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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

V/STOL wind-tunnel testing

Factors influencing effective program planning for V/STOL wind-tunnel testing are discussed. The planning sequence itself, which includes a short checklist of considerations that could enhance the value of the tests, is also described. Each of the considerations, choice of wind tunnel, type of model installation, model development and test operations, is discussed, and examples of appropriate past and current V/STOL test programs are provided. A short survey of the moderate to large subsonic wind tunnels is followed by a review of several model installations, from two-dimensional to large-scale models of complete aircraft configurations. Model sizing, power simulation, and planning are treated, including three areas is test operations: data-acquisition systems, acoustic measurements in wind tunnels, and flow surveying.

Koenig, D. G.↗
NASA NTRS1983

Directional velocity analyzer for measuring electron distribution functions in plasmas

A directional velocity analyzer has been developed for measuring electron distribution functions in plasmas. It contains a collimating aperture which selects particles from a narrow cone in velocity space and a retarding potential analyzer. The distribution function f(v, theta, phi) is obtained from a large number of analyzer traces taken at different angles theta, phi. In addition, the small analyzer can be moved in space and the measurements are time resolved so as to obtain the complete phase space information f(v,r,t). The large data flow of this seven-variable function is processed with a high-speed digital data-acquisition system. The new electron velocity analyzer is applicable over a wide parameter range in electron energies and densities. Various cases of anisotropic distributions such as beams, shells, tails, and drifts have been successfully investigated.

Stenzel, R. L.↗
NASA NTRS1984

Potential advantages of the spaced antenna method for operational wind profiling, part 3.1B

The problem of very short-range forecasting is twofold. It is necessary to understand the processes that are being forecasted, and data appropriate to the scale of interest has to be generated. Coherent VHF and UHF radars are being used for operational wind profiling and are providing part of the solution to the data-acquisition problem. The Profiler system operated by the Wave Propagation Laboratory at NOAA has already shown great promise. As a result, plans are being considred for expanding the network of radars to cover a larger area of the country. The Profiler uses what is commonly referred to as the Doppler method for measuring winds. Two beams are pointed off-vertical, and the Doppler shift of the echo determines the line-of-sight velocity. The velocity components along the beams are then translated to horizontal wind components. A number of possible advantages of the spaced antennas (SA) method for operational wind profiling are discussed.

Rottger, J.↗
NASA NTRS1986

Recent progress in the Urbana MST radar

The Urbana radar, which operates at 40.92 MHz with a peak power of about 1.2 MW into a 100 x 120 m phased array antenna was improved. An accelerated data-acquisition system, a beam-steering system, and a transmit/receive switch were installed. With these changes, the radar is in regular operations for two hours every day around local noon gathering stratospheric and mesospheric data. Special campaigns are mounted in addition under severe weather conditions.

Bowhill, S. A.↗
NASA NTRS1986

Studies of extended planetary atmospheres

Telescopic observations were made of gases and plasmas in the Jupiter system, and related phenomena such as the recently-discovered sodium atmosphere of Mercury. Sodium absorption in Io's atmosphere was observed to distances as large as 5 Io radii during the mutual-eclipse season of the Jovian satellites. Analysis of Jovian disk spectra has proceeded, as planned, from an emphasis on the H2 ortho-para ratio to analysis of methane absorptions and determination of cloud structure. Several 2-channel photometers were constructed in 1978 for the Uranus event at which the rings were discovered and a smaller, single-channel unit was built more recently. Although the photometers themselves are still fully usable, the data-acquisition systems have major deficiencies.

Hunten, D. M.↗
NASA NTRS1986

Microcomputer control of infrared detector arrays

A microcomputer-based data-acquisition system has been developed for astronomical observing with two-dimensional infrared detector arrays. The hardware used is a 16-bit, 8086/8087 based system operating at 8 MHz. Data rates of up to 454,000 pixels per second are supported. The hardware is operated using interactive software which supports several modes of data acquisition.

