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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Global astrometry with the space interferometry mission

The prospects for global astrometric measurements with the space interferometry mission (SIM) are discussed. The SIM mission will perform four microarcsec astrometric measurements on objects as faint as 20 mag using the optical interferometry technique with a 10 m baseline. The SIM satellite will perform narrow angle astrometry and global astrometry by means of an astrometric grid. The sensitivities of the SIM global astrometric performance and the grid accuracy versus instrumental parameters and sky coverage schemes are reported on. The problems in finding suitable astrometric grid objects to support microarcsec astrometry, and related ground-based observation programs are discussed.

Boden, A.↗
NASA NTRS1992

Advanced optical instruments technology

The science objectives for proposed NASA missions for the next decades push the state of the art in sensitivity and spatial resolution over a wide range of wavelengths, including the x-ray to the submillimeter. While some of the proposed missions are larger and more sensitive versions of familiar concepts, such as the next generation space telescope, others use concepts, common on the Earth, but new to space, such as optical interferometry, in order to provide spatial resolutions impossible with other concepts. However, despite their architecture, the performance of all of the proposed missions depends critically on the back-end instruments that process the collected energy to produce scientifically interesting outputs. The Advanced Optical Instruments Technology panel was chartered with defining technology development plans that would best improve optical instrument performance for future astrophysics missions. At this workshop the optical instrument was defined as the set of optical components that reimage the light from the telescope onto the detectors to provide information about the spatial, spectral, and polarization properties of the light. This definition was used to distinguish the optical instrument technology issues from those associated with the telescope, which were covered by a separate panel. The panel identified several areas for optical component technology development: diffraction gratings; tunable filters; interferometric beam combiners; optical materials; and fiber optics. The panel also determined that stray light suppression instruments, such as coronagraphs and nulling interferometers, were in need of general development to support future astrophysics needs.

Shao, Mike↗
NASA NTRS1988

Development and applications of optical interferometric micrometrology in the angstrom and subangstrom range

The recent development of the scanning electron tunneling microscope and the atomic force microscope requires absolute standards for measurements in the angstrom and subangstrom range. Optical interferometry with lasers and multiple mode laser resonances can provide absolute measurements as the laser wavelengths are very accurately known. A key feature of such measurements is the use of piezoelectric crystals as translators of the highest accuracy for very small disturbances. However, the dimensional changes of these crystals resulting from electrical potential changes depend on many variables, among them the method of mounting, so that accurate calibrations are necessary. Starting from advances in optical metrology made by physicists trying to find gravity waves, advances which led to measurements down to 10 to the -5 A, the author designed and built a much simpler system for the angstrom range. The major limiting factors were mechanical vibrations, air currents, thermal changes and laser instabilities.

Lauer, James L.↗
NASA NTRS2002

Manipulation of Micro Scale Particles in an Optical Trap Using Interferometry

This research shows that micro particles can be manipulated via interferometric patterns superimposed on an optical tweezers beam. Interferometry allows the manipulation of intensity distributions, and thus, force distributions on a trapped particle. To demonstrate the feasibility of such manipulation, 458 nm light, from an argon-ion laser, was injected into a Mach Zender interferometer. One mirror in the interferometer was oscillated with a piezoelectric phase modulator. The light from the interferometer was then injected into a microscope to trap a 9.75 micron polystyrene sphere. By varying the phase modulation, the sphere was made to oscillate in a controlled fashion.

