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All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Examining Periodic Solar-Wind Density Structures Observed in the SECCHI Heliospheric Imagers

We present an analysis of small-scale, periodic, solar-wind density enhancements (length scales as small as approximately equals 1000 Mm) observed in images from the Heliospheric Imager (HI) aboard STEREO-A. We discuss their possible relationship to periodic fluctuations of the proton density that have been identified at 1 AU using in-situ plasma measurements. Specifically, Viall, Kepko, and Spence examined 11 years of in-situ solar-wind density measurements at 1 AU and demonstrated that not only turbulent structures, but also nonturbulent, periodic density structures exist in the solar wind with scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall, Spence, and Kasper analyzed the alpha-to-proton solar-wind abundance ratio measured during one such event of periodic density structures, demonstrating that the plasma behavior was highly suggestive that either temporally or spatially varying coronal source plasma created those density structures. Large periodic density structures observed at 1 AU, which were generated in the corona, can be observable in coronal and heliospheric white-light images if they possess sufficiently high density contrast. Indeed, we identify such periodic density structures as they enter the HI field of view and follow them as they advect with the solar wind through the images. The smaller, periodic density structures that we identify in the images are comparable in size to the larger structures analyzed in-situ at 1 AU, yielding further evidence that periodic density enhancements are a consequence of coronal activity as the solar wind is formed.

Viall, Nicholeen M.↗
NASA NTRS1985

Lyman alpha coronagraph research sounding rocket program

The ultraviolet light coronagraph was developed and successfully flown on three rocket flights on 13 April 1979, 16 February 1980 and 20 July 1982. During each of these flights, the Ultraviolet Light Coronagraph was flown jointly with the White Light Coronagraph provided by the High Altitude Observatory. Ultraviolet diagnostic techniques and instrumentation for determining the basic plasma parameters of solar wind acceleration regions in the extended corona were developed and verified and the understanding of the physics of the corona through the performance, analysis and interpretation of solar observations advanced. Valuable UV diagnostics can be performed in the absence of a natural solar eclipse.

Parkinson, W. H.↗
NASA NTRS1990

Brown dwarfs as close companions to white dwarfs

The influence of the radiation flux emitted by a white dwarf primary on the evolution of a closely orbiting brown dwarf (BD) companion is investigated. Full stellar evolutionary calculations are presented for both isolated and thermal bath cases, including effects of large variations in the atmospheric grain opacities. High grain opacities significantly increase the radii of the BDs, but the thermal bath does not. The major influence of the thermal bath is to increase substantially the surface temperature and luminosity of the BD at a given age. These results are compared with the observational properties of the possible BD companion of the white dwarf G29-38. Inclusion of both physical effects, high grain opacities and thermal bath, increases the mass range (0.034-0.063 solar masses) of viable models significantly, yet the final determination of whether the object is indeed a BD requires improvements in the observations of the system's properties.

Stringfellow, Guy S.↗
NASA NTRS1991

High-luminosity single carbon stars in stellar and galactic evolution

In the solar neighborhood, approximately half of all intermediate mass main sequence stars with initially between 1 solar mass and about 5 solar masses become carbon stars with luminosities near 10,000 lunar luminosities for typically less than 1 million years. These high luminosity carbon stars lose mass at rates nearly always in excess of 10 to the -7th solar mass/yr and sometimes in excess of 0.00001 solar mass/yr. Locally, close to half of the mass returned into the interstellar medium by intermediate mass stars before they become white dwarfs is during the carbon star phase. A much greater fraction of lower metallicity stars become carbon-rich before they evolve into planetary nebulae, than do higher-metallicity stars; therefore, carbon stars are much more important in the outer than in the inner Galaxy.

