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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 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

A computer program for the identification of helicopter impulsive noise sources

A computer program is presented for calculating the source location of implusive noise in helicopters. The program (INSL) is written in FORTRAN for the CDC 7600 computer. Inputs are the rotor operating conditions and the time intervals (T) between rotor 1/rev index and impulsive noises as measured by different microphones. The outputs are the possible noise source locations in terms of rotor radial and azimuthal coordinates. Typical computer time for a run of six microphone measurements is 1.5 sec, and the cost is about 12 cents for the CDC 7600.

Lee, A.↗
NASA NTRS1977

Shuttle program: Ground tracking data program document shuttle OFT launch/landing

The equations for processing ground tracking data during a space shuttle ascent or entry, or any nonfree flight phase of a shuttle mission are given. The resulting computer program processes data from up to three stations simultaneously: C-band station number 1; C-band station number 2; and an S-band station. The C-band data consists of range, azimuth, and elevation angle measurements. The S-band data consists of range, two angles, and integrated Doppler data in the form of cycle counts. A nineteen element state vector is used in Kalman filter to process the measurements. The acceleration components of the shuttle are taken to be independent exponentially-correlated random variables. Nine elements of the state vector are the measurement bias errors associated with range and two angles for each tracking station. The biases are all modeled as exponentially-correlated random variables with a typical time constant of 108 seconds. All time constants are taken to be the same for all nine state variables. This simplifies the logic in propagating the state error covariance matrix ahead in time.

Lear, W. M.↗
NASA NTRS1977

An aerodynamic investigation of two 1.83-meter-diameter fan systems designed to drive a subsonic wind tunnel

An experimental, aerodynamic investigation was made of two 1.83 m diameter fan systems which are being considered for the repowered drive section of the 40- by 80-foot wind tunnel at NASA Ames Research Center. One system was low speed, the other was high speed. The low speed fan was tested at various stagger angles from 32.9 deg to 62.9 deg. At a fan blade stagger angle of 40.8 deg and operating at a tip speed of 1155 m/sec, the low speed fan developed 207.3 m of head. The high speed fan had a design blade stagger angle of 56.2 deg and was tested at this stagger angle only. The high speed fan operating at 191.5 m/sec developed 207.3 m of head. Radial distributions of static pressure coefficients, total pressure coefficients, and angles of swirl are presented. Radial surveys were conducted at four azimuth locations in front of the fan, and repeated downstream of the fan. Data were taken for various flow control devices and for two inlet contraction lengths.

Page, V. R.↗
NASA NTRS1977

Charge-coupled device data processor for an airborne imaging radar system

Processing of raw analog echo data from synthetic aperture radar receiver into images on board an airborne radar platform is discussed. Processing is made feasible by utilizing charge-coupled devices (CCD). CCD circuits are utilized to perform input sampling, presumming, range correlation and azimuth correlation in the analog domain. These radar data processing functions are implemented for single-look or multiple-look imaging radar systems.

Arens, W. E.↗
NASA NTRS1977

Heliocentric distance dependence of the interplanetary magnetic field

Recent and ongoing planetary missions have provided extensive observations of the variations of the Interplanetary Magnetic Field (IMF) both in time and with heliocentric distance from the sun. Large time variations in both the IMF and its fluctuations were observed. These are produced predominantly by dynamical processes in the interplanetary medium associated with stream interactions. Magnetic field variations near the sun are propagated to greater heliocentric distances, also contributing to the observed variablity of the IMF. Temporal variations on a time-scale comparable to or less than the corotation period complicate attempts to deduce radial gradients of the field and its fluctuations from the various observations. However, recent measurements inward to 0.46 AU and outward to 5 AU suggest that the radial component of the field on average decreases approximately as r to the minus second power, while the azimuthal component decreases more rapidly than the r to the minum first power dependence predicted by simple theory. This, and other observations, are discussed.

Behannon, K. W.↗
NASA NTRS1976

MHD solution of interplanetary disturbances generated by simulated velocity perturbations

An MHD time-dependent numerical simulation, restricted to the solar equatorial plane, is used to demonstrate the interplanetary disturbances caused by several simplified coronal holes. Each 'hole' is assumed to have a configuration such that the higher solar wind velocity produced within their longitudinal extent is Gaussian over a 7-day period at the inner boundary (0.3 AU) of the numerical simulation. A second, twin coronal hole is assumed to rotate on the solar disk behind its predecessor. It is shown that the first coronal hole-produced interplanetary shock ensemble is overtaken by the second ensemble because of the higher velocity, lower density environment into which the latter propagates. A number of features predicted by MHD similarity theory are confirmed by the numerical simulation. These features include (1) strong azimuthal magnetic and plasma density compression, accompanied with average temperature depression, at the contact surface between forward and reverse shock ensembles, and (2) increasing spatial separation distance between forward and reverse shocks.

