Modeling radiative transfer through three-dimensional inhomogeneous media can be computationally prohibitive while accounting for variation in the spatial, angular, and frequency domains. An effective strategy for mitigating these challenges is the use of reduced-order wide-band models that can lower the cost of resolving frequency dependence. Existing approaches are either strictly derived only for local thermodynamic equilibrium conditions or entail significant algorithmic complexity with limited generalizability. Thus, their suitability for complex gas mixtures in a state of strong non-equilibrium or overall robustness across diverse aerothermal regimes remains intrinsically constrained. The current work proposes a streamlined model-reduction methodology that builds upon a maximum entropy reinterpretation of Planck-averaging. This core principle is augmented with advancements that include a novel non-equilibrium grouping procedure (for combining individual frequencies into larger groups), gas flow-agnostic model-reduction, accommodation for non-Boltzmann internal state populations, and the ability to account for spectral overlap between disparate species. The efficacy of the new approach has been assessed by performing a series of one and three-dimensional radiative transfer calculations, involving both atomic and molecular species (including those that overlap in the frequency space), for Earth, Titan, and Mars atmospheric entries. The new reduced-order spectral databases retain accuracy throughout a broad envelope of non-equilibrium physical conditions without introducing extraneous overheads. Both total quantities-of-interest such as wall-incident heat flux as well as detailed spectral features are reliably captured while achieving a two to three orders-of-magnitude speed-up in comparison to line-by-line modeling.

This paper presents a history of the assumptions that led to backshell radiative heating being ignored for Earth entry prior to 2015. The errors in these assumptions are identified, which are the result of limitations in both the theory and relevant measurements available during the Apollo era. The process of including this new heating component within a few months of its discovery to the design of the Orion capsule for Artemis-1 is discussed, which required efficient simulation techniques developed at NASA over the past 20 years. Artemis-1 flight measurements indicate that this nearly missed radiative heating component was the dominant heating mechanism over a large section of the Orion backshell. This confirms the importance of identifying and including this backshell radiative heating component for the Orion backshell design, which will be used for future crewed Artemis flights.

A perspective on the luminous efficiency approach for determining the pre-atmospheric mass of a meteoroid from a measured light-curve is presented for meteors in the continuum flow regime. This perspective interprets the mass-loss rate evaluated from the luminous efficiency approach as a solution to the meteoroid surface energy balance, with the measured light-curve serving as a proxy for the radiative heating to the meteoroid surface. This differs from the standard interpretation that equates the radiation from the light-curve to a change in the kinetic energy of the meteor. Mathematically, the developed perspective is identical to the standard luminous efficiency approach, except that the deceleration term is shown to be extraneous. This perspective provides a clear relationship between the measured light-curve and the mass loss of a meteor, which is based on the observation that the radiative heating that drives the mass loss (through the surface energy balance) also provides the radiation for the light-curve. Furthermore, this perspective provides a simple mathematical framework for interpreting the impact of fragmentation on the luminous efficiency. This framework shows that the luminous efficiency of a fragmented meteoroid is a weighted sum of the luminous efficiency from the various fragments, which may each be assessed based on single-body simulations. To generate these single-body simulations, state-of-the-art flowfield and radiation simulations are performed for meteoroid diameters ranging from 0.02 to 100 m, velocities ranging from 12 to 24 km/s, and altitudes ranging from 20 to 50 km. The luminous efficiency values resulting from these simulations are distilled into a correlation and applied to trajectories resulting from the fragment cloud method. This allows the integral luminous efficiency to be computed using the developed luminous efficiency model and defined fragmentation framework. Both the silicon and visible passbands are considered. For the silicon passband, the computed integral luminous efficiency values track closely with the experimentally derived integral luminous efficiency model developed by Brown et al. (2002). This represents the first theoretical derivation of the integral luminous efficiency approach based on fully coupled radiation and ablation simulations with viscous effects, which also captures the impact of individual meteoroids that are combined using the developed fragmentation framework.

The impact of gas phase radiation scattering by dust particle presence in Mars entry scenarios is assessed using a suite of numerical tools. A hypersonic gas and dilute particle multiphase flow is simulated using a mixed continuum model and an efficient size distribution quadrature scheme. Radiative transport is simulated with a hybrid ray-tracing and P-1 spherical harmonics model. The NASA HARA radiation code and a Lorentz-Mie scattering model are used to predict the gas-particle mixture radiative properties. Application of the numerical suite to a representative case based on the Mars 2020 entry shows that, even at conditions in excess of the strongest recorded dust storm, the augmentation in surface radiative heat flux due to scattering alone is lower than 1%, and therefore negligible. Predictions with even higher dust loading conditions confirm that even highly uncertain dust mass profiles are unlikely to be a concern for the scattering augmentation mechanism.

