Results for “carbon based materials” — Page 8

NASA NTRSDate not supplied

Parallelized Carbon Oxidation and Surface Recession Model in Direct-Simulation Monte Carlo Code, SPARTA

Ablative thermal protection system (TPS) materials for spacecraft are composites that often consist of a carbon-based reinforcement and a polymeric matrix. During Earth re-entry, they endure high-temperature oxidation and surface recession. Oxidation is an important mechanism for ablation, sometimes leading to the weakening, spallation, or failure of the oxidized fibers at the surface and in the char layer. However, more details are required including accurate material properties of the fiber microstructure, whether the fibers recede homogenously or localized at pits, and the role of pyrolysis outgassing in order to evaluate the role oxidation plays in the degradation and failure mechanisms of these materials. In this work, we demonstrate a parallelizable oxidation-driven ablation model developed for detailed, large-scale simulations in the DSMC code SPARTA. We also develop robust algorithms which handle the conservation of the surface state after an ablation step. Finally, we verify our model for both simple and more complex chemistry as well as microstructures with reaction statistics, oxidation depth calculations, and detailed visualization of oxidation-induced material recession at the microscale.

V Arias↗

NASA NTRS1989

Working group written presentation: Atomic oxygen

Earlier Shuttle flight experiments have shown NASA and SDIO spacecraft designed for operation in low-Earth orbit (LEO) must take into consideration the highly oxidative characteristics of the ambient flight environment. Materials most adversely affected by atomic oxygen interactions include organic films, advanced (carbon-based) composites, thermal control coatings, organic-based paints, optical coatings, and thermal control blankets commonly used in spacecraft applications. Earlier results of NASA flight experiments have shown prolonged exposure of sensitive spacecraft materials to the LEO environment will result in degraded systems performance or, more importantly, lead to requirements for excessive on-orbit maintenance, with both conditions contributing significantly to increased mission costs and reduced mission objectives. Flight data obtained from previous Space Shuttle missions and results of the Solar Max recovery mission are limited in terms of atomic oxygen exposure and accuracy of fluence estimates. The results of laboratory studies to investigate the long-term (15 to 30 yrs) effects of AO exposure on spacecraft surfaces are only recently available, and qualitative correlations of laboratory results with flight results have been obtained for only a limited number of materials. The working group recommended the most promising ground-based laboratories now under development be made operational as soon as possible to study the full-life effects of atomic oxygen exposure on spacecraft systems.

Leger, Lubert J.↗

NASA NTRSDate not supplied

Simulation of Oxidative Etch Pit Formation and Growth on FiberForm

Erosion of carbon surfaces due to oxidation does not occur uniformly but through the formation of localized etch pits because of active surface sites. These active sites are formed due to the presence of atomic defects on the carbon surface and have much higher reactivity compared to average non-defective sites. Thus, these active sites are the first to react during ablation, resulting in their removal. This causes all the neighboring atoms to be defective, and increasing their reactivity, thus leading to localized carbon removal around these “active” sites. In this manner, these highly reactive defects serve as nucleation sites for the formation and growth of etch pits, with detrimental effects on the structural integrity. In order to understand the influence of these etch pits on the material properties of carbon fiber microstructures, we have developed a new capability within direct simulation Monte Carlo (DSMC) to capture the etch pit formation process. This capability is developed within the DSMC code SPARTA (Stochastic PArallel Rarefied-gas Time-accurate Analyzer) and can model the material removal in the presence of active sites leading to the formation of etch pits. The focus of the current work will be to study the effect of etch pits on the material properties of FiberForm, the precursor substrate of the PICA Thermal Protection System (TPS) material. The microstructure of virgin FiberForm obtained directly from X-ray microtomography scans is used within SPARTA to obtain the ablated geometries with etch pits. These pitted microstructures are then imported into the Porous Microstructure Analysis (PuMA) software and various material properties such as thermal conductivity, elasticity, and permeability are computed. The variation of these properties because of the complex evolution of the surface topology due to the formation of etch pits is studied and analyzed. Furthermore, the effect of pitting is compared to the case of uniform radial shrinking of fibers, which has been the standard for modelling ablation of carbon structures, and significant differences are observed. Thus, a physically realistic model of material removal through the formation of etch pits will be helpful in predicting the degradation of carbon-based TPS more accurately during oxidation; as well as other mechanisms such as spallation, which involves the removal of chunks of material into the flow due to the growth of etch pits. This will ultimately improve our understanding of the failure modes in these materials due to ablation.

