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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Characterizations of a KHz Pulsed Laser Detection System

A KHz Pulsed Laser Detection System was developed employing the concept of charge integration with an electrometer, in the NASA Goddard Space Flight Center, Code 618 Calibration Lab for the purpose of using the pulsed lasers for radiometric calibration. Comparing with traditional trans-impedance (current-voltage conversion) detection systems, the prototype of this system consists of a UV-Enhanced Si detector head, a computer controlled shutter system and a synchronized electrometer. The preliminary characterization work employs light sources running in either CW or pulsed mode. We believe this system is able to overcome the saturation issue when a traditional trans-impedance detection system is used with the pulsed laser light source, especially with high peak-power pulsed lasers operating at kilohertz repetition rates (e.g. Ekspla laser or KHz OPO). The charge integration mechanism is also expected to improve the stability of measurements for a pulsed laser light source overcoming the issue of peak-to-peak stability. We will present the system characterizations including signal-to-noise ratio and uncertainty analysis and compare results against traditional trans-impedance detection systems.

Ding, Leibo↗
NASA NTRS2021

ICESat-2 Pointing Calibration and Geolocation Performance

ICESat-2 science requirements are dependent on the accurate real-time pointing control (i.e. geolocation control) and post-processed geolocation knowledge of the laser altimeter surface returns. Pre-launch pointing alignment errors and post-launch pointing alignment variation result in large geolocation errors that must be calibrated on orbit. In addition, the changing sun-orbit geometry causes thermal-mechanical forced laser frame alignment variations at the orbit period and trends from days, weeks and months. Early mission analysis computed precise post-launch laser beam alignment calibration. The alignment calibration was uploaded to the spacecraft and enabled the pointing control performance to achieve 4.4 ± 6.0 m, a significant improvement over the 45 m (1 σ) mission requirement. Laser frame alignment calibrations are used to reduce the alignment bias and time variation, as well as the orbital variation contributions to geolocation knowledge error from 6 m to 1.7 m (1 σ). Relative beam alignment of the six beams is calibrated and shown to contribute between 0.5 ± 0.1 m and 2.4 ± 0.2 m of remaining geolocation knowledge error. Independent geolocation assessment based on comparison to high-resolution digital elevation models agrees well with the calibration geolocation error estimates. The analysis demonstrates the ICESat-2 mission is performing far better than its geolocation knowledge requirement of 6.5 m (1 σ) after the laser frame alignment bias variation and orbital variation calibrations have been applied. Remaining geolocation error is beam dependent and ranges from 2.5 m for beam 6 to 4.4 m for beam 2 (mean + 1 σ).

S. B. Luthcke↗
NASA NTRS1993

Calibration of the forward-scattering spectrometer probe - Modeling scattering from a multimode laser beam

Scattering calculations using a detailed model of the multimode laser beam in the forward-scattering spectrometer probe (FSSP) were carried out using a recently developed extension to Mie scattering theory. From this model, new calibration curves for the FSSP were calculated. The difference between the old calibration curves and the new ones is small for droplet diameters less than 10 microns, but the difference increases to approximately 10 percent at diameters of 50 microns. When using glass beads to calibrate the FSSP, calibration errors can be minimized by using glass beads of many different diameters, over the entire range of the FSSP. If the FSSP is calibrated using one-diameter glass beads, then the new formalism is necessary to extrapolate the calibration over the entire range.

Hovenac, Edward A.↗
NASA NTRS1993

Calibration of the Forward-scattering Spectrometer Probe: Modeling Scattering from a Multimode Laser Beam

Scattering calculations using a more detailed model of the multimode laser beam in the forward-scattering spectrometer probe (FSSP) were carried out by using a recently developed extension to Mie scattering theory. From this model, new calibration curves for the FSSP were calculated. The difference between the old calibration curves and the new ones is small for droplet diameters less than 10 micrometers, but the difference increases to approximately 10% at diameters of 50 micrometers. When using glass beads to calibrate the FSSP, calibration errors can be minimized, by using glass beads of many different diameters, over the entire range of the FSSP. If the FSSP is calibrated using one-diameter glass beads, then the new formalism is necessary to extrapolate the calibration over the entire range.

