Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Deltas”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

A modified adaptive delta modulator

This paper presents the results of a study in data compression of adaptive delta modulated video signals. The Song mode ADM is first investigated at a sampling rate of 16 Mbits/s and shown not to produce enough redundancy to warrant entropy encoding. A modified adaptive delta modulator algorithm is presented that operates at a sampling rate of 16 Mbits/s and does produce sufficient redundancy to yield a 40-50 percent data compression by using a simple code on 4 bit data blocks. Other techniques such as field interpolation and direct substitution are shown to increase the possible data compression further without noticeable degradation in the two input images used in this investigation. The effects of channel errors in the transmission of packet video over a computer network are considered. A leaky integrator is used to reduce the effects of channel errors in the data bits. It is shown that the effects of channel errors can be reduced by field interpolating those packets that can be shown to contain errors.

Barba, J.↗
NASA NTRS1982

Delta mission planning in the Shuttle transition era

Delta mission planning is aimed at providing Shuttle transition era user support which is flexible, dependable, and reliable. The flexibility of support is being enhanced by the development of a new Delta vehicle model, the 3920, capable of providing backup compatible performance for Shuttle SSUS-D (solid spinning upper stage) users. Reliable interfaces, flexible scheduling policies, and new launch facilities will help satisfy increased user demand.

Grimes, D. W.↗
NASA NTRS1982

Measurement and visualization of skin friction on the leeside of delta wings in supersonic flow

The reported investigation was conducted with the aid of the NASA Ames High Reynolds Number Wind Tunnel. The flow conditions considered involved free stream Mach numbers of 2 and 3, and a Reynolds number of approximately 10,000,000 p. m. The employed model was a delta wing with an angle of 70 deg. A method reported by Tanner (1977) was used for the measurement of the skin friction. This method involves the use of a laser interferometer to determine the change in the thickness of an oil film. The procedure can also be employed for a visualization of skin friction in the form of interferograms. The investigation shows that skin friction measurements can provide a significant contribution to a physical understanding of the flow processes at the delta wing.

Szodruch, J.↗
NASA NTRS1982

The Galileo Delta-VEGA mission to Jupiter

Project Galileo is to perform a more comprehensive investigation of the Jupiter system than was possible with Voyager. The Galileo spacecraft consists of both a planetary Orbiter and an atmospheric entry Probe. In connection with budgetary considerations and schedule problems, plans concerning the implementation of the project were changed a number of times. For the first seven months of 1982, the project Galileo was baselined as a Delta-VEGA transfer to be launched in 1985 by the Space Shuttle using the U.S. Air Force two-stage IUS as the upper stage augmented by a spacecraft Injection Module. The new mission and systems aspects of this 1985 Galileo Delta-VEGA baseline are compared to the prior 1985 Centaur direct transfer baseline. The techniques developed to virtually restore all the mission science in spite of greatly reduced launch vehicle performance are discussed. In July 1982, the U.S. Government reinstated the Centaur development and stipulated that Galileo be launched by Shuttle/Centaur in 1986.

Oneil, W. J.↗
NASA NTRS1982

The Delta improved second stage - First flight results

On July 16, 1982 the successful launch of the Landsat-D spacecraft marked a significant step in the evolutionary growth of the Delta launch vehicle. This growth is related to the development of the Improved Second Stage (ISS). The second utilization of the ISS occurred August 26, 1982 with the successful launch of the Canadian Telesat-F communications satellite. Used in conjunction with the PAM third stage, this spacecraft was placed in a geosynchronous transfer orbit with extremely high accuracy. The various steps in the 22-year history of the Delta launch vehicle are briefly examined. In mid-1979 it became apparent that the expendable-to-Shuttle transition time would increase over that previously planned. In connection with this development, it was decided to design the ISS. Attention is given to design details, a system description, the development schedule, aspects of performance capability, first flight results, and future performance improvements.

Grimes, D. W.↗
NASA NTRS1982

Error estimation for delta VLBI angle and angle rate measurements over baselines between a ground station and a geosynchronous orbiter

Baselines between a ground station and a geosynchronous orbiter provide high resolution Delta VLBI data which is beyond the capability of ground-based interferometry. The effects of possible error sources on such Delta VLBI data for the determination of spacecraft angle and angle rate are investigated. For comparison, the effects on spacecraft-only VLBI are also studied.