DSMC↗

NASA NTRSDate not supplied

Simulation of Oxidative Etch Pit Formation and Growth on FiberForm

Erosion of carbon surfaces due to oxidation does not occur uniformly but through the formation of localized etch pits because of active surface sites. These active sites are formed due to the presence of atomic defects on the carbon surface and have much higher reactivity compared to average non-defective sites. Thus, these active sites are the first to react during ablation, resulting in their removal. This causes all the neighboring atoms to be defective, and increasing their reactivity, thus leading to localized carbon removal around these “active” sites. In this manner, these highly reactive defects serve as nucleation sites for the formation and growth of etch pits, with detrimental effects on the structural integrity. In order to understand the influence of these etch pits on the material properties of carbon fiber microstructures, we have developed a new capability within direct simulation Monte Carlo (DSMC) to capture the etch pit formation process. This capability is developed within the DSMC code SPARTA (Stochastic PArallel Rarefied-gas Time-accurate Analyzer) and can model the material removal in the presence of active sites leading to the formation of etch pits. The focus of the current work will be to study the effect of etch pits on the material properties of FiberForm, the precursor substrate of the PICA Thermal Protection System (TPS) material. The microstructure of virgin FiberForm obtained directly from X-ray microtomography scans is used within SPARTA to obtain the ablated geometries with etch pits. These pitted microstructures are then imported into the Porous Microstructure Analysis (PuMA) software and various material properties such as thermal conductivity, elasticity, and permeability are computed. The variation of these properties because of the complex evolution of the surface topology due to the formation of etch pits is studied and analyzed. Furthermore, the effect of pitting is compared to the case of uniform radial shrinking of fibers, which has been the standard for modelling ablation of carbon structures, and significant differences are observed. Thus, a physically realistic model of material removal through the formation of etch pits will be helpful in predicting the degradation of carbon-based TPS more accurately during oxidation; as well as other mechanisms such as spallation, which involves the removal of chunks of material into the flow due to the growth of etch pits. This will ultimately improve our understanding of the failure modes in these materials due to ablation.

DSMC↗

NASA NTRS2013

Thermal and Structural Performance of Woven Carbon Cloth For Adaptive Deployable Entry and Placement Technology

Arcjet testing and analysis of a three-dimensional (3D) woven carbon fabric has shown that it can be used as a thermal protection system and as a load bearing structural component for a low ballistic coefficient hypersonic decelerator called ADEPT (Adaptive Deployable Entry and Placement Technology). Results of arcjet tests proved that the 3D woven carbon fabric can withstand flight-like heating while under flight-like biaxial mechanical loads representative of those encountered during shallow entry flight path angles into the atmosphere of Venus. Importantly, the arcjet test results have been used to extend a preliminary material thermal response model based on previous testing of the same 3D woven carbon fabric under uni-axial mechanical loading.

Carbon fabric↗

NASA NTRS1974

Model systems for life processes on Mars

In the evolution of life forms nonphotosynthetic mechanisms are developed. The question remains whether a total life system could evolve which is not dependent upon photosynthesis. In trying to visualize life on other planets, the photosynthetic process has problems. On Mars, the high intensity of light at the surface is a concern and alternative mechanisms need to be defined and analyzed. In the UV search for alternate mechanisms, several different areas may be identified. These involve activated inorganic compounds in the atmosphere, such as the products of photodissociation of carbon dioxide and the organic material which may be created by natural phenomena. In addition, a life system based on the pressure of the atmospheric constituents, such as carbon dioxide, is a possibility. These considerations may be important for the understanding of evolutionary processes of life on another planet. Model systems which depend on these alternative mechanisms are defined and related to presently planned and future planetary missions.