Jura, M.↗
NASA NTRS2001

Effects of Contamination, UV Radiation, and Atomic Oxygen on ISS Thermal Control Materials

Thermal control surfaces on the International Space Station (ISS) have been tailored for optimum optical properties. The space environment, particularly contamination, ultraviolet (UV) radiation, and atomic oxygen (AO) may have a detrimental effect on these optical properties. These effects must be quantified for modeling and planning. Also of interest was the effect of porosity on the reaction to simulated space environment. Five materials were chosen for this study based on their use on ISS. The thermal control materials were Z-93 white coating, silverized Teflon, chromic acid anodized aluminum, sulfuric acid anodized aluminum, and 7075-T6 aluminum. Some of the samples were exposed to RTV 560 silicone; others were exposed to Tefzel offgassing products. Two samples of Z-93 were not exposed to contamination as clean "controls". VUV radiation was used to photo-fix the contaminant to the material surface, then the samples were exposed to AO. All samples were exposed to 1000 equivalent sun-hours (ESH) of vacuum ultraviolet radiation (VUV) at the AZ Technology facility and a minimum of 1.5 x 10(exp 20) atoms/sq cm of AO at Marshall Space Flight Center. Half of the samples were exposed to an additional 2000 ESH of VUV at Huntington Beach prior to sent to AZ Technology. Darkening of the Z-93 white coating was noted after VUV exposure. AO exposure did bleach the Z-93 but not back to its original brightness. Solar absorptance curves show the degradation due to contamination and VUV and the recovery with AO exposure. More bleaching was noted on the Tefzel-contaminated samples than with the RTV-contaminated samples.

Visentine, Jim↗
NASA NTRS1991

Implanted 3He, 4He, and Xe in further studies of diamonds from Western Australia

In measurements of the noble gases in additional samples of diamonds from the Argyle and Ellendale lamproites in Western Australia we have failed to encounter any neon-rich stones such as showed solar-like isotopic compositions in earlier work. No neon was detected above the relatively high blank levels in our glass apparatus. White and brown diamonds showed no differences in noble gas content, nor did samples segregated by the color of long-wave UF fluorescence. The rare gas patterns in the 1.2 Ga Argyle pipe are largely consistent with implanted 3He, 4He, and fissiogenic Xe from U/Th in the matrix rock in which the diamonds have been stored for so long. These implanted species are absent in diamonds from the much younger (approximately 20 Ma) Ellendale pipe. We give implantation formulae for several models of inhomogeneously distributed U/Th. Differences in 3He content between pipe and alluvial Argyle samples are consistent with expected cosmogenic production in the latter. An expanded data base for helium and carbon isotopic data on the same samples supports a negative [4He]-delta 13C correlation seen earlier in work from our group, but if the Argyle samples, which contain light carbon, are corrected for implanted 4He, the correlation is considerably weakened. We no longer see an earlier 3He/4He-delta 13C correlation.

NASA Discipline Number 52-10↗
NASA NTRS2012

Science at the Goddard Space Flight Center

The Sciences and Exploration Directorate of the NASA Goddard Space Flight Center (GSFC) is the largest Earth and space science research organization in the world. Its scientists advance understanding of the Earth and its life-sustaining environment, the Sun, the solar system, and the wider universe beyond. Researchers in the Sciences and Exploration Directorate work with engineers, computer programmers, technologists, and other team members to develop the cutting-edge technology needed for space-based research. Instruments are also deployed on aircraft, balloons, and Earth's surface. I will give an overview of the current research activities and programs at GSFC including the James Web Space Telescope (JWST), future Earth Observing programs, experiments that are exploring our solar system and studying the interaction of the Sun with the Earth's magnetosphere.

White, Nicholas E.↗
NASA NTRSDate not supplied

An Overview of MaGIXS-2: The second flight of the Marshall Grazing Incidence X-ray Spectrometer

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket mission that completed a successful flight from the White Sands Missile Range on July 30, 2021. MaGIXS captured spatially resolved soft X-ray spectra from portions of two solar active regions during its roughly 5-minute flight. The instrument was originally designed as a grazing incidence slit spectrograph but flew in a slit-less configuration that produced overlapping spectroheliograms. For the second flight, MaGIXS-2, the instrument has been reconfigured to a more simplified optical layout that reuses the Wolter-I telescope and blazed varied-line space reflective grating. The field stop at the telescope focal plane and the finite conjugate spectrometer mirror pair have been removed – the telescope now directly feeds the grating. Additionally, an identical but new 2k x 1k CCD camera has been built for this flight. The MaGIXS-2 data product will again be overlapping spectroheliograms of at least one solar active region, but with improved resolution, a larger field of view and increased effective area. Here we present the updated instrument layout, the expected performance, the integration and calibration approach, and proposed future improvements, including the implementation of additional complimentary spectral diagnostics.

