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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 91 records · Page 5
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NASA NTRSDate not supplied

Roman Space Telescope - Demonstration of Integrated Thermal Control System Test for the Optical Telescope

On-orbit optical stability of the Nancy Grace Roman Space Telescope (RST) is a key requirement that enables multiple science objectives and drives multiple aspects of telescope design and analysis. Thermoelastic changes are typically large contributors to optical instability, and both extremely low CTE materials and extremely stable temperatures are needed to achieve the RST optical stability requirements. We will present the results from a test that demonstrated the L3Harris capability to sense and control temperatures to milli-kelvin levels of stability across a range of operating temperatures.

RST, Roman Space Telescope, Temperature Sensing, T↗
NASA NTRS1988

A very low frequency radio astronomy observatory on the Moon

Because of terrestrial ionospheric absorption, very little is known of the radio sky beyond 10 m wavelength. An extremely simple, low cost very low frequency radio telescope is proposed, consisting of a large array of short wires laid on the lunar surface, each wire equipped with an amplifier and a digitizer, and connected to a common computer. The telescope could do simultaneous multifrequency observations of much of the visible sky with high resolution in the 10 to 100 m wavelength range, and with lower resolution in the 100 to 1000 m range. It would explore structure and spectra of galactic and extragalactic point sources, objects, and clouds, and would produce detailed quasi-three-dimensional mapping of interstellar matter within several thousand parsecs of the Sun.

Douglas, James N.↗
NASA NTRS1974

Fabrication of an extreme ultraviolet glancing incidence telescope

A technique is described for use in the fabrication of glancing incidence telescopes which operate at large grazing angles (i.e., 8 to 15 degrees). Precision conic section plunge laps are used in a controlled grinding procedure to initially generate imaging surfaces which have a minimum of subsurface damage. A numerically controlled Moore Number 3 Measuring Machine is used throughout the fabrication procedure. Surface geometry accuracies on the order of one-tenth micron have been achieved.

Fleetwood, C. M.↗
NASA NTRS1999

Microwave Enhancement in Coronal Holes: Structure, Variability and Magnetic Nature

The microwave enhancement in coronal holes in comparison with the quiet Sun is a distinct and easily observed signature related to the magnetic activity. This has proven to be a new tool to study the solar atmospheric layer where the fast solar wind originates. We have developed a catalog of a large number of coronal holes using images obtained by SOHO's Extreme-ultraviolet Imaging Telescope in EUV and by the Nobeyama radioheliograph in microwaves. We also have high resolution longitudinal magnetograms obtained by SOHO's Michelson Doppler Imager. We present the statistical properties of the microwave enhancements and discuss the small-scale dynamics as revealed by the magnetograms and radioheliograms. We also discuss the geoeffectiveness of these coronal holes.

Gopalswamy, N.↗
NASA NTRS2008

Pulsars at the Highest Energies: Questions for the GLAST and ACT's

The recent announcement by the MAGIC team of pulsed gamma rays from the Crab Pulsar above 25 GeV and the launch of AGILE and the Gamma-ray Large Area Space Telescope (GLAST) offer the promise of major progress in understanding the most extreme emission from pulsar magnetospheres. While waiting for detailed results, we can formulate questions to be addressed, based on past measurements and theoretical modeling. This brief review will highlight promising approaches for research into high-energy pulsed radiation.

Thompson, Dave↗
NASA NTRSDate not supplied

Roman Space Telescope – Demonstration of Integrated Thermal Control System Test for the Optical Telescope Assembly

On-orbit optical stability of the Nancy Grace Roman Space Telescope (RST) is a key requirement that enables multiple science objectives and drives multiple aspects of telescope design and analysis. Thermoelastic changes are typically large contributors to optical instability, and both extremely low CTE materials and extremely stable temperatures are needed to achieve the RST optical stability requirements. We will present the results from a test that demonstrated the L3Harris capability to sense and control temperatures to milli-kelvin levels of stability across a range of operating temperatures.

