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

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Mapping the gas density with the kinematic Sunyaev-Zel’dovich and patchy screening effects: A self-consistent comparison

The secondary anisotropies of the cosmic microwave background (CMB) provide a wealth of astrophysical and cosmological information. Pairing measurements of the CMB temperature map obtained by DR5 of the Atacama Cosmology Telescope (ACT) with the imaging survey conducted by the Dark Energy Spectroscopic Instrument for the purposes of target selection, DECaLS DR9, we investigate two effects that are sensitive to the gas density 𝜏: kinematic Sunyaev-Zel’dovich (kSZ) and patchy screening or anisotropic screening (resulting from the Thomson scattering of CMB photons away from the line-of-sight by free electrons). In particular, we measure the stacked profiles of the gas density around luminous red galaxies (LRGs) at a mean redshift of 𝑧 ≈ 0.7. We detect the kSZ signal at 7.2⁢𝜎, and we find a signal at ∼ 4.1⁢𝜎 for the patchy screening estimator, which is in excess relative to the kSZ signal. We attribute this excess to contamination from CMB lensing. Here, we demonstrate the effect of lensing using 𝑁-body simulations, and we show that the screening signal is dominated by it. Accounting for lensing, our measurement places a 95% upper bound on the optical depth of the Extended DESI LRG sample of 𝜏 < 2.5 10 −4 for a mean value of the sample of 𝜏 ≈ 1.6 10 −4 . Furthermore, via hydro simulations, we show that the underlying optical depth signal measured by both effects (after removing the CMB lensing contribution) is in perfect agreement when adopting either a compensated aperture photometry (CAP) filter or a high-pass filter. Consistent with previous measurements, we see evidence for excess baryonic feedback around DESI LRGs in the patchy screening measurement. In the future, when both effects can be measured with high signal-to-noise, one can measure the amplitude ratio between them, which is proportional to the root-mean-square velocity of the host halo sample, and even place constraints on velocity-sensitive models such as modified gravity and phantom dark energy.

Astrophysical & cosmological simulations↗
DOE OSTI2025

Toward Higher-order Accuracy in Self-gravitating Hydrodynamics

High-order algorithms have emerged in numerical astrophysics as a promising avenue to reduce truncation error (proportional to a power of the linear resolution Δ x ) with only a moderate increase to computational expense. Significant effort has been placed in the development of finite-volume algorithms for (magneto)hydrodynamics; however, state-of-the-art astrophysical simulations tightly couple a plenitude of physics, additionally including gravity, photon transport, cosmic-ray transport, chemistry, and/or diffusion, to name a few. Algorithms frequently operator-split this additional physics (often a first-order error in time) and/or adopt a model wherein their evaluation is limited to second-order accuracy in space. In this work, we present a fourth-order-accurate finite-volume scheme for self-gravitating hydrodynamics on a uniform Cartesian grid. The method supplies source terms for the gravitational acceleration ( ρ g ) and gravitational energy release ( ρ v · g ) associated with fourth-order-accurate solutions to the Poisson equation. Our scheme (1) guarantees the conservation of total linear momentum while (2) decreasing (in proportion to Δ x 4 ) the effects of spurious heating and/or cooling associated with truncation error in the gravity. We demonstrate expected convergence rates for the algorithm by measuring errors in test problems evolving self-gravity modified linear waves and 3D polytropic equilibria. We test robustness of the algorithm by integrating an induced “inside-out” adiabatic collapse. We also discuss a method to smoothly downgrade the solution to second-order spatial accuracy to avoid spurious overshoots near steep density and/or pressure gradients.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1999

Modulation of Radiogenic Damage by Microgravity: Results From STS-76

The STS-76 (Shuttle-Mir 3) spaceflight provided an opportunity to test two questions about radiation responses in C. elegans. First, does the absence of gravity modify the dose-response relation for mutation and chromosome aberration and second, what are the features of the mutation spectrum resulting from exposure to cosmic rays? These questions were put to the test in space using the ESA "Biorack" facility which was housed in the Spacehab module aboard shuttle Atlantis. The mission flew in March, 1996 and was a shuttle rendezvous with the Russian space station Mir.

