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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

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NASA NTRS1985

Fast Dual Analog-to-Digital Converter

Unit delivers blocks of quadrature data to computer memory. Contains 105 integrated circuit packages in 19 by 3 1/2 inch (48.26 by 8.39 cm) rack mounted drawer with internal force air blower. Intended for synchronous sampling of quadrature pairs of data, samples with minimal skew (about 10 nanoseconds) using video-type high-speed sampling technology. Unit equipped for computer controlled self-testing. Originally developed for planetary radar data-acquisition system.

Wallis, D. E.↗

NASA NTRS1983

Intercontinental time and frequency transfer using a global positioning system timing receiver

The DSN has a requirement to maintain knowledge of the frequency offset between DSN stations with 3 x 10 to the minus 13th power and time offset within 10 microseconds. It is further anticipated that in the 1987-1990 era the requirement for knowledge of time offset between DSN stations will be less than 10 nanoseconds. JPL is using the Global Positioning System (GPS) Space Vehicles, as a development project, to transfer time and frequency over intercontinental distances between stations of the DSN and between the DSN and other agencies. JPL has installed GPS timing receivers at its tracking station near Barstow, California, and at its tracking station near Madrid, Spain. The details of the experiment and the data are reported. There is a discussion of the ultimate capabilities of these techniques for meeting the functional requirements of the DSN.

Clements, P. A.↗

NASA NTRS1984

Modular approach for satellite communication ground terminals

The trend in satellite communications is toward completely digital, time division multiple access (TDMA) systems with uplink and downlink data rates dictated by the type of service offered. Trunking terminals will operate in the 550 MBPS (megabit per second) region uplink and downlink, whereas customer premise service (CPS) terminals will operate in the 25 to 10 MBPS region uplink and in the 200 MBPS region downlink. Additional criteria for the ground terminals will be to maintain clock sychronization with the system and burst time integrity to within a matter of nanoseconds, to process required order-fire information, to provide adaptive data scrambing, and to compensate for variations in the user input output data rates, and for changes in range in the satellite communications links resulting from satellite perturbations in orbit. To achieve the required adaptability of a ground terminal to the above mentioned variables, programmable building blocks can be developed that will meet all of these requirements. To maintain system synchronization, i.e., all bursted data arriving at the satellite within assigned TDMA windows, ground terminal transmit data rates and burst timing must be maintained within tight tolerances. With a programmable synchronizer as the heart of the terminal timing generation, variable data rates and burst timing tolerances are achievable. In essence, the unit inputs microprocessor generated timing words and outputs discrete timing pulses.

Gould, G. R.↗

NASA NTRS1984

Radar altimetry over sea ice

To study the sea-ice interactive region in the Bering and Greenland Seas a series of experimental compaigns, the Marginal Ice Zone Experiment (MIZEX) has been planned. A major objective of MIZEX is the development of a capability to relate the morphology and distribution of the sea ice to atmospheric and oceanographic parameters in an overall model. During the first part of the MIZEX, a 13.7 GHz microwave radar altimeter/scatterometer having a pulse length of 16 nanoseconds was flown over the Bering Sea Marginal ice zone. On the same aircraft were the NASA GSFC 19 GHz Electronically Scanning Microwave Radiometer (ESMR), scanning radiometers and an infrared, nadir pointing, temperature sounder. The altimeter/scatterometer was operated in nadir pointing and conically scanning modes to collect measurements of reflectivity and pulse shapes. These will be related to sea-ice classifications, ocean wave spectra and coincident microwave and infrared radiometric measurements and laser profilometer surface roughness estimates.

Powell, J.↗

NASA NTRS1984

Progress in optical parametric oscillators

It is pointed out that tunable coherent sources are very useful for many applications, including spectroscopy, chemistry, combustion diagnostics, and remote sensing. Compared with other tunable sources, optical parametric oscillators (OPO) offer the potential advantage of a wide wavelength operating range, which extends from 0.2 micron to 25 microns. The current status of OPO is examined, taking into account mainly advances made during the last decade. Attention is given to early LiNbO3 parametric oscillators, problems which have prevented wide use of parametric oscillators, the demonstration of OPO's using urea and AgGaS2, progress related to picosecond OPO's, a breakthrough in nanosecond parametric oscillators, the first demonstration of a waveguide and fiber parametric amplification and generation, the importance of chalcopyrite crystals, and theoretical work performed with the aim to understand the factors affecting the parametric oscillator performance.