Imaging Spectrometer↗
NASA NTRS1995

The cooling of the white dwarf in U Geminorum following heating by two different outbursts

We present the analysis of 13 orbital phase-resolved IUE (large and small aperture) SWP spectra, sampling the quiescent intervals of the proptotype dwarf nova U Geminorum following two individual outbursts, the outburst of 1992, 29 August-14 September, and the outburst of 1993, 19 March-5 April. The quiescent interval following the outburst 29 August 1992 is the longest ever recorded. During quiescence, the photospheric radiation of the exposed white dwarf dominates the far ultrviolet. The variations in absorption line strengths and continum flux levels are analyzed as a function of both orbital phase and elapsed time, since the return to optical quiescence, by fitting the IUE spectra with a grid of high gravity, LTE, model atmospheres with solar composition constructed with TLUSTY and SYNSPEC (Hubeny, I. Tlusty and Synnspec: A Users Guide (1994)). We present evidence from both absorption line variations and continuum variations, as a function of time since the outbursts, that the white dwarf photosphere has cooled by several thousand degrees. Within the signal-to-noise limitations, we find no evidence of a difference in heating and cooling between the two outbursts.

Huang, Min↗
NASA NTRS1995

Very low mass stars and white dwarfs in NGC 6397

Deep Wide Field/Planetary Camera 2 (WFPC2) images in wide bands centered at 606 and 802 nm were taken with the Hubble Space Telescope (HST) 4.6 min from the center of the galactic globular cluster NGC 6397. The images were used to accurately position approximately 2120 stars detected in the field on a color magnitude diagram down to a limiting magnitude m(sub 814) approximately = m(sub I) approximately = 26 determined reliably and solely by counting statistics. A white dwarf sequence and a rich, narrow cluster main sequence are detected for the first time, the latter stretching from m(sub 814) = 18.5 to m(sub 814) = 24.0 where it becomes indistinguishable from the field population. Two changes of slope of the main sequence at m(sub 814) approximately = 20 and m(sub 814) approximately = 22.5 are evident. The corresponding luminosity function increases slowly from M(sub 814) approximately = 6.5 to 8.5 are expected from ground-based observations but then drops sharply from there dwon to the measurement limit. The corresponding mass function obtained bu using the only presently available mass-luminosity function for the cluster's metallicity rises to a plateau between approximately 0.25 and approximately 0.15 solar mass, but drops toward the expected mass limit of the normal hydrogen burning main sequence at approximately 0.1 solar mass. This result is in clear contrast to that obtained from the ground and implies either a substantial modification of the cluster's initial mass function due to dynamical evolution in its lifetime, or that very low mass stars are not produced in any dynamically significant amount by clusters of this type. The white dwarf sequence is in reasonable agreement with a cooling sequence of models of mass 0.5 solar mass at the canonical distance of NGC 6397 with a scatter that is most likely due to photometric errors, but may also reflect real differences in mass or chemical composition. Contamination from unresolved galaxies, which cannot be reliably identified with our filters, makes it difficult to meaningfully compare the observed white dwarf luminosity function with its theoretical counterpart.

Paresce, Francesco↗
NASA NTRS2005

Lunar and Planetary Science XXXVI, Part 17

The following topics were discussed: A Model for the Formation of Paterae on Io; LIBS-based Detection of As, Br, C, Cl, P, and S in the VUV Spectral Region in a Mars Atmosphere; Mass Independent Sulfur in Achondrites: Possible Evidence of Photochemistry in the Solar Nebula; Grain Size-dependent Viscosity and Oceans in Icy Satellites; Claritas Paleolake Studied from the MEX HRSC Data; Mars Express HRSC Colors of White Rock, Arabia, Mars; Lava and Flows of the Arcadia Region of Mars; Isotopic Composition of Lunar Soils and the Early Differentiation of the Moon; Trace Element Analysis of Lunar Soils by ICP-MS; Highly Siderophile Elements and Osmium Isotope Systematics in Ureilites: Are the Carbonaceous Veins Primary Components?; Evaporative Evolution of Martian Brines Based on Halogens in Nakhlites and MER Samples; Io from High-Resolution Galileo PPR Data Taken Simultaneously with SSI or NIMS Observations; Loki, Io: Groundbased Observations and a Model for Periodic Overturn; Deconstructing a Few Myths in the Interpretation of Satellite-Altitude Crustal Magnetic Field: Examples from Mars Global Surveyor; Semi-Autonomous Rover Operations: A Mars Technology Program Demonstration; Rotational Studies of Asteroids with Small Telescopes; Mineralogy and Temperature-induced Spectral Investigations of A-type Asteroids 246 Asporina and 446 Aeternitas; and Thermal History Calculations Versus Full Convection Models: Application to the Thermal Evolution of Mercury. Recent Solar-Proton Fluxes

