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At least 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Benchmarking Cylindrical Blast Wave Theory Against the OSIRIS-REx Sample Return Capsule Reentry

Weak shock theory based on cylindrical blast waves has been used to interpret meteor infrasound, but it has not been systematically benchmarked against a non-ablating hypersonic source with independently known parameters. The objective of this study is not to propose a new theoretical framework, but to evaluate the operational validity of the existing suite of blast radius formulations against a high-fidelity ground truth dataset. The OSIRIS-REx Sample Return Capsule reentry on 24 September 2023 provides such a benchmark because the capsule geometry, trajectory, and infrasound emission points are constrained from mission data and ray tracing, reducing source-side uncertainty associated with ablation. Using observations from 39 infrasound stations, this benchmarking study evaluates six published blast radius (${R}_{0}$ ) formulations and three weak-shock transition coefficients ( C ) within a stratified atmospheric propagation model to predict signal period and peak overpressure. The benchmarking identifies the Sakurai formulation as the best-performing formulation for non-ablating bodies, with the Jones/Plooster formulation performing comparably when a physically appropriate C is adopted. Sakurai and Jones/Plooster yield linear-period median absolute percentage residuals of 9% and 11%, respectively. The period predictions show only weak sensitivity to C at these propagation distances. The Mach-diameter approximation commonly used in meteor studies overestimates ${R}_{0}$ by more than a factor of 3 in the absence of ablation. Finally, these results establish a performance baseline for applying cylindrical blast wave theory to effectively non-ablating hypersonic bodies and demonstrate that the signal period is a robust observable for constraining ${R}_{0}$.

atmospheric entry↗
DOE OSTI2021

Determination of positive anode sheath in anodic carbon arc for synthesis of nanomaterials

In the atmospheric pressure anodic carbon arc, ablation of the anode serves as a feedstock of carbon for production of nanomaterials. It is known that the ablation of the graphite anode in this arc can have two distinctive modes with low and high ablation rates. The transition between these modes is governed by the power deposition at the arc attachment to the anode and depends on the gap between the anode and the cathode electrodes. Probe measurements combined with optical emission spectroscopy are used to analyze the voltage drop between the arc electrodes. These measurements corroborated previous predictions of a positive anode sheath (i.e. electron attracting sheath) in this arc, which appears in both low and high ablation modes. However, the positive anode sheath was determined to be ~3–8 V, significantly larger than ~0.5 V predicted by previous models. Thus, there are apparently other physical mechanisms not considered by these models that force the anode sheath to be electron attracting in both ablation regimes. Another key result is a relatively low electron temperature (~0.6 eV) obtained from OES using a collisional radiative model. This result partially explains a higher arc voltage (~20 V) required to sustain the arc current of 50–70 A than predicted by existing simulations of this discharge.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1962

Aerodynamic Evidence Pertaining to the Entry of Tektites into the Earth's Atmosphere

Evidence is presented which shows that the Australian and Java tektites entered the earth's atmosphere and experienced ablation by severe aerodynamic heating in hypervelocity flight. The laboratory experiments on hypervelocity ablation have reproduced ring-wave flow ridges and coiled circumferential flanges like those found on certain of these tektites. Systematic striae distortions exhibited in a thin layer beneath the front surface of australites also are reproduced in the laboratory ablation experiments, and are shown to correspond to the calculated distortions for aerodynamic ablation of a glass. About 98 percent of Australian tektites represent aerodynamically stable configurations during the ablative portion of an entry trajectory. Certain meteorites exhibit surface features similar to those on tektites.

