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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Isotopically enriched germanium detectors for astrophysical gamma-ray spectroscopy

A study is presented of the instrumental background in astrophysical gamma-ray spectrometers using isotopically enriched germanium detectors. Calculations show that the beta-decay background, which is the largest component between approximately 0.1 and 1.0 MeV in balloonborne and satellite spectrometers, is dominated by the activation of Ge-74. This component can be reduced by an order of magnitude using detectors enriched to more than 80 percent in (Ge-70). The predicted reduction in the total background for current balloonborne instruments is more than a factor of 1.7 between 0.2 and 1.0 MeV. For future satellite instruments, the reduction in this energy range is by more than a factor of 5.

Gehrels, Neil↗
NASA NTRS1992

Polarization aberration analysis of the Advanced X-ray Astrophysics Facility Telescope assembly

The Advanced X-ray Astrophysics Facility (AXAF) Telescope consists of six concentric paraboloid-hyperboloid pairs of mirrors that operate near grazing incidence. Because of the substantial polarization effects at large angles of incidence there has been concern regarding the feasibility of doing polarimetry near the telescope focal plane. The primary mirror is here shown to act as a tangentially directed half-wave linear retarder and almost completely to depolarize the linearly polarized component of the light. The secondary mirror introduces and additional half-wave of linear retardance. The two-mirror telescope assembly acts as a tangentially directed one-wave linear retarder. Each mirror depolarizes alone but together the two-mirror assembly preserves the polarization state. The net instrumental polarization effects are small and polarimetry is feasible with AXAF.

Chipman, Russell A.↗
NASA NTRS1991

Imaging pulse-counting detector systems for space ultraviolet astrophysics missions

A family of imaging, pulse-counting, photoelectric detector systems, the Multi-Anode Microchannel Arrays (MAMAs), are now under active development for use on a number of space ultraviolet astrophysics missions at far-ultraviolet (FUV) and extreme-ultraviolet wavelengths between about 300 and 28 nm. Specifically, MAMA detectors are being fabricated and tested for use in two instruments on the ESA/NASA Solar and Heliospheric Observatory mission, for the NASA Goddard Space Flight Center's Hubble Space Telescope Imaging Spectrograph, and for the prime FUV spectrograph of the Far Ultraviolet Spectroscopic Explorer FUSE/Lyman mission. The construction and performance characteristics of the different MAMA detector systems are described, and techniques for improving the spatial resolution of each of the detector systems by the use of custom application specific integrated circuits in the electronics are discussed.

Timothy, J. G.↗
NASA NTRS1987

A particle astrophysics magnet spectrometer facility for Space Station

Planning for and design tradeoff studies related to the particle astrophysics magnet spectrometer known as Astromag are presented. This facility is being planned for the Space Station Freedom and address questions regarding the origin and acceleration of cosmic rays, explore the synthesis of elements by making detailed measurements of cosmic ray isotopic composition, and search for evidence of antimatter and other cosmologically significant particles. This work was supported by an international study team which includes particle physicists and cosmic ray physicists.

Ormes, J. F.↗
NASA NTRS1989

Controls Astrophysics and Structures Experiment in Space (CASES) advanced studies and planning

The CASES (Controls, Astrophysics, and Structures Experiment in Space) program consists of a flight demonstration of CSI (Controls-Structures Interactions) technology on the Space Shuttle. The basis structure consists of a 32 m deployable boom with actuators and sensors distributed along its length. Upon deployment from the Orbiter bay, the CASES structure will be characterized dynamically and its deformations controlled by a series of experimental control laws; and cold gas thrusters at its tip will be used to orient the Orbiter to a fixed celestial reference. The scientific observations will consist of hard x-ray imaging, at high resolution, of the Sun and the Galactic center. The hard x-ray observations require stable (few arc min) pointing at these targets for one or more position-sensitive proportional counters in the Orbiter bay, which view the object to be imaged through an aperture-encoding mask at the boom tip. This report gives the concensus developed at the second CASES Science Working Group meeting, which took place at NASA Marshall Space Flight Center May 16-17, 1990. An earlier paper and scientific summaries are available and form the basis for the present discussion.