Source record↗
DOE OSTI2022

Integrated Heat Pump Thermal Storage and Power Cycle for CSP (Final Technical Report)

Pumped thermal energy storage (PTES) is a storage system that stores electricity in thermal reservoirs. In this project, methods of integrating PTES with concentrating solar power (CSP) systems were investigated and their feasibility evaluated. Hybrid "solar-PTES" devices can provide both flexible renewable power generation as well as a variety of electricity storage services. Techno-economic models of PTES and solar-PTES were developed and used to assess their performance, cost, and commercial viability. Systems were optimized using multi-objective optimization techniques. The value that these storage devices provide to the grid was estimated using production cost modelling. Key advances made in this project include the development of detailed techno-economic models that improve state-of-the-art assessments of these technologies. Off-design models were developed and used in grid-analysis models. This work describes for the first time how PTES and solar-PTES behave over a range of operating points and assesses the value that these systems can provide to the electrical grid. Feedback was obtained from experts in the field, which clarified key technological and economic barriers that must be addressed to improve the feasibility of these devices.

14 SOLAR ENERGY↗
DOE OSTI2024

Availability and Performance Loss Factors for U.S. PV Fleet Systems

In the PV Fleet Performance Data Initiative, we partner with photovoltaic (PV) fleet owners to collect time-series PV production data and publish aggregated, anonymized results. This report is an update of our previous publications, specifically a FY 2021 performance index publication and a FY 2022 fleet degradation analysis. In this analysis, we have increased our data participants and system totals by around 10% to 8.5 GW and 24,000 separate inverter data channels. Four major analysis topics are considered in this report: Performance Index (PI) trends, PV system availability, soiling losses, and PV system degradation. Performance Index and inverter availability are assessed on a larger set of data from our FY 2021 report: 1,128 systems compared with 200 systems from before. The increased number of systems is due to an improved data quality methodology, as well as introducing new systems to the analysis. Overall results are similar to previously published values - overall inverter availability is low in the first six months of system performance before reaching steady-state by the end of the first year. Excluding this six-month startup period, system-level aggregated data shows a median (P50) system availability of 0.99 and a lower 10th percentile (P90) value of 0.95 (Figure ES-1). A dependence on system size is also demonstrated, with worse inverter availability results for larger PV systems. Causes of this effect are under investigation, but may be impacted by inverter size, which also show lower availability for larger inverter sizes. This report also investigates PI, correcting for degradation, soiling, snow, and availability. Following these corrections, the median system PI over its entire lifetime is 0.95. PI values reported here are approximately 3% lower than what we presented in our previous FY 2021 report. Soiling loss is assessed in a comprehensive way for the first time in this report. Results are presented using the COmbined Degradation and Soiling (CODS) method, as implemented in RdTools (v3.0.0a4). Soiling values are presented for 255 systems, which indicated irradiance-weighted soiling loss greater than 1%. The values have been published in an updated NREL soiling map at nrel.gov/pv/soiling.html. Finally, we investigated system degradation using three different data analysis techniques: conventional RdTools (year-on-year (YOY)), CODS, and Performance Loss Rate (PLR) analysis. Overall degradation results are consistent with our previous publications. Rerunning conventional RdTools on our updated fleet shows that some data partners have systematically fallen below the median system degradation rate (change over time) of -0.75 %/year. A comparison with PLR analysis, which looks at change in annual PI over time, shows that median system degradation is consistent with -0.5% to -0.75% per year change. However, at the P90 value, system degradation is substantially faster. These two results are consistent and indicate that resulting degradation statistics depend to a great degree on the population of PV systems making up the analysis cohort and whether soiling impacts the systems. The use of CODS for degradation analysis provides a different method for degradation assessment, which explicitly excludes the impact of recoverable soiling on degradation analysis. Excluding soiling effects yields an annual system degradation around -0.5% per year on average. This indicates that a portion of system performance loss may be attributed to periodic soiling that is not fully recovered. This report provides PV system owners/operators with background and methods to analyze PV system performance, give guidance for expected cohort performance, and performance loss values for use in pro-forma financial models, which guide new-build system design and bankability reports.

