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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Laser techniques for arc jet plasma diagnostics; continuation of a feasibility and design study

This study is concerned with the continuation of a feasibility and design study of laser-based diagnostic techniques for the non-instrusive measurement of species concentrations, temperatures, and velocity in the low density, high enthalpy flow through the arc-heated wind tunnel facility (ARMSEF) at NASA/JSC. Last summer several laser-induced radiation scattering methods were investigated and some preliminary measurements of the spectral distribution of radiation emitted by the arc-heated gas flow were made. Based upon those preliminary measurements and subsequent investigations, four laser-induced radiation scattering methods were selected for further detailed study, and preliminary design of a measurement system has been undertaken. Further measurements of the spectral distribution of radiation emitted from the arc-heated free stream and shock layer flows, using a redesigned measurement system, have been made for one axial position in the flow for a range of tunnel operating power levels. Further study of the literature for physical property data, theoretical models of processes, and applications of the diagnostic methods has been also carried out.

Wierum, F. A.↗
NASA NTRS1986

Resonance ionization mass spectrometry for isotopic abundance measurements

Resonance ionization mass spectrometry (RIMS) is a relatively new laser-based technique for the determination of isotopic abundances. The resonance ionization process depends upon the stepwise absorption of photons from the laser, promoting atoms of the element of interest through progressively higher electronic states until an ion is formed. Sensitivity arises from the efficiency of the resonant absorption process when coupled with the power available from commercial laser sources. Selectivity derives naturally from the distinct electronic structure of different elements. This isobaric discrimination has provided the major impetus for development of the technique. Resonance ionization mass spectrometry was used for analysis of the isotopic abundances of the rare earth lutetium. Isobaric interferences from ytterbium severely effect the ability to measure small amounts of the neutron-deficient Lu isotopes by conventional mass spectrometric techniques. Resonance ionization for lutetium is performed using a continuous-wave laser operating at 452 nm, through a sequential two-photon process, with one photon exciting the intermediate resonance and the second photon causing ionization. Ion yields for microgram-sized quantities of lutetium lie between 10(6) and 10(7) ions per second, at overall ionization efficiencies approaching 10(-4). Discrimination factors against ytterbium greater than 10(6) have been measured. Resonance ionization for technetium is also being explored, again in response to an isobaric interference, molybdenum. Because of the relatively high ionization potential for Tc, three-photon, two-color RIMS processes are being developed.

Miller, C. M.↗
NASA NTRS1986

Optical technique to characterize heavy rain

A technique to measure the size and velocity of raindrops is presented and experimental and numerical results discussed. The technique bases the droplet size on the absolute intensity of the light scattered when the droplets cross a laser-based probe volume. The velocity is obtained from the Doppler frequency. A size range of 0.1 mm to 9 mm was covered with overlapping ranges. Experiments were conducted with simulated rain sprays except that the local LWC was much larger than the values encountered in natural rain. The accuracy of the size measurement was not strongly affected by spray interference, but it showed a clear dependence with the droplet shape. A simple numerical model based on the light reflected from ellipsoids attempts to explain the relationship between droplet shape and absolute scattered light.

Hess, C. F.↗
NASA NTRS1986

Short fatigue crack behavior in notched 2024-T3 aluminum specimens

Single-edge, semi-circular notched specimens of Al 2024-T3, 2.3 mm thick, were cyclicly loaded at R-ratios of 0.5, 0.0, -1.0, and -2.0. The notch roots were periodically inspected using a replica technique which duplicates the bore surface. The replicas were examined under an optical microscope to determine the initiation of very short cracks and to monitor the growth of short cracks ranging in length from a few tens of microns to the specimen thickness. In addition to short crack growth measurements, the crack opening displacement (COD) was measured for surface cracks as short as 0.035 mm and for through-thickness cracks using the Interferometric Strain/Displacement Gage (ISDG), a laser-based optical technique. The growth rates of short cracks were faster than the long crack growth rates for R-ratios of -1.0 and -2.0. No significant difference between short and long crack growth rates was observed for R = 0.0. Short cracks had slower growth rates than long cracks for R = 0.5. The crack opening stresses measured for short cracks were smaller than those predicted for large cracks, with little difference appearing for positive R-ratios and large differences noted for negative R-ratios.

Lee, J. J.↗
NASA NTRS1986

Laser remote sensing of the atmosphere

A guide to the extant literature concerning remote sensing of the atmosphere by laser-based devices is presented, with emphasis on surveys of the field as well as the most important recent results. Topics surveyed include measurements of aerosol constituents using lidar, the differential absorption lidar technique, the use of laser long-path differential absorption, Raman scattering techniques, and fluorescence lidar techniques. Special attention is given to measuring wind velocity using CO2 heterodyne lidar systems.