AERODYNAMIC HEATING↗
NASA NTRS2015

Thermal Protection System Mass Estimating Relationships for Blunt-Body, Earth Entry Spacecraft

System analysis and design of any entry system must balance the level fidelity for each discipline against the project timeline. One way to inject high fidelity analysis earlier in the design effort is to develop surrogate models for the high-fidelity disciplines. Surrogate models for the Thermal Protection System (TPS) are formulated as Mass Estimating Relationships (MERs). The TPS MERs are presented that predict the amount of TPS necessary for safe Earth entry for blunt-body spacecraft using simple correlations that closely match estimates from NASA's high-fidelity ablation modeling tool, the Fully Implicit Ablation and Thermal Analysis Program (FIAT). These MERs provide a first order estimate for rapid feasibility studies. There are 840 different trajectories considered in this study, and each TPS MER has a peak heating limit. MERs for the vehicle forebody include the ablators Phenolic Impregnated Carbon Ablator (PICA) and Carbon Phenolic atop Advanced Carbon-Carbon. For the aftbody, the materials are Silicone Impregnated Reusable Ceramic Ablator (SIRCA), Acusil II, SLA-561V, and LI-900. The MERs are accurate to within 14% (at one standard deviation) of FIAT prediction, and the most any MER under predicts FIAT TPS thickness is 18.7%. This work focuses on the development of these MERs, the resulting equations, model limitations, and model accuracy.

mass estimating relationship (MER)↗
NASA NTRS2015

Thermal Protection System Mass Estimating Relationships For Blunt-Body, Earth Entry Spacecraft

Mass estimating relationships (MERs) are developed to predict the amount of thermal protection system (TPS) necessary for safe Earth entry for blunt-body spacecraft using simple correlations that are non-ITAR and closely match estimates from NASA's highfidelity ablation modeling tool, the Fully Implicit Ablation and Thermal Analysis Program (FIAT). These MERs provide a first order estimate for rapid feasibility studies. There are 840 different trajectories considered in this study, and each TPS MER has a peak heating limit. MERs for the vehicle forebody include the ablators Phenolic Impregnated Carbon Ablator (PICA) and Carbon Phenolic atop Advanced Carbon-Carbon. For the aftbody, the materials are Silicone Impregnated Reusable Ceramic Ablator (SIRCA), Acusil II, SLA- 561V, and LI-900. The MERs are accurate to within 14% (at one standard deviation) of FIAT prediction, and the most any MER can under predict FIAT TPS thickness is 18.7%. This work focuses on the development of these MERs, the resulting equations, model limitations, and model accuracy.

Spacecraft↗
DOE OSTI2018

Evaluating the functionality and streamflow impacts of explicitly modelling forest-snow interactions and canopy gaps in a distributed hydrologic model

Many plot-scale observational studies found that snow cover dynamics in forest gaps are distinctly different from open and continuously forested areas, and canopy gaps have the potential to increase snow retention and alter the snow regime. However, our knowledge on forest-snow interactions in discontinuous forests with canopy gaps and their implications for forest and water management is far more limited. We address this knowledge gap through a major enhancement of a widely used distributed hydrologic model, DHSVM. We developed a canopy gap component as a unique vegetation type that is characterized on the subgrid scale, with physics-based representation of processes that allow independent evolution of snowpack in forest gaps. We validated the enhanced DHSVM for three experimental sites in close proximity consisting of a completely open site, a densely forested site, and a canopy gap site. Despite the scale mismatch between point measurements and grid-scale simulations, the modeled snow water equivalent (SWE) agreed reasonably well with the continuous observations collected during one full ablation season at all sites. Evaluation of snowpack energetics suggested that snow ablation at three sites was controlled primarily by net radiation that critically depends on the canopy cover and structure. While the rate of snowmelt remained relatively constant in the forest during the ablation season, the gap demonstrated marked temporal variability in ablation rate as a result of complex interplay between canopy structure of the adjacent forest and the angle of solar incidence. The comparison of this enhanced version to the original DHSVM highlighted the importance of explicitly accounting for forest impacts on the gap snowpack energy balance. Between the two versions, the greatest difference in snow ablation rates was found in smaller gaps. The enhanced model tends to predict notably later melt for small to medium canopy gaps (the ratio of gap radius to canopy height r/h = 1.3), and snow melt rates exhibit great sensitivity to changing gap size in medium-size gaps (0.5 = r/h = 1.3).

