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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Constant-Frequency Pulsed Phase-Locked-Loop Measuring Device

Constant-frequency pulsed phase-locked-loop measuring device is sensitive to small changes in phase velocity and easily automated. Based on use of fixed-frequency oscillator in measuring small changes in ultrasonic phase velocity when sample exposed to such changes in environment as changes in pressure and temperature. Automatically balances electrical phase shifts against acoustical phase shifts to obtain accurate measurements of acoustical phase shifts.

Yost, William T.↗
NASA NTRS2021

Retrieval Algorithm for the Column CO2 Mixing Ratio from Pulsed Multi-Wavelength Lidar Measurements

The retrieval algorithm for the column mixing ratio of CO2 from the measurements of a pulsed multi-wavelength integrated path differential absorption (IPDA) lidar is described. The lidar samples the shape of the 1572.33 nm CO2 absorption line at 15 or 30 wavelengths. The algorithm uses a least-squares fit between the CO2 line shape computed from a layered 10 atmosphere model to that sampled by the lidar. In addition to the column average CO2 dry air mole fraction (XCO2), several other parameters are also solved simultaneously from the fit. These include the Doppler shift in the received laser signal wavelengths, the product of the surface reflectivity and atmospheric transmission and a linear trend in the lidar receiver’s spectral response. The algorithm can also be used to solve for the average water vapor mixing ratio, which causes a secondary absorption in the wings of the CO2 absorption line under high humidity conditions. The least-squares fit is linearized about the 15 expected XCO2 value which allows the use of a standard linear least-squares fitting method and software tools. The standard deviation of the retrieved XCO2 is obtained from covariance matrix of the fit. An averaging kernel is defined similarly to that used for passive trace-gas sounding. Examples are presented of using the algorithm to retrieve XCO2 from the measurements from NASA Goddard’s airborne CO2 Sounder lidar made at a constant altitude and during spiral-down maneuvers.

Xiaoli Sun↗
NASA NTRS1967

Accuracy of laser measurements improved by pulse autocorrelator electronic system

Pulse autocorrelator electronic system discriminates between the dispersion effect of a disturbed laser signal and background noise by detecting multipath arrivals of Gaussian-shaped signal pulses. The autocorrelation function is time-dependent and can be determined by integrating the product of a received pulse and its delayed replicas.

Campanella, S. J.↗
NASA NTRS1977

Inexpensive pulse-train converter measures analog voltage

Converter measures small voltages or currents in presence of very large common-mode voltages (thousands of volts ac or dc). Advantages are low power consumption, transmission via single isolated channel, simplicity, and operation from single-polarity power supply.

Sturman, J. C.↗
NASA NTRS1979

Development of the Transient Pulse Monitor (TPM) for Scatha/P78-2

An instrumentation system developed for the detection of electrical transients on space vehicles is presented. The pulse monitor measures the electron pulse environment on a spacecraft at synchronous altitude, and characterizes signals produced by arcing between differentially charged elements on the spacecraft.

Adamo, R. C.↗
NASA NTRS1981

Satellite radar altimeters - Present and future oceanographic capabilities

Satellite radar altimeters have the ability to provide information related to ocean wave heights, wind speed, and currents. The present investigation has the objective to demonstrate the current capabilities and to indicate ways to increase the information content of the altimeter return through the use of wider bandwidth, higher pulse repetition frequencies (PRF), and multibeam. Altimeters aboard Skylab, Geos-3, and Seasat-1 have provided investigators with valuable experience in translating the radar observables into oceanic parameters. Basically, an altimeter transmits a narrow pulse and measures the time interval until the return energy from the ocean surface is received. That direct measure of the satellite altitude can be interpreted in terms of surface topography. Attention is given to altimeter oceanographic measurements, altimeter return pulse characteristics, satellite pointing and surface slopes, the adaptive tracker for terrain mapping, and a multibeam altimeter.

Townsend, W. F.↗
NASA NTRS1983

Evaluation of 20 workload measures using a psychomotor task in a moving-base aircraft simulator

The sensitivity and intrusion of 20 pilot workload assessment techniques were compared using a psychomotor loading task in a three degree-of-freedom moving-base aircraft simulator. The primary task was an instrument landing system approach and landing, with measures taken between the outer and middle markers. Three levels of psychomotor load were obtained by combined manipulation of random wind-gust disturbance level and pitch stability. Two rating scale measures and one control movement measure demonstrated sensitivity to all levels of load. Additionally, one time estimation measure and one pulse rate measure demonstrated sensitivity to some levels of load. No intrusion was found. The results of this experiment indicate that the sensitivities of workload estimation techniques vary widely, and that only a few techniques appear sensitive to psychomotor load.

