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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A simple antireflection overcoat for opaque coatings in the submillimeter region

An antireflection overcoat for opaque baffle coatings in the far infrared (FIR)/submillimeter region was made from a simple Teflon spray-on lubricant. The Teflon overcoat reduced the specular reflectance of four different opaque coatings by nearly a factor of two. Analysis, based on the interference term of a reflecting-layer model, indicates that in the submillimeter region the reduced reflectance depends primarily on the refractive index of the overcoat and very little on its thickness.

Smith, S. M.↗
NASA NTRS1986

Wide-angle flat field telescope

Described is an unobscured three mirror wide angle telescopic imaging system comprised of an input baffle which provides a 20 deg (Y axis) x 30 deg (X axis) field of view, a primary mirror having a convex spherical surface, a secondary mirror having a concave ellipsoidal reflecting surface, a tertiary mirror having a concave spherical reflecting surface. The mirrors comprise mirror elements which are offset segments of parent mirrors whose axes and vertices commonly lie on the system's optical axis. An iris diaphragm forming an aperture stop is located between the secondary and tertiary mirror with its center also being coincident with the optical axis and being further located at the beam waist of input light beams reflected from the primary and secondary mirror surfaces. At the system focus following the tertiary mirror is located a flat detector which may be, for example, a TV imaging tube or a photographic film. When desirable, a spectral transmission filter is placed in front of the detector in close proximity thereto.

Hallam, K. L.↗
NASA NTRS1986

Performance of the high speed anechoic wind tunnel at Lyon University

The characteristics of the feed duct, the wind tunnel, and the experiments run in the convergent-divergent anechoic wind tunnel at Lyon University are described. The wind tunnel was designed to eliminate noise from the entrance of air or from flow interactions with the tunnel walls so that noise caused by the flow-test structure interactions can be studied. The channel contains 1 x 1 x 0.2 m glass and metal foil baffles spaced 0.2 m apart. The flow is forced by a 350 kW fan in the primary circuit, and a 110 kW blower in the secondary circuit. The primary circuit features a factor of four throat reductions, followed by a 1.6 reduction before the test section. Upstream and downstream sensors permit monitoring of the anechoic effectiveness of the channel. Other sensors allow modeling of the flow structures in the tunnel. The tunnel was used to examine turbulent boundary layers in flows up to 140 m/sec, tubulence-excited vibrations in walls, and the effects of laminar and turbulent flows on the appearance and locations of noise sources.

Sunyach, M.↗
NASA NTRS1985

Application of the finite element method in the calculation of transmission loss of flat and curved panels

This investigation represents an extension of a study of Roussos (1985) who considered the noise transmission loss of a rectangular plate in an infinite baffle. Roussos, who employed an analytical formulation, considered an unstiffened plate. While it is difficult to consider stiffeners by means of analytical methods, the difficulties can be avoided by employing a finite element procedure. For this reason, the present study is concerned with the implementation of a finite element method. The representation of the panel transmission loss is discussed, and the determination of the panel motion by means of the finite element technique is described, taking into account an isotropic flat panel, the exciting force, an eigenvalue problem, the radiation pressure, a plate element, and a cylindrical shell element. Numerical results are considered for a flat panel, a curved panel, and a stiffened flat panel.

Koval, L. R.↗
NASA NTRS1986

First results from Spacelab 2

Preliminary results of physical experiments carried out during the Spacelab 2 Shuttle mission are summarized. Attention is given to experiments in the fields of plasma dynamics; solar physics; high-energy astrophysics; and astronomy. Plasma experiments included an ejectable plasma diagnosics package and measurements of the passive charging of the Shuttle vehicle in the surrounding space plasma. The solar physics instrument package consisted of a solar spectral irradiance monitor; a solar optical universal polarimeter (SOUP); and a solar helium abundance high-resolution telescope and spectrograph (HRTS). Astronomical observations were performed using a scanning infrared telescope (IRT) which consisted of a highly baffled herschelian telescope and 10 detectors covering wavelengths from 2 to 120 microns. Cosmic-ray nuclei were detected and analyzed using gas Cerenkov counters and a transition radiation detector. Addition experiments included a thin film fluid dynamics payload and analysis of blood samples taken from the mission specialists. Complete data records from the experiments have now been distributed for an analysis period which will take at least a year. A table listing the Spacelab 2 experiments and their principal investigators is provided.

