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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Electron beam fluorescence measurements in the Boeing hypersonic shock tunnel

The Calspan electron beam fluorescence (EBF) measurement system is described along with the results of measurements made in hypersonic flow. Numerous self-emitting metallic species were identified, many of which may be associated with an aging/erosion process within the B30HST. Because there were only 16 tunnel runs, it was only possible to obtain spectral measurements over a limited range of wavelengths and time sampling periods. Many spectral features of the flow remain uninvestigated. Because flow self-emission is important to all optical diagnostic techniques, it is recommended that additional spectral studies by performed. The three electron beam-excited species that were identified are nitrogen, helium, and nitric oxide. The high metallic radiation background interfered with attempts to obtain the time-wise variation of N2 density and He radiation with the optical fiber/PMT channels. In the case of the N2 density measurements the result of interference was increased uncertainty. Unfortunately, the interference caused the time-wise He measurements to fail completely. It is recommended that the electron beam be modulated to provide discrimination against the background radiation in future N2 density measurements. Careful data reduction produced useful measurements of N2 vibrational temperature, even though the high background from metallic species significantly increased measurement uncertainty. Perhaps the recommended additional spectral studies would reveal N2(+) First Negative System band-pair regions having less background. Detection of the He arrival was easily accomplished with the spectrometer/array detector system. Because of this, it is recommended that this means of detecting He arrival be used in the future. With proper calibrations of the system an He number density could be obtained. Although the flow conditions were out of limits for the run in which the NO spectrum was recorded, the usefulness of the NO spectrum for determination of free-stream rotational temperature was demonstrated and should be exploited in future experiments. Indeed, based on the strong NO signals, it is recommended that lower resolution NO spectra be obtained to provide a measure of NO vibrational temperature in the same manner that the N2 temperature was obtained.

Price, Linwood L.↗
NASA NTRS1979

Detection of hairline cracks in textured silicon solar cells

Using a focused laser scanner, the optical technique described in the present paper can be used to detect hairline cracks of the type occurring in solar cells subjected to surface texturing. The technique is capable of detecting cracks of the order of a few microns, which, otherwise, can be observed only under high magnification using an optical microscope. The technique consists of scanning a solar cell with a finely focused laser beam and recording the photoresponse (short circuit current or open circuit voltage) as a function of beam position. The presence of a crack is manifested by a sharp dip in the photoresponse.

Sopori, B. L.↗
NASA NTRS1979

Nonlinear development of an electromagnetic filamentation instability

A simplified model of an electromagnetic filamentation instability that arises when two counterstreaming electron beams pass through a uniform ion background is treated by statistical mechanical techniques borrowed from fluid turbulence theory. Accumulation of magnetic energy at long wavelengths is predicted, as observed in the numerical simulations of Lee and Lampe.

Montgomery, D.↗
NASA NTRS1980

Dynamic behavior of a beam drag-force anemometer

A cantilevered beam with strain gages attached to the fixed ends and the minimax technique were used in an experiment conducted to determine the dynamic behavior of a drag-force anemometer in high frequency, unsteady flow. In steady flow the output of the anemometer is proportional to stream velocity head and flow angle. Fluid mechanics suggests that, in unsteady flow, the output would also be proportional to the rate of change of fluid velocity. It was determined that effects due to the rate of change of fluid velocity are negligible for the probe geometry and frequencies involved.

Fralick, G. C.↗
NASA NTRS1980

Considerations for high accuracy radiation efficiency measurements for the Solar Power Satellite (SPS) subarrays

The relatively large apertures to be used in SPS, small half-power beamwidths, and the desire to accurately quantify antenna performance dictate the requirement for specialized measurements techniques. Objectives include the following: (1) For 10-meter square subarray panels, quantify considerations for measuring power in the transmit beam and radiation efficiency to + or - 1 percent (+ or - 0.04 dB) accuracy. (2) Evaluate measurement performance potential of far-field elevated and ground reflection ranges and near-field techniques. (3) Identify the state-of-the-art of critical components and/or unique facilities required. (4) Perform relative cost, complexity and performance tradeoffs for techniques capable of achieving accuracy objectives. the precision required by the techniques discussed below are not obtained by current methods which are capable of + or - 10 percent (+ or - dB) performance. In virtually every area associated with these planned measurements, advances in state-of-the-art are required.