Seibel, Robin↗
NASA NTRS2007

SIM Planetquest Science and Technology: A Status Report

Optical interferometry will open new vistas for astronomy over the next decade. The Space Interferometry Mission (SIM-PlanetQuest), operating unfettered by the Earth's atmosphere, will offer unprecedented astrometric precision that promises the discovery of Earth-analog extra-solar planets as well as a wealth of important astrophysics. Results from SIM will permit the determination of stellar masses to accuracies of 2% or better for objects ranging from brown dwarfs through main sequence stars to evolved white dwarfs, neutron stars, and black holes. Studies of star clusters will yield age determinations and internal dynamics. Microlensing measurements will present the mass spectrum of the Milky Way internal to the Sun while proper motion surveys will show the Sun's orbital radius and speed. Studies of the Galaxy's halo component and companion dwarf galaxies permit the determination of the Milky Way's mass distribution, including its Dark Matter component and the mass distribution and Dark Matter component of the Local Group. Cosmology benefits from precision (1-2%) determination of distances to Cepheid and RR Lyrae standard candles. The emission mechanism of supermassive black holes will be investigated. Finally, radio and optical celestial reference frames will be tied together by an improvement of two orders of magnitude. Optical interferometers present severe technological challenges. The Jet Propulsion Laboratory, with the support of Lockheed Martin Advanced Technology Center (LM ATC) and Northrop Grumman Space Technology (NGST), has addressed these challenges with a technology development program that is now complete. The requirements for SIM have been satisfied, based on outside peer review, using a series of laboratory tests and appropriate computer simulations: laser metrology systems perform with 10 picometer precision; mechanical vibrations have been controlled to nanometers, demonstrating orders of magnitude disturbance rejection; and knowledge of component positions throughout the whole test assembly has been demonstrated to the required picometer level. Technology transfer to the SIM flight team is now well along.

astrometry↗
NASA NTRS1975

Effect of starvation on film thickness and traction under elastohydrodynamic rolling and sliding conditions

Traction measurements under starved elastohydrodynamic conditions were obtained for a point-contact geometry. Simultaneous measurements of the film thickness and the location of the inlet lubricant boundary were made. Optical interferometry was used to measure film thickness. The thickness of a starved film for combined rolling and sliding conditions varies with the location of the inlet boundary in the same way as previously found for pure rolling conditions. When the fluid velocity distribution is calculated in the inlet region by a Reynolds lubrication analysis, backflow is seen to occur over a portion of the inlet region. Backflow is essential for the establishment of a flooded condition. The location of certain fluid velocity conditions within the inlet region, as suggested in the literature, does not adequately describe the onset of starvation. For the same slide-roll ratio a starved film was observed to possess greater traction than a flooded film. Traction measurements under starved conditions were also compared with those under flooded conditions for equivalent shear rates in the Hertzian region. When the shear rates within the Hertzian region were low and the film was severely starved, the measured tractions were lower than expected. This may be due to large shear stresses developed by the large pressure gradients that are generated in the inlet region when it is severely starved.

Wedeven, L. D.↗
NASA NTRS1976

Isothermal elastohydrodynamic lubrication of point contacts. 2: Ellipticity parameter results

A numerical solution of the isothermal elastohydrodynamic problem for point contacts is presented which reproduces all the essential features of experimental observations based upon optical interferometry. In particular, the two side lobes, in which minimum film thickness regions occur, emerge in the theoretical solutions. The influence of the ellipticity parameter on solutions to the point contact problem is explored. The ellipticity parameter k was varied from 1 (a ball on a plate) to 8 (a configuration approaching line contact). It is shown that the minimum film thickness can be related to the well known line contact solutions by a remarkably simple expression involving either k or the effective radius of curvature ratio R sub y/R sub x.

Hamrock, B. J.↗
NASA NTRS1975

Isothermal elastohydrodynamic lubrication of point contacts. II - Ellipticity parameter results

A numerical solution of the isothermal elastohydrodynamic problem for point contacts has been presented which reproduces all the essential features of the previously reported experimental observations based upon optical interferometry. In particular, the two 'side lobes' in which minimum film thickness regions occur are shown to emerge in the theoretical solutions. The influence of the ellipticity parameter upon solutions to the point contact problem has been explored in the present paper. The ellipticity parameter (k) was varied from one (a ball on a plate) to eight (a configuration approaching line contact), and it has been shown that both the central and minimum film thicknesses can be related to the well known line contact solutions by remarkably simple expressions involving either (k) or the effective radius of curvature ratio (Ry/Rx).