14 SOLAR ENERGY↗
NASA NTRS1983

The solar absolute spectral irradiance at 1216 A and 1800-3173 A - January 12, 1983

The full-disk solar spectral irradiance in the spectral range 1800-3173 A and at Lyman-alpha was obtained from a rocket observation above White Sands Missile Range, New Mexico, on January 12, 1983. Comparison with measurements made in May 1983 show no changes within the absolute errors of the experiment. The absolute calibration of the instruments for this flight was accomplished at the National Bureau of Standards Synchrotron Radiation Facility.

Mount, G. H.↗
NASA NTRS1985

The X-ray corona of Procyon

X-ray emission from the nearby system Procyon A/B (F5 IV + DF) was detected, using the IPC (Imaging Proportional Counter) on board the Einstein Observatory. Analysis of the X-ray pulse height spectrum suggests that the observed X-ray emission originates in Procyon A rather than in the white dwarf companion Procyon B, since the derived X-ray temperature, log T = 6.2, agrees well with temperatures found for quiescent solar X-ray emission. Modeling Procyon's corona with loops characterized by some apex temperature Tmax and emission length scale L, it is found that Tmax is well constrained, but L, and consequently the filling factor of the X-ray emitting gas, are essentially unconstrained even when EUV emission from the transition region is included in the analysis.

Schmitt, J. H. M. M.↗
NASA NTRS1987

Radio studies of large scale structures of the Sun's corona and transient activity

The use of meter-decimeter wavelength imaging observations for four different kinds of studies of solar coronal activity is discussed. (1) Large scale structure of the upper corona; daily imaging observations permit comparison of radio images with white light images from space and ground observation, generation of synoptic charts similar to white light coronagraph synoptic charts, and comparison of radio brightness enhancements and deficiencies with bright coronal streamers and coronal holes. (2) Relative positions of type III burst sources and coronal streamers as observed by Solwind experiment on the P-78-1 satellite and by the HAO C/P experiment aboard the SMM; infer the paths of type III emitting electrons in dense coronal streamers, and from multifrequency observations derive electron density distributions above active regions near the limb. (3) Non-flare associated type II/type IV bursts associated with coronal streamer disruption events; such type IV sources have a rather slow velocity (approx = to or less than 100 km/s) CMEs. (4) Meter-decimeter microbursts; these are short duration (2-10 sec) weak-type III-like bursts, produced at the fundamental plasma frequency by plasma radiation processes which have important differences from the standard mechanisms used to explain the strong type III bursts.

Kundu, Mukul R.↗
NASA NTRS1994

Discovery of a new white dwarf in a binary system (EUVE 0720-317) in the Extreme Ultraviolet Explorer survey and implications for the late stages of stellar evolution

A new precataclysmic binary is identified in the Extreme Ultraviolet Explorer (EUVE) all-sky survey. The bright source EUVE 0720-317 shows a hot hydrogen-rich white dwarf optical continuum with overlying narrow Balmer-line emission. Using high signal-to-noise ratio spectroscopy in the 4100-6700 A range, we identify a late-type companion and find a 1.3d periodic modulation in the emission-line velocities and strengths. This is the signature of Feige 24-type close binary systems. We determine the components' spectral types (DAO and dM0-2), orbital velocities (K(sub DAO) = 104 +/- 12 km/s, K(sub dM) = 96 +/- 7 km/s), and systemic velocity (gamma = 15 +/- 12 km/s). A first estimate of the white dwarf gravitational redshift, gamma(sub g) = 45 +/- 20 km/s, and theoretical mass-radius relationships imply R(sub DAO) = 0.010-0.016 solar radius and M(sub DAO) = 0.55-0.90 solar mass. The orbital inclination is therefore i greater than or equal to 52 deg, consistent with the large amplitude variations found in H-alpha equivalent widths that imply i greater than or equal to 42 deg. We show that the discovery of new close WD + MS binary systems in extreme ultraviolet (EUV) sky surveys has important implications for theory of common-envelope evolution, in particular for the predicted close binary birthrate and orbital and stellar parameters.

Vennes, Stephane↗