Mitz, M. A.↗

NASA NTRS2000

TPS Materials and Costs for Future Reusable Launch Vehicles

There is considerable interest in developing new reusable launch vehicles (RLVs) for reducing the cost of transporting payload to and from orbit. This work reviews thirteen candidate thermal protection system (TPS) options currently available for RLVs. It is useful to begin with the current Shuttle TPS layout as a reference. The nose cap and wing leading edge , which reach the highest temperatures, are made of reinforced carbon-carbon (RCC) that is protected from oxidation by an external coating (about 0.020" thick) of silicon-carbide. Most of the windward surface is 9 lb/cubic ft ceramic tiles (LI-900) with a thin (about 0.012") coating of Reaction Cured Glass (RCG). The leeward side of the vehicle is covered largely by AFRSI, a quilted ceramic blanket, and FRSI, a polyamide felt. These four materials can be considered first generation reusable TPS. Since the time of the Shuttle design, considerable progress has been made advancing TPS technologies in terms of thermal performance, robustness, and cost. For each of the major systems, a second generation ceramic TPS has been developed, tested, and characterized. Metallic-based systems have also been developed. For applications requiring RCC in the past, advanced carbon-carbon (ACC) is now available. This material has better mechanical properties, somewhat higher temperature capability to 2900F and greatly increased oxidation resistance. New carbon fiber reinforced silicon-carbide matrix composites (C/SiCs) have shown additional improvement in properties over ACC with use temperatures to 3000F and above. For rigid tiles, NASA Ames has made two significant advancements. The first is a tile substrate called Alumina Enhanced Thermal Barrier, or AETB, that incorporates alumina fibers for improved dimensional stability at high temperatures, to 2600F and above. This material can be made to densities as low as 8 lb/cubic ft. The second is a coating preparation called Toughened Uni-piece Fibrous Insulation, or TUFT, that penetrates about 0.1 in. into the tile substrate. The resulting composite, with a functionally gradient density near the surface, provides orders of magnitude increased damage resistance compared with RCG coated LI-900, with only a small weight increase. The TPS that combines these two developments is called AETB-8/TUFI and has been adopted for high damage areas on the Shuttles. Two notable developments have occur-red in flexible ceramic blanket technology. The first is aluminoborosilicate-based fibers with use temperatures of 2200F and above," in comparison to quartz and silica fiber used in AFRSI which have multi-use temperature limits of 1200 to 1400F. Blankets incorporating these new high temperature fibers are referred to as AFRSI-HT. The second is an integral weaving techniques that produces a fluted core blanket with a smoother surface and greater resistance to aero-acoustic noise, to levels as high as 170 dB. This Ames innovation is called Tailorable Advanced Blanket Insulation, or TABI. Finally, for felt-based TPS, Boeing is developing Polybenzimidazole Blanket Insulation, or PBI, with a multi-use temperature limit of 1000F and above, in contrast to Shuttle FRSI which has a multi-use temperature limit of about 700F. 1.6 NASA Langley and BF Goodrich (formerly Rohr Corp.) have led the development of metallic-based TPS. This activity uses essentially three approaches: metallic tiles which encase a fibrous ceramic batting in a box fabricated largely from metallic honeycombs, typically Nickel based alloys; metallic honeycomb sheets, made of Nickel-based alloys, incorporating a fibrous back-side insulation encapsulated in a metallic foil bag, providing reduced weight; and metallic multi-wall, which is comprised of dimpled Titanium metal sheets, which are stacked and then diffusion bonded at contact points to form the TPS. The Nickel-based systems can be used up to temperatures of about 1800F, and the Titanium system to about 100F. These thirteen TPS materials have pros and cons to their usage in terms of temperature capability, weight, initial cost, and maintenance. Carbon-carbon and C/SiC systems have the highest temperature capability but are relatively expensive and heavy, requiring significant time, expertise, and costly facilities and tools for design and fabrication. Second generation ceramic tiles are relatively light, durable, simple to fabricate and easy to install; however, waterproofing is a concern. Blankets and felts are light, simple, inexpensive, and easy to install over curved vehicle surfaces, but durability and waterproofing are concerns. Metallics are robust and appear to have eliminated waterproofing, but they tend to be heavy and relatively expensive, requiring costly facilities and tools. If thin metal sheets are used to reduce weights, then issues arise from possible metal fatigue and corrosion caused by thermal cycling, pressure oscillations, and environmental exposure. For application to future RLVs, system analyses show that a significant component of the vehicle life cycle cost is from the TPS; however, it is difficult to quantify and to compare the potential savings of advanced systems without performing full vehicle designs using each of the different options. Because this entails a considerable effort and also tends to submerge TPS cost impacts under unrelated vehicle design assumptions, there is a clear need for a simpler quantitative method to evaluate the cost impact of different TPS options. To this end, this work introduces a TPS life-cycle cost parameter which is easily computed and applicable to generic RLVs.