Peter Miller↗
NASA NTRS1984

IRAS observations of cometary dust

It is pointed out that solid material present in the coma and tail of a comet is revealed by the scattering of sunlight and thermal emission of absorbed solar radiation. The large beam size and low background of the cold Infrared Astronomy Satellite (IRAS) telescope make it extremely well suited to the measurement of faint diffuse thermal emission from solid grains associated with comets. The IRAS project was conducted jointly by the Netherlands, the United Kingdom, and the U.S. Its basic objective involved a survey of the sky in four wavelength regions centered on 12, 25, 60, and 100 microns. The present paper is mainly concerned with IRAS observations of the coma-nucleus regions as defined by the maximum in the intensity distribution. Attention is given to circumstances of comet observations, dust production rates, and a discussion of the results.

Walker, R. G.↗
NASA NTRS1999

Semiempirical Two-Dimensional Magnetohydrodynamic Model of the Solar Corona and Interplanetary Medium

We have developed a two-dimensional semiempirical MHD model of the solar corona and solar wind. The model uses empirically derived electron density profiles from white-light coronagraph data measured during the Skylub period and an empirically derived model of the magnetic field which is fitted to observed streamer topologies, which also come from the white-light coronagraph data The electron density model comes from that developed by Guhathakurta and coworkers. The electron density model is extended into interplanetary space by using electron densities derived from the Ulysses plasma instrument. The model also requires an estimate of the solar wind velocity as a function of heliographic latitude and radial component of the magnetic field at 1 AU, both of which can be provided by the Ulysses spacecraft. The model makes estimates as a function of radial distance and latitude of various fluid parameters of the plasma such as flow velocity V, effective temperature T(sub eff), and effective heat flux q(sub eff), which are derived from the equations of conservation of mass, momentum, and energy, respectively. The term effective indicates that wave contributions could be present. The model naturally provides the spiral pattern of the magnetic field far from the Sun and an estimate of the large-scale surface magnetic field at the Sun, which we estimate to be approx. 12 - 15 G. The magnetic field model shows that the large-scale surface magnetic field is dominated by an octupole term. The model is a steady state calculation which makes the assumption of azimuthal symmetry and solves the various conservation equations in the rotating frame of the Sun. The conservation equations are integrated along the magnetic field direction in the rotating frame of the Sun, thus providing a nearly self-consistent calculation of the fluid parameters. The model makes a minimum number of assumptions about the physics of the solar corona and solar wind and should provide a very accurate empirical description of the solar corona and solar wind Once estimates of mass density rho, flow velocity V, effective temperature T(sub eff), effective heat flux q(sub eff), and magnetic field B are computed from the model and waves are assumed unimportant, all other plasma parameters such as Mach number, Alfven speed, gyrofrequency, etc. can be derived as a function of radial distance and latitude from the Sun. The model can be used as a planning tool for such missions as Slar Probe and provide an empirical framework for theoretical models of the solar corona and solar wind The model will be used to construct a semiempirical MHD description of the steady state solar corona and solar wind using the SOHO Large Angle Spectrometric Coronagraph (LASCO) polarized brightness white-light coronagraph data, SOHO Extreme Ultraviolet Imaging Telescope data, and Ulysses plasma data.

Sittler, Edward C., Jr.↗
DOE OSTI2021

J2229+2725: an extremely low metallicity dwarf compact star-forming galaxy with an exceptionally high [O iii ]λ5007/[O ii ]λ3727 flux ratio of 53