Wierwille, W. W.↗
NASA NTRS1983

JPL pulsar timing observations. II - Geocentric arrival times

Monitoring of the behavior of naturally pulsating galactic radio sources, or pulsars, through regularly spaced measurements of pulse arrival times, has been conducted by several laboratories. A tabular presentation is here made of pulse arrival time measurements from the NASA Deep Space Network between late 1968 and early 1981. By expressing the measurements in ephemeris time, and referring them to the geocenter, usable tables of results have been generated for each pulsar listed in the first of the tables given. The considerations addressed by the tables are: (1) a necessary step in the study of pulsar dynamics is the reduction of topocentric arrival times to the barycenter of the solar system; (2) the tabulated data are accessible to all opinions as to the procedures to be used in interpreting arrival time data; and (3) different observing programs can usually be combined to produce an improvement in the total data set.

Downs, G. S.↗
NASA NTRS2010

Characterizing Methods of Measuring Flow-Mediated Dilation in the Brachial Artery

Regulation of vascular tone is one of the many important functions of the vascular endothelium. Endothelial dysfunction is a critical early event in the pathogenesis of atherosclerosis and occurs in the absence of angiographic disease. Flow-Mediated Dilation (FMD) is a noninvasive technique commonly used to evaluate endothelium-dependent vasodilation in humans and gauge the health of the cardiovascular system. Reductions in brachial artery FMD have been strongly correlated with disease progression and are predictive of future cardiac events. The flow stimulus for brachial artery FMD occurs as a result of the increased shear stress following deflation of an occlusion cuff around the upper arm. Using 2-dimensional ultrasound, changes in arterial diameter up to 5-minutes following cuff deflation are calculated from baseline image measurements. Along with pulsed Doppler measures of flow velocity through the artery, flow-mediated, endothelium-dependent vasodilation can be assessed. There is debate among investigators, however, about the proper positioning of the occlusion cuff during FMD testing. It is thought that placement of the cuff around the upper arm may not accurately reflect the impact of nitric oxide, a critically important molecule released as a result of the increased shear stress created by the FMD technique. Data suggest that the production of other endogenous metabolites may also contribute to FMD-related changes when positioning the cuff around the upper arm. To overcome the potential influence of such molecules, researchers now suggest that the occlusion cuff be placed below the elbow allowing a more precise estimate of nitric oxide mediated dilation. The purpose of this study is to compare the differences in FMD between the two methodologies of occlusion cuff placement. In addition, this study will determine the method that is easier for ultrasound technicians to perform and will produce a low coefficient of variance between technicians. Ultimately, the results of this study will help in tracking any adverse cardiovascular effects of spaceflight.

Callender, Ariane R.↗
NASA NTRS2011

Plasma Sheet Velocity Measurement Techniques for the Pulsed Plasma Thruster SIMP-LEX

The velocity of the first plasma sheet was determined between the electrodes of a pulsed plasma thruster using three measurement techniques: time of flight probe, high speed camera and magnetic field probe. Further, for time of flight probe and magnetic field probe, it was possible to determine the velocity distribution along the electrodes, as the plasma sheet is accelerated. The results from all three techniques are shown, and are compared for one thruster geometry.

Nawaz, Anuscheh↗
NASA NTRS2014

Airborne 2-Micron Double-Pulsed Integrated Path Differential Absorption Lidar for Column CO2 Measurement

Double-pulse 2-micron lasers have been demonstrated with energy as high as 600 millijouls and up to 10 Hz repetition rate. The two laser pulses are separated by 200 microseconds and can be tuned and locked separately. Applying double-pulse laser in DIAL system enhances the CO2 measurement capability by increasing the overlap of the sampled volume between the on-line and off-line. To avoid detection complicity, integrated path differential absorption (IPDA) lidar provides higher signal-to-noise ratio measurement compared to conventional range-resolved DIAL. Rather than weak atmospheric scattering returns, IPDA rely on the much stronger hard target returns that is best suited for airborne platforms. In addition, the IPDA technique measures the total integrated column content from the instrument to the hard target but with weighting that can be tuned by the transmitter. Therefore, the transmitter could be tuned to weight the column measurement to the surface for optimum CO2 interaction studies or up to the free troposphere for optimum transport studies. Currently, NASA LaRC is developing and integrating a double-Pulsed 2-micron direct detection IPDA lidar for CO2 column measurement from an airborne platform. The presentation will describe the development of the 2-micron IPDA lidar system and present the airborne measurement of column CO2 and will compare to in-situ measurement for various ground target of different reflectivity.