Hamrock, B. J.↗
NASA NTRS1978

Elastohydrodynamic film thickness measurements of artificially produced surface dents and grooves

Elastohydrodynamic (EHD) film thickness measurements using optical interferometry were made of artificially produced dents and grooves under rolling and sliding conditions. These measurements are compared to stylus traces of the dent and groove profiles to determine the local deformation associated with micro-EHD pressure generation. The surface geometry associated with the dents and grooves became intimately involved in the lubrication process itself, creating local pressure variations that substantially deformed the local surface geometry, particularly under sliding conditions. The rolling results implied surface initiated fatigue, and the sliding results showed clearly the EHD surface interactions that must occur prior to scuffing failure.

Wedeven, L. D.↗
NASA NTRS1979

Elastohydrodynamic film thickness measurements of artificially produced nonsmooth surfaces

Optical interferometry is used to measure the elastohydrodynamic (EHD) film thickness associated with artificially produced nonsmooth surfaces. The nonsmooth surfaces are produced by modifying the surfaces of highly-polished balls with irregularities in the form of multiple grooves and dents. By closely spacing these irregularities it is possible not only to produce depressions on the surface of the balls but also to generate pseudo asperities. The average roughness wavelength of this artificially-produced, nonsmooth, surface approximates the average fundamental roughness wavelength found on surfaces of some mechanical elements operating under concentrated contact. By comparing the measured film thickness profiles to the stylus traces of the irregularities, it was possible to observe the local deformations associated with micro-EHD pressure generation. In both pure rolling and pure sliding conditions the artificially-produced asperities are deformed and complete separation exists between them and the mating surface. Such findings demonstrate the importance of local surface topography and resulting micro-EHD effects on the film thickness between rough surfaces in concentrated contact. Sliding data are presented which demonstrate a severe constriction, caused by the irregularities, at the exit of the Hertzian region.

Cusano, C.↗
NASA NTRS1978

Elastohydrodynamic film thickness measurements of artificially produced surface dents and grooves

Elastohydrodynamic (EHD) film thickness measurements using optical interferometry have been made of artificially produced dents and grooves under rolling and sliding conditions. These measurements are compared to stylus traces of the dent and groove profiles to determine the local deformation associated with micro-EHD pressure generation. The surface geometry associated with the dents and grooves is seen to become intimately involved in the lubrication process itself, creating local pressure variations that substantially deform the local surface geometry, particularly under sliding conditions. The rolling results have implications concerning surface initiated fatigue and the sliding results show clearly the EHD surface interactions that must occur prior to scuffing failure.

Wedeven, L. D.↗
NASA NTRS1980

Fully flooded elastohydrodynamic lubricated elliptical contacts

Emphasis is on fully flooded, elastohydrodynamic lubricated, elliptical contacts. A fully flooded conjunction is one in which the film thickness is not significantly changed when the amount of lubricant is increased. A brief description of the relevant equations used in the elastohydrodynamic lubrication of elliptical contacts is given. The most important practical aspect of the elastohydrodynamic theory is the determination of the minimum film thickness within the contact. The maintenance of a fluid film of adequate magnitude is an essential feature of the correct operation of lubricated machine elements. The results presented show the influence of contact geometry on minimum film thickness as expressed by the ellipticity parameter and the dimensionless speed, load, and materials parameters. Film thickness equations are developed for materials of high elastic modulus, such as metal, and for materials of low elastic modulus, such as rubber. In addition to the film thickness equations that are developed, plots of pressure and film thickness are presented. These theoretical solutions for film thickness have all the essential features of previously reported experimental observations based on optical interferometry. Correlation between theory and experiments is also presented.

