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NASA NTRS1983

A search for Saturn electrostatic discharges in the Voyager plasma wave data

A search of Voyager spacecraft plasma wave data for evidence of Saturn electrostatic discharges, whose detection was suggested to be likely on the basis of radio astronomy observations, has yielded no evidence of this phenomenon. The statistical significance of this null result is analyzed, and its ramifications are commented upon. The explanations entertained for the lack of plasma wave observations of electrostatic discharges include the possibility that many events are of much shorter duration than previously reported, or that there may be a nonlinear distortion in the radio astronomy receiver employed which may have artificially broadened the spectrum of the discharges.

Kurth, W. S.↗

NASA NTRS1983

Asymptotic unbounded root loci - Formulas and computation

A new geometric way of computing the asymptotic behavior of unbounded root loci of a strictly proper linear time-invariant control system as loop gain goes to infinity is presented. Properties of certain restricted linear maps and nested restrictions of linear maps are developed, and formulas are obtained for the leading coefficient of the asymptotic values of the unbounded multivariable root loci are obtained in terms of eigenvalues of those maps. Published results and a certain simple null structure assumption are used to relate these asymptotic values to the structure at infinity of the Smith-McMillan form of the open loop transfer function. Explicit matrix formulas for the more abstract derived formulas are given and additional geometric insights are developed with orthogonal projections and singular value decomposition. Formulas for the pivots of the unbounded root loci are calculated and shown to have the same form as the coefficients of the unbounded asymptotic root loci.

Sastry, S. S.↗

NASA NTRS1983

A search for the Sunyaev-Zel'dovich effect at millimeter wavelengths

It is believed that X-ray emission from clusters of galaxies represents thermal bremsstrahlung from a hot plasma. According to Sunyaev and Zel'dovich (1972), the plasma column density and temperature derived from this model imply a measurable distortion of the cosmic background radiation (CBR) in the cluster direction. This distortion results from the Compton scattering of the CBR photons by the electrons in the plasma, resulting in an average increase of each photon. This process, known as the Sunyaev-Zel'dovich effect, is photon conserving and 'shifts' the CBR spectrum to higher frequencies. The result is a decrease of flux at frequencies below 7.5 per cm (the Rayleigh-Jeans region), and an increase above. The investigation is concerned with measurements of the Sunyaev-Zel'dovich effect at frequencies in the range from 3 to 10 per cm. Attention is given to the employed observing and analysis technique, and an initial null result for the cluster Abell 1795.

Meyer, S. S.↗

NASA NTRS1983

Beam forming networks for mm-wave satellite communications

Technology features of a beam forming network (BFN) employing ferrite devices to provide multiple beam antenna pattern control for satellites used in telecommunications are described. The BFN produces the phase and amplitude distribution for each horn in an antenna array, with the number of horns in the array being equal to the number of outputs in the BFN. One configuration involves microwave switches and permits illumination of a single feed horn at a time using ferrite latching circulators that function by reversing the circulation direction. A more flexible version, yielding a variable amplitude distribution across the feed horn array to accommodate changing traffic patterns or serving a TDMA system, includes the capability of forming nulls in the system with a variable phase shifter in the input ports. The antenna scan angles in phased arrays can be limited to 8 deg from center. Acceptable insertion losses have been demonstrated in BFN with hundreds of ports and switching rates as high as 10 kHz.

Sharon, T. E.↗

NASA NTRS1985

Zero-Net-Charge Air Ionizer

Instrument monitors air supplied by air ionizer and regulates ionizer to ensure net charge neutral. High-impedance electrometer and nulling control amplifier regulate output of air ionizer. Primarily intended to furnish ionized air having no net charge, instrument adaptable to generating air with positive or negative net charge is so desired. Useful where integrated circuit chips are manufactured, inspected, tested or assembled.

Woods, W. R., Jr.↗

NASA NTRS1983

LANDSAT 4 investigation of thematic mapper and multispectral scanner applications

Six different band combinations of TM data were selected for evaluation by four experienced photointerpreters who were asked to rank the band combinations according to the ease with which the category of image feature designated for each set of combinations could be distinguished. There were four sets of combinations selected for each category of image feature. Scenes of Oklahoma City, Oklahoma and of the Sacramento Valley, California area were enlarged to 1:250,000 and 2 cm circular chips were cut from each print. A nonparametric rank order test was carried out on the data to determine if the interpreters found no difference among the band combinations in ranking for the designated categories. Kendall's coefficient of concordance (W) was calculated and the significance of the W value was determined by a chi-square test. A table summarizes the results of the evaluation and shows the rank order of band combinations indicated as valid by rejection of the null hypothesis.

Lauer, D. T.↗

NASA NTRS1984

Growth and differentiation of mammalian embryonic tissues exposed to hypergravity in vivo and in vitro

In about 10 years or so, men and women from Earth will be long-term inhabitants of a space station aboard which plants and animals will be growing and developing in gravities other than that of Earth. The effect of gravitational changes on development was examined. It is indicated that differentiation is speeded up under excess G and slowed in low or null G. The effects of exposure to excess gravity on fusion of the embryonic mouse secondary palate were studied. During fusion, the palatal shelves first adhere by means of glycoproteins appearing along the medial epithelial edge (MEE). The contacting epithelia then reorganize and undergo programmed cell death, allowing the underlying mesenchymes to come in contact. The process of cell death occurs in vitro at about the same rate that it occurs in vivo.

