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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 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Goddard's new 39,000 cubic foot low frequency acoustic test facility

The Goddard Space Flight Center's 39,000 cu ft acoustic chamber for testing both shuttle-launched payloads and payloads launched by expendable vehicles is described. Chamber requirements and design problems are reviewed, and safety systems are discussed. It is shown that: (1) the maximum overall sound-pressure level obtained with two 10-kW transducers is 150 dB; (2) at least seven modes between 25 and 40 Hz have been identified in the preliminary evaluation of the chamber; (3) two discernible dips, localized to individual doors, occur in the LF spectrum, at 30-33 and 42-44 Hz; and (4) the reverberation times measured for 60-dB decay range from 7 sec at 40 Hz to a maximum of 19 sec at 125 Hz, with an average of 13.4 sec at 1000 Hz.

Kirchman, E.↗
NASA NTRS1981

Introduction to orbital flight planning (1)

This workbook is designed for students interested in space flight planning, who after training, may serve as flight planning aides. Routine flight planning activities requiring engineering-type calculations and analysis are covered. Practice exercises and brief instructions are given for the programming and use of the hand calculator as well as the calculation of position and velocity in the orbital plane. Calculation of relative orbital position is also covered with emphasis upon celestial coordinates and time measurement.

Blackwell, H. E.↗
NASA NTRS1982

Characterization of particles in the Langley 0.3 meter transonic cryogenic tunnel using hot wire anemometry

Hot wire anemometry was used to identify the nature of particles reportedly observed during free stream velocity measurements in the Langley 0.3-meter transonic cryogenic tunnel using a Laser Doppler Velocimeter. Since the heat-transfer process from the hot wire depends on the thermal conductivity and sticking capability of the particles, it was anticipated that the hot wire anemometer response would be affected differently upon impaction by liquid droplets and solid aerosols in the test gas stream. Based on the measured time response of the hot-wire anemometer in the cryogenic tunnel operated in the 0.3-0.8 Mach number range, it is concluded that the particles impacting the hot wire are liquid in nature rather than solid aerosols. It is further surmised that the liquid aerosols are unevaporated liquid nitrogen droplets used for cooling the tunnel test gas.

Singh, J. J.↗
NASA NTRS1983

Characteristics of low-energy plasma in the plasmasphere and plasma trough

Initial results of studies of low-energy plasma using the light ion mass spectrometer (LIMS) on the SCATHA satellite are presented. Results are discussed primarily for plasma flux in the noon to midnight local time sector, examining the behavior of the plasma with geomagnetic activity and local time. Measurements of the ion mass composition in this region for the energy ranges of the LIMS instrument are presented. Results of temperature measurements are given and a possible explanation for the difference between the whistler and OGO 5 plasmapause positions is suggested. The observed pitch angle distributions are presented, limited to a broad characterization of the plasma population. The effects of the spacecraft potential on the low-energy plasma measurements are considered.

Reasoner, D. L.↗
NASA NTRS1983

Reflectance Measurements, Part 2

Improving the productivity of spectroreflectometer readings taken to monitor induced contamination of lenses, mirrors, and coatings in the space environment are described. More sophisticated modelling techniques were applied to the laboratory data collected last summer in order to produce a more accurate model of the nonlinearities and noise sources of the instrumentation. This would ultimately allow for correction of known anomalies by the digital computer, yielding an anticipated order to magnitude improvement in the accuracy of the reflectance measurements, while reducing the total measuring time. The construction of and programming for a modernized version of the electronics used in Beckman DK-2 spectroreflectometers suffered because of a schedule lag in fabrication of a modified form of the carrier frequency pickoff. Separate development of the electronics and the computer programming was partially accomplished.

Brown, R. A.↗
NASA NTRS1985

Nonintrusive shaft speed sensor

Reusable rocket engines such as the Space Shuttle Main Engines (SSME), the Orbital Transfer Vehicles (OTV), etc., have throttling capabilities that require real-time, closed-loop control systems of engine propellant flows, combustion temperatures and pressures, and turbopump rotary speeds. In the case of the SSME, there are four turbopumps that require real-time measurement and control of their rotary speeds. Variable-reluctance magnetic speed sensors were designed, fabricated, and tested for all four turbopumps, resulting in the successful implementation and operation of three of these speed sensors during each of the 12 Shuttle flights.