Kozakoff, D. J.↗
NASA NTRS1981

Bulk and integrated acousto-optic spectrometers for radio astronomy

The development of sensitive heterodyne receivers (front end) in the centimeter and millimeter range, and the construction of sensitive RF spectrometers (back end) enable the spectral lines of interstellar molecules to be detected and identified. A technique was developed which combines acoustic bending of a collimated coherent light beam by a Bragg cell followed by detection by a sensitive array of photodetectors (thus forming an RF acousto-optic spectrometer (AOS). An AOS has wide bandwidth, large number of channels, and high resolution, and is compact, lightweight, and energy efficient. The thrust of receiver development is towards high frequency heterodyne systems, particularly in the millimeter, submillimeter, far infrared, and 10 micron spectral ranges.

Chin, G.↗
NASA NTRS1982

Radio frequency verification tasks related to a multiple aperture reflector system

The establishment of analytical methods for predicting the electromagnetic performance of multiple offset fed apertures for multiple beam large space antenna systems is highlighted. The development of experimental modeling techniques for verifying the analytical methods used in predicting the effects of surface roughness (pillows), scattering, and aperture coupling on RF performance is discussed.

Campbell, T. G.↗
NASA NTRS1983

User's manual for three-dimensional analysis of propeller flow fields

A detailed operating manual is presented for the prop-fan computer code (in addition to supporting programs) recently developed by Kutler, Chaussee, Sorenson, and Pulliam while at the NASA'S Ames Research Center. This code solves the inviscid Euler equations using an implicit numerical procedure developed by Beam and Warming of Ames. A description of the underlying theory, numerical techniques, and boundary conditions with equations, formulas, and methods for the mesh generation program (MGP), three dimensional prop-fan flow field program (3DPFP), and data reduction program (DRP) is provided, together with complete operating instructions. In addition, a programmer's manual is also provided to assist the user interested in modifying the codes. Included in the programmer's manual for each program is a description of the input and output variables, flow charts, program listings, sample input and output data, and operating hints.

Chaussee, D. S.↗
NASA NTRS1985

Potential spin-offs of the carbon dioxide observational platform system (CO-OPS) for remote sensing opportunities

Alternate remote sensing techniques that could utilize the slight losses of energy from the microwave beam which powers the NASA/MSFC Carbon Dioxide Observational Platform System (CO-OPS) to achieve the objectives of the U.S. Department of Energy (DOE) Carbon Dioxide Research Program's regional observational data requirements, ODRs, are addressed heuristically. The opportunity for regional remote sensing of the carbon dioxide and water vapor constituents in the atmosphere are discussed as a potential spin off of the CO-OPS. The CO-OPS is envisioned as a high altitude (approx. 25 km) observational platform system powered by microwave energy for regional observational use by the DOE in their Carbon Dioxide Research Program.

Stephens, J. B.↗
NASA NTRS1986

Computation of the radiation characteristics of a generalized phased array

With the advent of monolithic microwave integrated circuit (MMIC) technology, the phased array has become a key component in the design of advanced antenna systems. Array-fed antennas are used extensively in today's multiple beam satellite antennas. A computer program based on a very efficient numerical technique for calculating the radiated power (Romberg integration), directivity, and radiation pattern of a phased array is described. The formulation developed is very general, and takes into account arbitrary element polarization, E- and H-plane element pattern, element location, and complex element excitation. For comparison purposes sample cases have been presented. Excellent agreement has been obtained for all cases. Also included are a user guide and a copy of the computer program.