Urban, E. W.↗
NASA NTRS1986

Investigation of the components of the NAL high Reynolds number two-dimensional wind tunnel. Part 4: Design, construction and performance of the exhaust silencer

Presented is a description of the design construction and performance of the exhaust silencer for the NAL high Reynolds number two-dimensional transonic blow down wind tunnel, which was completed in October 1979. The silencer is a two-storied construction made of reinforced concrete, 40 m. long, 10 m. wide and 19 m. high and entirely enclosed by thick concrete walls. The upstream part of the first story, particularly, is covered with double walls, the thickness of the two walls being 0.3 m. (inner wall) and 0.2 m. (outer wall), respectively. A noise reduction system using three kinds of parallel baffles and two kinds of lined bends is adopted for the wind tunnel exhaust noise.

Sakakibara, S.↗
NASA NTRS1986

Simple antireflection overcoat for opaque coatings in the submillimeter region

An antireflection overcoat for opaque baffle coatings in the far-IR/submillimeter region has been made from a simple Teflon spray-on lubricant. The Teflon overcoat reduced the specular reflectance of four different opaque coatings by nearly a factor or 2. Analysis, based on the interference term of a reflecting-layer model, indicates that in the submillimeter region the reduced reflectance depends primarily on the refractive index of the overcoat and very little on its thickness.

Smith, S. M.↗
NASA NTRS1987

Low reflectance EUV materials - A comparative study

A study has been undertaken of the performance characteristics of a variety of surfaces and surface treatments for use on baffle materials in Extreme UV Explorer instrumentation, in order to ascertain which materials performed with the least overall scattering between 300 and 1200 A and thereby minimize this important background source. Seven scattering samples were measured: bead-blasted aluminum treated with alodine 600, bead-blasted aluminum, Kel-f, etched molybdenum, nickel-plated etched molybdenum, bead-blasted 304 stainless steel, and bead-blasted aluminum painted with Chemglaze Z-306. Attention is given to total reflectance of each material plotted against the graze angle for 304, 584, and 1216 A.

Jelinsky, Patrick↗
NASA NTRS1987

The effects of gas mixtures on ion engine erosion and performance

Erosion measurements were performed on a modified J-series 30 cm ion engine operating on xenon propellant. Erosion data was obtained by measuring the trench depth etched into masked polished metal samples for test durations of up to 24 hours. The data indicates that erosion is greatest at the cathode side of the baffle, with tantalum being the material with the least erosion of all materials tested. There is a clear indication of a significant reduction in erosion of all materials tested when nitrogen is added to the propellant. The technique used in these experiments requires test samples which are extremely smooth and flat.

Garner, Charles E.↗
NASA NTRS1987

The acoustic radiation damping of the modes of a rectangular panel

The acoustic damping for single modes of a finite rectangular panel, simply supported in an infinite baffle, is theoretically determined from the ratio of the acoustic energy radiated per cycle to the vibratory energy of the panel. Asymptotic solutions for the low-frequency region are presented for a panel mode driven at an arbitrary frequency and for a panel mode vibrating at its natural frequency. Curves of acoustic damping for a panel mode vibrating at resonance, as a function of the panel thickness-to-length ratio, are presented for various panel aspect ratios. For panels vibrating below the critical frequency, the damping depends on the aspect ratio with square panels developing the smallest value. For panels vibrating above the critical frequency, the damping is nearly independent of the aspect ratio.

Wallace, C. E.↗
NASA NTRS1988

Antireflection Overcoat For Submillimeter Wavelengths

Coating thickness not critical. Polytetrafluoroethylene antireflection overcoat reduces specular reflectance of opaque baffle coating by factor of nearly 2 at millimeter and infrared wavelengths. Easily applied by spraying Teflon(TM) Wet Lubricant (or equivalent) on opague coated surface. Though technique makes it difficult to control thickness of overcoat, experimental and theoretical studies indicate thickness has little effect because antireflective property based on creating graded-index absorber.

Smith, Sheldon M.↗
NASA NTRS1987

The measurement of boundary layers on a compressor blade in cascade. I - A unique experimental facility

A unique cascade facility is described which makes it possible to use LDV for measuring blade boundary layer profiles. Because of the need for a laser access window, the facility cannot rely on continuous blade pack suction to achieve stable flow. Instead, a combination of tailboards and strong suction upstream of the blade pack is used to create a two-dimensional periodic flow field at a chord Reynolds number of 500,000. The distribution of the upstream suction is controlled through a complex baffling system. Details of the inlet and outlet flow are documented using five-hole pressure probes, blade static-pressure measurements, and sublimation flow visualization. Experimental data are presented on the flow field on the suction surface of the blade, the pressure surface, and near-wake flow fields.