Duke, P. J.↗

NASA NTRS1984

Decoupled control analysis of a large flexible space antenna with linear quadratic regulator comparisons

A decoupled-control analysis was performed for a large flexible space antenna. Control involved commanding changes in the rigid-body modes or nulling disturbances in the flexible modes. The study provides parametric-type data which could be useful in the final design of a large space antenna control system. Results are presented to illustrate the effect on control requirements of (1) the number of modes controlled; (2) the number, type, and location of control actuators; and (3) variations in the closed-loop dynamics of the control system. Comparisons are given between the decoupled-control results and those obtained by using a linear quadratic regulator approach. Time history responses are presented to illustrate the effects of the control procedures.

Young, J. W.↗

NASA NTRS1983

Design considerations for high-power VHF radar transceivers: The Poker Flat MST radar phase control system

Sixty-four separate 50-kW peak-power transmitters are distributed throughout the 200 x 200 meter Poker Flat MST radar antenna array. The relative phase of each transmitter is automatically controlled by a 64-channel unit located in the main building at the edge of the antenna. The phase control unit is described. In operation the RF pulse from a transmitter coupler is power divided and compared with the phase reference in a mixer. The mixer output is low-pass filtered and sampled near the center of the resulting video pulse by an amplifying sample-and-hold integrated circuit. Phase control is effected by maintaining the mixer output pulse near zero volts by amplifying the sample-and-hold output which then drives the voltage-controlled phase shifter in the direction to null the mixer output. The voltage-controlled shifter achieves over 360 deg phase shift in the range from 0.7 to 24 volts. When the voltage into the shifter tracks to either voltage limit the wrap-around control resets the voltage so that the shifter is always operating within its control range.

Ecklund, W. L.↗

NASA NTRS1984

Thermal bifurcation in the upper solar photosphere inferred from heterodyne spectroscopy of OH rotational lines

Low noise high spectral resolution observations of two pure rotation transitions of OH from the solar photosphere were obtained. The observations were obtained using the technique of optically null-balanced infrared heterodyne spectroscopy, and consist of center-to-limb line profiles of a v=1 and a v=0 transition near 12 microns. These lines should be formed in local thermodynamic equilibrium (LTE), and are diagnostics of the thermal structure of the upper photosphere. The v=0 R22 (24.5)e line strengthens at the solar limb, in contradiction to the predictions of current one dimensional photospheric models. Data for this line support a two dimensional model in which horizontal thermal fluctuations of order + or - 800K occur in the region Tau (sub 5000) approximately .001 to .01. This thermal bifurcation may be maintained by the presence of magnetic flux tubes, and may be related to the solar limb extensions observed in the 30 to 200 micron region.

Deming, D.↗

NASA NTRS1984

A comparison between GO/aperture-field and physical-optics methods for offset reflectors

Both geometrical optics (GO)/aperture-field and physical-optics (PO) methods are used extensively in the diffraction analysis of offset parabolic and dual reflectors. An analytical/numerical comparative study is performed to demonstrate the limitations of the GO/aperture-field method for accurately predicting the sidelobe and null positions and levels. In particular, it is shown that for offset parabolic reflectors and for feeds located at the focal point, the predicted far-field patterns (amplitude) by the GO/aperture-field method will always be symmetric even in the offset plane. This, of course, is inaccurate for the general case and it is shown that the physical-optics method can result in asymmetric patterns for cases in which the feed is located at the focal point. Representative numerical data are presented and a comparison is made with available measured data.

Rahmat-Samii, Y.↗

NASA NTRS1984

Pioneer 10 search for gravitational waves - No evidence for coherent radiation from Geminga

Attempts to identify a periodic gravitational wave signal from the binary Geminga in the reduced Doppler data from the Pioneer 10 spacecraft are reported. The study was performed to examine the possibility that the observed 160 min solar oscillation is driven by a gravitational wave from the binary, which has a period exactly one cycle different from the solar oscillation. Three 12 hr passes of Doppler data from Pioneer 10, now beyond the orbit of Neptune, were subjected to FFT analysis to detect a spectral gravitational wave signature. None was found. Least squares analysis of all low noise data from 1981 to characterize the amplitude and phase of a signal from Geminga also produced a null result. Finally, an upper bound was calculated for the polarization component of the potentially observable gravitational strain.

Anderson, J. D.↗

NASA NTRS1984

Does Mckuer's Law Hold for Heart Rate Control via Biofeedback Display?

Some persons can control their pulse rate with the aid of a biofeedback display. If the biofeedback display is modified to show the error between a command pulse-rate and the measured rate, a compensatory (error correcting) heart rate tracking control loop can be created. The dynamic response characteristics of this control loop when subjected to step and quasi-random disturbances were measured. The control loop includes a beat-to-beat cardiotachmeter differenced with a forcing function from a quasi-random input generator; the resulting error pulse-rate is displayed as feedback. The subject acts to null the displayed pulse-rate error, thereby closing a compensatory control loop. McRuer's Law should hold for this case. A few subjects already skilled in voluntary pulse-rate control were tested for heart-rate control response. Control-law properties are derived, such as: crossover frequency, stability margins, and closed-loop bandwidth. These are evaluated for a range of forcing functions and for step as well as random disturbances.

