SOI MESFETS for Radiation-Hardened DC-to-DC Converters; Silicon Heat Pipe Array; Adaptive Phase Delay Generator; High-Temperature, Lightweight, Self-Healing Ceramic Composites for Aircraft Engine Applications; Treatment to Control Adhesion of Silicone-Based Elastomers; High-Temperature Adhesives for Thermally Stable Aero-Assist Technologies; Rockballer Sample Acquisition Tool; Rock Gripper for Sampling, Mobility, Anchoring, and Manipulation; Advanced Magnetic Materials Methods and Numerical Models for Fluidization in Microgravity and Hypogravity; Data Transfer for Multiple Sensor Networks Over a Broad Temperature Range; Using Combustion Synthesis to Reinforce Berms and Other Regolith Structures; Visible-Infrared Hyperspectral Image Projector; Three-Axis Attitude Estimation With a High-Bandwidth Angular Rate Sensor Change_Detection.m; AGATE: Adversarial Game Analysis for Tactical Evaluation; Ionospheric Simulation System for Satellite Observations and Global Assimilative; Modeling Experiments (ISOGAME); An Extensible, User- Modifiable Framework for Planning Activities; Mission Operations Center (MOC) - Precipitation Processing System (PPS) Interface Software System (MPISS); Automated 3D Damaged Cavity Model Builder for Lower Surface Acreage Tile on Orbiter; Mixed Linear/Square-Root Encoded Single-Slope Ramp Provides Low-Noise ADC with High Linearity for Focal Plane Arrays; RUSHMAPS: Real-Time Uploadable Spherical Harmonic Moment Analysis for Particle Spectrometers; Powered Descent Guidance with General Thrust-Pointing Constraints; X-Ray Detection and Processing Models for Spacecraft Navigation and Timing; and Extreme Ionizing-Radiation-Resistant Bacterium

Source record↗
NASA NTRS2018

Climates of Warm Earth-Like Planets. I. 3D Model Simulations

We present a large ensemble of simulations of an Earth-like world with increasing insolation and rotation rate. Unlike previous work utilizing idealized aquaplanet congurations we focus our simulations on modern Earth-like topography. The orbital period is the same as modern Earth, but with zero obliquity and eccentricity. The atmosphere is 1 bar N2-dominated with CO2=400 ppmv and CH4=1 ppmv. The simulations include two types of oceans; one without ocean heat transport (OHT) between grid cells as has been commonly used in the exoplanet literature, while the other is a fully coupled dynamic bathtub type ocean. The dynamical regime transitions that occur as day length increases induce climate feedbacks producing cooler temperatures, rst via the reduction of water vapor with increasing rotation period despite decreasing shortwave cooling by clouds, and then via decreasing water vapor and increasing shortwave cloud cooling, except at the highest insolations. Simulations without OHT are more sensitive to insolation changes for fast rotations while slower rotations are relatively insensitive to ocean choice. OHT runs with faster rotations tend to be similar with gyres transporting heat poleward making them warmer than those without OHT. For slower rotations OHT is directed equator-ward and no high latitude gyres are apparent. Uncertainties in cloud parameterization preclude a precise determination of habitability but do not a affect robust aspects of exoplanet climate sensitivity. This is the first paper in a series that will investigate aspects of habitability in the simulations presented herein. The datasets from this study are open source and publicly available.

