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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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NASA NTRS1976

Spacecraft self-contamination due to back-scattering of outgas products

The back-scattering of outgas contamination near an orbiting spacecraft due to intermolecular collisions was analyzed. Analytical tools were developed for making reasonably accurate quantitative estimates of the outgas contamination return flux, given a knowledge of the pertinent spacecraft and orbit conditions. Two basic collision mechanisms were considered: (1) collisions involving only outgas molecules (self-scattering) and (2) collisions between outgas molecules and molecules in the ambient atmosphere (ambient-scattering). For simplicity, the geometry was idealized to a uniformly outgassing sphere and to a disk oriented normal to the freestream. The method of solution involved an integration of an approximation of the Boltzmann kinetic equation known as the BGK (or Krook) model equation. Results were obtained in the form of simple equations relating outgas return flux to spacecraft and orbit parameters. Results were compared with previous analyses based on more simplistic models of the collision processes.

Robertson, S. J.↗
NASA NTRS2011

Combining Satellite and in Situ Data with Models to Support Climate Data Records in Ocean Biology

The satellite ocean color data record spans multiple decades and, like most long-term satellite observations of the Earth, comes from many sensors. Unfortunately, global and regional chlorophyll estimates from the overlapping missions show substantial biases, limiting their use in combination to construct consistent data records. SeaWiFS and MODIS-Aqua differed by 13% globally in overlapping time segments, 2003-2007. For perspective, the maximum change in annual means over the entire Sea WiFS mission era was about 3%, and this included an El NinoLa Nina transition. These discrepancies lead to different estimates of trends depending upon whether one uses SeaWiFS alone for the 1998-2007 (no significant change), or whether MODIS is substituted for the 2003-2007 period (18% decline, P less than 0.05). Understanding the effects of climate change on the global oceans is difficult if different satellite data sets cannot be brought into conformity. The differences arise from two causes: 1) different sensors see chlorophyll differently, and 2) different sensors see different chlorophyll. In the first case, differences in sensor band locations, bandwidths, sensitivity, and time of observation lead to different estimates of chlorophyll even from the same location and day. In the second, differences in orbit and sensitivities to aerosols lead to sampling differences. A new approach to ocean color using in situ data from the public archives forces different satellite data to agree to within interannual variability. The global difference between Sea WiFS and MODIS is 0.6% for 2003-2007 using this approach. It also produces a trend using the combination of SeaWiFS and MODIS that agrees with SeaWiFS alone for 1998-2007. This is a major step to reducing errors produced by the first cause, sensor-related discrepancies. For differences that arise from sampling, data assimilation is applied. The underlying geographically complete fields derived from a free-running model is unaffected by solar zenith angle requirements and obscuration from clouds and aerosols. Combined with in situ dataenhanced satellite data, the model is forced into consistency using data assimilation. This approach eliminates sampling discrepancies from satellites. Combining the reduced differences of satellite data sets using in situ data, and the removal of sampling biases using data assimilation, we generate consistent data records of ocean color. These data records can support investigations of long-term effects of climate change on ocean biology over multiple satellites, and can improve the consistency of future satellite data sets.

Gregg, Watson↗
NASA NTRS2021

Chapter 13: Errors and Uncertainties Associated with Quasi-Global Satellite Precipitation Products

Measuring precipitation on a global scale is only possible from satellite platforms. Satellite precipitation estimates are based on geosynchronous infrared sensors on geostationary satellites, characterized by high sampling frequency, and polar-orbiting microwave sensors on low-Earth-orbiting satellites with less-frequent sampling. Assessing satellite product performance is fundamental to infer the reliability of such estimates and effectively use them in water resources management, extreme event characterization, disease control, or weather forecasting. Nevertheless, errors and uncertainties associated with satellite precipitation products are often masked due to temporal and spatial sampling, as well as bias-corrections against a reference dataset. Moreover, the verification of satellite precipitation products is easier over land areas, where rain gauges and ground radars are available as benchmark, but extremely limited over the oceans. Substantial work still remains to better quantify relative and absolute errors and uncertainties within satellite-based precipitation products over land and oceans.