Rossano, G. S.↗
NASA NTRS1986

Imaging by time-tagging photons with the multi-anode microchannel array detector system

The capability and initial use of the Multi-Anode Microchannel Array (MAMA) detector in the time-tag mode is reported. The detector hardware currently in use consists of a visible-light detector tube with a semitransparent photocathode proximity-focused to a high-gain curved-channel microchannel plate MCP. The photoevents are detected by a (256 x 1024)-pixel coincidence-anode array with pixel dimensions of 25 x 25 microns connected to charge-sensitive amplifiers and event-detection circuitry. In the time-lag mode, the detector delivers the pixel address and the time of arrival for each detected photon to an accuracy of 10 microns. The maximum count rate is limited by the speed of data-acquisition hardware. The MAMA detector in the time-lag mode is currently being evaluated in programs of astrometry and speckle imaging.

Timothy, J. G.↗
NASA NTRS1988

Computerized Analysis Of Thermal-Diffusivity Data

Improved data-acquisition and data-analysis system for thermal-diffusivity measurements using flash method incorporates digital oscilloscope and microcomputer for rapid reduction of experimental data. In thermal-diffusivity apparatus thin specimen heated on one face by pulsed xenon flashlamp, subsequent temperature rise on opposite face monitored by infrared detector. Thermal diffusivity estimated from thickness of specimen and from time after initial pulse during which temperature rise reaches half maximum value. Accuracy of estimate improved by correcting temperature measurements for radiative loss of heat from specimen and for finite duration and specific waveform of flashlamp pulse. System devised for use in high-temperature measurements of thermoelectric materials.

Chmielewski, Artur B.↗
NASA NTRS1988

Fade measurements at L-band and UHF in mountainous terrain for land mobile satellite systems

Fading results related to land mobile satellite communications at L-band (1502 MHz) and UHF (870 MHz) are described. These results were derived from an experiment performed in a series of canyon passes in the Boulder, Colorado region of the US. The experimental configuration involved a helicopter as the source platform, which maintained a relatively fixed geometry with a mobile van containing the receiver and data-acquisition system. An unobstructed line of sight between the radiating sources and the receiving van was, for the most part, also maintained. In this configuration, the dominant mechanism causing signal fading (or enhancement) is a result of multipath. The resulting fade distributions demonstrated that at the 1 percent and 5 percent levels, 5.5- and 2.6-dB fades were on the average exceeded at L-band and 4.8- and 2.4-dB at UHF, respectively, for a path elevation angle of 45 deg. The canyon results as compared with previous roadside-tree-shadowing results demonstrate that the deciding factor dictating fade margin for future land mobile satellite systems is tree shadowing rather than fades caused by multipath.

Vogel, Wolfhard J.↗
NASA NTRS1988

Attitude determination and control subsystem for the TOPEX satellite

The Ocean Topography Experiment satellite will carry a modular Attitude Determination and Control Subsystem (ADCS) which contains all equipment required for attitude determination, stabilization, and control, as well as hydrazine thruster firing control, during all mission phases. Attention is presently given to the ADCS's architecture, constituent hardware components, performance requirements, and predicted on-orbit performance compliance, with emphasis on the design and analysis of the Normal Mission Mode control algorithm furnishing the primary scientific data-acquisition operational mode. This mode's attitude determination and control of on-orbit performance is predicted to better than 43 arcsec.

Dennehy, C. J.↗
NASA NTRS1989

Data-Processing System For Test Airplane

Real-time display of data on performance supports decisions regarding maneuvers. Data from sensors aboard airplane transmitted to control station on ground for immediate processing and display. Data-acquisition subsystem aboard airplane uses both pulse code modulation and frequency modulation for transmission of sensor data on operation of engine, performance of airplane, and conditions in atmosphere. No data recorded on aircraft.

Ray, R. J.↗
NASA NTRS1988

Image processing in optical astronomy

Successful efforts to enhance optical-astronomy images through digital processing often exploit such 'weaknesses' of the image as the objects' near-symmetry, their preferred directionality, or a differentiation in spatial frequency between the object or objects and superimposed clutter. Attention is presently given to the calibration of a camera prior to astronomical data-acquisition, methods for the enhancement of faint surface brightness features, automated target detection and extraction techniques, the importance of the geometric transformations of digital imagery, the preparation of two-dimensional histograms, and the application of polarization.