Courter, B. J.↗

NASA NTRS1984

Polarization of radio molecular lines and mapping of magnetic field direction

Two level calculations by others for the linear polarizations expected for molecular emission lines from interstellar clouds are extended by considering a number of coupled rotational states of a diatomic molecule. Higher transitions commonly have strengths comparable with that of the J=1-0 transition so that depolarization due to coupling between the various J states might be expected to reduce the predicted linear polarization. The significance of the null observational results obtained recently by Wannier, Scoville, and Barvainis is assessed. The inclusion of additional states tends to decrease the maximum polarizations, though the calculated polarization is increased under conditions for which superthermal excitation occurs.

Deguchi, S.↗

NASA NTRS1984

Moderate lift-to-drag aeroassist

Significant performance benefits are realized via aerodynamic braking and/or aerodynamic maneuvering on return from higher altitude orbits to low Earth orbit. This approach substantially reduces the mission propellant requirements by using the aerodynamic drag, D, to brake the vehicle to near circular velocity and the aerodynamic lift, L, to null out accumulated errors as well as change the orbital inclination to that required for rendezvous with the Space Shuttle Orbiter. Broad concept evaluations were performed and the technology requirements and sensitivities for aeroassisted OTV's over a range of vehicle hypersonic L/D from 0.75 to 1.5 were systematically identified and assessed. The aeroassisted OTV is capable of evolving from an initial delivery only system to one eventually capable of supporting manned roundtrip missions to geosynchronous orbit. Concept screening was conducted on numerous configurations spanning the L/D = 0.75 to 1.5 range, and several with attractive features were identified. Initial payload capability was evaluated for a baseline of delivery to GEO, six hour polar, and Molniya (12 hours x 63.4 deg) orbits with return and recovery of the aeroassist orbit transfer vehicle (AOTV) at LEO. Evolutionary payload requirements that were assessed include a GEO servicing mission (6K up and 2K return) and a manned GEO mission (14K roundtrip).

Florence, D. E.↗

NASA NTRS1985

Simulation studies of time-control procedures for the advanced air traffic control system

The problem of mixing aircraft equipped with time-controlled guidance systems and unequipped aircraft in the terminal area has been investigated via a real-time air traffic control simulation. These four-dimensional (4D) guidance systems can predict and control the touchdown time of an aircraft to an accuracy of a few seconds throughout the descent. The objectives of this investigation were to (1) develop scheduling algorithms and operational procedures for various traffic mixes that ranged from 25% to 75% 4D-equipped aircraft; (2) examine the effect of time errors at 120 n. mi. from touchdown on touchdown time scheduling of the various mix conditions; and (3) develop efficient algorithms and procedures to null the initial time errors prior to reaching the final control sector, 30 n. mi. from touchdown. Results indicate substantial reduction in controller workload and an increase in orderliness when more than 25% of the aircraft are equipped with 4D guidance systems; initial random errors of up to + or - 2 min can be handled via a single speed advisory issued in the arrival control sector, thus avoiding disruption of the time schedule.

Tobias, L.↗

NASA NTRS1985

Nuclear Science Symposium, 31st and Symposium on Nuclear Power Systems, 16th, Orlando, FL, October 31-November 2, 1984, Proceedings

Topics related to physics instrumentation are discussed, taking into account cryostat and electronic development associated with multidetector spectrometer systems, the influence of materials and counting-rate effects on He-3 neutron spectrometry, a data acquisition system for time-resolved muscle experiments, and a sensitive null detector for precise measurements of integral linearity. Other subjects explored are concerned with space instrumentation, computer applications, detectors, instrumentation for high energy physics, instrumentation for nuclear medicine, environmental monitoring and health physics instrumentation, nuclear safeguards and reactor instrumentation, and a 1984 symposium on nuclear power systems. Attention is given to the application of multiprocessors to scientific problems, a large-scale computer facility for computational aerodynamics, a single-board 32-bit computer for the Fastbus, the integration of detector arrays and readout electronics on a single chip, and three-dimensional Monte Carlo simulation of the electron avalanche in a proportional counter.

Biggerstaff, J. A.↗

NASA NTRS1985

Collisional tearing in a field-reversed sheet pinch assuming nonparallel propagation

Linear tearing in a collisional reversed-field sheet pinch is examined assuming that the wave vector k is not parallel to the equilibrium magnetic field. Equilibrium and magnetic geometry are defined, and a set of perturbed moment equations is derived assuming quasi-parallel propagation. It is shown that the usual expression for collisional growth is recovered, assuming that k sub y = 0. It is shown that the y component of momentum balance requires the generation of nonzero dJ sub x well away from the null, and an interial coupling when z not equal to 0. The effects of k sub y not equal to 0 on the growth rate are discussed.

Quest, K. B.↗