Deutsch, Steven↗
NASA NTRS1987

A transportable hemispherical illumination system for making reflectance factor measurements

An artificial source of stable, hemispherical illumination has been developed to facilitate the collection of reflectance factor measurements of targets of interest in a laboratory environment. The light source consists of a 76 cm (30 in.) aluminum hemisphere which has been coated internally with barium sulfate paint. Illumination is provided by two banks of lamps, each consisting of eight 62-W quartz halogen bulbs which have tungsten filaments. An internal baffle precludes the viewing of any direct beam of light. A simple metal structure has been developed to hold the hemisphere and all peripheral equipment, such as spectrometers, radiometers, and cameras, in place during data collection. The entire setup can be easily disassembled and packed in airline approved shipping cases to facilitate transportation to remote laboratory facilities. This illumination system has been used during the past three years to collect spectral reflectance factor data of tree branch samples and seedlings in support of an on-going study to investigate the effect of acidic deposition on forest vegetation.

Williams, Darrel L.↗
NASA NTRS1989

Potential uses of vacuum bubbles in noise and vibration control

Vacuum bubbles are new acoustic elements which are dynamically more compliant than the gas volume they replace, but which are statically robust. They are made of a thin metallic shell with vacuum in their cavity. Consequently, they pose no danger in terms of contamination or fire hazard. The potential of the vacuum bubble concept for noise and vibration control was assessed with special emphases on spacecraft and aircraft applications. The following potential uses were identified: (1) as a cladding, to reduce sound radiation of vibrating surfaces and the sound excitation of structures, (2) as a screen, to reflect or absorb an incident sound wave, and (3) as a liner, to increase low frequency sound transmission loss of double walls and to increase the low frequency sound attenuation of muffler baffles. It was found that geometric and material parameters must be controlled to a very high accuracy to obtain optimal performance and that performance is highly sensitive to variations in static pressure. Consequently, it was concluded that vacuum bubbles have more potential in spacecraft applications where static pressure is controlled more than in aircraft applications where large fluctuations in static pressure are common.

Ver, Istvan L.↗
NASA NTRS1988

Radiance standards

Two radiometric calibration sources that are utilized by various groups are maintained and operated. One source is a 6-ft diameter sphere and the other a 4-ft diameter hemisphere. Both are internally coated with multiple layers of barium sulfate and house an array of 12 tungsten filament-quartz iodine lamps that provide a uniform diffuse target of radiance traceable to NBS. The lamps are baffled and arranged so that they are not part of the scene during calibrations. Both systems have a 10-inch viewing aperture. The hemisphere is somewhat more versatile in that the aperture can be changed and the system is movable so calibrations can be done at other sites. Together, these systems have supported numerous GSFC projects and missions during this review period. They are listed.

Lester, D. L.↗
NASA NTRS1988

Solar maximum mission fine pointing sun sensor dawn and dusk errors flight data and model analysis

SMM flight system control errors occurring at spacecraft dawn and dusk are analyzed. The errors are associated with the fine pointing sun sensor (FPSS), which is a primary component of the SMM attitude control system. It is shown that the source of the FPSS dawn/dusk distortion is the incomplete masking of sunlight reflected off the earth by the optical baffle covering the FPSS sensor heads onboard the SMM during periods of orbit dawn and dusk. For the most part, the modeled behavior of the FPSS under dawn and dusk lighting conditions matches the observed behavior in the SMM flight data.

Kulp, D. R.↗
NASA NTRS1988

Space vehicle glow and its impact on spacecraft systems

Spacecraft glow poses a contamination threat to low orbital altitude optical sensor systems. The complexity of the phenomena entails a multifaceted approach to system design for vehicle glow minimization. In the case of Space Shuttle cloud glow, which involves line and band emission, filtering and careful optical sensor wavelength selection may also prove useful; Space Shuttle thruster glow mitigation entails the limitation of thruster firings during sensor operations. Careful selection of instrument baffle materials and coatings, as well as control of surface temperatures, are recommended as ways of limiting glow impact for instruments directed in the direction of vehicle movement.

Garrett, H. B.↗
NASA NTRS1989

Calculation of solar attenuation coefficient using ACCOS V along a critical scattering path

An appraisal of the optical properties of the AVHRR is made for a proposed orbital trajectory which results in an unexpected solar stray-light path; i.e., bypassing the external scan mirror and Cassegrain telescope and proceeding directly to the inner conical baffle. This stray-light path is directed onto an internal beamsplitter which, in turn, is directly observed by the detectors. Stray-light analysis, as a goal, seeks to remove or minimize the influence of such critical scattering paths. The AVHRR path is evaluated using a standard optical ray-tracing program, ACCOS V. To determine the expected sensor degradation, a calculation of the expected attenuation coefficient of scattered sunlight in the AVHRR sensor is estimated based on this important critical scattering path.

Ames, Alan J.↗