Planetary systems↗
NASA NTRS2014

Local ISM 3D Distribution and Soft X-ray Background Inferences for Nearby Hot Gas

Three-dimensional (3D) interstellar medium (ISM) maps can be used to locate not only interstellar (IS) clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae, and are filled by hot gas. To demonstrate this, and to derive a clearer picture of the local ISM, we compare our recent 3D IS dust distribution maps to the ROSAT diffuse Xray background maps after removal of heliospheric emission. In the Galactic plane, there is a good correspondence between the locations and extents of the mapped nearby cavities and the soft (0.25 keV) background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust to gas ratio and homogeneous 106 K hot gas filling the cavities, we modeled in a simple way the 0.25 keV surface brightness along the Galactic plane as seen from the Sun, taking into account the absorption by the mapped clouds. The data-model comparison favors the existence of hot gas in the solar neighborhood, the so-called Local Bubble (LB). The inferred mean pressure in the local cavities is found to be approx.9,400/cu cm K, in agreement with previous studies, providing a validation test for the method. On the other hand, the model overestimates the emission from the huge cavities located in the third quadrant. Using CaII absorption data, we show that the dust to CaII ratio is very small in those regions, implying the presence of a large quantity of lower temperature (non-X-ray emitting) ionized gas and as a consequence a reduction of the volume filled by hot gas, explaining at least part of the discrepancy. In the meridian plane, the two main brightness enhancements coincide well with the LB's most elongated parts and chimneys connecting the LB to the halo, but no particular nearby cavity is found towards the enhancement in the direction of the bright North Polar Spur (NPS) at high latitude. We searched in the 3D maps for the source regions of the higher energy (0.75 keV) enhancements in the fourth and first quadrants. Tunnels and cavities are found to coincide with the main bright areas, however no tunnel nor cavity is found to match the low-latitude b > or approx. 8deg, brightest part of the NPS. In addition, the comparison between the 3D maps and published spectral data favors a NPS central source region location beyond 230 pc, i.e. at larger distance than usually considered. Those examples illustrate the potential use of more detailed 3D distributions of the nearby ISM for the interpretation of the diffuse soft X-ray background.

Xray Emission↗
NASA NTRS1992

Ozone response to a CO2 doubling - Results from a stratospheric circulation model with heterogeneous chemistry

A spectral 3D model of the stratosphere has been used to study the sensitivity of polar ozone with respect to a carbon dioxide increase. The lower stratospheric cooling associated with an imposed CO2 doubling may increase the probability of polar stratospheric cloud (PSC) formation and this affect ozone. The ozone perturbation obtained with the inclusion of a simple parameterization for heterogeneous chemistry on PSCs is compared to that relative to a pure homogeneous chemistry. In both cases the temperature perturbation is determined by a CO2 doubling, while the total chlorine content is kept at the present level. It is shown that the lower temperature may increase the depth and the extension of the ozone hole by extending the area amenable to PSC formation. It may be argued that this effect, coupled with an increasing amount of chlorine, may produce a positive feedback on the ozone destruction.

Pitari, G.↗
NASA NTRS1992

The VRT gas turbine combustor - Phase II

An innovative annular combustor configuration is being developed for aircraft and other gas turbine engines. This design has the potential of permitting higher turbine inlet temperatures by reducing the pattern factor and providing a major reduction in NO(x) emission. The design concept is based on a Variable Residence Time (VRT) technique which allows large fuel particles adequate time to completely burn in the circumferentially mixed primary zone. High durability of the combustor is achieved by dual-function use of the incoming air. In Phase I, the feasibility of the concept was demonstrated by water analogue tests and 3D computer modeling. The flow pattern within the combustor was as predicted. The VRT combustor uses only half the number of fuel nozzles of the conventional configuration. In Phase II, hardware was designed, procured, and tested under conditions simulating typical supersonic civil aircraft cruise conditions to the limits of the rig. The test results confirmed many of the superior performance predictions of the VRT concept. The Hastelloy X liner showed no signs of distress after nearly six hours of tests using JP5 fuel.