Forest-Snow Dynamics, Canopy Gap, Snow Hydrology, ↗
DOE OSTI2018

Effects of Plume Hydrodynamics and Oxidation on the Composition of a Condensing Laser-Induced Plasma

High-temperature chemistry in laser ablation plumes leads to vapor-phase speciation, which can induce chemical fractionation during condensation. In this work, using emission spectroscopy acquired after ablation of a SrZrO 3 target, we have experimentally observed the formation of multiple molecular species (ZrO and SrO) as a function of time as the laser ablation plume evolves. Although the stable oxides SrO and ZrO 2 are both refractory, we observed emission from the ZrO intermediate at earlier times than SrO. We deduced the time-scale of oxygen entrainment into the laser ablation plume using an 18 O 2 environment by observing the in-growth of Zr 18 O in the emission spectra relative to Zr 16 O, which was formed by reaction of Zr with 16 O from the target itself. Using temporally resolved plume-imaging, we determined that ZrO formed more readily at early times, volumetrically in the plume, while SrO formed later in time, around the periphery. Lastly, using a simple temperature-dependent reaction model, we have illustrated that the formation sequence of these oxides subsequent to ablation is predictable to first order.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Shock drive capabilities of a 30-Joule laser at the matter in extreme conditions hutch of the Linac Coherent Light Source

In this paper, we measure the shock drive capabilities of a 30 J, nanosecond, 527 nm laser system at the matter in extreme conditions hutch of the Linac Coherent Light Source. Using a velocity interferometer system for any reflector, we ascertain the maximum instantaneous ablation pressure and characterize its dependence on a drive laser spot size, spatial profile, and temporal profile. We also examine the effects of these parameters on shock spatial and temporal uniformity. Our analysis shows the drive laser capable of generating instantaneous ablation pressures exceeding 160 GPa while maintaining a 1D shock profile. We find that slope pulses provide higher instantaneous ablation pressures than plateau pulses. Our results show instantaneous ablation pressures comparable to those measured at the Omega Laser Facility in Rochester, NY under similar optical drive parameters. In conclusion, we analyze how optical laser ablation pressures are compare with known scaling relations, accounting for variable laser wavelengths.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Intricate structure of the plasma Rayleigh–Taylor instability in shock tubes

Spikes and bubbles grow on unstable interfaces that are accelerated in high-energy-density conditions. If a shock propagates ahead of the interface, the plasma can be heated to extreme conditions where conduction and radiation fluxes influence the hydrodynamics. For example, a National Ignition Facility experiment found reduced single-mode nonlinear mixed-width growth in conditions scaled from a supernova explosion. We present high-resolution two-dimensional radiation hydrodynamic simulations with the Flash code that quantitatively reproduce the experiment. Radiative fluxes are primarily responsible for ablating the spike and removing the mushroom caps. The ablated plasma increases the mixed mass and forms a low-density halo with spikes forming in both directions. This is considerably more complex than classical instability. The halo is sensitive to ablative physics, so radiographing it may aid in the verification of energy transport modeling. Although ablation changes the spike shape, it has little effect on the overall mixed width for these parameters. This is because ablation enhances the bubble velocity but it has the opposite effect on the spike. The radiation transport instead suppresses the growth via increasing the shocked foam density, thus decreasing the Atwood number. Furthermore, a terminal velocity model including the rarefaction expansion agrees with the experimental mixed-width growth.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Characterizing the effects of drive asymmetries, component offsets, and joint gaps in double shell capsule implosions