Nelson, Gregory↗
NASA NTRS2021

Gravitational analog of the canonical acoustic black hole in Einstein-scalar-Gauss-Bonnet theory

In this work, in the context of modified gravity, a curved spacetime analogous to the 'canonical acoustic black hole (CABH)' is constructed. The source is a self-interacting scalar field which is non-minimally coupled to gravity through the Gauss–Bonnet invariant. The scalar-Gauss–Bonnet coupling function is characterized by three positive parameters: σ with units of (length), μ with units of (length)4, and a dimensionless parameter s, thus defining a three-parameter model for which the line element of CABH is a solution. The spacetime is equipped with spherical and static symmetry and has a single horizon determined in Schwarzschild coordinates by the region r = μ^(1/4). The solution admits a photon sphere at r = (3μ)^(1/4), and it is shown that in the region (3μ)^(1/4) ⩽ r < ∞ the scalar field satisfies the null, weak, and strong energy conditions. Nonetheless, the model with s = 1 has major physical relevance since for this case the scalar field is well defined in the entire region r ⩾ μ^(1/4), while for s ≠ 1 the scalar field blows up on the horizon.

Pedro Cañate↗
NASA NTRS2021

Cosmology with the Roman Space Telescope - Multiprobe Strategies

We simulate the scientific performance of the Nancy Grace Roman Space Telescope High Latitude Survey (HLS) on dark energy and modified gravity. The 1.6-yr HLS Reference survey is currently envisioned to image 2000 deg2 in multiple bands to a depthof∼26.5 in Y, J, H and to cover the same area with slit-less spectroscopy beyond z=3. The combination of deep, multiband photometry and deep spectroscopy will allow scientists to measure the growth and geometry of the Universe through a variety of cosmological probes (e.g. weak lensing, galaxy clusters, galaxy clustering, BAO, Type Ia supernova) and, equally, it will allow an exquisite control of observational and astrophysical systematic effects. In this paper, we explore multiprobe strategies that can be implemented, given the telescope’s instrument capabilities. We model cosmological probes individually and jointly and account for correlated systematics and statistical uncertainties due to the higher order moments of the density field. We explore different levels of observational systematics for the HLS survey (photo-z and shear calibration) and ultimately run a joint likelihood analysis in N-dim parameter space. We find that the HLS reference survey alone can achieve a standard dark energy FoM of>300 when including all probes. This assumes no information from external data sets, we assume a flat universe however, and includes realistic assumptions for systematics. Our study of the HLS reference survey should be seen as part of a future community-driven effort to simulate and optimize the science return of the Roman Space Telescope.

Cosmological parameters↗
NASA NTRS2012

Modified Process Reduces Porosity when Soldering in Reduced Gravity Environments

A modified process yields lower levels of internal porosity for solder joints produced in reduced-gravity environments. The process incorporates both alternative materials and a modified procedure. The process provides the necessary cleaning action to enable effective bonding of the applied solder alloy with the materials to be joined. The modified process incorporates a commercially available liquid flux that is applied to the solder joint before heating with the soldering iron. It is subsequently heated with the soldering iron to activate the cleaning action of the flux and to evaporate most of the flux, followed by application of solder alloy in the form of commercially available solid solder wire (containing no flux). Continued heating ensures adequate flow of the solder alloy around and onto the materials to be joined. The final step is withdrawal of the soldering iron to allow alloy solidification and cooling of the solder joint.

Watson, Kevin↗
NASA NTRSDate not supplied

Demonstration of Fluid Dynamics for Plant Growing Systems in Varied Gravity Environments Through Scaled Capillary Models

The development of reliable and bioregenerative crop growth production systems is vital for human exploration into deep space. As humans prepare for space travel beyond LEO, scientists need to find a way to provide reliable and adequate water delivery for all stages of the plant's life cycle. Past production systems struggled with this and often led to overwatering in the system. To better understand this issue, NASA's Plant Water Management (PWM) experiments were able to model fluid flow through granular substrates, specifically a clay-based material arcilite, in 0-G. The PWM study can help researchers to predict fluid flow through the systems, however their model only works for an arcilite based system and was unable to account for different stages of plant growth. For future missions, payload requirements to support crop production system will need to be limited, leading to the use of in situ resources. This project aims to validate the PWM experiments as well as incorporate various materials into the design for growth systems. To meet these objectives, a series of terrestrial experiments will be deployed to mimic all gravities. By modifying the material, fluid, and size of the test subjects, the effect of Earth's gravity can be minimized. This project will aid researchers in the design of future crop production systems for surface missions by creating a refined model that can be used at all stages of plant growth and utilize in situ resources.