Wu, S. C.↗
NASA NTRS1983

The application of near-nadir Delta-k radar techniques to geodetic altimetry and oceanographic remote sensing

This paper first examines the extension of two-frequency, or Delta-k near-nadir remote sensing techniques to off-nadir radar altimetry. A different approach to sea state sensing is investigated which appears to offer much higher accuracy. The second section examines the Delta-k method of sensing rough surface area correlation or ocean wavenumber spectrum. The technique shows promise of directly sensing this parameter, in contrast with synthetic-aperture radar methods which are based on complex wave interaction mechanisms and mathematical transformations requiring the acquisition of voluminous data.

Miller, L. S.↗
NASA NTRS1983

The Delta band dissociation of nitric oxide - A potential mechanism for coupling thermospheric variations to the mesosphere and stratosphere

Depletion of solar radiation at discrete wavelengths by nitric oxide has a significant impact on the dissociation rate of this gas in the delta(0, 0) and delta(1, 0) bands. Inclusion of the opacity provided by a typical NO profile reduces the dissociation rate in the upper stratosphere to 50-75 pct of that predicted when the optical depth calculation omits this contribution. A substantial fraction of the NO column abundance as measured near the stratopause resides in the lower thermosphere where correlations of NO with solar and magnetic activity are well documented. Variations in the thermospheric NO abundance therefore modulate the radiation field at the precise wavelengths absorbed by this molecule in the mesosphere and upper stratosphere. Predicted changes in the dissociation rate arising from a varying thermospheric opacity exceed 8 pct throughout the mesosphere and reach 15 pct between 65 km and 95 km.

Frederick, J. E.↗
NASA NTRS1983

Electron impact excitation from a 1 Delta g state of molecular oxygen

First measurements of electron impact excitation on the O2 a delta-one sub g metastable state to a higher bound state, pi-one sub u, is reported. The data were taken at an incident electron energy of 500 eV and scattering angles of 0 deg to 15 deg. A superelastic electron scattering experiment was performed on the pure oxygen target gas in order to establish the composition of the discharged oxygen and to confirm the existence of delta-one sub g molecules in the interaction region. The electron-impact energy loss spectrum obtained is shown. The electronic assignment of the upper state which produces the vibrational structure was determined to be pi-one sub u by examining the potential energy curves of O2 and applying the electric dipole selection rules. The relative line intensities were obtained and used to determine the Morse potential for the pi-one sub u state.

Khakoo, M. A.↗
NASA NTRS1982

The Delta-K ocean wave spectrometer - Aircraft measurements and theoretical system analysis

Measurements of the relative strength of ocean surface wave spectral components have been made from an aircraft using the two-frequency microwave resonance technique. A coherent Ku-band radar was used to study the Bragg type resonance matching (at the difference frequency Delta-f) to the surface wave components. The spatial spectrum of the surface reflectivity modulation was then computed as the value of Delta-f was varied over a matching range of approximately 15 150 m in surface wavelength. This paper contains experimental results from flights conducted during the 1979 MARSEN project and the 1980 ARSLOE project, and the objective here is to present the radar results in terms of the variety of surface illumination geometries encountered. It will be shown that the MARSEN results, with the narrow footprint, are consistent with a one-dimensional theoretical approach and that the ARSLOE results, with a symmetric beam pattern, agree well with the existing two-dimensional theory.

Weissman, D. E.↗
NASA NTRS1982

Digital TV tri-state delta modulation system for Space Shuttle ku-band downlink

A tri-state delta modulation/demodulation (TSDM) technique which provides for efficient run-length coding of constant-intensity segments of a TV picture is described. Aspects of the hardware implementation of a high-speed TSDM transmitter and receiver for black-and-white TV or field-sequential color or NTSC format color are reviewed. Run-length encoding of the TSDM output can consistently reduce the required channel data rate well below one bit per sample. As compared with a bistate delta modulation system, the present technique eliminates granularity in the reconstructed video without degrading rise or fall times. About 40 chips are used by TSDM when used to handle the luminance information in a color link. A possible overall space and ground functional configuration to accommodate Shuttle digital TV with scrambling for privacy is presented.

Udalov, S.↗
NASA NTRS1984

Numerical and experimental determination of secondary separation on delta wings in subsonic flow

A quasi-three-dimensional boundary layer method for conical inviscid flows is presented. The model was developed to characterize the flow fields over slender delta wings, particularly the shed vortex sheet. A steady, incompressible, laminar boundary layer is assumed and a solution is obtained with the Smith (1966) finite difference code. Predictions are compared with oil flow patterns and surface pressure measurements for 74 and 80 deg delta wings at 0-20 deg angles of attack. The model is capable of accurately predicting the secondary separation lines. Inviscid velocities derived from panel methods lead, however, to inaccurate pressure distributions.

