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  • 1
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    Microwave and optical lunar transponders (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The scientific areas which used data from the Lunar Laser Ranging Experiment, collected from measurements to the Apollo 11, 14, and 15 and Lunakhod 2, include lunar science (i.e., studies of variations in the lunar angular orientation from that for uniform rotation, lunar tidal displacements, and the lunar mass distribution), geodynamics, astrometry, and gravitational physics. This paper argues that the placement of microwave and optical transponders on the moon would improve the accuracy of laser range measurements by nearly two orders of magnitude and would simplify the measurements. The K-band microwave transponders would be operated at the lunar base and at two remote sites on the moon surface, yielding much improved lunar libration and tidal displacement measurements. A two-wavelength laser transponder also would be operated at the lunar base, allowing accurate tropospheric propagation corrections to be made. This would introduce major improvements in measurements of the lunar orbit and of the earth's rotation, and in tests of general relativity.
    Keywords: ASTRONOMY
    Type: Astrophysics from the Moon; Feb 05, 1990 - Feb 07, 1990; Annapolis, MD; United States
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  • 2
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    The advanced cosmic microwave explorer - A millimeter-wave telescope and stabilized platform (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: We have developed and flown a 1 m diameter Gregorian telescope system for measurements of anisotropy in the Cosmic Background Radiation (CBR). The telescope is incorporated in a balloon-borne stabilized platform with arcminute stabilization capability. To date, the system has flown four times and observed from the ground at the South Pole twice. The telescope has used both coherent and incoherent detectors. We describe the development of the telescope, pointing platform, and one of the receivers employed in making measurements of the CBR. Performance of the system during the first flight and operation on the ground at the South Pole are described, and the quality of the South Pole as a millimeter wave observing site is discussed.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 406; 1; p. 12-25.
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  • 3
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    Determination of the extragalactic-planetary frame tie from joint analysis of radio interferometric and lunar laser ranging measurements (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources provide the basis for defining an accurate non-rotating reference frame in terms of angular positions of the sources. Measurements of the distance from the Earth to the Moon and to the inner planets provide the basis for defining an inertial planetary ephemeris reference frame. The relative orientation, or frame tie, between these two reference frames is of interest for combining Earth orientation measurements, for comparing Earth orientation results with theories referred to the mean equator and equinox, and for determining the positions of the planets with respect to the extragalactic reference frame. This work presents an indirect determination of the extragalactic-planetary frame tie from a combined reduction of VLBI and Lunar Laser Ranging (LLR) observations. For this determination, data acquired by LLR tracking stations since 1969 have been analyzed and combined with 14 years of VLBI data acquired by NASA's Deep Space Network since 1978. The frame tie derived from this joint analysis, with an accuracy of 0.003 sec, is the most accurate determination obtained so far. This result, combined with a determination of the mean ecliptic (defined in the rotating sense), shows that the mean equinox of epoch J2000 is offset from the x-axis of the extragalactic frame adopted by the International Earth Rotation Service for astrometric and geodetic applications by 0.078 sec +/- 0.010 sec along the y-direction and y 0.019 sec +/- 0.001 sec. along the z-direction.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 287; 1; p. 279-289
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  • 4
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    Radiative signatures from impact of Comet Shoemaker-Levy-9 on Jupiter (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The visible optical power emitted from the expansion plumes from 0.4 and 2 km diameter fragments of Shoemaker-Levy are expected to be, approximately 25% and comparable to, the visible solar flux reflected from Jupiter, respectively, for several minutes, and could be easily observed by sensors on the Galileo spacecraft. Earth-based observers can detect these plumes as these expand over the SW limb of Jupiter and come into earth view some minutes after impact!