Viviana Maggioni↗
DOE OSTI2022

Substructure in the stellar halo near the Sun: I. Data-driven clustering in integrals-of-motion space

Context. Merger debris is expected to populate the stellar haloes of galaxies. In the case of the Milky Way, this debris should be apparent as clumps in a space defined by the orbital integrals of motion of the stars. Aims. Our aim is to develop a data-driven and statistics-based method for finding these clumps in integrals-of-motion space for nearby halo stars and to evaluate their significance robustly. Methods. We used data from Gaia EDR3, extended with radial velocities from ground-based spectroscopic surveys, to construct a sample of halo stars within 2.5 kpc from the Sun. We applied a hierarchical clustering method that makes exhaustive use of the single linkage algorithm in three-dimensional space defined by the commonly used integrals of motion energy E, together with two components of the angular momentum, L z and L ⊥ . To evaluate the statistical significance of the clusters, we compared the density within an ellipsoidal region centred on the cluster to that of random sets with similar global dynamical properties. By selecting the signal at the location of their maximum statistical significance in the hierarchical tree, we extracted a set of significant unique clusters. By describing these clusters with ellipsoids, we estimated the proximity of a star to the cluster centre using the Mahalanobis distance. Additionally, we applied the HDBSCAN clustering algorithm in velocity space to each cluster to extract subgroups representing debris with different orbital phases. Results. Our procedure identifies 67 highly significant clusters (> 3σ), containing 12% of the sources in our halo set, and 232 subgroups or individual streams in velocity space. In total, 13.8% of the stars in our data set can be confidently associated with a significant cluster based on their Mahalanobis distance. Inspection of the hierarchical tree describing our data set reveals a complex web of relations between the significant clusters, suggesting that they can be tentatively grouped into at least six main large structures, many of which can be associated with previously identified halo substructures, and a number of independent substructures. This preliminary conclusion is further explored in a companion paper, in which we also characterise the substructures in terms of their stellar populations. Conclusions. Our method allows us to systematically detect kinematic substructures in the Galactic stellar halo with a data-driven and interpretable algorithm. The list of the clusters and the associated star catalogue are provided in two tables available at the CDS.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1976

AE 6: A model environment of trapped electrons for solar maximum

A projected inner zone electron model environment, AE 6, for the epoch 1980 is presented. It is intended to provide estimates of mission fluxes that spacecraft will encounter in the coming solar maximum years. AE 6 is presented by graphs of omnidirectional integral flux as a function of L shell, the ambient magnetic field B, and the energy E. Results of orbital integrations for altitudes from 150 n.m. to 18,000 n.m. are given for circular orbits with four different inclinations, using the AE 6 and the AE 4 solar maximum models for the inner and outer zones, respectively. The derivation of AE 6 is described, and a brief comparison is given of the radial profiles of equatorial fluxes from several related models. A short summary of the associated computer programs is included.

Teague, M. J.↗
NASA NTRS1986

Spacecraft charging in the auroral plasma: Progress toward understanding the physical effects involved

The work is presented in four parts. First, main differences between the plasma environments in geostationary orbit and low polar orbit with regard to high-voltage charging situations are reviewed. Next, results are presented from a calculation of secondary-electron escape currents from negatively-charged spacecraft surfaces having various orientations relative to the local magnetic-field direction. It is shown that for finite ranges of combinations of electric and magnetic field directions, secondary-electron escape is completely suppressed and therefore cannot help to discharge the spacecraft. In such circumstances, secondary electrons may travel distances many times their gyroradii before reimpacting, and this may produce greatly increased secondary-electron surface currents. Thirdly, a simple rough estimate of the required conditions for high-voltage auroral-zone charging is developed. The results suggest that for any given spacecraft, surface potentials are likely to depend more strongly on the ratio of ambient flux of high-energy electrons to that of all ions, than on any other environmental parameter. Finally, preliminary results are presented of numerical simulation work directed toward testing this hypothesis. Numerical instabilities encountered in doing this simulation work probably are closely related to physical sensitivities inherent in the physics of the ion wake behind the spacecraft, and especially to beam-like constituents of the ion population in the wake.

Laframboise, J. G.↗
NASA NTRS1987

Baseline estimation from simultaneous satellite laser tracking

Simultaneous Range Differences (SRDs) to Lageos are obtained by dividing the observing stations into pairs with quasi-simultaneous observations. For each of those pairs the station with the least number of observations is identified, and at its observing epochs interpolated ranges for the alternate station are generated. The SRD observables are obtained by subtracting the actually observed laser range of the station having the least number of observations from the interpolated ranges of the alternate station. On the basis of these observables semidynamic single baseline solutions were performed. The aim of these solutions is to further develop and implement the SRD method in the real data environment, to assess its accuracy, its advantages and disadvantages as related to the range dynamic mode methods, when the baselines are the only parameters of interest. Baselines, using simultaneous laser range observations to Lageos, were also estimated through the purely geometric method. These baselines formed the standards the standards of comparison in the accuracy assessment of the SRD method when compared to that of the range dynamic mode methods. On the basis of this comparison it was concluded that for baselines of regional extent the SRD method is very effective, efficient, and at least as accurate as the range dynamic mode methods, and that on the basis of a simple orbital modeling and a limited orbit adjustment. The SRD method is insensitive to the inconsistencies affecting the terrestrial reference frame and simultaneous adjustment of the Earth Rotation Parameters (ERPs) is not necessary.