Rasky, Dan J.↗

NASA NTRSDate not supplied

Simulation of etch pit formation through active sites in carbon fiber micro-structures

Erosion of carbon due to oxidation does not occur uniformly but through localized etch pit formation as a result of active surface sites. In this work we demonstrate a newly developed capability to capture pitting of carbon fiber microstructures such as FiberForm, which is commonly used as the base material for NASA’s spacecraft ablative thermal protection systems (TPS). The simulations are performed at the meso-scale in order to capture the pit formation and growth using direct simulation Monte Carlo (DSMC), specifically using the Stochastic PArallel Rarefied-gas Time-accurate Analyzer (SPARTA) code. Legacy and latest models both assume uniform reactivity of carbon surface sites with oxygen even at the meso-scale level. However, in reality the carbon surface has locally different reaction rates due to the presence of defects at the atomic scale. The defective nature of these sites enhances their reactivity with atmospheric gases compared to the non-defective sites (2-3 orders of magnitude) and are termed as “active sites”. Thus, these sites tend to be the first to react and eventually get removed through the formation of gasses such as CO, CO2, and CN. Their removal results in all the neighboring atoms becoming defective, thus leading to chain reaction of localized carbon removal and formation of etch pits. Capturing the formation of pits during the ablation simulation of carbon micro-structures is critical to predicting their structural failure. Recently a detailed surface chemistry framework was developed in SPARTA, capable of incorporating various reaction mechanisms such as adsorption, desorption, Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms. We have implemented the capability of a single surface having multiple site sets with different reactivities within this framework. We have used this feature to model the presence of active sites on carbon surfaces, whose reactivity is orders of magnitude higher than that of the passive sites due to the presence of defects. The active site fraction is a property of surface elements within SPARTA and is directly proportional to the local reactivity of each surface element. By introducing an initial distribution of the active site fraction across the carbon surface and propagating it in a manner that mimics the evolution of real reacting carbon surfaces, we can capture the formation and growth of etch pits as a result of surface consumption reactions such as oxidation.

DSMC↗

NASA NTRSDate not supplied

Simulation of Etch Pit Formation in DSMC Through Active Sites in Carbon Fiber Micro-Structures