Plant Biology↗
NASA NTRS1980

The effect of reduced gravity on solidification microstructures of NH4Cl-H2O alloys

The effect of gravity on the columnar-to-equiaxed microstructural transition was studied in small samples of NH4Cl-H2O. The behavior of the samples during laboratory (one gravity) experiments was contrasted with their behavior during a (low gravity) sounding rocket flight. In one gravity, the columnar zone accounted for 25 to 100 pct of the structure, depending on the superheat and orientation of the chill. Grain multiplication occurred by showering and by convection induced dendrite arm remelting. Convection was caused by both thermal gradients and solutal gradients. In low gravity, however, completely columnar structures were obtained; all grain multiplication mechanisms were entirely suppressed. Reduced gravity also modified the thermal conditions and caused the liquid to cool more slowly. This resulted in a steeper temperature gradient in the liquid ahead of the solidification interface. 'Big bang' type nucleation occurred in two of the samples, distributing nuclei throughout the liquid. Despite this, an equiaxed zone did not form, indicating that the most significant effect of low gravity on this experiment was modification of the thermal conditions.

Papazian, J. M.↗
NASA NTRS1982

VHF power scattered from the mesosphere at mid-latitudes

Scattered power profiles from the Urbana VHF radar have been analyzed. Coherent power returns from the mesosphere (60-90 km) show that a large portion of these returns occur in well-defined stable layers lasting for more than 6 hours in some cases. It is concluded that some of these layers may be caused by standing diurnal tides. Short time variation in scattered power is attributed to internal gravity waves modifying the amplitude and altitude of maximum vertical shear in the horizontal wind. Correlation time of the scattered signal varies with altitude as well as with scattered power. Seasonal averages of the scattered power show a broad peak around 76 km. The decrease in scattered power below 76 km appears because of a decrease in the electron density gradient, while the decrease above 76 km is due to a decrease in the intensity of turbulence. The amplitude of short-period gravity waves shows a decrease with altitude below 66 km, attributed to the Brunt-Vaisala barrier, and a slight increase with altitude above 70 km. The dominant period of the vertical oscillations shows an increase above 63 km, giving further evidence that the high-frequency oscillations present below 63 km cannot propagate to higher altitudes.

Royrvik, O.↗
NASA NTRS1964

Problems of Fire Prevention and Extinguishment in Space Cabins

The problems of prevention and extinguishment of fires in space cabins are, except for a few specific situations, not much different from those at sea level or in aircraft conditions. The unusual atmospheric environment and limitations of space and firefighting equipment compound the general problem. The zero-gravity environment modifies firefighting procedures in a rather profound way and will be given detailed treatment in this report.

CHEMICAL EXTINGUISHER↗
NASA NTRS2022

Extension and Validation of the Pendulum Model for Longitudinal Solar Prominence Oscillations

Context. Longitudinal oscillations in prominences are common phenomena on the Sun. These oscillations can be used to infer the geometry and intensity of the filament magnetic field. Previous theoretical studies of longitudinal oscillations made two simplifying assumptions: uniform gravity and semicircular dips on the supporting flux tubes. However, the gravity is not uniform and realistic dips are not semicircular. Aims. Our aim is to understand the effects of including the nonuniform solar gravity on longitudinal oscillations and explore the validity of the pendulum model with different flux-tube geometries. Methods. We first derived the equation describing the motion of the plasma along the flux tube including the effects of nonuniform gravity, yielding corrections to the original pendulum model. We also computed the full numerical solutions for the normal modes and compared them with the new pendulum approximation. Results. We find that the nonuniform gravity introduces a significant modification in the pendulum model. We also found a cut-off period; i.e., the longitudinal oscillations cannot have a period longer than 167 min. In addition, considering different tube geometries, the period depends almost exclusively on the radius of curvature at the bottom of the dip. Conclusions. We conclude that nonuniform gravity significantly modifies the pendulum model. These corrections are important for prominence seismology, because the inferred values of the radius of curvature and minimum magnetic-field strength differ substantially from those of the old model. However, we find that the corrected pendulum model is quite robust and is still valid for noncircular dips.

Sun: corona↗
NASA NTRS2009

Effect of Changing the Center of Gravity on Human Performance in Simulated Lunar Gravity