Dedes, George C.↗
NASA NTRS1991

Worldwide photometry of the January 1989 Tau Persei eclipse

New UBV photoelectric photometry of Tau Persei obtained at 19 different observatories during its recent January 1989 eclipse is presented. Mideclipse occurred at JD 2 447 542.31 + or - 0.01. The resulting light curve, though not complete at all phases, is solved for the elements with the help of two quantities derived from spectroscopy: the eclipse is 84 percent total at mideclipse, and the ratio of the radii is 0.135 + or - 0.01. Radii relative to the semimajor axis are 0.0236 for the G5 giant and 0.0032 for the A2 star. With a reasonable total mass assumed, the absolute radii say the A2 star could be luminosity class V or somewhat evolved and the G5 star is between III and II but could be closer to II. The G5 giant is brighter than the A2 star by 1.72 mag in V and the color excess in B - V is 0.06 mag, both quantities consistent (within uncertainties) with earlier estimates of Ake (1986). The eclipse duration, from first to fourth contact, is 2.09 day. The orbital inclination is 88.74 deg, consistent with what McAlister derived from speckle interferometry. Because of the large (e = 0.73) eccentricity, there is no secondary eclipse at all.

Hall, Douglas S.↗
NASA NTRS1992

Concerted hydrogen atom exchange between three HF molecules

We have investigated the termolecular reaction involving concerted hydrogen exchange between three HF molecules, with particular emphasis on the effects of correlation at the various stationary points along the reaction. Using an extended basis, we have located the geometries of the stable hydrogen-bonded trimer, which is of C(sub 3h) symmetry, and the transition state for hydrogen exchange, which is of D(sub 3h) symmetry. The energies of the exchange reation were then evaluated at the correlated level, using a large atomic natural orbital basis and correlating all valence electrons. Several correlation treatments were used, namely, configration interaction with single and double excitations, coupled-pair functional, and coupled-cluster methods. We are thus able to measure the effect of accounting for size-extensivity. Zero-point corrections to the correlated level energetics were determined using analytic second derivative techniques at the SCF level. Our best calculations, which include the effects of connected triple excitations in the coupled-cluster procedure, indicate that the trimer is bound by 9 +/- 1 kcal/mol relative to three separate monomers, in excellent agreement with previous estimates. The barrier to concerted hydrogen exchange is 15 kcal/mol above the trimer, or only 4.7 kcal/mol above three separated monomers. Thus the barrier to hydrogen exchange between HF molecules via this termolecular process is very low.

Komornicki, Andrew↗
NASA NTRS2016

C/NOFS Remote Sensing of Ionospheric Reflectance

Alfvn waves play critical roles in the electrodynamic coupling of plasmas at magnetically conjugate regions in near-Earth space. Associated electric (E*) and magnetic (dec B*) field perturbations sampled by sensors on satellites in low-Earth orbits are generally super positions of incident and reflected waves. However, lack of knowledge about ionospheric reflection coefficients (alpha) hinders understanding of generator outputs and load absorption of Alfvn wave energies. Here we demonstrate a new method for estimating using satellite measurements of ambient E* and dec B* then apply it to a case in which the Communication Navigation Outage Forecasting System (CNOFS) satellite flew conjugate to the field of view of a 630.0 nm all-sky imager at El Leoncito, Argentina, while medium-scale traveling ionosphere disturbances were detected in its field of view. In regions of relatively large amplitudes of E* and B*,calculated values ranged between 0.67 and 0.88. This implies that due to impedance mismatches, the generator ionosphere puts out significantly more electromagnetic energy than the load can absorb. Our analysis also uncovered caveats concerning the methods range of applicability in regions of low E* and B*. The method can be validated in future satellite-based auroral studies where energetic particle precipitation fluxes can be used to make independent estimates of alpha.