    Keywords: ASTRONOMY
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 14; p. 1551-1553
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  • 5
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    Spectroscopy of the young cluster Blanco 1 (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We present spectroscopic observations of some 115 stars of the cluster Blanco 1, extending from the Ca II(H,K) region to the Ca II(I-R) triplet, supporting an age similar to that of the young cluster alpha Persei. The H-alpha absorption equivalent with vs (B - V) diagram forms a well-defined locus, with decreasing absorption equivalent width for decreasing effective temperature, akin to solar neighborhood dwarfs. A large spread in the Ca II surface flux, as a function of (B - V), also indicates the presence of a high degree of surface inhomogeneity, synonymous with high magnetic activity in young stars. A drop-off in the Ca II flux at (B - V) = 1.0 is also similar to the solar neighborhood stars, and shows that the primary chromospheric cooling changes from the Ca II and Mg II lines to the Balmer lines. The mean chromospheric temperature for stars at 4800 K lies between 8000 K and 10,000 K, based on theoretical models, which is somewhat higher than the older solar neighborhood dwarfs. The high mean Ca II surface flux of the sample is also consistent with that of other young clusters. We were able to measure the equivalent width of the Li(6708) line, whose strength as a function of (B - V) indicates an age similar to the young cluster alpha Persei. The lithium abundance decreases with decreasing effective temperature, consistent with the premise of lithium depletion in stars with larger convection zones. Using published photometry and a recent Zero Age Main Sequence (ZAMS) fitting method, we also re-define the distance to the cluster to be 246 pc.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 292; 2; p. 439-449
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  • 6
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    Developing technologies for lunar-based astronomy (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Prospects for lunar-based astronomy and the development of the required technologies are briefly reviewed. A systematic approach to lunar-based astronomy includes a progression in capability from small automated telescopes to the 16-meter reflector on the moon. A next step beyond the 16-meter reflector will be a Lunar Optical/Ultraviolet/Infrared Synthesis Array. Intermediate steps are represented by the Lunar Transit Telescope and the Lunar Cluster Telescope Experiment. Priorities for the required technology development are identified.
    Keywords: ASTRONOMY
    Type: In: Engineering, construction, and operations in space III: Space '92; Proceedings of the 3rd International Conference, Denver, CO, May 31-June 4, 1992. Vol. 2 (A93-41976 17-12); p. 1853-1864.
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  • 7
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    The Multi-Spectral Solar Telescope Array. II - Soft X-ray/EUV reflectivity of the multilayer mirrors (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have developed seven compact soft X-ray/EUV (XUV) multilayer coated and two compact FUV interference film coated Cassegrain and Ritchey-Chretien telescopes for a rocket borne observatory, the Multi-Spectral Solar Telescope Array. We report here on extensive measurements of the efficiency and spectral bandpass of the XUV telescopes carried out at the Stanford Synchrotron Radiation Laboratory.
    Keywords: ASTRONOMY
    Type: In: Multilayer and grazing incidence X-ray(EUV optics; Proceedings of the Meeting, San Diego, CA, July 22-24, 1991 (A93-39658 15-74); p. 432-445.
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  • 8
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    Solar observations with the Multi-Spectral Solar Telescope Array (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne solar observatory which was succesfully launched on May 13, 1991, from the White Sands Missile Range, NM. Ultrahigh resolution, full-disk solar X-ray, EUV, and FUV images were obtained with the MSSTA Herschelian, Cassegrain, and Ritchey-Chretien telescopes. We describe the payload and provide some preliminary scientific results from the flight.
    Keywords: ASTRONOMY
    Type: In: Multilayer and grazing incidence X-ray(EUV optics; Proceedings of the Meeting, San Diego, CA, July 22-24, 1991 (A93-39658 15-74); p. 175-187.
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  • 9
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    Sungrazing comets observed by the Solar Maximum Mission coronagraph (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The 10 sun-grazing comets (all members of the Kreutz group) detected by the white-light coronagraph of the SMM satellite during its 6-year operational lifetime are described. Numerical data are summarized in tables, and images are provided. Consideration is given to the question of detectability, apparent motions and orbits, coma brightness variations, tail behavior, and occurrence rates. The data are shown to confirm the episodic nature of sun-grazing events, as suggested by Marsden (1967).
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 90; 96-106
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  • 10
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    Luni-solar precession - Determination from lunar laser ranges (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two decades oflunar laser ranges have been analyzed to determine corrections to the earth's luni-solar precession constant and 18.6 yr nutation coefficients. The correction to the IAU-adopted precession constant is -2.7 + or - 0.4 milliarcsec/yr (mas/yr), giving the luni-solar precession constant as 50.3851 arcsec/yr at J2000. The 18.6 yr nutation of the pole is found to be 3.0 + or - 1.5 mas larger in magnitude than the 1980 IAU series. The correction to the annual term, previously discovered by VLBI, is found to be 1.8 + or - 0.5 mas if assumed to be a circular correction to the nutation of the pole.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 241; 1, Ja
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