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  • 1
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    The microwave spectra of the asteroids Pallas, Vesta, and Hygiea (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Microwave observations of Pallas, Vesta, and Hygiea at 2 and 6 cm wavelength yield brightness temperatures that are much lower than would be expected for a rapidly rotating blackbody. An analysis of the wavelength dependence of the observed brightness temperatures shows that, as was found for Ceres, these asteroids may be covered by a layer of material with the physical properties of finely divided dust. Models with layer depths of greater than 6 cm (Pallas), 6 cm (Vesta), and 8 cm (Hygiea) were found to represent well the variation in emissivity at radio wavelengths. The properties of the underlying layer are not well constrained by the microwave observations. It does appear that the real part of the dielectric vector for the substrate is similar to that of basaltic rock. Major compositional changes, if any, must take place at depths greater than about 10 cm. No evidence for water ice was found. Disk-resolved observations of the 2-cm emission of Vesta yield physical dimensions consistent with the recently published speckle-interferometry results.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 98; 335-340
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    The Low Frequency Space Array (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: The Low Frequency Space Array (LFSA) is a conceptual mission to survey the entire sky and to image individual sources at frequencies between 1.5 and 26 MHz, a frequency range over which the earth's ionosphere transmits poorly or not at all. With high resolution, high sensitivity observations, a new window will be opened in the electromagnetic spectrum for astronomical investigation. Also, extending observations down to such low frequencies will bring astronomy to the fundamental limit below which the galaxy becomes optically thick due to free-free absorption. A number of major scientific goals can be pursued with such a mission, including mapping galactic emission and absorption, studies of individual source spectra in a frequency range where a number of important processes may play a role, high resolution imaging of extended sources, localization of the impulsive emission from Jupiter, and a search for coherent emission processes.
    Keywords: ASTRONOMY
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Automated telescope scheduling (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: With the ever increasing level of automation of astronomical telescopes the benefits and feasibility of automated planning and scheduling are becoming more apparent. Improved efficiency and increased overall telescope utilization are the most obvious goals. Automated scheduling at some level has been done for several satellite observatories, but the requirements on these systems were much less stringent than on modern ground or satellite observatories. The scheduling problem is particularly acute for Hubble Space Telescope: virtually all observations must be planned in excruciating detail weeks to months in advance. Space Telescope Science Institute has recently made significant progress on the scheduling problem by exploiting state-of-the-art artificial intelligence software technology. What is especially interesting is that this effort has already yielded software that is well suited to scheduling groundbased telescopes, including the problem of optimizing the coordinated scheduling of more than one telescope.
    Keywords: ASTRONOMY
    Type: NASA-CR-186279 , NAS 1.26:186279 , PREPRINT-SERIES-306
    Format: application/pdf
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  • 4
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    Automated observation scheduling for the VLT (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: It is becoming increasingly evident that, in order to optimize the observing efficiency of large telescopes, some changes will be required in the way observations are planned and executed. Not all observing programs require the presence of the astronomer at the telescope: for those programs which permit service observing it is possible to better match planned observations to conditions at the telescope. This concept of flexible scheduling has been proposed for the VLT: based on current and predicted environmental and instrumental observations which make the most efficient possible use of valuable time. A similar kind of observation scheduling is already necessary for some space observatories, such as Hubble Space Telescope (HST). Space Telescope Science Institute is presently developing scheduling tools for HST, based on the use of artificial intelligence software development techniques. These tools could be readily adapted for ground-based telescope scheduling since they address many of the same issues. The concept are described on which the HST tools are based, their implementation, and what would be required to adapt them for use with the VLT and other ground-based observatories.
    Keywords: ASTRONOMY
    Type: NASA-CR-186282 , NAS 1.26:186282 , PREPRINT-SERIES-307
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  • 5
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    Imaging and data processing with the Low Frequency Space Array (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: The Low Frequency Space Array (LFSA) is being designed to image the entire sky at extremely low radio frequencies with arcmin to subarcmin resolution. To accomplish this goal, data from LFSA will be continuously integrated for many months and then be used with aperture synthesis techniques to produce images. The three dimensional nature of LFSA and the effects of orbital geometry make LFSA a continuously evolving array which has an excellent synthesized point-response function. After transforming the data to produce an initial image, it is possible to remove low-level sidelobe responses remaining in the image and thereby produce a high dynamic-range image. Interference (both man-made and from solar-system objects) is a potential problem for LFSA, but appropriate data handling techniques are available which should eliminate any of its effects.
    Keywords: ASTRONOMY
    Format: text
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  • 6
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    Artificial intelligence approaches to astronomical observation scheduling (1988)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Automated scheduling will play an increasing role in future ground- and space-based observatory operations. Due to the complexity of the problem, artificial intelligence technology currently offers the greatest potential for the development of scheduling tools with sufficient power and flexibility to handle realistic scheduling situations. Summarized here are the main features of the observatory scheduling problem, how artificial intelligence (AI) techniques can be applied, and recent progress in AI scheduling for Hubble Space Telescope.
    Keywords: ASTRONOMY
    Type: NASA-CR-186277 , NAS 1.26:186277 , PREPRINT-SERIES-304 , International Workshop on Data, Analysis in Astronomy; Jun 20, 1988 - Jun 27, 1988; Erice; Italy
    Format: application/pdf
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