Erosion of carbon due to oxidation does not occur uniformly but through localized etch pit formation because of active surface sites. In this work we demonstrate a newly developed capability to capture pitting of carbon fiber microstructures such as FiberForm, which is commonly used as the base material for NASA’s spacecraft ablative thermal protection systems (TPS). The simulations are performed at the meso-scale in order to capture the pit formation and growth using direct simulation Monte Carlo (DSMC), specifically using the Stochastic PArallel Rarefied-gas Time-accurate Analyzer (SPARTA) code. Legacy and latest models both assume uniform reactivity of carbon surface sites with oxygen even at the meso-scale level. However, in reality the carbon surface has locally different reaction rates due to the presence of defects at the atomic scale. The defective nature of these sites enhances their reactivity with atmospheric gases compared to the non-defective sites (2-3 orders of magnitude) and are termed as “active sites”. Thus, these sites tend to be the first to react and eventually get removed through the formation of gases such as CO, CO2, and CN. Their removal results in all the neighboring atoms becoming defective, thus leading to chain reaction of localized carbon removal and formation of etch pits. Capturing the formation of pits during the ablation simulation of carbon micro-structures is critical to predicting their structural failure. Recently a detailed surface chemistry framework was developed in SPARTA, capable of incorporating various detailed surface reaction mechanisms. We have implemented the capability of a single surface having multiple site sets with different reactivities within this framework. We have used this feature to model the presence of active sites on carbon surfaces, whose reactivity is orders of magnitude higher than that of the passive sites due to the presence of defects. The active site fraction is a property of surface elements within SPARTA and is directly proportional to the local reactivity of each surface element. By introducing an initial distribution of the active site fraction across the carbon surface and propagating it in a manner that mimics the evolution of real reacting carbon surfaces, we can capture the formation and growth of etch pits as a result of surface consumption reactions such as oxidation.

DSMC↗

NASA NTRSDate not supplied

DSMC Simulation of Etch Pit Formation Through Active Sites in Carbon Fiber Micro-Structures

Erosion of carbon due to oxidation does not occur uniformly but through localized etch pit formation because of active surface sites. In this work we demonstrate a newly developed capability to capture pitting of carbon fiber microstructures such as FiberForm, which is commonly used as the base material for NASA’s spacecraft ablative thermal protection systems (TPS). The simulations are performed at the meso-scale in order to capture the pit formation and growth using direct simulation Monte Carlo (DSMC), specifically using the Stochastic PArallel Rarefied-gas Time-accurate Analyzer (SPARTA) code. Legacy and latest models both assume uniform reactivity of carbon surface sites with oxygen even at the meso-scale level. However, in reality the carbon surface has locally different reaction rates due to the presence of defects at the atomic scale. The defective nature of these sites enhances their reactivity with atmospheric gases compared to the non-defective sites (2-3 orders of magnitude) and are termed as “active sites”. Thus, these sites tend to be the first to react and eventually get removed through the formation of gases such as CO, CO2, and CN. Their removal results in all the neighboring atoms becoming defective, thus leading to chain reaction of localized carbon removal and formation of etch pits. Capturing the formation of pits during the ablation simulation of carbon micro-structures is critical to predicting their structural failure. Recently a detailed surface chemistry framework was developed in SPARTA, capable of incorporating various detailed surface reaction mechanisms. We have implemented the capability of a single surface having multiple site sets with different reactivities within this framework. We have used this feature to model the presence of active sites on carbon surfaces, whose reactivity is orders of magnitude higher than that of the passive sites due to the presence of defects. The active site fraction is a property of surface elements within SPARTA and is directly proportional to the local reactivity of each surface element. By introducing an initial distribution of the active site fraction across the carbon surface and propagating it in a manner that mimics the evolution of real reacting carbon surfaces, we can capture the formation and growth of etch pits as a result of surface consumption reactions such as oxidation.

DSMC↗

NASA NTRS1992

Flight-vehicle materials, structures, and dynamics - Assessment and future directions. Vol. 3 - Ceramics and ceramic-matrix composites

The present volume discusses ceramics and ceramic-matrix composites in prospective aerospace systems, monolithic ceramics, transformation-toughened and whisker-reinforced ceramic composites, glass-ceramic matrix composites, reaction-bonded Si3N4 and SiC composites, and chemical vapor-infiltrated composites. Also discussed are the sol-gel-processing of ceramic composites, the fabrication and properties of fiber-reinforced ceramic composites with directed metal oxidation, the fracture behavior of ceramic-matrix composites (CMCs), the fatigue of fiber-reinforced CMCs, creep and rupture of CMCs, structural design methodologies for ceramic-based materials systems, the joining of ceramics and CMCs, and carbon-carbon composites.