Singh, Upendra N.↗
NASA NTRS1976

Measurement of lake ice thickness with a short-pulse radar system

Measurements of lake ice thickness were made during March 1975 at the Straits of Mackinac by using a short-pulse radar system aboard an all-terrain vehicle. These measurements were compared with ice thicknesses determined with an auger. Over 25 sites were explored which had ice thicknesses in the range 29 to 60 cm. The maximum difference between radar and auger measurements was less than 9.8 percent. The magnitude of the error was less than + or - 3.5 cm. The NASA operating short-pulse radar system used in monitoring lake ice thickness from an aircraft is also described.

Cooper, D. W.↗
NASA NTRS1977

Short pulse radar used to measure sea surface wind speed and SWH

A joint airborne measurement program is being pursued by NRL and NASA Wallops Flight Center to determine the extent to which wind speed and sea surface significant wave height (SWH) can be measured quantitatively and remotely with a short pulse (2 ns), wide-beam (60 deg), nadir-looking 3-cm radar. The concept involves relative power measurements only and does not need a scanning antenna, Doppler filters, or absolute power calibration. The slopes of the leading and trailing edges of the averaged received power for the pulse limited altimeter are used to infer SWH and surface wind speed. The interpretation is based on theoretical models of the effects of SWH on the leading edge shape and rms sea-surface slope on the trailing-edge shape. The models include the radar system parameters of antenna beam width and pulsewidth.

Hammond, D. L.↗
NASA NTRS1995

PPT Thrust Stand

A torsional-type thrust stand has been designed and built to test Pulsed Plasma Thrusters (PPT's) in both single shot and repetitive operating modes. Using this stand, momentum per pulse was determined strictly as a function of thrust stand deflection, spring constant, and natural frequency. No empirical corrections were required. The accuracy of the method was verified using a swinging impact pendulum. Momentum transfer data between the thrust stand and the pendulum were consistent to within 1%. Following initial calibrations, the stand was used to test a Lincoln Experimental Satellite (LES-8/9) thruster. The LES-8/9 system had a mass of approximately 7.5 kg, with a nominal thrust to weight ratio of 1.3 x 10(exp -5). A total of 34 single shot thruster pulses were individually measured. The average impulse bit per pulse was 266 microN-s, which was slightly less than the value of 300 microN-s published in previous reports on this device. Repetitive pulse measurements were performed similar to ordinary steady-state thrust measurements. The thruster was operated for 30 minutes at a repetition rate of 132 pulses per minute and yielded an average thrust of 573 microN. Using average thrust, the average impulse bit per pulse was estimated to be 260 microN-s, which was in agreement with the single shot data. Zero drift during the repetitive pulse test was found to be approximately 1% of the measured thrust.

Haag, Thomas W.↗
NASA NTRS1980

Langmuir probe measurements of double-layers in a pulsed discharge

Langmuir probe measurements were carried out which confirm the occurrence of double-layers in an argon positive column. Pulsing the discharge current permitted probe measurements to be performed in the presence of the double-layer. Supplementary evidence, obtained from DC and pulsed discharges, indicated that the double-layers formed in the two modes of operation were similar. The double-layers observed were weak and stable; their relation to other classes of double-layers are discussed, and directions for future work are suggested.

Levine, J. S.↗
NASA NTRS1980

Langmuir probe measurements of double-layers in a pulsed discharge

Langmuir probe measurements have been carried out which confirm the occurrence of double-layers in an argon positive column. Pulsing the discharge current permitted probe measurements to be performed in the presence of the double-layer. Supplementary evidence, obtained from dc and pulsed discharges, indicated that the double-layers formed in the two modes of operation were similar. The double-layers observed were weak and stable; their relation to other classes of double-layers is discussed, and directions for future work are suggested.

Levine, J. S.↗