Wu, S. T.↗
NASA NTRS1991

Information technologies for astrophysics circa 2001

It is easy to extrapolate current trends to see where technologies relating to information systems in astrophysics and other disciplines will be by the end of the decade. These technologies include miniaturization, multiprocessing, software technology, networking, databases, graphics, pattern computation, and interdisciplinary studies. It is less easy to see what limits our current paradigms place on our thinking about technologies that will allow us to understand the laws governing very large systems about which we have large data sets. Three limiting paradigms are as follows: saving all the bits collected by instruments or generated by supercomputers; obtaining technology for information compression, storage, and retrieval off the shelf; and the linear model of innovation. We must extend these paradigms to meet our goals for information technology at the end of the decade.

Denning, Peter J.↗
NASA NTRS1993

An astrophysics data program investigation of spatial structure of supernova remnants

The final report on astrophysics data program investigation of spatial structure of supernova remnants for the period 1 Aug. 1989 to 31 Jul. 1991 is presented. The goal of the project was the study of the spatial structure of supernova remnants (SNR's) as observed in the x-ray band. A number of software tools were developed for the analysis: (1) a program to fit various geometric models to high resolution x-ray data, and (2) programs for Fourier Transform analysis of clumping in SNR's. These programs were applied to high resolution imager (HRI) data on the young galactic SNR's Tycho and Kepler with some success.

Hughes, John P.↗
NASA NTRS1992

NASA's future plans for space astronomy and astrophysics

A summary is presented of plans for the future NASA astrophysics missions called SIRTF (Space Infrared Telescope Facility), SOFIA (Stratospheric Observatory for Infrared Astronomy), SMIM (Submillimeter Intermdiate Mission), and AIM (Astrometric Interferometry Mission), the Greater Observatories, and MFPE (Mission From Planet Earth). Technology needs for these missions are briefly described.

Kaplan, Mike↗
NASA NTRS1992

Rapid time variations and radiative instabilities of astrophysical masers

The time-varying intensities are obtained for astrophysical masers that are radiatively unstable. Numerical integrations of the time-dependent, nonlinear equations of radiative transfer are performed with the usual approximation of a linear maser. At long times after changes in the physical conditions, the intensity of maser radiation reaches an asymptotic behavior and oscillates permanently in these idealized calculations with a period that is related to the length of the maser divided by the speed of light. The intensity varies by more than a factor of 10. These intensities depend upon the same four parameters as we originally found to determine the regime for radiative instabilities based on a stability analysis of the steady state. A detailed comparison is made between the predictions of the stability analysis and the time variations of the intensities. Calculations are performed for interacting pairs as well as isolated, individual masers.

Scappaticci, Gerardo A.↗
NASA NTRS1992

Astrophysical Li-7 as a product of big bang nucleosynthesis and galactic cosmic-ray spallation

The astrophysical Li-7 abundance is considered to be largely primordial, while the Be and B abundances are thought to be due to galactic cosmic ray (GCR) spallation reactions on top of a much smaller big bang component. But GCR spallation should also produce Li-7. As a consistency check on the combination of big bang nucleosynthesis and GCR spallation, the Be and B data from a sample of hot population II stars is used to subtract from the measured Li-7 abundance an estimate of the amount generated by GCR spallation for each star in the sample, and then to add to this baseline an estimate of the metallicity-dependent augmentation of Li-7 due to spallation. The singly reduced primordial Li-7 abundance is still consistent with big bang nucleosynthesis, and a single GCR spallation model can fit the Be, B, and corrected Li-7 abundances for all the stars in the sample.

Olive, Keith A.↗
NASA NTRS1990

Astrophysics from the moon

Ideas presented at the Workshop on Astrophysics from the moon, held in Annapolis, Maryland, in February 1990, are discussed. Consideration is given to the formation of stars and planetary systems, the possibility of earthlike planets among the nearby stars, the possible existence of life and intelligence elsewhere, the current status of the sun and other stars, the evolution of the early universe, and environmental and site considerations for initial observatories.