Lorre, Jean J.↗
NASA NTRS1990

Detecting Boundary-Layer Transition In Cold Environments

Transition-detection study conducted in Langley 0.3-Meter Transonic Cryogenic Tunnel, using specialized hot-film system designed specifically for use in cryogenic wind tunnels. Quantitative transition-location data obtained at nearly cryogenic conditions, 360 degree R (200 K) represents first definitive transition Reynolds numbers obtained in cryogenic wind tunnel. Multichannel data-acquisition system processes data from 40 hot-film sensors by use of desktop computer. Concept enables on-line determination of boundary-layer transition in such cryogenic wind tunnels as National Transonic Facility.

Johnson, C. B.↗
NASA NTRS1990

ACTS Propagation Program

The ACTS Propagation Program, initiated to develop the propagation effects data for use in the design of future satellite systems, is described. The initial phase of the program uses the ESA's Olympus satellite to provide measurements of the fade slope, depth, and duration of propagation. The results will be applied to develop power control algorithms in time for the ACTS launch in 1992. The plan calls for the development of about 10 propagation terminals, with each terminal consisting of a two-channel receiver, a two-channel radiometer, and a data-acquisition system, which will be loaned to different research centers and universities for data collection and analysis.

Davarian, Faramaz↗
NASA NTRS1989

A transition detection study at Mach 1.5, 2.0, and 2.5 using a micro-thin hot-film system

A boundary-layer transition detection study was conducted in the NASA Langley unitary plan wind tunnel with an array of microthin hot films on a flat plate at Mach numbers 1.5, 2.0, and 2.5 and Reynolds numbers (1.0-4.5) x 10 to the 6th/ft. Transition locations were obtained online from the variation of normalized rms voltages from an array of hot-film sensors for both natural transition and a grit-induced wedge of turbulence. The effects of Mach number and Reynolds number on the location and length of the transition region for the two types of transition are presented from the online data. Also shown are the unit Reynolds number effects on transition Reynolds number, voltage-versus-time traces, spectra, and the data-acquisition system.

Johnson, Charles B.↗
NASA NTRS1990

Dynamics of the outgoing turbulent boundary layer in a Mach 5 unswept compression ramp interaction

Wall pressure fluctuations have been measured under the unsteady separation shock and on the ramp face in an unswept Mach 5 compression ramp interaction. The freestream Reynolds number was 51.0 x 10 to the 6th/m, and the incoming turbulent boundary layer developed on the tunnel floor under approximately adiabatic wall temperature conditions. Standard data-acquisition methods, as well as real-time and posttest conditional sampling techniques were used. The results show that the mean and rms pressure levels are strong functions of separation shock position. At all stations on the ramp, from the corner to where the pressure reaches the theoretical inviscid value, the pressure signals have two dominant components: a low frequency component characteristic of the global unsteadiness, which correlates with the separation shock motion, and a higher frequency component associated with turbulence. The former is the major contributor to the overall signal variance.

Gramann, Richard A.↗
NASA NTRS1989

Evaluation of large format electron bombarded virtual phase CCDs as ultraviolet imaging detectors

In conjunction with an external UV-sensitive cathode, an electron-bombarded CCD may be used as a high quantum efficiency/wide dynamic range photon-counting UV detector. Results are presented for the case of a 1024 x 1024, 18-micron square pixel virtual phase CCD used with an electromagnetically focused f/2 Schmidt camera, which yields excellent simgle-photoevent discrimination and counting efficiency. Attention is given to the vacuum-chamber arrangement used to conduct system tests and the CCD electronics and data-acquisition systems employed.

Opal, Chet B.↗
NASA NTRS1989

Penn State Imaging X-ray Spectrometer

The design and performance of a CCD X-ray camera developed at Penn State are described. The camera uses a frame-store CCD as the detector element. A laboratory version using a PC-based CCD controller and data-acquisition system and a thermoelectric cooler is being used for laboratory testing. This camera has been used to measure read noise of less than 1.5 e(-) with the serial clocks running backwards to suppress dark current. The energy resolution at 5.9 keV with the CCD running in its normal configuration is 120 eV. A flight version of this camera is being built to make spectrally resolved images of the Pup A SNR.

Burrows, David N.↗