A methodology for creating incident shocks with similarity to the backshell radiative heating environment on planetary probes is presented. Two test series were carried out in the Electric Arc Shock Tube (EAST) at NASA Ames to quantify the backshell environment for planned and executed missions entering the atmospheres of Mars and Titan. The comparison of measured radiance in the shock tube to simulated post shock radiation levels is used to quantify the uncertainty in the model. This model uncertainty may then be related back to the flight condition to assess the error in the flight heating prediction. Tests for Mars entry show the shock tube measurements to be bracketed between two kinetic models by 2–7

The radiative heating environment for the Mars Sample Return Sample Retrieval Lander is analyzed for the 8 km/s entry interface velocity resulting from a potential 2031 launch date. This is notably faster than previous Mars missions like Mars Science Laboratory and Mars 2020, which had entry interface velocities around 6 km/s. The increased speed shifts the dominant radiative mechanisms on the vehicle forebody from CO2 infrared bands to CO fourth positive and CN bands, which are more sensitive to nonequilibrium flowfield and radiation models than the CO2 infrared bands. To address the significant uncertainties in these nonequilibrium models, this work compiles the best available nominal modeling parameters and their corresponding uncertainties. At the peak radiative heating forebody surface location, the upper limit parametric uncertainty is near 100%, while on the afterbody, the upper limit parametric uncertainty is near 50%. The shock-tube informed bias analysis results in values 10% higher than the nominal on the forebody and 24% higher on the afterbody. An approach is suggested for combining the parametric uncertainty and shock-tube informed bias into a radiative heating margin, which may be adjusted to the level of conservatism desired by the project.

The objective of this work was to assess the impact of flowfield–material response coupling on reproducing near-surface temperatures within the Mars 2020 forebody thermal protection system. Both equilibrium and nonequilibrium coupled material response approaches were considered. Turbulent transition estimates were included in the flowfield modeling based on transition times inferred from flight measurements. A coupled equilibrium ablation model was found to overpredict the in-depth temperatures near the surface by over 100 K in the stagnation region and by about 200 K near the leeside shoulder, which was subject to turbulent heating augmentation. For nonequilibrium surface chemistry, two finite rate models were used to model the chemical process on the vehicle surface. The first was a model consisting of N 2 catalysis and CO 2 recombination, and the second was a model consisting of only N 2 and O 2 catalysis. Near the stagnation point, the N 2 and CO 2 model was found to be within about 3% of the peak temperature near the surface; however, overprediction of the in-depth temperatures was observed early in the trajectory, similar to the equilibrium surface chemistry model. The N 2 and O 2 catalysis model was found to significantly underpredict near-surface in-depth temperatures.

The current study investigates how uncoupled and coupled numerical simulations of flow dynamics and material response affect ablation around the shoulder region of an entry capsule heatshield in space missions like the Mars Sample Return (MSR) project. A new computational tool named Ares, developed at NASA Ames Research Center (ARC), is applied to carry out the coupled simulations, and the thermal protection system (TPS) material considered is three-dimensional mid-density carbon phenolic (3MDCP). First, an experimental campaign in an Interactive Heating Facility (IHF) at NASA ARC is used to validate the material model and the solver. Then an Earth-entry flight trajectory is considered to investigate the coupling effects on an MSR-relevant aeroshell for the current work. An axisymmetric domain is used to maintain computational efficiency due to the simple aeroshell geometry and the nature of freestream with zero-degree angle of attack. Thermodynamics inside the solid domain and near the shoulder is compared between coupled and uncoupled simulations at different times.Interestingly, it has been observed that coupled simulations lead to earlier and larger recessions throughout the heat shield surface. In addition, coupled simulations are closer to the experiment and recess the heat shield surface more physically. Overall, this investigation demonstratesAres’s current capability to conduct coupled simulations for an aeroshell used in planetary entry missions.

A direct solution approach for surface erosion in particle-laden hypersonic flows is extended for use in low-cost twoway coupled solutions of dilute gas-particle flows. The trajectory control volume method, which uses a sparse set of probe particles to predict surface erosion distributions on general vehicles, is reformulated for the solution of source terms by mean trajectory subdivision and computing a flux differencing. The approach is verified successfully against a boundary-layer solution and shown to agree well with experimental measurements. A representative Mars entry case, with conditions and geometry based on the ExoMars Schiaparelli capsule, is solved with the approach to study the impact of two-way coupling on surface heating and erosion. Results indicate that, for realistic loading conditions, heating is largely unmodified compared to one-way coupled results at peak heating trajectory conditions, and no measureable difference is observed in the surface erosion rate. At exaggerated loading conditions high enough to observe coupling effects, the worst-case collisional heating can increase heating by up to 60%.