Fan, Y. X.↗

NASA NTRS1985

Fast Control Sequencer

Unit faster than conventional circuits and contains fewer integrated circuits. Fast logic controller accommodates three delays before second half cycle of clock signal strobes status latch: Outputs of pipeline register must settle; selected input status line signal must propagate through status multiplexer and arrive at status latch; and it takes 3 nanoseconds for status latch set up before strobed. During second half cycle, output-enable line produces next instruction and applies it to pipeline register.

Lahmeyer, C. R.↗

NASA NTRS1985

Satellite Time- and Frequency-Transfer System

Time synchronized at distant points within nanosecond. Report describes satellite-borne time-and frequency-transfer system proposed for synchronization of clocks at stations around Earth. Orbiting hydrogen-maser clock and frequency standard communicate by microwave links with Earth stations using hydrogen masers as local clocks. Pulsed-laser time-transfer sub-system also operated concurrently, either synchronized or unsynchronized with microwave subsystems.

Vessot, R. F. C.↗

NASA NTRS1985

Remote sensing of directional wave spectra using the surface contour radar

A unique radio-oceanographic remote sensing instrument was developed. The 36 GHz airborne Surface Contour Radar (SCR) remotely produces a real-time topographical map of the sea surface beneath the aircraft. It can routinely produce ocean directional wave spectra with off-line data processing. The transmitter is a coherent dual-frequency device that uses pulse compression to compensate for the limited available power at Ka band. The radar has selectable pulse widths of 1, 2, 4, and 10 nanoseconds. The transmitting antenna is a 58 lambda horn fed dielectric lens whose axis is parallel to the longitudinal axis of the aircraft. It illuminates an elliptical mirror which is oriented 45 deg to the lens' longitudinal axis to deflect the beam towards the region beneath the aircraft. The mirror is oscillated in a sinusoidal fashion through mechanical linkages driven to a variable speed motor to scan the transmitter beam (1.2 deg X 1.2 deg) with + or - 16 deg of the perpendicular to the aircraft wings in the plane perpendicular to the aircraft flight direction.

Walsh, E. J.↗

NASA NTRS1983

Ionospheric limitations to time transfer by satellite

The ionosphere can contribute appreciable group delay and phase change to radio signals traversing it; this can constitute a fundamental limitation to the accuracy of time and frequency measurements using satellites. Because of the dispersive nature of the ionosphere, the amount of delay is strongly frequency-dependent. Ionospheric compensation is necessary for the most precise time transfer and frequency measurements, with a group delay accuracy better than 10 nanoseconds. A priori modeling is not accurate to better than 25%. The dual-frequency compensation method holds promise, but has not been rigorously experimentally tested. Irregularities in the ionosphere must be included in the compensation process.

Knowles, S. H.↗

NASA NTRS1985

EAS Cerenkov measurements of the composition of the cosmic ray flux around 10 to the 16th power eV

Information can be obtained about the nature of a primary cosmic ray by looking at the way in which an extensive air shower (EAS) develops in the atmosphere. Heavy nuclei give rise to showers that develop high in the atmosphere and the depth of maximum development is subjected to much smaller fluctuations than is the case for showers originating from protons. This development is followed by optical methods based on the observations of Cerenkov light or fluorescence light. The Cerenkov observations have two complementary techniques: measurement of the time profile of the Cerenkov pulse with resolution of a few nanoseconds and measurement of the lateral distribution of the Cerenkov light. In each case the measured quantities must be related to some characteristic development parameters.

Dawson, B. R.↗

NASA NTRS1985

Vehicle Charging And Potential (VCAP)

The vehicle charging and potential (VCAP) payload includes a small electron accelerator capable of operating in a pulsed mode with firing pulses ranging from 600 nanoseconds to 107 seconds (100 milliamps at 1000 volts), a spherical retarding potential analyzer - Langmuir probe, and charge current probes. This instrumentation will support studies of beam plasma interactions and the electrical charging of the spacecraft. Active experiments may also be performed to investigate the fundamental processes of artificial aurora and ionospheric perturbations. In addition, by firing the beam up the geomagnetic field lines of force (away from the Earth) investigations of parallel electric field may be performed.