Acosta, R. J.↗
NASA NTRS1986

Construction and control of large space structures

Recent NASA research efforts on space construction are reviewed. Preliminary results of the EASE/ACCESS Shuttle experiments are discussed. A 45-foot beam was constructed on orbit in 30 minutes using a manual assembly technique at a work station. A large tetrahedron was constructed several times using a free floating technique. The capability of repair, utilities installation, and handling the structures using a mobile foot restraint on the RMS was also demonstrated. Implications of the experiments for space station are presented. Models of 5-meter space station structure together with neutral buoyancy simulations suggest manual assembly techniques are feasible. Selected research on control of flexible structures is discussed.

Card, M. F.↗
NASA NTRS1986

Construction and control of large space structures

Recent NASA research efforts on space construction are reviewed. Preliminary results of the EASE/ACCESS Shuttle experiments are discussed. A 45-foot beam was constructed on orbit in 30 minutes using a manual assembly technique at a work station. A large tetrahedron was constructed several times using a free floating technique. The capability of repair, utilities installation, and handling the structures using a mobile foot restraint on the RMS was also demonstrated. Implications of the experiments for Space Station are presented. Models of 5-meter Space Station structure together with neutral buoyancy simulations suggest manual assembly techniques are feasible. Selected research on control of flexible structures is discussed. To support planned flight experiments, studies of the design and optimal placement of distributed active dampers are underway.

Card, M. F.↗
NASA NTRS1985

Structural parameter identification of distributed systems using finite element approximation

A system identification technique is developed for classes of distributed systems using finite element approximations. Vibrating systems represented by partial differential equations have physical parameters associated with mass, stiffness, and damping distributions which need to be known in order to properly control and design mathematical models of the system. In order to identify these parameters a weighted least-squares algorithm and modified Newton-Raphson method is used for the identification process. The theory and technique is demonstrated by estimating the system parameters of a vibrating cantilever beam made up of several different structural properties.

Lee, K. Y.↗
NASA NTRS1988

Computational aspects of sensitivity calculations in transient structural analysis

A key step in the application of formal automated design techniques to structures under transient loading is the calculation of sensitivities of response quantities to the design parameters. This paper considers structures with general forms of damping acted on by general transient loading and addresses issues of computational errors and computational efficiency. The equations of motion are reduced using the traditional basis of vibration modes and then integrated using a highly accurate, explicit integration technique. A critical point constraint formulation is used to place constraints on the magnitude of each response quantity as a function of time. Three different techniques for calculating sensitivities of the critical point constraints are presented. The first two are based on the straightforward application of the forward and central difference operators, respectively. The third is based on explicit differentiation of the equations of motion. Condition errors, finite difference truncation errors, and modal convergence errors for the three techniques are compared by applying them to a simple five-span-beam problem. Sensitivity results are presented for two different transient loading conditions and for both damped and undamped cases.

Greene, William H.↗
NASA NTRS1987

Excimer laser system for atmospheric remote sensing of ozone

A high-power narrow-linewidth XeCl excimer laser system developed for use by NASA in the remote sensing of atmospheric ozone is described. The laser system is designed for incorporation in a DIAL lidar utilizing stimulated Raman generation for the reference wavelength and sophisticated data averaging techniques. The laser output has a linewidth of 0.002 nm and a beam divergence of 0.15 mrad (FWHM). The laser was operated over a six-hour period with a constant average power of 18 W and a wavelength stable to within + or - 0.0006 nm.

Tan, K. O.↗
NASA NTRS1988

Extended fine structures in the electron energy loss spectrum of InAs

The possibility of using electron energy loss fine structure (EELFS) for the characterization of thin pseudomorphic quantum wells of InAs and GaAs(100) is investigated. It is shown that the EELFS technique can yield reliable radial distribution functions for bulk InAs, provided beam-induced sample degradation is controlled stringently. Additional improvements in the data collection procedures, including better control of the sample condition, are required as well as more detailed work on separating contributions from multiple edges in the data analysis.

Schowengerdt, F. D.↗