Barkhoudarian, S.↗
NASA NTRS1984

Effects of line-of-sight velocity on spaced-antenna measurements, part 3.5A

Horizontal wind velocities in the upper atmosphere, particularly the mesosphere, have been measured using a multitude of different techniques. Most techniques are based on stated or unstated assumptions about the wind field that may or may not be true. Some problems with the spaced antenna drifts (SAD) technique that usually appear to be overlooked are investigated. These problems are not unique to the SAD technique; very similar considerations apply to measurement of horizontal wind using multiple-beam Doppler radars as well. Simply stated, the SAD technique relies on scattering from multiple scatterers within an antenna beam of fairly large beam width. The combination of signals with random phase gives rise to an interference pattern on the ground. This pattern will drift across the ground with a velocity twice that of the ionospheric irregularities from which the radar signals are scattered. By using spaced receivers and measuring time delays of the signal fading in different antennas, it is possible to estimate the horizontal drift velocities.

Royrvik, O.↗
NASA NTRS1985

Theoretical and experimental analyses of the performance of two-color laser ranging systems

The statistical properties of the signals reflected from the retroreflector equipped satellites were studied. It is found that coherence interference between pulse reflections from retroreflectors of different ranges on the array platform is the primary cause of signal fluctuations. The performance of a cross-correlation technique to estimate the differential propagation time is analyzed by considering both shot noise and speckle. For the retroreflector arrays, timing performance is dominated by interference induced speckle, and the differential propagation time cannot be resolved to better than the pulse widths of the received signals. The differential timing measurements obtained over a horizontal path are analyzed. The ocean-reflected pulse measurements obtained from the airborne two-color laser altimeter experiment are presented.

Im, K. E.↗
NASA NTRS1985

Study of the time-differentiated particle flux density at various distances from EAS axis

The EAS time structure is studied using the enlarged EAS array of the Moscow State University. The time measurements are made using 22 scintillators which form 13 rectanges of 180x190 sq m size covering the entire array area. The array is triggered by a signal of 4-fold coincidences of the pulses from the detectors forming each of the rectangles. The data were obtained during 2200 hours of the array operation in 1984. A total of 816 showers, to which at least 14 of 22 scintillator detectors responded, were selected among all those detected. The coordinates of the EAS axis in the observation plane and the EAS sizes were determined by the maximum likelihood method using a computer on the assumption that the electron LDF is the NKG form. A total of 492 showers in the interval of EAS size Ne = 5x10 to the 6th power - 2x10 to the 8th power (N bar e = 1.7x 10 to the 7th power) with zenith angles theta or = 45 deg and axes within the array are analyzed.

Atrashkevich, V. G.↗
NASA NTRS1985

Helios 1 energetic particle observations of the solar gamma-ray/neutron flare events of 1982 June 3 and 1980 June 21

The characteristics of the energetic particles associated with the solar gamma-ray/neutron flare events of June 3, 1982 and June 21, 1980 observed by the Goddard cosmic-ray experiment on Helios 1 (at heliocentric distances of 0.57 and 0.54 AU, respectively) differ in several important respects from typical sonar particle increases. In particular, the June 3, 1982 event has a proton energy spectrum which fits a remarkable flat power law in kinetic energy with a spectral index of 1.2, an electron/proton ratio of 1 at 4 MeV, and a small but well-defined precursor event that began some 3 hr before the impulsive flare increase. Similar energetic particle precursors were observed for the gamma-ray associated 1980 June 21 and June 7 flare events. At energies less than about 40 MeV, the particle onset time measured for the June 3, 1982 event is anomalous, suggesting that these lower energy particles may have been released at the sun about 1-2 minutes before the higher energy particles.