Hovenac, Edward A.↗
NASA NTRS2017

Unreported Emission Lines of Rb, Ce, La, Sr, Y, Zr, Pb and Se Detected Using Laser-Induced Breakdown Spectroscopy

Information on emission lines for major and minor elements is readily available from the National Institute of Standards and Technology (NIST) as part of the Atomic Spectra Database. However, tabulated emission lines are scarce for some minor elements and the wavelength ranges presented on the NIST database are limited to those included in existing studies. Previous work concerning minor element calibration curves measured using laser-induced break-down spectroscopy found evidence of Zn emission lines that were not documented on the NIST database. In this study, rock powders were doped with Rb, Ce, La, Sr, Y, Zr, Pb and Se in concentrations ranging from 10 percent to 10 parts per million. The difference between normalized spectra collected on samples containing 10 percent dopant and those containing only 10 parts per million were used to identify all emission lines that can be detected using LIBS (Laser-Induced Breakdown Spectroscopy) in a ChemCam-like configuration at the Mount Holyoke College LIBS facility. These emission spectra provide evidence of many previously undocumented emission lines for the elements measured here.

LIBS↗
NASA NTRS1991

The lightcraft project

Rensselaer Polytechnic Institute has been developing a transatmospheric 'Lightcraft' technology which uses beamed laser energy to propel advanced shuttle craft to orbit. In the past several years, Rensselaer students have analyzed the unique combined-cycle Lightcraft engine, designed a small unmanned Lightcraft Technology Demonstrator, and conceptualized larger manned Lightcraft - to name just a few of the interrelated design projects. The 1990-91 class carried out preliminary and detailed design efforts for a one-person 'Mercury' Lightcraft, using computer-aided design and finite-element structural modeling techniques. In addition, they began construction of a 2.6 m-diameter, full-scale engineering prototype mockup. The mockup will be equipped with three robotic legs that 'kneel' for passenger entry and exit. More importantly, the articulated tripod gear is crucial for accurately pointing at, and tracking the laser relay mirrors, a maneuver that must be performed just prior to liftoff. Also accomplished were further design improvements on a 6-inch-diameter Lightcraft model (for testing in RPI's hypersonic tunnel), and new laser propulsion experiments. The resultant experimental data will be used to calibrate Computational Fluid Dynamic (CFD) codes and analytical laser propulsion models that can simulate vehicle/engine flight conditions along a transatmospheric boost trajectory. These efforts will enable the prediction of distributed aerodynamic and thruster loads over the entire full-scale spacecraft.

Messitt, Don G.↗
NASA NTRS1982

Measurement of the dispersive and refractive indices of germanium using diode lasers

Germanium Fabry-Perot etalons are commonly used in diode laser spectroscopy to establish relative frequency calibration scales for molecular absorption spectra. Typically the channel spectrum of the etalon is recorded simultaneously with the molecular spectrum as the laser injection current is tuned linearly, and the etalon free spectral range (fringe spacing) is used to measure the frequency separations among lines in the molecular spectrum. For this purpose, the etalon free spectral range must be known for the measurement wavelength, and this in turn relies on knowledge of the etalon length and the dispersive index at this wavelength. It is pointed out that the most satisfactory approach is to measure directly the free spectral range or dispersive index of the etalon at the wavelength of interest. A description is presented of measurements of this type, performed near 7.9 and 10.1 micrometers for a 7.7-cm long germanium etalon.