Dejarnette, F. R.↗
NASA NTRS1984

Determining highly elliptical earth orbits with VLBI and Delta-VLBI

This paper shows the feasibility of using Very Long Baseline Interferometric (VLBI) data acquired by the Deep Space Network to navigate highly elliptical earth orbiting satellites. The planned mission orbit of the Ion Release Module of the Active Magnetospheric Particle Tracer Explorers is used as a reference for developing strategies and provides the first opportunity for a possible flight demonstration with a spacecraft in a highly elliptical orbit. The navigation accuracy improvements achievable with VLBI and Delta-VLBI data types are determined for comparison with the capabilities of a reference Doppler strategy. The results show that strategies using wideband Delta-VLBI measurements taken near periapse perform best, determining apoapse position to an order of magnitude better than conventional Doppler, while also substantially reducing the required antenna support.

Frauenholz, R. B.↗
NASA NTRS1985

Method and apparatus for Delta Kappa synthetic aperture radar measurement of ocean current

A synthetic aperture radar (SAR) employed for delta k measurement of ocean current from a spacecraft without the need for a narrow beam and long observation times. The SAR signal is compressed to provide image data for different sections of the chirp band width, equivalent to frequencies and a common area for the separate image fields is selected. The image for the selected area at each frequency is deconvolved to obtain the image signals for the different frequencies and the same area. A product of pairs of signals is formed, Fourier transformed and squared. The spectrum thus obtained from different areas for the same pair of frequencies are added to provide an improved signal to noise ratio. The shift of the peak from the center of the spectrum is measured and compared to the expected shift due to the phase velocity of the Bragg scattering wave. Any difference is a measure of current velocity v sub o (delta k).

Jain, A.↗
NASA NTRS1983

Correlation of infrared reflectance ratios at 2.3 microns/1.6 micron and 1.1 micron/1.6 micron with delta O-18 values delineating fossil hydrothermal systems in the Idaho batholith

Reflectance ratios from laboratory spectra and airborne multispectral images are found to be strongly correlated with delta O-18 values of granite rocks in the Idaho batholith. The correlation is largely a result of interactions between hot water and rock, which lowered the delta O-18 values of the rocks and produced secondary hydrous material. Maps of the ratio of reflectivities at 2.3 and 1.6 microns should delineate fossil hydrothermal systems and provide estimates of alteration intensity. However, hydrous minerals produced during deuteric alteration or weathering cannot be unambiguously distinguished in remotely sensed images from the products of propylitic alteration without the use of narrow-band scanners. The reflectivity at 1.6 micron is strongly correlated with rock density and may be useful in distinguishing rock types in granitic terranes.

Gillespie, A. R.↗
NASA NTRS1985

An attached flow design of a noninterfering leading edge extension to a thick delta wing

The analytical procedure presented for leading edge extension (LEE) determination, in keeping with such design criteria as noninterference at the wing design point, is applied to thick delta wings. The LEE device thus defined is to be mounted on a wing along a dividing stream surface that is associated with an attached flow design lift coefficient greater than zero. The delta wing in question is of twisted and cambered type. It is demonstrated that span reductions for the candidate LEEs has the most detrimental effect on overall aerodynamic efficiency, irrespective of area or shape.

Ghaffari, F.↗
NASA NTRS1986

Basic studies on delta wing flow modifications by means of apex fences

The effectiveness of apex fences on a 60-deg delta wing at low speeds was experimentally investigated. Resembling highly swept spoilers in appearance, the fences are designed to fold out of the wing apex region upper surface near the leading edges, where they generate a powerful vortex pair. The intense suction of the fence vortices augments lift in the apex region, the resulting positive pitching moment being utilized to trim trailing edge flaps for lift augmentation during approach and landing at relatively low angles of attack. The fences reduce the apex lift at high angles of attack, leading to a desirable nose-down moment. The above projected functions of the apex fence device were validated and quantified through low speed tunnel tests, comprising upper surface pressure surveys on a semispan model and balance measurements on a geometrically similar fully span wing/body configuration. Fence parameters such as area, shape, hinge position and deflection angle were investigated. Typical results are presented indicating the apex fence potential in controlling the longitudinal characteristics of a tail-less delta.

Hoffler, K. D.↗
NASA NTRS1986

Viscous vortical flow calculations over delta wings

Two approaches to calculate turbulent vortical flows over delta wing configurations are illustrated. The first is for a simple delta wing at low speeds using the boundary layer approximation to treat the effects of the secondary separation. The second is for the supersonic case of a generic fighter using the NASA Ames parabolized Navier/Stokes method. Test/theory comparisons are given in both cases.

Blom, G.↗