Dryer, M.↗
NASA NTRS1975

Meteorological Radar Facility for the Space Shuttle

A proposed meteorological radar facility for Space Shuttle missions is described as a device suitable for providing vertical profiles of the precipitation distribution in the atmosphere above land masses and over ocean, thus ensuring three-dimensional mapping of the hydrometeor-precipitation distribution in the atmosphere. Some performance characteristics essential to orbiting meteorological radar systems and typical parameters are discussed, including large swath width, narrow beamwidth, frequency agility, and antenna configuration and orientation. Also discussed are the capabilities of the device as a test bed sensor with multiple mode capability, being able to operate in real aperture/pulse radar, real aperture/pulse Doppler and synthetic azimuth processing modes.

Eckerman, J.↗
NASA NTRS1976

Accretion onto magnetized neutron stars - Normal mode analysis of the interchange instability at the magnetopause

Results are reported for a linearized hydromagnetic stability analysis of the magnetopause of an accreting neutron star. The magnetosphere is assumed to be slowly rotating, and the plasma just outside the magnetopause is assumed to be weakly magnetized. The plasma layer is assumed to be bounded above by a shock wave and to be thin compared with the radius of the magnetosphere. Under these circumstances, the growing modes are shown to be localized in the direction parallel to the zero-order magnetic field, but the structure of the modes is still similar to the flute mode. An expression for the growth rate at each magnetic latitude is obtained in terms of the magnitude of the gravitational acceleration normal to the surface, the azimuthal mode number, the radius of the magnetosphere, the height of the shock above the magnetopause, and the effective Atwood number which embodies the stabilizing effects of favorable curvature and magnetic tension. The effective Atwood number is calculated, and the stabilizing effects of viscosity and aligned flow parallel to the magnetopause are discussed.

Arons, J.↗
NASA NTRS1976

Observation of a north-south anisotropy of atmospheric radiation at balloon altitudes

Measurements have been made of an azimuthal asymmetry of atmospheric radiation at balloon altitudes and mid-latitudes. The measured asymmetry is 6% peak to peak in the north-south direction at energies above 500 keV. A lack of east-west asymmetry indicates that the arrival direction of the atmospheric radiation is highly decoupled from that of the primary radiation. Present models of secondary atmospheric radiation production and transport do not quantitatively agree with the observations.

Fishman, G. J.↗
NASA NTRS1977

Effects of random phase changes on the formation of synthetic aperture radar imagery

The effects of Gaussian random fluctuation and linear change of the echo phase on the response of the azimuth matched processor of a synthetic aperture radar (airborne or spaceborne for ocean-surface sensing) is analyzed numerically. It is found that the random fluctuation would not alter appreciably the processor response if its standard deviation is less than pi, while its normalized correlation time is larger than 1. If these two bounding conditions are not satisfied, then the sidelobe level becomes relatively large and overshadows the central peak. In the case of linear displacement it is found that the main effect is the spatial displacement of the point scatterer in the image plane.

Elachi, C.↗
NASA NTRS1977

Measurement of stray radiance in the High Altitude Observatory's Skylab coronagraph

The paper outlines two techniques used for determining the instrumental stray radiance from orbital results obtained with the Skylab white light coronagraph. The first technique employs images of the lunar disk made near the time of solar eclipse to compare the apparent contrasts of maria and highlands recorded by the coronograph with those of previous studies and then determine the magnitude of the stray radiance and its variation along a radius. The second method determines the azimuthal variation of the stray radiance by measuring the change in the net radiance of a point in the coronal images as the image is rotated.

Csoeke-Poeckh, A.↗
NASA NTRS1977

Measurements of the reaction e/+/e/-/ yielding gamma-gamma at center-of-mass energies in the range 6.2-7.4 GeV

The cross section for the pair-annihilation reaction e(+)e(-) yields gamma-gamma were measured at center-of-mass energies in the range 6.2-7.4 GeV and at production angles close to 90 deg. The experimental apparatus consisted of two identical spectrometers which were set to view the luminous region at SPEAR-II from opposite directions at an azimuthal angle of 45 deg. In each spectrometer there was a NaI(TI) crystal 20 radiation lengths thick and 30 in. in diameter to measure the gamma-ray energies. Annihilation events were detected by an electronic trigger which required only the observation in coincidence of more than 0.2 GeV in each NaI(TI) crystal within + or - 15 nsec of the crossing beams. The observed rates of pair-annihilation events were found to be in agreement with those expected from quantum electrodynamics (QED) at all the center-of-mass energies used.

