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At least 703 records · Page 39

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NASA NTRS1990

Method and apparatus for determining optical absorption and emission characteristics of a crystal or non-crystalline fiber

This invention relates generally to spectroscopy and, more particularly, to a method and apparatus for performing spectroscopic analysis of crystal and noncrystalline fibers. The invention provides a complete absorption curve for a material using a crystal fiber which can be more easily produced than the types of samples required for other methods of obtaining substantially the same absorption curve for identical materials.

Byvik, Charles E.↗

NASA NTRS1989

Middle Atmosphere Program. Handbook for MAP, volume 29. Part 1: Extended Abstracts, International Symposium on Solar Activity Forcing of the Middle Atmosphere. Part 2: MASH Workshop

The proceedings of the symposium is presented. Eight different sessions were presented: (1) Papers generally related to the subject; (2) Papers on the influence of the Quasi Biennial Oscillation; (3) Papers on the influence of the solar electromagnetic radiation variability; (4) Papers on the solar wind and high energy particle influence; (5) Papers on atmospheric circulation; (6) Papers on atmospheric electricity; (7) Papers on lower ionospheric variability; and (8) Solar posters, which are not included in this compilation.

Lastovicka, Jan↗

NASA NTRS1989

The orbital inclination of A0620 - 00 measured polarimetrically

The mass of the degenerate primary in A0620 - 00 is inferred from its spectroscopic mass function to be not less than 3.2 solar masses, making it an excellent candidate for a black hole. The exact value of the mass depends on the orbital inclination. The inclination of a binary system can be determined from the shape of its Stokes parameter light curves if the linear polarization of the system varies as a function of orbital phase. A0620 - 00 over one 8-hour binary period was observed with the 4.5-m equivalent MMT. Its polarization in the visible is variable with orbital phase. The standard theory of Brown et al. (1978) was used to derive an orbital inclination of i = 57 deg (+20 deg, -50 deg), where the error is the 90-percent confidence interval. An inclination of i = 57 deg corresponds to a mass of the compact primary of 6.6 solar masses, but the large uncertainty in the measured value of the inclination allows the derived mass of A0620 - 00 to be as low as 3.8 solar masses. If this is taken to be the maximum mass of any degenerate configuration consistent with general relativity except a black hole, then the mass of A0620 - 00 is still not well enough determined to conclude that it must be a black hole.

Dolan, Joseph F.↗

NASA NTRS1990

Test of the gravitational redshift effect at Saturn

The results of a test of the gravitational redshift effect at Saturn are reported. Measurements of the redshift were obtained with the Voyager 1 spacecraft during its encounter with Saturn in 1980. Because the spacecraft was equipped with an ultrastable crystal oscillator (USO), it is possible to test the redshift effect at an interesting level of accuracy. Assuming that radiation in the Saturn magnetosphere has had a negligible effect on the USO, the prediction of general relativity to an accuracy of 1 percent is verified. This limit could be of interest for constraining possible alternative theories of gravity.

Krisher, Timothy P.↗

NASA NTRS1989

High precision lunar tracking for laser ranging

Laser ranging to lunar surface retroreflectors has provided a valuable source of data for the investigation of the lunar orbit, the earth's orientation in space, general relativity, and many other aspects of solar system dynamics. Due to the moon's relatively large distance, and the requirement to keep the beam from the relatively low-power laser very narrow, acquiring this data type requires very accurate telescope pointing and tracking capabilities. The nominal requirement is to keep the telescope on target within approximately 1 arcsec of its predicted location for at least several minutes. An expansion of this requirement and the methods used to accomplish this high precision pointing are presented. Difficulties encountered and a few future goals of automating the McDonald station are also discussed.

Ricklefs, Randall L.↗

NASA NTRS1990

Tracking Gravity Probe B gyroscope polhode motion

The superconducting Gravity Probe B spacecraft is being developed to measure two untested predictions of Einstein's theory of general relativity by using orbiting gyroscopes; it possesses an intrinsic magnetic field which rotates with the rotor and is fixed with respect to the rotor body frame. In this paper, the path of the rotor spin axes is tracked using this trapped magnetic flux as a reference. Both the rotor motion and the magnetic field shape are estimated simultaneously, employing the higher order components of the magnetic field shape.