Grant, William B.↗
NASA NTRS1986

Short fatigue cracks in notched aluminum specimens

The short-crack fatigue behavior in notched specimens of Al 2024-T3 was studied at values of the stress ratio, R, equal to 0.5, 0.0, -1.0, and -2.0. Crack growth was monitored using a replica technique for cracks ranging in length from a few tens of a micron to the specimen's thickness (2.3 mm). Crack opening displacement was measured for surface cracks as short as 0.035 mm using the interferometric strain/displacement gage, a laser-based optical technique described by Sharpe (1982). It was found that the growth rates of short cracks were faster than the rates of long cracks for R values of -1.0 and -2.0. No significant difference was observed for R = 0.0, and at R = 0.5, the short cracks actually grew more slowly that the long ones. At all R values, the closure stresses measured for short cracks were smaller than those predicted for large cracks.

Lee, J. J.↗
NASA NTRS1987

Air- and oxygen-broadening coefficients for the O2 rotational line at 60.46/cm

Using an NBS laser-based tunable far-infrared spectrometer, the air- and oxygen-broadening coefficients were measured for the J = 10 - 10, N = 11 - 9 O2 rotational transition at 60.46/cm (1.812 THz). The air-broadening coefficient is 5.04 + or - 0.38 x 10 to the -7th/cm/Pa (0.0511 + or - 0.0039/cm/atm) (HWHM) at 245 + or - 6 K; the oxygen-broadening coefficient is 4.92 + or - 0.47 x 10 to the -7th/cm/Pa (0.0499 + or - 0.0048/cm/atm) (HWHM) at 259 + or -2 K. These direct experimental measurements of the air-broadening coefficient should improve the accuracy of retrieval calculations for far-infrared stratospheric balloon experiments which use O2 rotational lines to calibrate the viewing geometry.

Jennings, D. A.↗
NASA NTRS1988

Laser pyrometry

A method of determining the emissivity of a hot target from a laser-based reflectance measurement which is conducted simultaneously with a measurement of the target radiance is described. Once the correct radiance and emissivity are determined, one calculates the true target temperature from these parameters via the Planck equations. The design and performance of a laser pyrometer is described. The accuracy of laser pyrometry and the effect of ambient radiance are addressed.

Stein, Alexander↗
NASA NTRS1987

Advanced communications, tracking, robotic vision technology for space applications

Recent advancements in the areas of tracking, communications, and robotics vision sensors being pursued within NASA, as applicable to space programs, are presented. Optical and laser-based communications and tracking systems and applications to space programs are discussed. Communication systems for multiple access, broadband, high data rate, and efficient operations are given. Current efforts at 20/30 GHz and millimeter wave bands are summarized. The use of optical data processing in control system applications for rendezvous and docking is presented. Robotics vision, based on television, laser, and microwave sensors for space applications, is discussed. The fusion of these technologies for remote control, station keeping, tracking, inspection, and satellite repair is detailed.

Krishen, Kumar↗
NASA NTRS1988

Semiconductor lasers for space sensor applications

Despite their intrinsic power limitations, semiconductor laser diodes are essential for laser-based spaceborne sensor systems covering a wide spectral range, fulfilling such roles as pumping and injection-locking. They may also be used as direct sources in shorter-range operations. AlGaAs laser arrays have been developed for 810-nm band pumping in Nd:YAG lasers otherwise emitting at 1.064 nm. Additional roles include their use as low-power injection seeds, locking a solid-state laser into a specific desired wavelength.

Katz, Joseph↗
NASA NTRS1988

An experimental study of the closure behavior of short and long cracks

Experiments were conducted on 2024-T3 aluminum specimens. The laser-based interferometric strain/displacement optical system was used to measure crack opening displacement. The displacement data were measured near the crack tip, at the crack mouth, and at other locations along the crack line for both short and long cracks. The dependence of opening load ratio on measurement locations was observed. The ratio decreased systematically as the measurement locations moved away from the crack tip. However, the ratio stayed roughly the same for the near tip surface measurements at various crack lengths.

Su, X.↗
NASA NTRS1988

COD measurements at various positions along a crack

Load versus crack-opening-displacement (COD) was measured at various positions along the border of a fatigue crack as it grew from a small surface crack on the edge of an aluminum specimen into a through-the-thickness crack. Displacements were measured with a laser-based interferometric system with a gage length of 70 microns and a resolution of 0.01 micron. These load-COD curves can be used to determine opening loads and thereby investigate the effect of closure on the growth of small cracks. In general, the opening loads decrease as the crack grows.

Sharpe, W. N., Jr.↗
NASA NTRS1991

Cryogenic combustion laboratory

The objective is to establish a major experimental laboratory for studying fundamental processes such as mixing and combustion under liquid rocket engine conditions. The capability of this laboratory will include operation using a variety of fuel and oxidizer systems including liquid oxygen and liquid hydrocarbons. In addition to providing the proper facilities for supplying and controlling these fuels and oxidizers, a specific effort is being made to provide a state-of-the-art diagnostic capability for combustion measurements. In particular, optical and laser-based techniques are being emphasized for measurements of species, velocities, and spray characteristics.