Subjective measures of physical exertion, compensation, and controllability while performing tasks in simulated reduced gravity can be affected by changing the center of gravity (CG) of the overall system. The CG of the overall system is defined as the combined CG of the subject, the spacesuit, and the equipment required to change the CG. PURPOSE: To determine if changing the CG affects subjective ratings of suited human performance in simulated lunar gravity. METHODS: A custom weight support structure interfaced with the lunar prototype spacesuit, allowing manipulation of the CG. Weight locations to alter CG were based on a reference subject (81.6 kg, 182.9 cm). Six subjects (80.0 +/- 10.6 kg, 182.3 +/- 6.2 cm) completed 4 tasks (walking, kneel/stand, rock pickup, and shoveling) with system CG at 3 different locations (B=4.8/1.0, C=7.6/14.4, and P=11.2/20.1 cm aft/above the standard subject?s CG). Lunar gravity (0.17-g) was simulated by parabolic flight. Suited testing was performed at 29.6 kPa with a combined suit and structure mass of 181 kg. In all conditions, subjects provided ratings of perceived exertion (RPE) and the gravity compensation and performance scale (GCPS) upon completion of each task. RESULTS: Mean RPE and GCPS were highest at P for all tasks. Variability was greatest at B and lowest at C, and large variations between subjects at the same CG existed for both RPE and GCPS. These trends were not consistent with results from unsuited CG studies performed in other underwater and overhead suspension lunar gravity simulations. CONCLUSION: Modifying CG during suited testing at lunar gravity seems to affect subjective human performance. However, variation in subjective ratings at a given CG location indicates that further study is needed to determine the interactions among lunar gravity simulation, system CG, system mass, and subject characteristics such as anthropometry, strength, and fitness.

Chappell, Steven P.↗
NASA NTRS1976

Can Malin's gravitational-field equations be modified to obtain a viable theory of gravity

Malin's (1975) gravitational theory, which was recently shown by Lindblom and Nester (1975) to be incorrect, is modified by means of a recently proposed method for obtaining viable gravitational theories. The resulting self-consistent theory, which is in effect a Rastall-type modification of the Einstein theory, exhibits nonconservation of momentum, yet agrees with all experimental limits known to date within the post-Newtonian approximation framework.

Smalley, L. L.↗
NASA NTRS1999

Experimental and Analytical Study of Two-Phase Flow in Microgravity

A two-phase test loop has been designed and constructed to generate the necessary data for two-phase pressure drop and Critical Heat Flux (CHF) under reduced gravity conditions. A series of airplane trajectory tests aboard NASA KC-135 were performed and the data was used to evaluate the applicability of the earth gravity models for prediction of the reduced gravity data. Several commonly used correlations for the two-phase friction multiplier and critical heat flux were used to predict the data. It was generally concluded that the two-phase pressure drop can be predicted by the earth gravity correlations. The critical heat flux under reduced gravity conditions did not show a strong dependence on mass flow rate and the measured CHF were generally lower than the equivalent 1g conditions. The earth gravity models need to be modified for application to reduced gravities.

Abdollahian, D.↗
NASA NTRS1988

Gravity waves in the upper atmosphere of Venus

The transfer function model of Mayr et al. (1984, 1987) for a dissipative multiconstituent atmosphere on earth was modified to describe gravity waves in the thermosphere of Venus in terms of spherical and Fourier harmonics. This model is used to interpret density perturbations in CO2, O, and He which were observed with the orbital neutral mass spectrometer on Pioneer Venus. Results indicate that, in agreement with observations, for localized sources in the lower atmosphere and thermosphere of the same magnitude day and night, the computed wave amplitudes at satellite altitudes are about a factor of 3 to 5 larger during the night than during the day (due to the large night to day increase in the thermospheric temperature); waves excited in the lower atmosphere propagate more obliquely, and geometric attenuation and dissipation are less important than for the thermosphere. Due to wind-induced diffusion, the computed wave amplitudes for CO2, O, and He are of comparable magnitude (with the magnitude of CO2 being the largest).

Mayr, H. G.↗
NASA NTRS2020

Massive Galaxies Impede Massive Outflows

A set of 66 3D hydrodynamical simulations explores how galactic stellar mass affects three-phase, starburst-driven outflows. Simulated velocities are compared to two basic analytic models: with and without a gravitational potential. For stellar mass <1010 M ⊙, simulated velocities match those of both analytical models and are unaffected by the potential; above they reduce significantly as expected from the analytic model with gravity. Gravity also affects total outflow mass and each of the three phases differently. Outflow masses in the hot, warm, and cold phases each scale with stellar mass as $\mathrm{log}{M}_{* }\,=$ −0.25, −0.97, and −1.70, respectively. Thus, the commonly used Chevalier & Clegg analytic model should be modified to include gravity when applied to higher-mass galaxies. In particular, using M82 as the canonical galaxy to interpret hydrodynamical simulations of starburst-driven outflows from higher-mass galaxies will underestimate the retarding effect of gravity. Using the analytic model of Johnson & Axford with realistic thermalization efficiency and mass loading, I find that only galaxy masses lesssim10(exp 11.5) M(⊙) can outflow.

Ryan Tanner↗