Mcdonald, F. B.↗
NASA NTRS1986

Global Timing With Low- and High-Orbiting Satellites

Report summarizes method for synchronizing clocks at intercontinental distances employing satellites of Global Positioning System (GPS) in high Earth orbit and transit satellite in orbit at relatively low altitude of about 1,300 km. When fully implemented, method expected to supply precise time measurements for world-wide communication and navigation.

Wu, S. C.↗
NASA NTRS1985

Monitoring of inventory in enclosed turbulent liquid tanks using floating gamma-ray sources

An accurate and simple technique utilizing a low-intensity gamma-ray source floating in a vertical tube, whose configuration is tank geometry and size dependent, is shown to eliminate the disturbing effects of turbulent fluid on enclosed tank liquid inventory measurement. The vertical tube aligns the source with detectors positioned outside of the tank, and collapses the turbulent liquid surface to a true average level. The exit attenuation of the information carrying high energy gamma rays is insensitive to liquid surface tubulence, and sensing probe penetrations are not necessary. It is found that for a half-full tank, 1.0 percent statistical error, and 1-s measuring times, that a 220 C Ce-137 source is required for an 8-ft high tank. Consistent experimental results are found for the dual detector method, and results indicate that the accuracy of the scanning side detector method is dependent on the quality of the collimator and degree of lower level energy discrimination.

Klein, R. M.↗
NASA NTRS1986

Real-time atmospheric absorption spectra for in-flight tuning of an airborne dial system

Real-time measurements of atmospheric absorption spectra are displayed and used to precisely calibrate and fix the frequency of an Alexandrite laser to specific oxygen absorption features for airborne Differential Absorption Lidar (DIAL) measurements of atmospheric pressure and temperature. The DIAL system used contains two narrowband tunable Alexandrite lasers: one is electronically scanned to tune to oxygen absorption features for on-line signals while the second is used to obtain off-line (nonabsorbed) atmospheric return signals. The lidar operator may select the number of shots to be averaged, the altitude, and altitude interval over which the signals are averaged using single key stroke commands. The operator also determines exactly which oxygen absorption lines are scanned by comparing the line spacings and relative strengths with known line parameters, thus calibrating the laser wavelength readout. The system was used successfully to measure the atmospheric pressure profile on the first flights of this lidar, November 20, and December 9, 1985, aboard the NASA Wallops Electra aircraft.

Dombrowski, M.↗
NASA NTRS1988

Calculating Percent Gel For Process Control

Reaction state of thermosetting resin tracked to assure desired properties. Rate of gel determined as function of temperature by measuring time to gel of part of graphite fabric impregnated with Hexcel R120 (or equivalent) phenolic resin.

Webster, Charles Neal↗
NASA NTRS1987

Alkali metal thermoelectric converter (AMTEC) electrode lifetime studies

Experimental studies are being conducted at JPL to identify long life, high area power density electrodes for AMTEC. Power versus time measurements are being made in a demountable electrode test cell and, for longer term experiments, a self-contained recirculating cell. The experimental apparatus and procedures are described in detail. The results show that thin film molybdenum electrodes can be designed to produce power near 0.5 W/sq cm for over two hundred hours. Also, platinum/tungsten electrodes exhibit power densities that are stable near 0.5 W/sq cm. If the performance of these electrodes is verified for longer periods (thousands of hours), then practical AMTEC systems will be possible.

Bankston, C. Perry↗
NASA NTRS1988

Minority-carrier lifetime analysis of silicon epitaxy and bulk crystals with nonuniformly distributed defects

Existing analyses of the pulsed response of an MOS capacitor for minority-carrier lifetime determination result in a lifetime value averaged over most of the depletion region width. In this report, an analysis of MOS C-t data is presented that enables minority-carrier generation lifetime to be plotted as a function of depletion region depth. The technique is shown to be useful for samples with bulk or buried interfacial layer defects that have defect-free surfaces. Data are presented for intrinsically gettered bulk crystals and extrinsically gettered Si(2-pct Ge) epitaxial layers with misfit dislocations. In addition, for samples that do have uniform lifetimes, the measurement time required for determining carrier lifetime has been reduced by more than an order of magnitude.

Radzimski, Zbignew↗