Hilger, E.↗
NASA NTRS1977

Boundary-value problem for plasma centrifuge at arbitrary magnetic Reynolds numbers

We solve in closed form the boundary-value problem for the partial differential equations which describe the (azimuthal) rotation velocity and induced magnetic fields in a cylindrical plasma centrifuge with ring electrodes of different radii and an external, axial magnetic field. The electric field, current density, and velocity distributions are discussed in terms of the Hartmann number H and the magnetic Reynolds number R. For small Hall coefficients, the induced magnetic field does not affect the plasma rotation. As a result of the Lorentz forces, the plasma rotates with speeds as high as 100,000 cm/sec around its axis of symmetry at typical conditions, so that the lighter (heavier) ion and atom components are enriched at (off) the center of the discharge cylinder.

Wilhelm, H. E.↗
NASA NTRS1977

Spiral approach navigation concepts for VTOL aircraft using a microwave landing system

Spiral approaches adjacent to the active runways of CTOL airports have been proposed as a means of effectively interfacing CTOL and VTOL landing operations. Assuming an airport equipped with a Microwave Landing System (MLS), a VTOL aircraft following a spiral approach path might, depending on the specific trajectory, pass alternatively in and out of the linear coverage of the MLS and thereby suffer degraded navigation performance. The objective of this study was to employ essentially state-of-the-art aided inertial navigation concepts to explore the expected navigation performance operating in the environment just described. Results show that aided inertial concepts utilizing simple body-mounted inertia systems may be adequate for an instrument landing if the MLS azimuth and Distance Measuring Equipment (DME) signal coverages extend to within a few feet of the ground.

Mcgee, L. A.↗
NASA NTRS1977

Radial variation of lunar crater rim topography

The paper presents results of determinations of variations of rim topography as a function of range from the crater rim for a group of morphologically fresh craters. It is found that the rate at which exterior crater topography converges with the surrounding surface is highly variable among different radial directions at individual craters as well as between different craters, and that at several craters, oblique impact appears to have contributed to azimuthal elevation/range variations.

Settle, M.↗
NASA NTRS1977

Dilation of force-free magnetic flux tubes

A general study is presented of the mapping functions which relate the magnetic-field profiles across a force-free rope in segments subjected to various external pressures. The results reveal that if the external pressure falls below a certain critical level (dependent on the flux-current relation which defines the tube), the magnetic profile consists of an invariant core sheathed in a layer permeated by an azimuthal magnetic field.

Frankenthal, S.↗
NASA NTRS1976

Mariner 10 interplanetary magnetic field results

Interplanetary magnetic field data obtained by Mariner 10 between November 1973 and March 1974 are examined. Though large variations in the field due to the effects of high speed streams and stream-stream interactions were observed, on average the large scale interplanetary magnetic field radial component was found to have a distance dependence of r to the minus 2.0 plus or minus 0.3, while the azimuthal field component was found to vary as r to the minus 1.3 plus or minus 0.4, and a dependence of r to the minus 1.4 plus or minus 0.6 was found for the component normal to the solar equatorial plane. A close correspondence was found between the magnetic field stream signatures and persistent but evolving coronal hole regions on the sun, and a clear pattern of large southward fields in stream interaction regions and high levels of field fluctuations within the high-speed streams was detected.

Behannon, K. W.↗
NASA NTRS1977

Construction and interpretation of a digital inertia image

An image representing the thermal inertia in the vicinity of Pisgah Crater and Lavic Lake in Southern California has been generated from visible, near IR, and thermal images taken from aircraft. Construction of the thermal inertia image required radiometric calibration and geometric rectification of the acquired images as well as registration to a topographic map. The Kahle thermal model used in the construction of the thermal inertia image requires specification of albedo, topographic slope and slope azimuth, diurnal temperature range and local meteorological conditions. Albedo information was derived from the visible image; digital topographic information was computed from digitized stereo aerial photographs; and thermal ranges were calculated by subtracting the predawn from the afternoon thermal image data. Our computed values of thermal inertia were in close agreement with published values for similar surface materials. Thermal inertia provides complementary information to conventional images of reflected solar radiation for use in lithologic mapping.

Gillespie, A. R.↗