Levine, Stanley R.↗

NASA NTRS2013

Material Property Characterization of AS4/VRM-34 Textile Laminates

Several material properties (modulus, strengths, and fracture toughness) of a textile composite have been evaluated to provide input data to analytical models of Pultruded Rod Stiffened Efficient Unitized Structure (PRSEUS). The material system is based on warp-knitted preforms of AS4 carbon fibers and VRM-34 epoxy resin, which have been processed via resin infusion and oven curing. Tensile, compressive, shear, and fracture toughness properties have been measured at ambient and elevated temperatures. All specimens were tested in as-fabricated (dry) condition. Specimens were tested with and without through-thickness stitching.

Grenoble, Ray W.↗

NASA NTRS1993

A combustion products analyzer for contingency use during thermodegradation events on spacecraft

The Toxicology Laboratory at JSC and Exidyne Instrumentation Technologies (EIT) have developed a prototype Combustion Products Analyzer (CPA) to monitor, in real time, combustion products from a thermodegradation event on board spacecraft. The CPA monitors the four gases that are the most hazardous compounds (based on the toxicity potential and quantity produced) likely to be released during thermodegradation of synthetic materials: hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen cyanide (HCN), and carbon monoxide (CO). The levels of these compounds serve as markers to assist toxicologists in determining when the cabin atmosphere is safe for the crew to breathe following the contingency event. The CPA is a hand-held, battery-operated instrument containing four electrochemical sensors, one for each target gas, and a pump for drawing air across the sensors. The sensors are unique in their small size and zero-g compatibility. The immobilized electrolytes in each sensor permit the instrument to function in space and eliminate the possibility of electrolye leaks. The sample inlet system is equipped with a particulate filter that prevents clogging from airborne particulate matter. The CPA has a large digital display for gas concentrations and warming signals for low flow and low battery conditions. The CPA has flown on 13 missions beginning with STS 41 in Oct. 1990. Current efforts include the development of a microprocessor, an improved carbon monoxide sensor, and a ground-based test program to evaluate the CPA during actual thermodegradation of selected materials.

Wilson, Steve↗

NASA NTRS1998

Assessment of Uncertainty in the Determination of Activation Energy for Polymeric Materials

An assessment of the experimental uncertainty in obtaining the kinetic activation energy from thermogravimetric analysis (TGA) data is presented. A neat phenolic resin, Borden SC1O08, was heated at three heating rates to obtain weight loss vs temperature data. Activation energy was calculated by two methods: the traditional Flynn and Wall method based on the slope of log(q) versus 1/T, and a modification of this method where the ordinate and abscissa are reversed in the linear regression. The modified method produced a more accurate curve fit of the data, was more sensitive to data nonlinearity, and gave a value of activation energy 75 percent greater than the original method. An uncertainty analysis using the modified method yielded a 60 percent uncertainty in the average activation energy. Based on this result, the activation energy for a carbon-phenolic material was doubled and used to calculate the ablation rate In a typical solid rocket environment. Doubling the activation energy increased surface recession by 3 percent. Current TGA data reduction techniques that use the traditional Flynn and Wall approach to calculate activation energy should be changed to the modified method.

Darby, Stephania P.↗

NASA NTRS1974

Adhesion, friction and Auger spectroscopy analysis of a commercial cobalt base aircraft turbine shroud alloy

A commercially used cast cobalt base alloy was investigated as a turbine shroud material which revealed a surface enriched with tungsten and carbon suggesting a surface layer of tungsten carbide. Adhesion and friction of this segregated surface layer are higher than for the bulk cobalt base alloy composition. Auger spectroscopy analysis of the segregation of tungsten in the alloy indicates that it occurs between 850 and 1000 C.