Burke, W. J.↗
NASA NTRS2018

Journey 'Round the Sun: STEREO Science and Spacecraft Performance Results

The Solar TErrestrial RElations Observatory (STEREO) was originally designed as a two to five year heliocentric orbit mission to study coronal mass ejections (CMEs), solar energetic particles (SEPs), and the solar wind. After over ten years of continuous science data collection, the twin NASA STEREO observatories have significantly advanced the understanding of Heliophysics. This mission was the first to image CMEs all the way from the Sun to Earth and to observe the entire sphere of the Sun at one time. STEREO has demonstrated the importance of a point of view beyond the Sun-Earth line to significantly improve CME arrival time estimates and in understanding CME structure and trajectories and the longitudinal distribution of SEPs. STEREO was also the first to use one launch vehicle to insert two spacecraft into opposing heliocentric orbits, undergo a 3.5 month long superior solar conjunction, implement unattended daily science operations on two deep space observatories, maintain 7 arcsec continuous pointing without gyros, and detect and attempt to recover a spacecraft after a 22-month long communications anomaly at a range of 2 AU. This paper discusses the significant performance results after the first ten years of operations of the STEREO mission from its journey around the Sun.

Ossing, Daniel A.↗
NASA NTRSDate not supplied

Implementation of Machine Learning Methods for Crater-Based Navigation

Terrain Relative Navigation methods require surface feature detectors to gain information from images used to improve on-board state estimates. This paper presents the development of a crater detection method based on Machine Learning that can extract data from optical images with different crater shapes and sizes, under varying lighting conditions. This work includes an automated capability for generating labeled training data and iterative testing of the neural network-based crater detector. Preliminary results are included to quantify the detector’s accuracy compared to a known crater catalog, given a set of real lunar images from the Lunar Reconnaissance Orbiter.

Sofia G Catalan↗
NASA NTRS1990

Initial estimate of NOAA-9 SBUV/2 total ozone drift: Based on comparison with re-calibrated TOMS measurements and pair justification of SBUV/2

Newly recalibrated version 6 Total Ozone Mapping Spectrometer (TOMS) data are used as a reference measurement in a comparison of monthly means of total ozone in 10 degree latitude zones from SBUV/2 and the nadir measurements from TOMS. These comparisons indicate a roughly linear long-term drift in SBUV/2 total ozone relative to TOMS of about 2.5 Dobson units per year at the equator over the first three years of SBUV/2. The pari justification technique is also applied to the SBUV/2 measurements in a manner similar to that used for SBUV and TOMS. The higher solar zenith angles associated with the afternoon orbit of NOAA-9 and the large changes in solar zenith angle associated with its changing equator crossing time degrade the accuracy of the pair justification method relative to its application to SBUV and TOMS, but the results are consistent with the SBUV/2-TOMS comparisons, and show a roughly linear drift in SBUV/2 of 2.5 to 4.5 Dobson units per year in equatorial ozone.

Wellemeyer, C. G.↗
NASA NTRS1996

Numerical simulation of iodine speciation in relation to water disinfection aboard manned spacecraft I. Equilibria

Elemental iodine (I2) is currently used as the drinking water disinfectant aboard the Shuttle Orbiter and will also be incorporated into the water recovery and distribution system for the International Space Station Alpha. Controlled release of I2 is achieved using the Microbial Check Valve (MCV), a flow-through device containing an iodinated polymer which imparts a bacteriostatic residual concentration of approximately 2mg/L to the aqueous stream. During regeneration of MCV canisters, I2 concentrations of approximately 300 mg/L are used. Dissolved iodine undergoes a series of hydrolytic disproportionation and related reactions which result in the formation of an array of inorganic species including: I-, I3-, HOI, OI-, IO3-, HIO3, I2OH-, I2O(-2), and H2OI+. Numerical estimation of the steady-state distribution of inorganic iodine containing species in pure water at 25 degrees C has been achieved by simultaneous solution of the multiple equilibrium expressions as a function of pH. The results are reported herein.