Hamrock, B. J.↗
NASA NTRS1980

Surface temperatures and glassy state investigations in tribology

Measurements were made of the limiting shear stress for two naphthenic oils of differing molecular weight and three blends of the lower molecular weight oil and polymers of differing molecular weight. All reached the same limiting shear stress for the same temperature and pressure; although the polymer solutions reduced the limiting shear stress by about fifteen percent. A falling body viscometer was constructed to operate to 230 C and to 0.6 GPa and another was constructed to extend the pressure range to 1.1 GPa. A concentrated contact simulator was developed which allows recording of the traction force while the slide-roll ratio is continuously varied and the rolling speed is maintained essentially constant. Measurement of lubricant minimum film thickness of elliptical EHD contacts of various aspect ratios were made by optical interferometry. The experimental data were thirty percent greater than that predicted by the Hamrock and Dowson model. Preliminary development of the application of a scanning infrared radiation system to a tribological system was completed.

Bair, S.↗
NASA NTRS1979

Elastohydrodynamic film thickness measurements of artificially-produced nonsmooth surfaces

Optical interferometry is used to measure the elastohydrodynamic (EHD) film thickness associated with artificially produced, nonsmooth surfaces. The nonsmooth surfaces are produced by modifying the surfaces of highly-polished balls with irregularities in the form of multiple grooves and dents. By closely spacing these irregularities, it is possible not only to produce depressions on the surface of the balls but also to generate pseudo asperities. The average roughness wavelength of this artificially-produced, nonsmooth surface approximates the average fundamental roughness wavelength found on surfaces of some mechanical elements operating under concentrated contact. By comparing the measured film thickness profiles to the stylus traces of the irregularities, it is possible to observe the local deformations associated with micro-EHD pressure generation. In both pure rolling and pure sliding conditions, the artificially-produced 'asperities' are deformed and complete separation exists between them and the mating surface. Such findings demonstrate the importance of local surface topography and resulting micro-EHD effects on the film thickness between rough surfaces in concentrated contact. In addition, sliding data are presented which demonstrate a severe constriction, caused by the irregularities, at the exit of the Hertzian region.

Cusano, C.↗
NASA NTRS1981

Surface temperatures and glassy state investigations in tribology, part 4

Measurements were made of the limiting shear stress for two naphthenic oils of differing molecular weight and three blends of the lower molecular weight oil and polyalkylmethacrylate polymers of differing molecular weight. The two base oils reached the same limiting shear stress for the same temperature and pressure. This was also true for all the polymer solutions although the polymer reduced the limiting shear stress by about 15 percent. It is shown that limiting stress is more a function of material type than viscosity or molecular weight. A new falling body viscometer was constructed to operate to 230 C and 0.6 GPa. Another viscometer was constructed to extend the pressure range to 1.1 GPa. A concentrated contact simulator was developed which allows recording of the traction force while the slide-roll ratio is continuously varied and the rolling speed is maintained essentially constant by a single drive motor. The configuration is that of a crowned roller against a disk. Measurement of lubricant minimum film thickness of elliptical EHD contacts of various aspect ratios were made by optical interferometry. The data collected were used to evaluate the Hamrock and Dowson minimum film thickness model over a range of contract ellipticity ratio where the major axis of the contact ellipse was aligned both parallel and perpendicular to the direction of motion. A statistical analysis of the measured film thickness data showed that on the average the experimental data were 30 percent greater than the film thickness predicted by the model. Preliminary development of the application of a scanning infrared radiation system to a tribo-system was completed.

Bair, S. S.↗
NASA NTRS1980

An experimental evaluation of the Hamrock and Dowson minimum film thickness equation for fully flooded EHD point contacts

Fifty-seven measurements of the minimum lubricant film separating the elastohydrodynamically lubricated point contact of a steel crowned roller and a flat sapphire disk were made by an optical interferometry technique. The data collected were used to evaluate the Hamrock and Dowson minimum EHD film thickness model over a practical range of contact ellipticity ratio where the major axis of the contact ellipse is aligned both parallel and perpendicular to the direction of motion. A statistical analysis of the measured film thickness data showed that on the average the experimental data averaged 30 percent greater film thickness than the Hamrock and Dowson model predicts.

Koye, K. A.↗
NASA NTRS1981

Effects of artificially produced defects on film thickness distribution in sliding EHD point contacts

The effects of artificially produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact were investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, were held stationary at various locations within and in the vicinity of the contact region while the disk was rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.

Cusano, C.↗