Roberts, W. T.↗

NASA NTRS1985

Adsorption and recombination of hydrogen atoms on a model graphite surface

The adsorption and recombination of atomic hydrogen on a model graphite grain have been examined in a series of calculations in which a modified, iterative, extended Hueckel program was used. The hydrogen atom is found to be chemisorbed at a site with a zero-point binding energy of 0.7 eV and at an equilibrium distance of 2.25 A above the site. Despite a barrier of about 0.4 eV between adjacent sites, calculations suggest that at temperatures as low as 10 K, an H atom will tunnel through to adjacent sites in less than one nanosecond. However, a potential barrier to the recombination of two hydrogen atoms has been found which displays high sensitivity to the mutual arrangement of the two hydrogen atoms with respect to the graphite surface. Results show that at very low temperatures, recombinations can occur only by tunneling. Consistent with experiment, the region in which H2 begins to form exhibits a repulsive potential with respect to possible chemisorption of the incipient H2 entity.

Aronowitz, S.↗

NASA NTRS1985

MLRS - A lunar/artificial satellite laser ranging facility at the McDonald Observatory

Experience from lunar and satellite laser ranging experiments carried out at McDonald Observatory has been used to design the McDonald Laser Ranging Station (MLRS). The MLRS is a dual-purpose installation designed to obtain observations from the LAGEOS satellite and lunar targets. The instruments used at the station include a telescope assembly 0.76 meters in diameter; a Q-switched doubled neodymium YAG laser with a pulse rate of three nanoseconds; and a GaAs photodetector with Fabry-Perot interferometric filter. A functional diagram of the system is provided. The operating parameters of the instruments are summarized in a table.

Shelus, P. J.↗

NASA NTRS1986

Electro-optical Tuning of Fabry-Perot Interferometers

Compact unit operates much faster than conventional piezoelectric scanners. High voltage creates electric field in Pockels cell, changing refractive properties. Cell changes optical path length between mirrors without mechanically moving anything in gap. High voltage varied rapidly to scan interferometer. Voltage applied longitudinally or transversely, depending on type of Pockels cell. New electro-optic scanner scans given range in one-millionth time of piezoelectric scanner - tens to hundreds of nanoseconds per interferometer order. Also reducing size of interferometer.

Schwemmer, G. K.↗

NASA NTRS1986

MOSFET Power Controller

High current and voltage controlled remotely. Remote Power Conroller includes two series-connected banks of parallel-connected MOSFET's to withstand high current and voltage. Voltage sharing between switch banks, low-impedance, gate-drive circuits used. Provided controlled range for turn on. Individually trimmable to insure simultaneous switching within few nanoseconds during both turn on and turn off. Control circuit for each switch bank and over-current trip circuit float independently and supplied power via transformer T1 from inverter. Control of floating stages by optocouplers.

Mitchell, J.↗

NASA NTRS1986

Vehicle Charging And Potential (VCAP)

Roberts, B.↗

NASA NTRS1984

Measurement of temperature and density fluctuations in turbulence using an ultraviolet laser

Noninvasive measurement of density and temperature fluctuations in turbulent air flow was examined. The approach used fluorescence of oxygen molecules which are selectively excited by a tunable vacuum ultraviolet laser beam. The strength of the fluorescence signal and its dependence on laser wavelength vary with the density and temperature of the air in the laser beam. Because fluorescence can be detected at 90 degrees from the beam propagation direction, spatial resolution in three dimensions, rather than path-integrated measurements can be achieved. With spatial resolutions of the order of a millimeter and at supersonic air velocities it is necessary to perform each measurement in a time of the order of a microsecond; this is possible by by using laser pulses of ten nanosecond duration. In this method atmospheric O2 is excited by the emission of a tunable ArF excimer laser, and the fluorescence, which spans the 210 to 420 range, is detected by an ultraviolet phototube.

Massey, G. A.↗

NASA NTRS1986

Operational characteristics of Wedge and Strip image readout systems

Application of the Wedge and Strip readout system in microchannel plate detectors for the Extreme Ultraviolet Explorer and FAUST space astronomy programs is discussed. Anode designs with high resolution (greater than 600 x 600 pixels) in imaging and spectroscopy applications have been developed. Extension of these designs to larger formats (100 mm) with higher resolution (3000 x 3000 pixels) are considered. It is shown that the resolution and imaging are highly stable, and that the flat field performance is essentially limited by photon statistics. Very high speed event response has also been achieved with output pulses having durations of less than 10 nanoseconds.

Siegmund, O. H. W.↗