Buckley, D. H.↗

NASA NTRS2005

A Materials Compatibility and Thermal Stability Analysis of Common Hydrocarbon Fuels

A materials compatibility and thermal stability investigation was conducted using five common liquid hydrocarbon fuels and two structural materials. The tests were performed at the NASA Glenn Research Center Heated Tube Facility under environmental conditions similar to those encountered in regeneratively cooled rocket engines. Scanning-electron microscopic analysis in conjunction with energy dispersive spectroscopy (EDS) was utilized to characterize the condition of the tube inner wall surface and any carbon deposition or corrosion that was formed during selected runs. Results show that the carbon deposition process in stainless steel tubes was relatively insensitive to fuel type or test condition. The deposition rates were comparable for all fuels and none of the stainless steel test pieces showed any signs of corrosion. For tests conducted with copper tubing, the sulfur content of the fuel had a significant impact on both the condition of the tube wall and carbon deposition rates. Carbon deposition rates for the lowest sulfur fuels (2 ppm) were slightly higher than those recorded in the stainless steel tubes with no corrosion observed on the inner wall surface. For slightly higher sulfur content (25 ppm) fuels, nodules that intruded into the flow area were observed to form on the inner wall surface. These nodules induced moderate tube pressure drop increases. The highest sulfur content fuels (400 ppm) produced extensive wall pitting and dendritic copper sulfide growth that was continuous along the entire tube wall surface. The result of this tube degradation was the inability to maintain flow rate due to rapidly increasing test section pressure drops. Accompanying this corrosion were carbon deposition rates an order of magnitude greater than those observed in comparable stainless steel tests. The results of this investigation indicate that trace impurities in fuels (i.e. sulfur) can significantly impact the carbon deposition process and produce unacceptable corrosion levels in copper based structural materials.

Meyer, M. L.↗

NASA NTRS2003

Space Colonization Using Space-Elevators from Phobos

A novel approach is examined for creating an industrial civilization beyond Earth. The approach would take advantage of the unique configuration of Mars and its moon Phobos to make a transportation system capable of raising mass from the surface of Mars to space at a low cost. Mars would be used as the primary location for support personnel and infrastructure. Phobos would be used as a source of raw materials for space-based activity, and as an anchor for tethered carbon-nanotube-based space-elevators. One space-elevator would terminate at the upper edge of Mars' atmosphere. Small craft would be launched from Mars' surface to rendezvous with the moving elevator tip and their payloads detached and raised with solar powered loop elevators to Phobos. Another space-elevator would be extended outward from Phobos to launch craft toward the Earth/Moon system or the asteroid belt. The outward tip would also be used to catch arriving craft. This approach would allow Mars to be colonized, and allow transportation of people and supplies from Mars to support the space industry. In addition, large quantities of material obtained from Phobos could be used to construct space habitats and also supply propellant and material for space industry in the Earth/Moon system as well as around Mars.

Weinstein, Leonard M.↗

NASA NTRS2016

X-ray Micro-Tomography of Ablative Heat Shield Materials

X-ray micro-tomography is a non-destructive characterization technique that allows imaging of materials structures with voxel sizes in the micrometer range. This level of resolution makes the technique very attractive for imaging porous ablators used in hypersonic entry systems. Besides providing a high fidelity description of the material architecture, micro-tomography enables computations of bulk material properties and simulations of micro-scale phenomena. This presentation provides an overview of a collaborative effort between NASA Ames Research Center and Lawrence Berkeley National Laboratory, aimed at developing micro-tomography experiments and simulations for porous ablative materials. Measurements are carried using x-rays from the Advanced Light Source at Berkeley Lab on different classes of ablative materials used in NASA entry systems. Challenges, strengths and limitations of the technique for imaging materials such as lightweight carbon-phenolic systems and woven textiles are discussed. Computational tools developed to perform numerical simulations based on micro-tomography are described. These enable computations of material properties such as permeability, thermal and radiative conductivity, tortuosity and other parameters that are used in ablator response models. Finally, we present the design of environmental cells that enable imaging materials under simulated operational conditions, such as high temperature, mechanical loads and oxidizing atmospheres.Keywords: Micro-tomography, Porous media, Ablation

tomography↗