NASA Discipline Environmental Health↗
NASA NTRS2018

Journey 'Round the Sun: STEREO Science and Spacecraft Performance Results

The Solar TErrestrial RElations Observatory (STEREO) was originally designed as a two- to five-year heliocentric orbit mission to study coronal mass ejections (CMEs), solar energetic particles (SEPs), and the solar wind. After over ten years of continuous science data collection, the twin NASA STEREO observatories have significantly advanced the understanding of Heliophysics. This mission was the first to image CMEs all the way from the Sun to Earth and to observe the entire sphere of the Sun at one time. STEREO has demonstrated the importance of a point of view beyond the Sun-Earth line to significantly improve CME arrival time estimates and in understanding CME structure and trajectories and the longitudinal distribution of SEPs. STEREO was also the first to use one launch vehicle to insert two spacecraft into opposing heliocentric orbits, undergo a 3.5-month-long superior solar conjunction, implement unattended daily science operations on two deep space observatories, maintain 7 arcsec continuous pointing without gyros, and detect and attempt to recover a spacecraft after a 22-month long communications anomaly at a range of 2 AU (Astronomical Units). This paper discusses the significant performance results after the first ten years of operations of the STEREO mission from its journey around the Sun.

Ossing, Daniel A.↗
DOE OSTI2024

Estimating Carbon Dioxide Emissions in Two California Cities Using Bayesian Inversion and Satellite Measurements

NASA's Orbiting Carbon Observatories (OCO-2 and OCO-3) provide measurements of column-averaged carbon dioxide concentrations (XCO 2 ) with sufficient spatial resolution and precision to constrain bottom-up estimates of CO 2 fluxes at regional scales. We use Bayesian inversion methods assimilating satellite retrievals to improve estimates of CO 2 fluxes in the South Coast Air Basin (SoCAB) which surrounds Los Angeles, and in the San Francisco Bay Area Air Basin (SFBA). We study 2020 to understand the impact of the COVID-19 lockdowns and an active wildfire season. Our results indicated that a 50% (30%) reduction in CO 2 emissions relative to 2015 during the COVID-19 lockdown period was consistent with OCO measurements for SFBA (SoCAB). We find that posterior wildfire emissions differed significantly from the prior at the scale of individual wildfires, though with large uncertainties, and that wildfire emissions in SFBA are significant, attributing 72% of the region's CO 2 emissions during August 2020 to wildfires.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Prospects for gravitational wave and ultra-light dark matter detection with binary resonances beyond the secular approximation

Precision observations of orbital systems have recently emerged as a promising new means of detecting gravitational waves and ultra-light dark matter, offering sensitivity in new regimes with significant discovery potential. These searches rely critically on precise modeling of the dynamical effects of these signals on the observed system; however, previous analyses have mainly only relied on the secularly-averaged part of the response. We introduce here a fundamentally different approach that allows for a fully time-resolved description of the effects of oscillatory metric perturbations on orbital dynamics. We find that gravitational waves and ultra-light dark matter can induce large oscillations in the orbital parameters of realistic binaries, enhancing the sensitivity to such signals by orders of magnitude compared to previous estimates.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Hydrogen Atom Abstraction from an Os II (NH 3 ) 2 Complex Generates an Os IV (NH 2 ) 2 Complex: Experimental and Computational Analysis of the N–H Bond Dissociation Free Energies and Reactivity

We report double hydrogen atom abstraction from (TMP)Os II (NH 3 ) 2 (TMP = tetramesitylporphyrin) with phenoxyl or nitroxyl radicals leads to (TMP)Os IV (NH 2 ) 2 . This unusual bis(amide) complex is diamagnetic and displays an N-H resonance at 12.0 ppm in its 1 H NMR spectrum. 1 H- 15 N correlation experiments identified a 15 N NMR spectroscopic resonance at –267 ppm. Experimental reactivity studies and density functional theory calculations support relatively weak N-H bonds of 73.3 kcal/mol for (TMP)Os II (NH 3 ) 2 and 74.2 kcal/mol for (TMP)Os III (NH 3 )(NH 2 ). Cyclic voltammetry experiments provide an estimate of the pK a of [(TMP)Os III (NH 3 ) 2 ] + . In the presence of Barton’s base, a current enhancement is observed at the Os(III/II) couple, consistent with an ECE event. Spectroscopic experiments confirmed (TMP)Os IV (NH 2 ) 2 as the product of bulk electrolysis. Double hydrogen atom abstraction is influenced by π donation from the amides of (TMP)Os IV (NH 2 ) 2 into the d orbitals of the Os center, favoring the formation of (TMP)Os IV (NH 2 ) 2 over N-N coupling. This π donation leads to a Jahn-Teller distortion that splits the energy levels of the d xz and d yz orbitals of Os, results in a low spin electron configuration, and leads to minimal aminyl character on the N atoms, rendering (TMP)Os IV (NH 2 ) 2 unreactive towards amide-amide coupling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