Jennings, D. E.↗
NASA NTRS2019

Method for the Absolute Calibration of the Location and Orientation of Large-Format Detectors Using Laser Radar

A method of mapping pixel locations of a detector array includes measuring a location on the detector array, initiating a frame readout of the detector array, measuring a location of one or more metrology targets on the detector array, analyzing the frame readout to identify a pixel at the location on the detector array, and defining a location of the identified pixel with respect to the location of the one or more metrology targets. Subsequent measurement of the metrology targets alone by another metrology system allows one to infer the six degree of freedom alignment of the detector array in space.

Coulter, Phillip↗
NASA NTRSDate not supplied

Initial On-Orbit Spectral Calibration of the PACE Ocean Color Instrument

The NASA Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission Project Science Team has used Ocean Color Instrument (OCI) measurements of Fraunhofer lines in spectra of sunlight reflected by the solar diffuser and measurements of atmospheric absorption bands in cloudtop and ocean spectra to characterize the spectral calibration of OCI on orbit. Multiple lines have been analyzed for both the ultraviolet to visible (UVVIS, 340−607 nm) and visible to near-infrared (VISNIR, 597−897 nm) grating spectrographs. The spectrographs yield hyperspectral observations with 5 nm bandwidths and 0.625 nm sampling intervals. The on-orbit observations have been compared with the prelaunch spectral calibration of OCI performed by the Goddard Laser for Absolute Measurement of Radiance (GLAMR) during thermal vacuum testing to track any changes in the calibration since launch. The calibration analyzed the line positions and strengths for the Fraunhofer lines for each spectrograph by comparing the solar spectra measured by OCI with predicted solar spectra derived from the solar reference spectrum and the BRDF of the solar diffuser, convolved with the OCI relative spectral responses. The calibration also compared the line positions of the atmospheric absorption bands with the model transmissions used by the PACE Project. The line position comparisons show that the root mean square (RMS) spectral difference between the measured and predicted spectra is 0.15 nm, the average spectral shift is 0.062 nm, and the residual spectral dispersion over the wavelength range of the Fraunhofer lines is 0.17 nm. All three estimates of the spectral accuracy of OCI meet the instrument functional requirement of a spectral accuracy of 0.5 nm and are well within the 0.625 nm sampling interval of the data. The line strength comparisons between measured and predicted spectra are essentially the same. These results show that the spectral calibration of OCI on orbit has not drifted since the prelaunch calibration of OCI by GLAMR and that the on-orbit spectral calibration of OCI is stable over time. These results also provide a baseline for monitoring the future spectral performance of OCI on orbit.

Radiometric Calibration↗
NASA NTRS1972

A description of the lunar ranging station at McDonald Observatory.

The equipment of this station which has been in operation since the deployment of the first corner reflector by the Apollo 11 astronauts. The McDonald 2.7-m telescope is used for both transmission and reception of pulsed ruby laser light during three 45-minute daily laser runs about three weeks in a month. The present laser pulse width, timing system, calibration procedures, and signal levels are designed to achieve ranging with an accuracy to 1 nanosecond. The data rates obtained since September, 1970, are consistent with the scientific commitments of the lunar ranging program. Most of the over 200 acquisitions obtained have an accuracy to better than plus or minus 30 cm. Details of the telescope matching optics, guiding and timing equipment, and calibration procedures are discussed. Representative lunar range data are included.

Silverberg, E. C.↗
NASA NTRS1991

GLOBE backscatter - Climatologies and mission results

The Global Backscatter Experiment (GLOBE) goals require intensive study of the global climatology of atmospheric aerosol backscatter at IR wavelengths. Airborne and ground-based lidars have been developed to measure atmospheric backscatter profiles at CO2 laser wavelengths. Descriptions of the calibration techniques and selected measurement results are presented.