This work provides a numerical study of how double shell capsule deformations caused by drive asymmetries and fabrication imperfections affect implosion symmetry and neutron yield. Hydrodynamics simulations are performed in two dimensions and focus on low-mode deformations that are caused by corresponding asymmetries in the Hohlraum drive, component offsets, and ablator joint gaps. By providing a parameter study of these features, our goal is to understand the dominant sources for inner shell deformation and yield degradation. The discussed capsules are composed of an aluminum ablator with a chromium inner shell. The latter encloses a carbon-deuterium foam ball that serves as fuel. We find that for clean capsules, even-numbered low-mode asymmetries in the drive are imprinted on the ablator and smoothly transferred to the inner shell during shell collision. The resulting deformation of the inner shell is more pronounced with larger fuel radius, while the yield is inversely proportional to the amplitude of the drive asymmetry and varies by factors ≤4 in comparison with clean simulations. Capsule component offsets in the vertical direction and ablator thickness nonuniformity result in p1-type deformations of the imploding inner shell. Finally, joint gaps have the largest effect in deforming the ablator and inner shell and degrading yield. While small gap widths (1 μm) result in prolate inner shells, larger gap widths (4 μm) cause an oblate deformation. More importantly, capsules with a small outer gap (1 μm) experience a dramatic drop in yield, typically <3% of a clean simulation.

Goodarzi, S. (ORCID:000000018556489X)↗
DOE OSTI2025

Room temperature buffer gas beam of metastable state titanium atoms

We produce beams of neutral titanium (Ti) atoms in their metastable 3d3(F4)4sa5F5 state by laser ablation into He, N2, and Ar buffer gases. The high temperatures associated with the ablation process populate the a5F5 level without the need for optical pumping. Remarkably, we observe that Ti atoms in the a5F5 state survive thousands of collisions with He and Ar buffer gas atoms without being quenched to lower-energy states. We study the yield of Ti atoms when ablated into buffer gases of varying species and pressure, quantify quenching rates and diffusion cross sections based on simple models, and provide insight into optimal design parameters for an ablation cell. Using a 3.3 cm ablation cell with interchangeable exit apertures, we produce metastable atom beams and quantify their brilliance and velocity distributions as functions of buffer gas pressure.

Schrott, Jackson↗
DOE OSTI2026

Wetted-foam target stability for laser-direct-drive inertial confinement fusion

Using highly resolved three-dimensional radiation-hydrodynamic simulations, the effects of wetted-foam (WF) ablators in direct-drive inertial confinement fusion cryogenic implosions on the OMEGA laser were investigated. The performance of these implosions was compared with that of implosions using targets with solid-plastic ablators. Simulations considering WF ablators as a homogeneous material show no mitigation of the effects of laser imprint, where the absence of this mitigation can be attributed to the use of picket pulses. Heterogeneous random-structure WF ablators introduce large short-wavelength perturbations, which are seeded by WF inhomogeneities. These perturbations exceed the perturbations seeded by the imprint and cause an additional reduction in implosion performance when the average pore size in the WF exceeds ~0.2 μm. Foam-seeded perturbations are expected to be less damaging in more stable high-adiabat (⁠ ≳ 5⁠) implosions. Here, the perturbations introduced by the WF ablators can be substantially reduced by using a foam matrix with a layered structure instead of a random one. Further study of the effects of WFs in ignition designs of the MJ laser energy scale is required in the perspective of future inertial fusion energy mass production.