Melconian, Jerry O.↗
NASA NTRSDate not supplied

Three-dimensional in Situ Observations of Polycrystalline Microstructure Evolution During Directional Solidification of Transparent Alloys Aboard the ISS and Quantitative Comparison with Numerical Modeling

Cellular/dendritic microstructures formed during solidification have a crucial influence on the mechanical properties of a wide range of structural alloys. By minimizing the amount of gravity-induced convection in the liquid, directional solidification experiments using transparent organic alloys conducted in the DECLIC-DSI onboard the International Space Station have provided unique 3D in situ observations of the spatiotemporal evolution of the solid-liquid interface during the formation of cellular and dendritic microstructures under purely diffusive growth conditions in polycrystalline samples containing several grains with a small misorientation with respect to the temperature gradient. Those observations have made it possible to perform benchmark quantitative comparisons with the predictions of state-of-the-art phase-field simulations of microstructure formation in 3D on experimentally relevant length and time scales. This talk will report quantitative comparisons between microgravity experiments and phase-field simulations in succinonitrile-camphor alloys of two different compositions that shed new light on the role of subgrain boundaries in the spatiotemporal evolution of the primary cellular spacing and the selection of dendritic array structures.

Kaihua Ji↗
NASA NTRS2017

Abstract - Belbas, Nicholas (EC2)

Originally, I was brought into the Design and Analysis Branch in the Crew and Thermal Systems to work on administrative tasks like archiving and scheduling. However, I ended up splitting my time between secretarial tasks and a technical project. My technical project was originally meant to be a wireless sensor package for the 20ft Spacecraft Thermal Vacuum Chamber in the B7 High Bay. I would be using a miniature wifi development board and a temperature/humidity sensor along with custom 3D modeling to accomplish this. However, after some discussion with my technical mentor, the plan was changed to a mobile autonomous self-charging sensor platform. A mobile platform will allow the sensors to be moved around without depressurizing the chamber. Also, the self-charging aspect of the package allows for almost unlimited time in the chamber. If the on-board battery runs low, the robot can easily be driven to its charging dock and continue to transmit while charging. The driving base is based around a Raspberry Pi 3 board with a 12C PMW DC Motor controller and a PWM controller driving two small gear motors. The sensor transmitter itself is a RHT03 temperature and humidity sensor and Cozir CO2 sensor connected to an ESP8266 Huzzah board. The power distribution system utilizes a pair of 3.7v 3600mah lipo batteries wired to Powerboost 500 boards. Also, the self-charging mechanism utilizes two 12v-max inductive charging coils wired into the same Powerboost boards as the battery. The Raspberry pi is running Python 3.3 for the driving base and Javascript MJPEG library for transmitting live video from the onboard camera. The sensor package is running Arduino-based C++ and the program capturing the data is running PyqtGraph Python and HTML. The shell of the robot itself is a 3D printed case that will (work in progress) snap together. The photo to the left shows the two halves separated from each other. The black shell contains the power distribution boards and connectors while the white shell contains the driving base and data systems.

Belbas, Nicholas↗
NASA NTRS1987

Simplified curve fits for the thermodynamic properties of equilibrium air

New, improved curve fits for the thermodynamic properties of equilibrium air have been developed. The curve fits are for pressure, speed of sound, temperature, entropy, enthalpy, density, and internal energy. These curve fits can be readily incorporated into new or existing computational fluid dynamics codes if real gas effects are desired. The curve fits are constructed from Grabau-type transition functions to model the thermodynamic surfaces in a piecewise manner. The accuracies and continuity of these curve fits are substantially improved over those of previous curve fits. These improvements are due to the incorporation of a small number of additional terms in the approximating polynomials and careful choices of the transition functions. The ranges of validity of the new curve fits are temperatures up to 25 000 K and densities from 10 to the -7 to 10 to the 3d power amagats.