Santoro, R. J.↗
NASA NTRS1991

Laser diagnostics on a hypersonic combustor

NASA-Langley has implemented a laser-based multipoint/multiparameter diagnostics system at its hypersonic direct-connect combustor, in order to measure both temperature and majority species densities in two dimensions, using spatially-scanned CARS; in addition, line-imaged measurements of radical densities are simultaneously generated by LIF at any of several planes downstream of the fuel injector. Initial experimental trials have demonstrated successful detection of one-dimensional images of OH density, as well as CARS N2-temperature measurements, in the turbulent reaction zone of the hypersonic combustor.

Taylor, David J.↗
NASA NTRS1990

NASA programs in advanced sensors and measurement technology for aeronautical applications

NASA involvement in the development, implementation, and experimental use of advanced aeronautical sensors and measurement technologies is presently discussed within the framework of specific NASA research centers' activities. The technology thrusts are in the fields of high temperature strain gages and microphones, laser light-sheet flow visualization, LTA, LDV, and LDA, tunable laser-based aviation meteorology, and fiber-optic CARS measurements. IR thermography and close-range photogrammetry are undergoing substantial updating and application. It is expected that 'smart' sensors will be increasingly widely used, especially in conjunction with smart structures in aircraft and spacecraft.

Conway, Bruce A.↗
NASA NTRS1990

A software system for laser design and analysis

A laser-material database and laser-modeling software system for designing lasers for laser-based Light Detection And Ranging (LIDAR) systems are presented. The software system consists of three basic sections: the database, laser models, and interface software. The database contains the physical parameters of laser, optical, and nonlinear materials required by laser models. The models include efficiency calculations, electrooptical component models, resonator, amplifier, and oscillator models, and miscellaneous models. The interface software provides a user-friendly interface between the user and his personal data files, the database, and models. The structure of the software system is essentially in place, while future plans call for upgrading the computer hardware and software in order to support a multiuser multitask environment.

Cross, P. L.↗
NASA NTRS1990

Scientific applications of frequency-stabilized laser technology in space

A synoptic investigation of the uses of frequency-stabilized lasers for scientific applications in space is presented. It begins by summarizing properties of lasers, characterizing their frequency stability, and describing limitations and techniques to achieve certain levels of frequency stability. Limits to precision set by laser frequency stability for various kinds of measurements are investigated and compared with other sources of error. These other sources include photon-counting statistics, scattered laser light, fluctuations in laser power, and intensity distribution across the beam, propagation effects, mechanical and thermal noise, and radiation pressure. Methods are explored to improve the sensitivity of laser-based interferometric and range-rate measurements. Several specific types of science experiments that rely on highly precise measurements made with lasers are analyzed, and anticipated errors and overall performance are discussed. Qualitative descriptions are given of a number of other possible science applications involving frequency-stabilized lasers and related laser technology in space. These applications will warrant more careful analysis as technology develops.

Schumaker, Bonny L.↗
NASA NTRSDate not supplied

Laser Forming of Sheet Metal for In-Space Manufacturing Applications

As the in-space economy matures, the migration of typically Earth-bound manufacturing methods, such as metal forming and joining, up to space will be required to meet the increasing demand for refueling and supply depots, habitats, laboratories, lunar surface structures, and sites for deep-space exploration shipbuilding. Only in this way can the magnitude of individual structures begin to exceed what can be launched, deployed, docked, or inflated and allow true economies of scale to be unlocked in space. However, typical terrestrial methods of forming and shaping sheet metal require massive machinery with the ability to deflect reaction forces to a large mass in a fixed reference frame (Earth). To both limit up-mass required for manufacture and to mitigate the issues of reaction forces in the relative reference frames of space, a non-contact, laser-based method of forming metal sheet is proposed. NASA Marshall Space Flight Center (MSFC), in cooperation with DARPA and the University of Florida (UF), have begun investigation of non-contact methods of laser forming sheet metal in thermal vacuum (TVAC) conditions to great success. To date, several grades of aluminum, stainless steel, and titanium coupons have been formed via laser-induced internal stresses in these metals at both ambient atmosphere and vacuum conditions. Temperatures in these tests ranged from -120 to 60 C, and though the total energy required to induce strain does vary with workpiece temperature and environmental pressure, the method remains predictable and controllable for the materials investigated. It is believed that this method will revolutionize manufacturing in-space as it not only continues to build upon the capabilities of the laser (sensing, marking, cutting, drilling, joining, and now forming) as an all-in-one tool, but also reduces the need to counteract forming forces as would be required in mechanical bending. In theory, all required stress to induce bending is generated through thermal gradient and strain within the workpiece, meaning that the need for reaction control and fuel expense on-orbit will be limited. Archimedes once stated, “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world”. With a laser as our lever and our workpiece its own fulcrum, we can move the world’s manufacturing into space.

Laser↗