Igumenshchev, I. V. [University of Rochester, NY (↗
DOE OSTI2017

Plasma fuelling with cryogenic pellets in the stellarator TJ-II

Cryogenic pellet injection is a widely used technique for delivering fuel to the core of magnetically confined plasmas. Indeed, such systems are currently functioning on many tokamak, reversed field pinch and stellarator devices. A pipe-gun-type pellet injector is now operated on the TJ-II, a low-magnetic shear stellarator of the heliac type. Cryogenic hydrogen pellets, containing between 3×10 18 and 4×10 19 atoms, are injected at velocities between 800 and 1200 m s -1 from its low-field side into plasmas created and/or maintained in this device by electron cyclotron resonance and/or neutral beam injection heating. In this paper, the first systematic study of pellet ablation, particle deposition and fuelling efficiency is presented for TJ-II. From this, light-emission profiles from ablating pellets are found to be in reasonable agreement with simulated pellet ablation profiles (created using a neutral gas shielding-based code) for both heating scenarios. In addition, radial offsets between recorded light-emission profiles and particle deposition profiles provide evidence for rapid outward drifting of ablated material that leads to pellet particle loss from the plasma. Finally, fuelling efficiencies are documented for a range of target plasma densities (~4×10 18 – ~2×10 19 m -3 ). These range from ~20%– ~85% and are determined to be sensitive to pellet penetration depth. Additional observations, such as enhanced core ablation, are discussed and planned future work is outlined.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

High-Temperature Sapphire Pressure Sensors for Harsh Environments

The project aimed to develop and characterize an optical pressure sensor capable of withstanding high temperatures, up to 1000 °C. Survivability in harsh environments was enabled using sapphire for both the substrate and the optical fibers, therefore mitigating thermal expansion mismatch. Such material cannot be machined through conventional microfabrication techniques, and unique additive and subtractive methods had to be studied and implemented. Subtractive methods included laser-machining the sapphire substrate using a picosecond laser machining tool. At first, the parameters of importance were theoretically and experimentally evaluated such that the fluence, the pulse spacing, and the number of passes were found to strongly influence the laser ablation process. A simulation tool was designed to predict the final pattern when inputting a set of parameters and a profile. This model was complemented with laser ablation material physics models and Bayesian uncertainty analysis for one dimensional and three dimensional ablation processes. An additive process called thermocompression bonding was studied in order to seal the diaphragm substrate to the back cavity. At first, bonding strength using this technique was examined using the chevron-notch method that allow to determine the fracture toughness of this bond. This parameter is independent of the geometry used and therefore can be extended to other geometries used in actual sensor bonding. A theoretical and experimental study of internal damage caused by the laser micromachining of the sapphire material was carried out. The research identified enhanced strength and fracture toughness along laser ablated surfaces. This was determined using bend bar specimens and Vicker’s microindentations. Softening of the plasticity behavior (as indicated by nanoindentation experiments) was also investigated using finite deformation plasticity modeling via a contact mechanics finite element simulation. Good correlations between experiments and the model were achieved to determine material parameters that can be used in future MEMS based sensor design and modeling to minimize sensor failure loads. The enhanced strength and fracture toughness was determined to be due to compressive residual stress near laser ablated surfaces. This was confirmed through x-ray spectra taken along different crystal structure planes in combination and Bayesian uncertainty analysis. The Bayesian analysis inferred the entire residual strain tensor (six components) and the residual stress tensor. The results illustrated compressive in-plane stress was the most likely cause of enhanced strength and toughness after laser machining. Due to major equipment failures, a parallel route for fabricating the sensor was taken, using commercially available sapphire removal method (subtractive) and ceramic adhesive bonding (additive). The fully-packaged sensor utilized laser micromachining for the sapphire substrate fabrication and was comprised only of high-temperature-compatible materials. Calibration tests of the sensor in both room-temperature and high-temperature plane-wave tubes showed good linearity and consistent frequency response, in the tested frequency range. The sensor also showed good thermal stability in tests up to 300 °C, proving the fiber-optic lever and its packaging process to be a promising approach for high-temperature measurements. The calibration from 23 °C to 300 °C gave a raw sensitivity of 3.9 × 10 -7 V/Pa and a normalized sensitivity of 9.8 × 10 -8 Pa -1 which were consistent within the temperature range. The sensor had a resonance at 16.3 kHz and a flat band (±3 dB) up to 10.3 kHz. The noise floor of the sensor at 1 kHz was 316 nV/Hz 1/2 , resulting in a MDP of 0.8 Pa. Previously, diaphragm delamination due to CTE mismatch was found at 500 °C, causing packaging failure. Unfortunately high temperature validation in hot jet environment could not be made in time. In the future, it is suggested that the two sapphire substrates be bonded by thermal compression bonding with an intermediate platinum layer instead of using an alumina-based adhesive, and therefore achieve higher temperature capacity up to 1000 °C.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1972

Silica reinforcement and char reactions in the Apollo heat shield.

