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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 541 records · Page 30
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NASA NTRS1972

Precision star-tracking telescope

The design, construction, and preliminary testing of a new high accuracy star tracking telescope for the laboratory model of the Stanford gyro relativity experiment are described. The function of the telescope in the final flight experiment is to define (by reference to a suitable star) a direction in space for comparison with the relativistic precession of a group of gyroscopes. The design of the telescope has been strongly affected by designs for other portions of the overall experiments, for example the gyroscopes, the attitude control system of the satellite, and the instrumentation system used in processing relativity data. Main goals for the star tracker are: (1) independent readout of angular position in two planes; (2) absolute null stability over a one year period of mechanical parts; (3) readout linear to 0.001 arc-seconds over + or - 0.05 arc-second; (4) noise performance leading to a resolution of 0.05 arc-second in 0.1 second observation time of the chosen reference star; and (5) provision for automatic gain control capable of matching the gains of the gyroscopes and telescope readouts to 1% or better.

Fairbank, W. M.↗
NASA NTRS1971

A method of computing periods of cyclic phenomena.

Use of an analysis of Expected Mean Square Deviations to search for periodicities in an observational data sample is described. The statistic for testing the null hypothesis of nonperiodicity is derived from a partitioning of the total sum of squared deviations from the mean. Unlike most existing methods, the present one does not require equally spaced observations. No assumptions are made concerning the statistical nature of spacing intervals. The method is illustrated by numerical examples.

Jurkevich, I.↗
NASA NTRS1972

NGC 1068, 3C 273, and Scorpius X-1 - Circular polarization disputed.

Discussion of data for the Seyfert galaxy NGC 1068, the quasar 3C 273, and the X-ray source Sco X-1, for all of which it has been claimed or strongly suggested that they have large circular polarization of the order of 1% (Severny et al., 1971). In contrast the present authors obtained unambiguously null results with upper limits about 0.05% for NGC 1068 and 3C 273. For Sco X-1 no statistically significant polarization was found on three nights, and only some marginal evidence for a fluctuation or transient polarization on one night.

Kemp, J. C.↗
NASA NTRS1972

Equations of motion in the linear approximation.

Attempt to develop a gauge-invariant theory of the motion of singularities in an n-dimensional Riemannian space. A gauge-invariant theory is developed for a nongeodetic particle represented by a time-like world line in the linearized field theory. The solution of the basic algebraic and differential equations is to be constructed from the source line, the future null cones emanating from it, a scale factor, and nothing else, and the leading term of the solution is the Schwarzschild field. A class of possible solutions is examined, and it is shown that this class contains just one acceptable member - namely, a particle in constant acceleration.

Robinson, I.↗
NASA NTRS1973

A technique to eliminate false lock in PCM demodulation

One loop provides error signal which adjusts voltage controlled oscillator. Second loop multiplies input signal with generated in-phase signal. Both signals are integrated over bit period. First loop detects null which indicates lockup, and second loop emphasizes impact signal information.

Kobayashi, H. S.↗
NASA NTRS1974

Means for mapping radiated fields and for measuring differential movement of antenna elements

Null seeking system uses two transponders located at selected points on dish to detect phase-front of received signal. One signal line has continuously variable phase shifter driven by reversible stepmotor. Each of two transponders on dish is a dipole with mixer crystal between elements. Crystal is driven, in turn, by 181.6MHz signal carried by miniature coaxial cable.

Lundy, C. C.↗
NASA NTRS1972

Advanced figure sensor operations and maintenance manual

This manual contains procedures for installing, operating, and maintaining the optical figure sensor and its associated electronic controls. The optical figure sensor, a system of integrated components, comprises: (1) a phase measuring modified interferometer employing a single frequency 6328 A laser, and a Vidissector; (2) a two-axis automatic thermal compensation control mount; (3) a five degree of freedom manual adjustment stand; and (4) a control console. This instrument provides real time output data of optical figure errors for spherical mirrors, and is also capable of measuring aspherical mirrors if a null corrector is added.

Robertson, H. J.↗
NASA NTRS1973

An experimental study of slot injection into a supersonic stream

An experimental investigation of two-dimensional tangential-slot injection into a turbulent boundary layer at a freestream Mach number of 2.4 has been conducted. Nearly adiabatic surface temperatures were maintained during all tests. Static and pitot pressure profiles at four stations downstream of the slot were obtained. Skin friction was measured at the last three stations with a self-nulling balance. Schlieren photographs of the flow field were also obtained. Most of the data were obtained with slot Mach numbers of 0.31 and 0.66 corresponding to slot pressure less than and equal to stream static pressure, respectively. For the latter matched-pressure case, tangential slot injection reduced the surface shear at the three measuring stations by about 60 to 20 percent for increasing downstream distances from the slot of 12 to 28 slot heights. However, for the other case where slot pressure was less than stream static pressure, the effect of injection was to increase the shear by about 90 percent at the last downstream station of 28 slot heights. This increase in shear is attributed to the rapid acceleration of the low speed injectant stream by the high speed main stream and the increasing pressure through the recompression zone which is absent for the matched pressure case.

Kenworthy, M.↗
NASA NTRS1972

Doppler frequency in interplanetary radar and general relativity

The change of frequency of an interplanetary radar signal sent from the earth to another planet or to a space probe is worked out according to general relativity. The Schwarzschild spacetime is employed and its null geodesics control the motion of the signals. Exact Doppler frequency formulas are derived for one-way and two-way radar in terms of an arbitrary Schwarzschild radial coordinate. A reduction to the special relativity case is used to interpret the formulas in terms of the relative radial velocity of emitter and target. The general relativity corrections are worked out approximately for each of three possible Schwarzschild radial coordinates, and a numerical example is given. The amount of the correction is different according as one or the other of the Schwarzschild coordinates is identified with the radius vector deduced from classical celestial mechanics. The identification problem is discussed.