Mumma, Michael J.↗
NASA NTRS1992

Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991

The present volume on testing the AGN paradigm discusses black holes, accretion disks, high-energy continuum jets, AGN geometry, and the broad-line region. Attention is given to the search for black holes in galaxy nuclei, the structure of M32 at red wavelengths, testing the AGN paradigm for the Milky Way, and relativistic fluid flows in the magnetized Schwarzschild spacetime. Topics addressed include orbital models for the periodic X-ray flares of NGC 6814, observational evidence for thin AGN disks, X-ray Fe line studies, and the role of the UV bump in line emission. Also discussed are signatures of black hole accretion disks, rapid variability in AGN and accretion disk hot spots, relativistic jets in AGN, and the radiation field in astrophysical jets.

Holt, Stephen S.↗
NASA NTRS1993

Relaxation of molecular velocities and spectral line profiles of astrophysical masers

The rates at which the velocities of water molecules relax to a Maxwellian distribution are calculated under conditions that are representative of those in astrophysical water masers. Populations are calculated as a function of velocity for the lowest 40 rotational energy levels of ortho-water in order to make a detailed determination of the velocity relaxation rate. Relaxation rates for the 22 GHz maser at H2 densities of 10 exp 9/cu cm are 2.0/s and 5.1/s for temperatures of 400 K and 1000 K, respectively. Under these and other conditions, as well as for other maser transitions, the relaxation rate far exceeds the loss rate - usually by more than a factor of 10. Thus maser lines can remain narrow up to intensities that are at least a factor of 10 greater than the saturation intensity, and to path lengths that are at least a factor of 10 greater than the path length at which saturation occurs. Relaxation is dominated by the effects of trapped infrared radiation, though elastic and inelastic collisions are also included in the calculations. These relaxation rates, together with the observed line breadths of the 22 GHz masers, provide limits on maser luminosities which indicate that the brightest 22 GHz masers are highly beamed, with solid angles smaller than 10 exp -5 to 10 exp -4 Sr.

Anderson, Nels↗
NASA NTRS1992

NASA's future plans for space astronomy and astrophysics

NASA's plans in the field of space astronomy and astrophysics through the first decade of the next century are reviewed with reference to specific missions and mission concepts. The missions discussed include the Space Infrared Telescope Facility, the Stratospheric Observatory for Infrared Astronomy, the Submillimeter Intermediate Mission, the Astrometric Interferometry Mission, the Greater Observatories program, and Mission from Planet Earth. Plans to develop optics and sensors technology to enable these missions are also discussed.

Kaplan, Michael S.↗
NASA NTRS1993

Extension of rezoned Eulerian-Lagrangian method to astrophysical plasma applications

The rezoned Eulerian-Lagrangian procedure developed by Brackbill and Pracht (1973), which is limited to simple configurations of the magnetic fields, is modified in order to make it applicable to astrophysical plasma. For this purpose, two specific methods are introduced, which make it possible to determine the initial field topology for which no analytical expressions are available. Numerical examples illustrating these methods are presented.

Song, M. T.↗
NASA NTRS1991

The X-ray Spectrometer - A cryogenic instrument on the Advanced X-ray Astrophysics Facility

The X-ray Spectrometer (XRS) is an instrument on the Advanced X-ray Astrophysics Facility (AXAF), the third of NASA's Great Observatories scheduled for launch in 1998. The XRS detectors have a resolution of approximately 10 eV over the range 0.3 - 10 keV. To achieve this resolution, the detectors are maintained at or below 0.1 Kelvin using an adiabatic demagnetization refrigerator inside a superfluid helium dewar. In addition, split-Stirling-cycle mechanical coolers are used to extend the anticipated on-orbit helium lifetime to a minimum of 4 years. This paper describes the challenges of developing this hybrid cryogenic system and presents an overview of the current design of the system.

Breon, Susan R.↗
NASA NTRS1992

Controls, astrophysics, and structures experiment in space ground test facility

This paper describes the initial configuration of the NASA Marshall Space Flight Center (MSFC) Controls/Structures Interaction Advanced Development Facility (CSI ADF), which is a ground test facility (GTF) for the proposed Controls, Astrophysics, and Structures Experiment in Space (CASES). The laboratory has been developed for the purpose of implementing, testing, and evaluating CSI modeling, control system design, failure analysis, and system identification techniques on a representative large space structure. The facility has been configured to represent as closely as possible an actual flight article.

Bukley, Angelia P.↗