Srinivasan, S.↗
NASA NTRS2017

NIR-Driven Moist Upper Atmospheres of Synchronously Rotating Temperate Terrestrial Exoplanets

H2O is a key molecule in characterizing atmospheres of temperate terrestrial planets, and observations of transmission spectra are expected to play a primary role in detecting its signatures in the near future. The detectability of H2O absorption features in transmission spectra depends on the abundance of water vapor in the upper part of the atmosphere. We study the three-dimensional distribution of atmospheric H2O for synchronously rotating Earth-sized aquaplanets using the general circulation model (GCM) ROCKE-3D, and examine the effects of total incident flux and stellar spectral type. We observe a more gentle increase of the water vapor mixing ratio in response to increased incident flux than one-dimensional models suggest, in qualitative agreement with the climate-stabilizing effect of clouds around the substellar point previously observed in GCMs applied to synchronously rotating planets. However, the water vapor mixing ratio in the upper atmosphere starts to increase while the surface temperature is still moderate. This is explained by the circulation in the upper atmosphere being driven by the radiative heating due to absorption by water vapor and cloud particles, causing efficient vertical transport of water vapor. Consistently, the water vapor mixing ratio is found to be well-correlated with the near-infrared portion of the incident flux. We also simulate transmission spectra based on the GCM outputs, and show that for the more highly irradiated planets, the H2O signatures may be strengthened by a factor of a few, loosening the observational demands for a H2O detection.

Fujii, Yuka↗
NASA NTRSDate not supplied

Investigation of Lunar-Inspired Geopolymer Concrete Formulations Mixed and Cured in Microgravity on the International Space Station (ISS)

The research outlined in this presentation investigates the use of various lunar regolith simulants in geopolymer lunar concrete mixes mixed and cured on the International Space Station (ISS). The motivation for this work is to study the effects of gravity on the microstructure of alkali-activated materials cured with heat, and to develop materials for the construction of long-term infrastructure on the lunar surface with in-situ resource utilization (ISRU). ISRU for construction materials reduces the cost and mass of payloads related to lunar construction. The advantage of geopolymer concrete as opposed to traditional portland cement concrete is that water acts as a medium for the polymerization reaction and leaves the system throughout the process, reducing its demand. Twelve samples of lunar regolith simulant and a solution composed of sodium hydroxide and sodium silicate were sent to the ISS. The three simulants were OPRH2N, OPRL2N, and JSC-1AF, using only particles less than 53 µm in diameter to increase reactivity of the simulant. Simulant to solution ratios were determined by workability while mixing. The simulant and solution were sealed Burst Pouches® along with 2 other sealed bags to prevent material from leaking. Crew member F-14 conducted testing on the ISS by introducing the solution to the simulant in the Burst Pouch®, mixing the sample with a spatula, and then clamping the specimen in the fresh state to prevent flow inside the Burst Pouch®. These specimens were then put in a thermos heated to 80C via sealed drinking water bags to cure for 24 hours with a temperature logger. The cured specimens remained in microgravity for at least 28 days and were returned from the ISS in February 2025. The specimens were then brought to the NASA Marshall Space Flight Center (MSFC) to analyze. Material characterization consisted of conducting Micro-CT tests of entire samples in their sealed apparatus to a resolution of 25µm. 2D image slices were saved in each orthogonal direction of each specimen at a 0.03 mm step size from the 3D model to conduct analytical porosity calculations. Representative samples from each specimen were sampled to perform helium gas pycnometery and were then mounted in resin for SEM imaging, EDS, and nanoindentation. Porosity was analyzed analytically using micromechanics modelling with the assistance of the NASA Multiscale Analysis Tool (NASMAT), as well as the NASA Advanced Supercomputing (NAS) servers (V. Saseendran & N. Yamamoto, 2024). Density was measured using helium gas pycnometery and was then compared to the theoretical density for experimental porosity calculation. Due to the samples’ non-uniform shape being cured in a pouch, traditional compression and tensile strength testing could not be performed. Nanoindentation was conducted at Clarkson University to determine the microhardness and reduced modulus of elasticity. Results from flight samples can be compared to ground samples currently in DLR’s possession to determine the effect on microstructure from being mixed and cured in microgravity. This study gives further insight and understanding of geopolymer lunar concrete and its viability as a lunar construction material with ISRU.

Adam Johnson↗