ABSTRACT Using the Large Binocular Telescope (LBT)/Multi-Object Dual Spectrograph (MODS), we have obtained optical spectroscopy of one of the most metal-poor dwarf star-forming galaxies (SFGs) in the local Universe, J2229+2725. This galaxy with a redshift z = 0.0762 was selected from the Data Release 16 of the Sloan Digital Sky Survey (SDSS). Its properties derived from the LBT observations are most extreme among SFGs in several ways. Its oxygen abundance 12 + logO/H = 7.085 ± 0.031 is among the lowest ever observed for an SFG. With its very low metallicity, an absolute magnitude Mg = −16.39 mag, a low stellar mass M⋆ = 9.1 × 106 M⊙, and a very low mass-to-light ratio M⋆/Lg ∼ 0.0166 (in solar units), J2229+2725 deviates strongly from the luminosity–metallicity relation defined by the bulk of the SFGs in the SDSS. J2229+2725 has a very high specific star formation rate sSFR ∼ 75 Gyr−1, indicating very active ongoing star formation. Three other features of J2229+2725 are most striking, being the most extreme among lowest metallicity SFGs: (1) a ratio O32 = I([O iii]λ5007)/I([O ii]λ3727) ∼ 53, (2) an equivalent width of the H β emission line EW(H β) of 577 Å, and (3) an electron number density of ∼1000 cm−3. These properties imply that the starburst in J2229+2725 is very young. Using the extremely high O32 in J2229+2725, we have improved the strong-line calibration for the determination of oxygen abundances in the most metal-deficient galaxies, in the range 12 + logO/H $\lesssim$ 7.3.

Izotov, Y. I.↗
NASA NTRS2012

Exploring the Extreme Universe with the Fermi Gamma-Ray Space Telescope

In ways similar to experiments in nuclear and particle physics, high-energy astrophysics usesgamma rays and energetic charged particles toprobe processes that involve large energy transfers.Since its launch in 2008, the international Fermi Gamma-Ray Space Telescope has been exploringnatural particle accelerators and the interactionsof high-energy particles in the universe. Withsources ranging from thunderstorms on Earth to galaxies and exploding stars in distant parts of the cosmos, the telescopes subjects of study are almostas diverse as were those of the scientist whose name it bears.

extreme↗
NASA NTRS1986

A reflection grating spectrometer for the X-ray Multi-Mirror (XMM) space observatory - Design and calculated performance

Attention is given to a spectrometer design candidate for the X-ray Multi-Mirror observatory, being planned by the European Space Agency as a long-lived large-area array of telescopes. The science requirement of moderate resolution spectroscopy in a two octave region with extremely high throughput leads to the use of grazing incidence reflection gratings. It is noted that the sensitivity of the instrument is sufficient to permit the first spectral detection of soft X-ray features in external galaxies.

Hettrick, Michael C.↗
NASA NTRS2021

Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through Far-ultraviolet Observations

We present the discovery of an extreme flaring event from Proxima Cen by the Australian Square Kilometre Array Pathfinder(ASKAP), Atacama Large Millimeter/submillimeter Array(ALMA), Hubble Space Telescope(HST),Transiting Exoplanet Survey Satellite(TESS), and the du Pont Telescope that occurred on 2019 May 1. In the millimeter and FUV, this flare is the brightest ever detected, brightening by a factor of>1000 and>14,000 as seen by ALMA and HST, respectively. The millimeter and FUV continuum emission trace each other closely during the flare, suggesting that millimeter emission could serve as a proxy for FUV emission from stellar flares and become a powerful new tool to constrain the high-energy radiation environment of exoplanets. Surprisingly, optical emission associated with the event peaks at a much lower level with a time delay. The initial burst has an extremely short duration, lasting for<10 s. Taken together with the growing sample of millimeter M dwarf flares, this event suggests that millimeter emission is actually common during stellar flares and often originates from short burst-like events.

Stellar activity↗
NASA NTRS2019

Comparing Long-Duration Gamma-Ray Flares and High-Energy Solar Energetic Particles

Little is known about the origin of the high-energy and sustained emission from solar long-duration gamma-ray flares (LDGRFs) identified with the Compton Gamma Ray Observatory, the Solar Maximum Mission, and now Fermi. Though the Fermi Large Area Telescope (LAT) has identified dozens of flares with LDGRF signatures, the nature of this phenomenon has been a challenge to explain due to both extreme energies and long durations. The highest-energy emission has generally been attributed to pion production from the interaction of 300 MeV protons with the ambient matter. The extended duration suggests that particle acceleration occurs over large volumes extending high in the corona, either from stochastic acceleration within large coronal loops or from back precipitation from coronal mass ejection–driven shocks. It is possible to test these models by making a direct comparison between the properties of the accelerated ion population producing the γ-ray emission derived from the Fermi/LAT observations and the characteristics of solar energetic particles (SEPs) measured by the Payload for Matter-Antimatter Exploration and Light Nuclei Astrophysics spacecraft in the energy range corresponding to the pion-related emission detected with Fermi. For 14 of these events, we compare the two populations—SEPs in space and the interacting particles at the Sun—and discuss the implications in terms of potential sources. Our analysis shows that the two proton numbers are poorly correlated, with their ratio spanning more than 5 orders of magnitude, suggesting that the back precipitation of shock-acceleration particles is unlikely to be the source of the F emission.