Keiser, George M.↗

NASA NTRS1990

Gradiometry coexperiments to the gravity probe B and step missions

The Gravity Probe-B (GP-B) spacecraft, designed to test predictions of general relativity, will fly in the mid 1990s. It will carry four electrostatically suspended gyroscopes in a cryogenic environment and will have a drag-free control system to minimize disturbances on the gyroscopes. The Stanford Test of Equivalence Principle (STEP) spacecraft, to fly later, will carry a set of test masses under very similar conditions. The possibility of using differential measurements of the GP-B gyroscopes suspension forces and the STEP tests mass displacement readout to form single-axis gravity gradiometers is explored. It is shown that the noise in the suspension systems is sufficiently small in the relevant frequency range, and that enough information is collected to compensate for the spacecrafts' attitude motion. Finally, using Breakwell's flat-earth approximation, these experiments are compared to other geodesy experiments and predict the contribution they can make to the knowledge of the Earth's geopotential.

Tapley, M.↗

NASA NTRS1990

Clevis joint for deployable space structures

This invention relates generally to pin clevis joints, and more particularly, to zero play pin clevis joints for connecting structural members of a deployable space structure. A joint includes a pin, a tang, and a shackle. The pin is tapered at the same angle as the bores extending through the projections of the shackle and the tang. A spring washer biases the tang onto the tapered sidewall of the pin. The invention solves the free play problem associated with deployable space structures by using a tapered pin which is held in tapered holes by the spring washers.

Rhodes, Marvin D.↗

NASA NTRS1990

Microwave and optical lunar transponders

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.

Bender, P. L.↗

NASA NTRS1992

Geodetic Precession Vs. Frame Dragging

Report discusses precession of freely falling or orbiting gyroscope with respect to geodetic precession and frame-dragged precession, predicted by metric theories of gravitation. Geodetic precession caused by motion of gyroscope in gravitational field of massive body; frame-dragged precession caused by gravitomagnetic interaction, which is magnetic-like effect caused by motion of massive body. Both effects small. Relevant to investigations in orbital mechanics, navigation, and general relativity.

Krisher, Timothy P.↗

NASA NTRS1990

Model compilation: An approach to automated model derivation

An approach is introduced to automated model derivation for knowledge based systems. The approach, model compilation, involves procedurally generating the set of domain models used by a knowledge based system. With an implemented example, how this approach can be used to derive models of different precision and abstraction is illustrated, and models are tailored to different tasks, from a given set of base domain models. In particular, two implemented model compilers are described, each of which takes as input a base model that describes the structure and behavior of a simple electromechanical device, the Reaction Wheel Assembly of NASA's Hubble Space Telescope. The compilers transform this relatively general base model into simple task specific models for troubleshooting and redesign, respectively, by applying a sequence of model transformations. Each transformation in this sequence produces an increasingly more specialized model. The compilation approach lessens the burden of updating and maintaining consistency among models by enabling their automatic regeneration.

Keller, Richard M.↗

NASA NTRS1991

A measurement of planetary relativistic deflection

The technique of differential VLBI, over two DSN California-Australia baselines, is used to measure the angular deflection of the ray path of P0201 + 113 when it passed within 200 arcsec of Jupiter on March 21, 1988. Its angular position was measured 10 times over 4 hr on that date, with a similar measurement set on April 2, 1988, to detect the differential angular deflection of the ray path. According to general relativity, the expected gravitational bend of the ray path averaged over the March experiment duration was approximately 300 microarcsec, projected onto the two California-Australia baselines over which it was measured. Measurement accuracies of the order of 160 microarcsec were obtained for each of the ten differential measurements. The chi(2) per degree of freedom of the data for the noise and tropospheric fluctuations fully accounted for the scatter in the measured angular deflections. The chi(2) per degree of freedom for the hypothesis of no gravitational deflection by Jupiter was 4.1, which rejects the no-deflection hypothesis with greater than 99.999-percent confidence.