A small population of stem cells in the developing Drosophila central nervous system generates the large number of different cell types that make up the adult brain. To achieve this, these neural stem cells (neuroblasts, NBs) divide asymmetrically to produce non-identical daughter cells. The balance between stem cell self-renewal and neural differentiation is regulated by various cellular machinery, including transcription factors, chromatin remodelers, and RNA-binding proteins. The list of these components remains incomplete, and the mechanisms regulating their function are not fully understood, however. Here, we identify a role for the RNA-binding protein Modulo (Mod; nucleolin in humans) in NB maintenance. We employ transcriptomic analyses to identify RNA targets of Mod and assess changes in global gene expression following its knockdown, results of which suggest a link with notable proneural genes and those essential for neurogenesis. Mod is expressed in larval brains and its loss leads to a significant decrease in the number of central brain NBs. Stem cells that remain lack expression of key NB identity factors and exhibit cell proliferation defects. Mechanistically, our analysis suggests these deficiencies arise at least in part from altered cell cycle progression, with a proportion of NBs arresting prior to mitosis. Overall, our data show that Mod function is essential for neural stem cell maintenance during neurogenesis.

The Mars Sample Return Earth Entry System is the first entry vehicle designed for a planned NASA mission to utilize a woven thermal protection system as well as a 52.5 degree sphere cone forebody geometry. As a result, insufficient aeroheating experimental data exist to compare with computational predictions. In order to obtain a set of validation data for computational models, a wind tunnel test campaign was funded by the Mars Sample Return Earth Entry System project in the NASA Langley Mach 6 air tunnel. The first entry in the test campaign was completed in April of 2023, which was an investigation of turbulent heating augmentation due to woven thermal protection system roughness on the 52.5 degree Earth Entry System vehicle forebody geometry. This test entry produced the first ever experimental aeroheating data on a 52.5 deg sphere-cone geometry as well as one of the first NASA experimental aeroheating data sets on a woven surface roughness pattern. Data obtained from this test campaign are being directly leveraged to support the NASA flight program, as experimental results are being utilized to validate the computational models that characterize the aeroheating environment that the vehicle experiences and predict turbulent surface heating levels and margins across the woven surface. Additionally, this is an extremely important data set for validating computational solutions on roughness-resolved grids.

NASA's Probabilistic Asteroid Impact Risk (PAIR) model assesses the likelihood of potential damage for asteroid impact scenarios. Fast-running models are used to capture the effects of different hazards. This paper looks specifically at local ground damage hazards, including blast overpressure and thermal radiation damage, for large object impact scenarios. A sensitivity study is conducted to determine which parameters, and over what ranges, cause impact risks to become sensitive to thermal damage. Two additional thermal models with different approaches are used for comparison. The study determined the current thermal model is most sensitive to the luminous efficiency parameter that reflects the model's uncertainty in the amount of energy contributing to the thermal radiation damage. This sensitivity was most apparent for the highest severity damage levels. Comparisons of the three models showed that, in addition to sensitivities within the models, the impact risks are also sensitive to the choice of thermal model. The study results were applied to the 2023 Planetary Defense Conference hypothetical asteroid impact scenario (800 m diameter, 10.29 Gt energy), and parameter ranges of interest were determined. At the serious damage level, luminous efficiencies above 0.006 (0.6%) showed a small chance of thermal playing an important role, while luminous efficiencies above 0.0008 (0.08%) led to thermal playing a significant role at the unsurvivable damage severity level. Study results are used to identify key areas where additional model refinement and better knowledge of asteroid properties may be important for improving damage estimates.

A relationship is developed for evaluating the initial meteoroid diameter based on the measured absolute visual magnitude prior to fragmentation. This approach provides an alternative to the luminous efficiency approach for evaluating the size of a meteoroid from a measured lightcurve. The developed relationship, which is valid for asteroidal meteoroids with entry velocities below 30 km/s and initial diameters greater than 10 cm, is written as D=0.0556×10−0.182M60km−0.0562V60km, where D is the initial meteoroid diameter in m, M60km is the absolute visual magnitude measured at an altitude of 60 km, and V60km is the velocity in km/s at 60 km altitude. This relationship is enabled by the insights provided by recent computational fluid dynamics and radiation simulations, which show that for an unfragmented meteoroid, the M60km value is a much stronger function of meteoroid diameter than the meteor ablation rate or meteoroid composition. This relationship is also enabled by the recent increase in the number of meteor events with calibrated lightcurves and recovered meteorites. In addition to providing the meteorite density, which enables a more accurate conversion between meteoroid mass and size, the recovered meteorites enable a diameter based on radionuclide or noble gas analyses. This provides an alternative to the dynamic mass and infrasound-based diameters, which results in three different meteor diameter assessments that are independent of the luminous efficiency. These three approaches are used to develop the present relationship between the meteor diameter and M60km. The altitude of 60 km is chosen for developing this relationship because it is high enough to minimize the potential for fragmentation and low enough for ablation to have reached a steady-state. This altitude is also low enough to avoid significant measurement noise in the lightcurve, which may be present at higher altitudes due to weaker emission and a longer measurement distance.