Nolfo, G. A. de↗
NASA NTRS2019

All-Sky Medium-Energy Gamma-Ray Observatory (AMEGO)

The gamma-ray energy range from a few hundred keV (kiloelectronvolts) to a few hundred MeV (megaelectronvolts) has remained largely unexplored since the pioneering but limited observations by COMPTEL (The Imaging Compton Telescope) on the CGRO (Compton Gamma Ray Observatory) (1991-2000). Fundamental astrophysics questions can be addressed by a mission in the MeV range, from astrophysical jets and extreme physics of compact objects to a large population of unidentified objects. Such a mission will also provide critical inputs for multimessenger astrophysics by identifying and exploring the astrophysical objects that produce gravitational waves and neutrinos. To address these questions, we are developing AMEGO: All-sky Medium Energy Gamma-ray Observatory, as a NASA probe-class mission, to investigate the energy range from 200 keV to greater than10 GeV with good energy (ranging from less than 1 percent at the low end to approximately 10 percent at the high end) and angular resolution (from 2 to 6 degrees depending on energy) and with sensitivity a factor of 20-50 better than previous instruments. Measurements at these energies are challenging, mainly due to the fact that two photon interaction processes, Compton scattering and pair production, compete. These interaction processes require different approaches in both detection and data analysis, and consequently in the instrument concept. AMEGO will be capable of measuring both Compton-scattering events at lower energies and pair-production events at higher energies. AMEGO will also have sensitivity to linear polarization of detected radiation at a level of 20 percent minimum detectable polarization from a source 1 percent of the Crab intensity, observed for 106 seconds. AMEGO will be operating mainly in scanning (discovery) mode with a field-of-view of 2.5 sr (Special Relativity) (20 percent of the sky observation any time), with the capability to be pointed to particular regions of interest..

Moiseev, Alexander↗
DOE OSTI2023

Multimessenger Characterization of Markarian 501 during Historically Low X-Ray and γ-Ray Activity

We study the broadband emission of Mrk 501 using multiwavelength observations from 2017 to 2020 performed with a multitude of instruments, involving, among others, MAGIC, Fermi's Large Area Telescope (LAT), NuSTAR, Swift, GASP-WEBT, and the Owens Valley Radio Observatory. Mrk 501 showed an extremely low broadband activity, which may help to unravel its baseline emission. Nonetheless, significant flux variations are detected at all wave bands, with the highest occurring at X-rays and very-high-energy (VHE) γ-rays. A significant correlation (>3σ) between X-rays and VHE γ-rays is measured, supporting leptonic scenarios to explain the variable parts of the emission, also during low activity. This is further supported when we extend our data from 2008 to 2020, and identify, for the first time, significant correlations between the Swift X-Ray Telescope and Fermi-LAT. We additionally find correlations between high-energy γ-rays and radio, with the radio lagging by more than 100 days, placing the γ-ray emission zone upstream of the radio-bright regions in the jet. Furthermore, Mrk 501 showed a historically low activity in X-rays and VHE γ-rays from mid-2017 to mid-2019 with a stable VHE flux (>0.2 TeV) of 5% the emission of the Crab Nebula. The broadband spectral energy distribution (SED) of this 2 yr long low state, the potential baseline emission of Mrk 501, can be characterized with one-zone leptonic models, and with (lepto)-hadronic models fulfilling neutrino flux constraints from IceCube. We explore the time evolution of the SED toward the low state, revealing that the stable baseline emission may be ascribed to a standing shock, and the variable emission to an additional expanding or traveling shock.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2005