Treuhaft, R. N.↗

NASA NTRS1992

Equilibrium stellar systems with spindle singularities

Equilibrium sequences of axisymmetric Newtonian clusters that tend toward singular states are constructed. The distribution functions are chosen to be of the form f = f(E, Jz). The numerical method then determines the density and gravitational potential self-consistently to satisfy Poisson's equation. For the prolate models, spindle singularities arise from the depletion of angular momentum near the symmetry axis. While the resulting density enhancement is confined to the region near the axis, the influence of the spindle extends much further out through its tidal gravitational field. Centrally condensed prolate clusters may contain strong-field regions even though the spindle mass is small and the mean cluster eccentricity is not extreme. While the calculations performed here are entirely Newtonian, the issue of singularities is an important topic in general relativity. Equilibrium solutions for relativistic star clusters can provide a testing ground for exploring this issue. The methods used in this paper for building nonspherical clusters can be extended to relativistic systems.

Shapiro, Stuart L.↗

NASA NTRS1993

Voyager 2 Test Of The Radar Time-Delay Effect

Report presents analysis of radio range measurements generated during superior solar conjunction of Voyager 2 spacecraft in December 1985. One in continuing series of studies directed toward verifying prediction, according to theory of general relativity, that electromagnetic signal propagating near Sun is delayed by solar gravitational field.

Krisher, Timothy P.↗

NASA NTRS1993

Dynamic pattern matcher using incomplete data

This invention relates generally to pattern matching systems, and more particularly to a method for dynamically adapting the system to enhance the effectiveness of a pattern match. Apparatus and methods for calculating the similarity between patterns are known. There is considerable interest, however, in the storage and retrieval of data, particularly, when the search is called or initiated by incomplete information. For many search algorithms, a query initiating a data search requires exact information, and the data file is searched for an exact match. Inability to find an exact match thus results in a failure of the system or method.

Johnson, Gordon G.↗

NASA NTRS1992

Determining the nuclear equation of state from neutron-star masses and radii

A method is developed for determining the nuclear equation of state directly from a knowledge of the masses and radii of neutron stars. This analysis assumes only that equilibrium neutron-star matter has the stress-energy tensor of an isotropic fluid with a barotropic equation of state, and that general relativity describes a neutron star's internal gravitational field. We present numerical examples which illustrate how well this method will determine the equation of state when the appropriate observational data become available.

Lindblom, Lee↗

NASA NTRS1992

Astrophysical bags - A new paradigm for active galactic nuclei?

Active galaxies are believed to consist of a compact nucleus, the standard model for which is a massive black hole or a cluster of black holes. A different paradigm is considered here, deriving from quark confinement theory in QCD. It is an 'astrophysical bag', modelled after the 'hadron bags' of particle physics which have already been studied in astrophysics as quark stars. Another interpretation of the cosmological constant in general relativity, and possibly a new quasar redshift formula, are introduced. As a highly-energetic object, this model may resolve the baryonic matter problem for fuelling AGN accretion processes which black hole paradigms cannot account for. Here, baryons, cosmic rays, and neutrinos are free.

Wilson, Thomas L.↗

NASA NTRS1993

The Galileo solar redshift experiment

From the October 1989 launch to the first December 1990 earth gravity assist, we regularly obtained frequency measurements of the spacecraft clock - an ultrastable crystal oscillator (USO) supplied by Frequency Electronics, Inc. The solar gravitational redshift in frequency was readily detectable, and because of the unique variations in heliocentric distance we could separate the general relativistic effects from the USO's intrinsic frequency variations. We have verified the total frequency shift predicted by general relativity to 0.5 percent accuracy, and the solar gravitational redshift to 1 percent accuracy.

Krisher, Timothy P.↗