Menzies, Robert T.↗
NASA NTRS1997

An Experimental Study of a Radially Arranged Thin Film Heat Flux Gauge

A new thin-film heat-flux gauge was designed and fabricated on three different substrate materials. Forty pairs of Pt-Pt/10% Rh thermocouple junctions were deposited in a circular pattern on the same plane of the substrate. Over the thermocouples, 5 and 10 micron thick thermal resistance layers were deposited to create a temperature gradient across those layers. Calibration and testing of these gauges were carried out in an arc-lamp calibration facility. The heat flux calculated from the gauge output is in good agreement with the value obtained from the pre-calibrated standard sensor. A CO2 laser was also used to test the steady-state and dynamic responses of the heat-flux gauge. During the steady-state test, the time constant for the heating period was 30 s. The frequency response of the heat-flux gauge was measured in the frequency domain using a CO2 laser and a chopper. The responses from an infrared detector and the heat-flux gauge were measured simultaneously and compared. It was found that the thin-film heat-flux gauge has a dynamic frequency response of 3 kHz.

Cho, Christoper S. K.↗
NASA NTRS2001

Characterization of Measurement Error Sources in Doppler Global Velocimetry

Doppler global velocimetry uses the absorption characteristics of iodine vapor to provide instantaneous three-component measurements of flow velocity within a plane defined by a laser light sheet. Although the technology is straightforward, its utilization as a flow diagnostics tool requires hardening of the optical system and careful attention to detail during data acquisition and processing if routine use in wind tunnel applications is to be achieved. A development program that reaches these goals is presented. Theoretical and experimental investigations were conducted on each technology element to determine methods that increase measurement accuracy and repeatability. Enhancements resulting from these investigations included methods to ensure iodine vapor calibration stability, single frequency operation of the laser and image alignment to sub-pixel accuracies. Methods were also developed to improve system calibration, and eliminate spatial variations of optical frequency in the laser output, spatial variations in optical transmissivity and perspective and optical distortions in the data images. Each of these enhancements is described and experimental examples given to illustrate the improved measurement performance obtained by the enhancement. The culmination of this investigation was the measured velocity profile of a rotating wheel resulting in a 1.75% error in the mean with a standard deviation of 0.5 m/s. Comparing measurements of a jet flow with corresponding Pitot measurements validated the use of these methods for flow field applications.

Meyers, James F.↗
NASA NTRS1992

Saturated fluorescence measurements of the hydroxyl radical in laminar high-pressure C2H6/O2/N2 flames

Saturation of a transition of the OH molecule in high-pressure flames is demonstrated by obtaining saturation curves in C2H6/O2/N2 laminar flames at 1, 6.1, 9.2, and 12.3 atm. Quantitative fluorescence measurements of OH number density at pressures to 12.3 atm are presented. To assess the efficacy of the balanced cross-rate model for high-pressure flames, laser-saturated fluorescence measurements, which were calibrated in an atmospheric-pressure flame, are compared with absorption measurements at 3.1 and 6.1 atm. At 3.1 atm the absorption and fluorescence measurements compare well. At 6.1 atm, however, the concentrations given by lasre-saturated fluorescence are about 25 percent lower than the absorption values, indicating some depletion of the laser-coupled levels beyond that at atmospheric pressure. By using a reasonable estimate for the finite sensitivity to quenching, it is anticipated that fluorescence measurements that are calibrated at 1 atm can be applied to flames at about 10 atm with absolute errors within +/- 50 percent.

Carter, Campbell D.↗
NASA NTRS2014

Optical Multi-Gas Monitor Technology Demonstration on the International Space Station