Reactions of the silica reinforcement fiber and ablation char of the Apollo heat shield have been investigated by laboratory tests in an arc image furnace (at temperature levels up to 5000 R, pressures up to 0.7 atm, and heat flux similar to reentry) and by an actual reentry test. Microchemical analyses and X-ray diffraction studies have been made to determine the presence of SiC formation in the char. Experimental data and analytical predictions of thermal and density profiles have been compared for the ablation of virgin heat shield and precharred materials to determine the effects of SiC formation on ablation performance. In all analyses, general agreement was found between chemical composition and the thermal predictions for laboratory tests and reentry materials. In all ablated materials, SiC was formed in the front surface of the char. The highest SiC content found was 58% by weight and found in a high-pressure environment. The SiC formed was found to act as a heat sink in the ablation process and can lower the front surface temperature by 300 R.

Cagliostro, D. E.↗
NASA NTRS1973

Heat shielding for Venus entry probes.

Two contrasted approaches to ablative thermal protection of Venus entry probes are presented - a typical carbonaceous charring ablator and a dielectric reflective ablator. The interesting observation in this study is that mass loss is not the controlling variable in heat-shield sizing. A heat-soak problem determines the carbon phenolic sizing. For Teflon, the material thickness required to accomplish reflection is the sizing factor. The total heat-shield weight required to handle either steep or shallow entry is computed to be 13% less for a Teflon shield (if at least 3.2 mm are required for reflection) than for a charring ablator shield. If an efficient reflective backing is used with Teflon, the thickness can be reduced 1.0 mm and the computed weight is 31% less for Teflon than for the charring ablator. Such weight reductions may significantly increase the science payload weight of the miniprobes.

Peterson, D. L.↗
NASA NTRS1978

Carbonaceous materials subjected to extreme heating - A comparison of numerical simulation and experiments

The ablation of carbonaceous materials in a hydrogen-helium stream has been simulated using a charring materials ablator computer code. These results are compared with the first ablation data to be obtained from the Ames-NASA Giant Planet Pilot Facility. Test stream diagnostics and ablation effects on convective and radiative heat transfer are discussed since these parameters constitute important input data to the numerical simulation. Graphite ablation was predicted to within 10 to 20%, and carbon-phenolic somewhat less accurately.

Davy, W. C.↗
NASA NTRS1988

Standardization of the carbon-phenolic materials and processes. Vol. 2: Test methods and specifications

Carbon-phenolic composite materials are used in the ablation process in the nozzles of the Space Shuttle Main Engine. The nozzle is lined with carbon cloth-phenolic resin composites. The extreme heat and erosion of the burning propellant are controlled by the carbon-phenolic composite by means of ablation, a heat and mass transfer process in which a large amount of heat is dissipated by sacrificailly removing material from a surface. Phenolic materials ablate with the initial formation of a char. The depth of the char is a function of the heat conduction coefficient of the composite. The char layer is a poor conductor so it protects the underlying phenolic composite from the high heat of the burning propellant. The nozzle component ablative liners (carbon cloth-phenolic resin composites) are tape wrapped, hydroclave and/or autoclave cured, machined and assembled. The tape consists of prepreg broadcloth. The materials flow sheet for the nozzle ablative liners is given. The prepreg is a three component system: phenolic resin, carbon cloth, and carbon filler. This is Volume 2 of the report, Test Methods and Specifications.

Hall, William B.↗