AbstractDuring embryogenesis, the Drosophila heart forms a lumen, the posterior region of which is increased in diameter and corresponds to the heart proper. To identify the transcriptional control of this morphogenetic process, we analyzed the formation and enlargement of the heart lumen in mutants for the myogenic transcription factor geneMyocyte enhancer factor-2(Mef2). We found thatMef2contributes to both lumen formation and lumen expansion, the latter through a requirement for bothMef2and the cardiogenic genetinman(tin) to activate the collagen geneMultiplexin(Mp). To determine if Tin and MEF2 act directly upon theMpgene, we identified an enhancer whose activity recapitulates the cardiac expression ofMp. This enhancer contains binding sites for both Tin and MEF2 and is activated in tissue culture by MEF2 but not Tin. We did not observe synergistic activation of the enhancer when the factors were in combination, despite documenting a direct physical interaction between Tin and MEF2 in vitro. In vivo, the Tin sites are required for normal enhancer activity, whereas mutation of the MEF2 sites results in expanded expression of an enhancer-lacZreporter, suggesting that transcriptional repression may also contribute to regulation ofMp. Our studies underline how transcription factors must utilize combinatorial interactions to achieve organ-specific and region-specific patterns of gene expression and cell morphogenesis.

The present study demonstrates our in-house material response solver, Icarus's capability to simulate the ablative conditions, including pyrolysis effects due to the interaction between hypersonic boundary layers and the thermal protection system (TPS). A conceptual aeroshell shoulder design, which undergoes mission-relevant flow and material conditions, is selected for the demonstration purpose. LAURA, a structured flow solver, is used to solve flow around the shoulder at several trajectory points of a flight path. The aerothermal dataset obtained from LAURA is used to enforce boundary conditions on the aeroshell wall to simulate ablation processes. The two-layered material system is stacked with HEEET (TPS) and Aluminum (actual material). A set of base parameters, such as the angle of material orientation with respect to the flow direction, convective heat-transfer co-efficient, and aerothermal boundary conditions on the rear end of the HEEET material layer, is selected to conduct a base-case simulation. A small amount of recession was observed, indicating that the design should be fine to go through the selected flow and material conditions. Furthermore, the parameters mentioned above are individually altered and are observed to affect the shoulder design's recession compared to the base case. Verification of our Icarus setup was also carried out using a one-dimensional grid and FIAT, a one-dimensional material-response solver, to build credibility for our results. As the current work is an uncoupled fluid-material-response simulation, a local sharp mesh deformation in the recessed surface near the shoulder corner is observed.

Asymmetric cell division (ACD) allows stem cells to generate differentiating progeny while simultaneously maintaining their own pluripotent state. ACD involves coupling mitotic spindle orientation with cortical polarity cues to direct unequal segregation of cell fate determinants. In Drosophila neural stem cells (neuroblasts; NBs), spindles orient along an apical-basal polarity axis through a conserved complex of Partner of Inscuteable (Pins; human LGN) and Mushroom body defect (Mud; human NuMA). While many details of its function are well known, the molecular mechanics that drive assembly of the cortical Pins/Mud complex remain unclear, particularly with respect to the mutually exclusive Pins complex formed with the apical scaffold protein Inscuteable (Insc). Here we identify Hu li tai shao (Hts; human Adducin) as a direct Mud-binding protein, using an aldolase fold within its head domain (HtsHEAD) to bind a short Mud coiled-coil domain (MudCC) that is adjacent to the Pins-binding domain (MudPBD). Hts is expressed throughout the larval central brain and apically polarizes in mitotic NBs where it is required for Mud-dependent spindle orientation. In vitro analyses reveal that Pins undergoes liquid-liquid phase separation with Mud, but not with Insc, suggesting a potential molecular basis for differential assembly mechanics between these two competing apical protein complexes. Furthermore, we find that Hts binds an intact Pins/Mud complex, reduces the concentration threshold for its phase separation, and alters the liquid-like property of the resulting phase separated droplets. Domain mapping and mutational analyses implicate critical roles for both multivalent interactions (via MudCC oligomerization) and protein disorder (via an intrinsically disordered region in Hts; HtsIDR) in phase separation of the Hts/Mud/Pins complex. Our study identifies a new component of the spindle positioning machinery in NBs and suggests that phase separation of specific protein complexes might regulate ordered assembly within the apical domain to ensure proper signaling output.