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  • 1
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    Modeling of electron time variations in the radiation belts (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: A review of the temporal variation in the trapped electron population of the inner and outer radiation zones is presented. Techniques presently used for modeling these zones are discussed and their deficiencies identified. An intermediate region is indicated between the zones in which the present modeling techniques are inadequate due to the magnitude and frequency of magnetic storms. Future trends are examined, and it is suggested that modeling of individual magnetic storms may be required in certain L bands. An analysis of seven magnetic storms is presented, establishing the independence of the depletion time of the storm flux and the storm magnitude. Provisional correlation between the storm magnitude and the Dst index is demonstrated.
    Keywords: SPACE RADIATION
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  • 2
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    Some Considerations for Precision Metrology of Thin X-Ray Mirrors (2008)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Determination of the shape of very thin x-ray mirrors employed in spaced-based telescopes continues to be challenging. The mirrors shapes are not readily deduced to the required accuracy because the mount induced distortions are often larger than the uncertainty tolerable for the mission metrology. In addition to static deformations, dynamic and thermal considerations are exacerbated for this class of mirrors. We report on the performance of one temporary mounting scheme for the thin glass mirrors for the Constellation-X mission and prospects for deducing their undistorted shapes.
    Keywords: Optics
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  • 3
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    Plastic scintillators in coincidence for the study of multi-particle production of sea level cosmic rays in dense medium (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Cosmic ray particles at sea level penetrate a thick layer of dense medium without appreciable interaction. These penetrating particles are identified with muons. The only appreciable interaction of muons are by knock on processes. A muon may have single, double or any number of knock on with atoms of the material so that one, two, three or more particles will come out from the medium in which the knock on processes occur. The probability of multiparticle production is expected to decrease with the increase of multiplicity. Measurements of the single, double, and triple particles generated in a dense medium (Fe and Al) by sea level cosmic rays at 22.42 N. Lat. and 114.20 E. Long. (Hong Kong) are presented using a detector composed of two plastic scintillators connected in coincidence.
    Keywords: SPACE RADIATION
    Type: SH-9.1-11 , 19th Intern. Cosmic Ray Conf - Vol. 5; p 494-497; NASA-CP-2376-VOL-5
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  • 4
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    Measurement of the wave-normal vector of proton whistlers on Ogo 6. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Description of the first experimental determination of the wave-normal vector of proton whistlers in the ionosphere. Between the crossover frequency and the proton gyrofrequency, both right-hand and left-hand modes of propagation can occur for upgoing waves. Theoretically, the amount of energy in the respective modes depends on theta, the angle between the wave normal and the magnetic field. For proton whistlers with only left-hand mode energy between the crossover and proton gyrofrequency, theta ranged from 36 to 51 deg. For proton whistlers with strong right-hand and left-hand mode signals, theta ranged from 24 to 29 deg. The result is in good agreement with Wang's (1971) collisionless mode-coupling model. The angle between the wave normal and the vertical is found to increase with increasing altitude.
    Keywords: SPACE RADIATION
    Type: NSSDC-ID-69-051A-22-PM , Journal of Geophysical Research; 77; Feb. 1
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  • 5
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    High Angular Resolution and Lightweight X-Ray Optics for Astronomical Missions (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: X-ray optics with both high angular resolution and lightweight is essential for further progress in x-ray astronomy. High angular resolution is important in avoiding source confusion and reducing background to enable the observation of the most distant objects of the early Universe. It is also important in enabling the use of gratings to achieve high spectral resolution to study, among other things, the myriad plasmas that exist in planetary, stellar, galactic environments, as well as interplanetary, inter-stellar, and inter-galactic media. Lightweight is important for further increase in effective photon collection area, because x-ray observations must take place on space platforms and the amount of mass that can be launched into space has always been very limited and is expected to continue to be very limited. This paper describes an x-ray optics development program and reports on its status that meets these two requirements. The objective of this program is to enable Explorer type missions in the near term and to enable flagship missions in the long term.
    Keywords: Optics
    Type: GSFC.CP.5268.2011 , SPIE meeting; Aug 21, 2011 - Aug 25, 2011; San Diego, CA; United States
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  • 6
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    Next Generation Astronomical X-ray Optics: High Angular Resolution, Light Weight, and Low Production Cost (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: X-ray astronomy depends on the availability of telescopes with high resolution and large photon collecting areas. Since x-ray observation can only be carried out above the atmosphere, these telescopes must be necessarily lightweight. Compounding the lightweight requirement is that an x-ray telescope consists of many nested concentric shells, which further require that x-ray mirrors must also be geometrically thin to achieve high packing efficiency. This double lightweight and geometrically thin requirement poses significant technical challenges in fabricating the mirrors and in integrating them into mirror assemblies. This paper reports on the approach, strategy and status of our x-ray optics development program whose objective is to meet these technical challenges at modest cost to enable future x-ray missions, including small Explorer missions in the near term, probe class missions in the medium term, and large flagship missions in the long term.
    Keywords: Optics
    Type: GSFC.JA.7104.2012 , SPIE Proceedings; 8843
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  • 7
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    Toward a Complete Metrological Solution for the Mirrors for the Constellation-X Spectroscopy X-ray Telescope (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present an overview update of the metrological approach to be employed for the segmented mirror fabrication for Constellation-X spectroscopy x-ray telescope. We compare results achieved to date with mission requirements. This is discussed in terms of inherent capability versus in-practice capability.
    Keywords: Optics
    Type: SPIE Conference: Optics and Photonics 2007; Aug 26, 2007 - Aug 30, 2007; San Diego, CA; United States
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  • 8
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    On the origin of variable 511 keV line emission from the Galactic center region (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Variable narrow-line emission at 511 keV, due to positron annihilation, has been observed from the region of the Galactic center for over a decade with high-resolution Ge spectrometers. The variable nature of this emission suggests that a significant fraction of the observed radiation is produced by a single source in the central region of the Galaxy. Recent observations with an imaging gamma-ray spectrometer of low energy resolution have revealed a daylong burst of annihilation radiation from the X-ray source 1E 1740.7-2042 located at an angular distance of 0.9 deg from the Galactic center and aligned with a dense molecular cloud. It is proposed that the variable narrow 511 keV line emission is due to positrons released impulsively (time scale of about 1 day) from 1E 1740.7-2942 into the molecular cloud where they slow down and annihilate on a longer time scale of up to a year.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 392; 2 Ju
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  • 9
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    A review of the near-earth radiation environment (1978)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The spatial volume surrounding the earth out to 30 earth radii has been divided into the five regions known as the interplanetary medium, magnetosheath, plasma sheet, high-latitude magnetotail, and inner magnetosphere. In each region, the primary attributes of the particle populations and available models are described, and integral energy spectra covering the range from 10 to 10 billion eV are shown. The effects of the solar cycle on future projections are discussed.
    Keywords: SPACE RADIATION
    Type: Photovoltaic Specialists Conference; Jun 05, 1978 - Jun 08, 1978; Washington, DC
    Format: text
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