Mcvittie, G. C.↗
NASA NTRS1973

Input frequency requirements for identification through Liapunov methods

A theorem is derived which specifies a sufficient number of input frequencies to guarantee identification of an unknown noise free linear plant. Since all of the referenced work relates to sufficient conditions for nulling of the parameter error vector, it is to be expected that various conditions on the system to be identified will have been imposed. It was found that some of these conditions appear to be necessary while others do not. The main contribution is to provide a theorem which considers the effect of unknown parameters in the state equation upon the frequency requirements.

Kim, C. H.↗
NASA NTRS1972

Circular polarimetry of fifteen interesting objects.

The results of a search are presented for circular polarization of visible light in 15 objects, including two eclipsing binaries, six magnetic Ap stars, three planetary nebulae, Hubble's Nebula, M87, Sirius, and the Orion A region. On the whole, the results were null, down to typical upper limits for q of 0.01 per cent. A complete description of the used photoelastic polarimeter is given, with special attention to the incidental linear-circular conversion.

Kemp, J. C.↗
NASA NTRS1972

Electrostatic waves in the magnetosphere.

Electric dipole antennas on magnetospheric spacecraft measure E field components of many kinds of electromagnetic waves. In addition, lower hybrid resonance emissions are frequently observed well above the ionosphere. The Ogo 5 plasma wave experiment has also detected new forms of electrostatic emissions that appear to interact very strongly with the local plasma particles. Greatly enhanced wave amplitudes have been found during the expansion phases of substorms, and analysis indicates that these emissions produce strong pitch angle diffusion. Intense broadband electrostatic turbulence is also detected at current layers containing steep magnetic field gradients. This current-driven instability is operative at the bow shock and also at field null regions just within the magnetosheath, and at the magnetopause near the dayside polar cusp. The plasma turbulence appears to involve ion acoustic waves, and the wave particle scattering provides an important collisionless dissipation mechanism for field merging.

Scarf, F. L.↗
NASA NTRS1973

Prediction and measurement of the proportionality constant in statistical energy analysis of structures.

The fundamental equation of statistical energy analysis (SEA) states that the average power flow between two coupled vibrating systems is proportional to the difference in their average modal energies. Under certain circumstances it is possible to estimate the proportionality constant by modifying system boundary conditions on the separated systems and calculating or measuring changes in the systems. Newland's estimate, based upon blocking part of the system, is reexamined, and limitations are discussed. Three alternative methods which circumvent blocking are presented. These were applied to predict power flow in experiments on coupled beams and on coupled plates wherein power flow through the coupling was measured directly as a product of force times velocity. The measurements support the fundamental SEA relation, including the null power point where the average modal energies are equal.

Lotz, R.↗
NASA NTRS1973

Note on the 1972 Giacobinid meteor shower.

It is shown that the 1972 Giacobinid meteor shower was extremely weak with a peak activity of two to three visual meteors per hour. Only two meteor spectra were obtained from the 17 slitless spectrograph systems operated by the Langley Research Center. The largely unexpected, essentially null results of the 1972 Giacobinid meteor shower observations are indicative of the present limited understanding and predictability of cosmic dust storms.

Harvey, G. A.↗
NASA NTRS1973

Space station capability for research in rotational hypogravity

Certain capabilities provided in preliminary designs of orbital space stations for research in rotational hypogravity are outlined. Also indicated are alternative configurations that are being considered. Principal addresses are members of an international community of physiologists whose work in earth oriented, as well as space oriented, physiology can be supported through observation under the background environment of null gravity. Their participation in originating and devising advanced experiments and in developing requirements is expected to enhance final design of the selected space station and to make the research program more meaningful.

Keller, G.↗
NASA NTRS1973

Spacetimes with Killing tensors

The characteristics of the Killing equation and the Killing tensor are discussed. A conformal Killing tensor is of interest inasmuch as it gives rise to a quadratic first integral for null geodesic orbits. The Einstein-Maxwell equations are considered together with the Bianchi identity and the conformal Killing tensor. Two examples for the application of the considered relations are presented, giving attention to the charged Kerr solution and the charged C-metric.

Hughston, L. P.↗
NASA NTRS1973

New two-metric theory of gravity with prior geometry

A Lagrangian-based metric theory of gravity is developed with three adjustable constants and two tensor fields, one of which is a nondynamic 'flat space metric' eta. With a suitable cosmological model and a particular choice of the constants, the 'post-Newtonian limit' of the theory agrees, in the current epoch, with that of general relativity theory (GRT); consequently the theory is consistent with current gravitation experiments. Because of the role of eta, the gravitational 'constant' G is time-dependent and gravitational waves travel null geodesics of eta rather than the physical metric g. Gravitational waves possess six degrees of freedom. The general exact static spherically-symmetric solution is a four-parameter family. Future experimental tests of the theory are discussed.

Lightman, A. P.↗
NASA NTRS1974

Multiple beam communicating satellites with remote beam steering and beam shaping

Multiple beam phased arrays are shown to enhance the performance of several anticipated geostationary communications satellite programs because of the greater efficiency and flexibility of the phased array. It is shown that the efficiency of arrays can be significantly greater than corresponding multiple feed dishes and that the problems of crossover loss and performance degradation with parts failures are thereby avoided. On an open loop basis, it is shown that a multiple beam array can provide higher EIRP over a coverage area. On a closed loop basis, it is shown that an adaptive array can provide nulling of unwanted signals while simultaneously providing gain in the direction of a desired signal.

Sielman, P. F.↗