There are a variety of both portable and fixed gas monitors onboard the International Space Station (ISS). Devices range from rack-mounted mass spectrometers to hand-held electrochemical sensors. An optical Multi-Gas Monitor has been developed as an ISS Technology Demonstration to evaluate long-term continuous measurement of 4 gases. Based on tunable diode laser spectroscopy, this technology offers unprecedented selectivity, concentration range, precision, and calibration stability. The monitor utilizes the combination of high performance laser absorption spectroscopy with a rugged optical path length enhancement cell that is nearly impossible to misalign. The enhancement cell serves simultaneously as the measurement sampling cell for multiple laser channels operating within a common measurement volume. Four laser diode based detection channels allow quantitative determination of ISS cabin concentrations of water vapor (humidity), carbon dioxide, ammonia and oxygen. Each channel utilizes a separate vertical cavity surface emitting laser (VCSEL) at a different wavelength. In addition to measuring major air constituents in their relevant ranges, the multiple gas monitor provides real time quantitative gaseous ammonia measurements between 5 and 20,000 parts-per-million (ppm). A small ventilation fan draws air with no pumps or valves into the enclosure in which analysis occurs. Power draw is only about 3 W from USB sources when installed in Nanoracks or when connected to 28V source from any EXPRESS rack interface. Internal battery power can run the sensor for over 20 hours during portable operation. The sensor is controlled digitally with an FPGA/microcontroller architecture that stores data internally while displaying running average measurements on an LCD screen and interfacing with the rack or laptop via USB. Design, construction and certification of the Multi-Gas Monitor were a joint effort between Vista Photonics, Nanoracks and NASA-Johnson Space Center (JSC). Vista Photonics developed the core technology and built the sensor. Nanoracks designed, constructed the enclosure, interfaces, and battery power management circuitry, integrated all subsystems into the enclosure, and then managed the certification tests, documentation and manifesting. The unit was calibrated in the JSC Toxicology Laboratory. The Multi-Gas Monitor is manifested to fly as a technology demonstration to the ISS in November 2013 and will operate for at least 6 months with data sent to the ground for evaluation. The primary goal is to demonstrate long term interference free operation in the real spacecraft environment.

Pilgrim, Jeffrey S.↗
NASA NTRS2004

Recent Results in ICESat Geolocation Parameter Calibration from Range Residual Analysis

The Ice, Cloud and land Elevation Satellite (ICESat), launched on January 12, 2003, carries the Geoscience Laser Altimeter System (GLAS), which has a primary measurement of short-pulse laser-ranging to the Earths surface at 1064 nm wavelength at a rate of 40 pulses per second. The instrument has collected (at the time of this writing) over 540 million observations of the Earth's surface including precise elevation measurements of the ice sheets, sea ice roughness and thickness, ocean and land surface elevations and surface reflectivity. The accurate geolocation of GLASs surface returns, the spots from which the laser energy reflects on the Earths surface, is a critical issue in the scientific application of these data. Pointing, ranging, timing and orbit errors must be compensated to accurately geolocate the laser altimeter surface returns. Towards this end, the laser range observations can be fully exploited in an integrated residual analysis to accurately calibrate these geolocation/instrument parameters. The ICESat laser altimeter data have been simultaneously processed as direct altimetry from ocean sweeps and around-the-world scans along with dynamic crossovers in order to calibrate pointing ranging and timing. The analysis has resolved complex time varying signal resulting from thermal variations of instrument pointing and boresite shadowing. The calibration methodology and current calibration results are discussed along with future efforts and current geolocation accuracies.

Luthcke, Scott B.↗
NASA NTRS2021

Melt Pool Imaging using a Configurable Architecture Additive Testbed System

This paper describes the inline (coaxial to laser) near infrared (NIR) camera sensor on the Configurable Architecture Additive Testbed (CAAT). The CAAT is an instrument that provides the capability to investigate laser based additive manufacturing (AM) processes and is configured for the metal powder bed fusion process. A low cost NIR camera is radiometrically calibrated to obtain coaxial, inline, imagery of laser generated melt pools. The camera capabilities, system optical path, and the uncertainty in the temperature measurement from NIR surface area scans on a bare titanium alloy plate are presented and discussed. The surface radiance measurements are compared to optical microscopy images of the melt pool width and depth. A metallic additive manufacturing process thermal model is developed in order to predict thermal distributions during laser scanning. The predicted thermal distributions by the model for different configurations are compared to the coaxial NIR measurements and discussed.

Additive manufacturing↗