Thermal System Verification and Model Validation for NASA's Cryogenic Passively Cooled James Webb Space Telescope (JWST)

A thorough and unique thermal verification and model validation plan has been developed for NASA s James Webb Space Telescope. The JWST observatory consists of a large deployed aperture optical telescope passively cooled to below 50 Kelvin along with a suite of several instruments passively and actively cooled to below 37 Kelvin and 7 Kelvin, respectively. Passive cooling to these extremely low temperatures is made feasible by the use of a large deployed high efficiency sunshield and an orbit location a! !he L2 Lagrange p~in!. Another enabling feature is the scale or size of the observatory that allows for large radiator sizes that are compatible with the expected power dissipation of the instruments and large format Mercury Cadmium Telluride (HgCdTe) detector arrays. This passive cooling concept is simple, reliable, and mission enabling when compared to the alternatives of mechanical coolers and stored cryogens. However, these same large scale observatory features, which make passive cooling viable, also prevent the typical flight configuration fully-deployed thermal balance test that is the keystone to most space missions thermal verification plan. JWST is simply too large in its deployed configuration to be properly thermal balance tested in the facilities that currently exist. This reality, when combined with a mission thermal concept with little to no flight heritage, has necessitated the need for a unique and alternative approach to thermal system verification and model validation. This paper describes the thermal verification and model validation plan that has been developed for JWST.

Parrish, Keith↗
NASA NTRS2005

Thermal System Verification and Model Validation for NASA's Cryogenic Passively Cooled James Webb Space Telescope

A thorough and unique thermal verification and model validation plan has been developed for NASA s James Webb Space Telescope. The JWST observatory consists of a large deployed aperture optical telescope passively cooled to below 50 Kelvin along with a suite of several instruments passively and actively cooled to below 37 Kelvin and 7 Kelvin, respectively. Passive cooling to these extremely low temperatures is made feasible by the use of a large deployed high efficiency sunshield and an orbit location at the L2 Lagrange point. Another enabling feature is the scale or size of the observatory that allows for large radiator sizes that are compatible with the expected power dissipation of the instruments and large format Mercury Cadmium Telluride (HgCdTe) detector arrays. This passive cooling concept is simple, reliable, and mission enabling when compared to the alternatives of mechanical coolers and stored cryogens. However, these same large scale observatory features, which make passive cooling viable, also prevent the typical flight configuration fully-deployed thermal balance test that is the keystone to most space missions thermal verification plan. JWST is simply too large in its deployed configuration to be properly thermal balance tested in the facilities that currently exist. This reality, when combined with a mission thermal concept with little to no flight heritage, has necessitated the need for a unique and alternative approach to thermal system verification and model validation. This paper describes the thermal verification and model validation plan that has been developed for JWST. The plan relies on judicious use of cryogenic and thermal design margin, a completely independent thermal modeling cross check utilizing different analysis teams and software packages, and finally, a comprehensive set of thermal tests that occur at different levels of JWST assembly. After a brief description of the JWST mission and thermal architecture, a detailed description of the three aspects of the thermal verification and model validation plan is presented.

Cleveland, Paul E.↗
NASA NTRS1982

X-ray and extreme ultraviolet imaging using layered synthetic microstructures

Up to now designers of X-ray optical instruments such as microscopes and telescopes have been compelled to use mirrors operating at small glancing angles. However, using vapor deposition techniques, it is now possible to build multilayered thin film structures in which the individual layers have thicknesses comparable with a wavelength of X-rays. These devices operate in a manner exactly analogous to multilayer dielectric coatings at visible wavelengths and can be used to increase the X-ray and extreme ultraviolet reflectivity of surfaces at large glancing angles. These X-ray mirrors have numerous potential applications in X-ray optics. Attention is given to X-ray images with a normal incidence mirror, and applications of multilayer optics. Single-mirror telescopes for solar/stellar astronomy are discussed, taking into account solar corona and transition region studies, and X-ray and extreme ultraviolet astronomy. Hybrid X-ray telescopes are also considered.

Underwood, J. H.↗