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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 1,063 records · Page 59

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NASA NTRS1983

Science program for an imaging radar receiving station in Alaska. Report of the science working group

It is argued that there would be broad scientific benefit in establishing in Alaska an imaging radar receiving station that would collect data from the European Space Agency's Remote Sensing Satellite, ERS-1. This station would acquire imagery of the ice cover from the American territorial waters of the Beaufort, Chukchi, and Bering Seas. This station, in conjunction with similar stations proposed for Kiruna, Sweden, and Prince Albert, Canada would provide synoptic coverage of nearly the entire Arctic. The value of such coverage to aspects of oceanography, geology, glaciology, and botany is considered.

Source record↗

NASA NTRS1990

Geodetic positioning of the Aerospace Electronics Research Lab (ERL) Osborne Time Transfer Receiver (TTR) using the GPS NAVSTAR Block I satellites

Aerospace has routinely processed the Osborne Time Transfer Receiver (TTR) data for the purpose of monitoring the performance of ground and GPS atomic clocks in near real-time with on-line residual displays and characterizing clock stability with Allan Variance calculations. Recently, Aerospace added the ability to estimate the TTR's location by differentially correcting the TTR's location in the WGS84 reference system. This new feature is exercised on a set of TTR clock phase data and Sub-meter accurate station location estimates of the TTR at the Aerospace Electronic Research Lab (ERL) are obtained.

Liu, Anthony S.↗

NASA NTRS1992

A Highly Digital Front End For GPS Receivers

In digital front end of GPS receiver, half-subharmonic sampling of incoming radio-frequency signal followed by summing operation produces desired baseband output in filtered and sampled form. Design generates baseband samples in guadrature with exactness in quadrature separation surpassing analog implementations. Advantages include compactness, lower cost, greater accuracy, and greater reliability.

Thomas, J. Brooks↗

NASA NTRS1991

Photovoltaic receivers for laser beamed power in space

There has recently been a resurgence of interest in the use of beamed power to support space exploration activities. One of the most promising beamed power concepts uses a laser beam to transmit power to a remote photovoltaic array. Large lasers can be located on cloud-free sites at one or more ground locations and illuminate solar arrays to a level sufficient to provide operating power. Issues involved in providing photovoltaic receivers for such applications are discussed.

Landis, Geoffrey A.↗

NASA NTRS1992

Multi-user satellite communications system using an innovative compressive receiver

There is a need for an onboard simultaneous multi-channel demodulation system for a satellite communications system. Studies indicate that Convolve Multiply Convolve (CMC) filtering with surface acoustic wave (SAW) dispersive delay lines will eliminate the necessity of onboard satellite channelized filters of complex fourier transform processors. The reason for choosing the CMC technique is its ability to perform Fourier transformations in a shorter time with less space and power consumption than digital Fourier transform processors. Each ground terminal in this multi-users communications system is remotely located and operates independently; hence, a method of synchronizing the transmission of these users is presented which utilizes the existing Global Positioning System (GPS) system. Each ground user is equipped with a low cost ground terminal that has a synchronization subsystem attached to it. The system design of an onboard Multi-channel Receiver and Demodulator utilizes Quadrature Phase Shift Keying (QPSK) as the modulation technique. This technique provides the best figure of merit, i.e., the lowest transmitter power requirement per communication channel.

Staples, Edward J.↗

NASA NTRS1992

Solar thermal energy receiver

A plurality of heat pipes in a shell receive concentrated solar energy and transfer the energy to a heat activated system. To provide for even distribution of the energy despite uneven impingement of solar energy on the heat pipes, absence of solar energy at times, or failure of one or more of the heat pipes, energy storage means are disposed on the heat pipes which extend through a heat pipe thermal coupling means into the heat activated device. To enhance energy transfer to the heat activated device, the heat pipe coupling cavity means may be provided with extensions into the device. For use with a Stirling engine having passages for working gas, heat transfer members may be positioned to contact the gas and the heat pipes. The shell may be divided into sections by transverse walls. To prevent cavity working fluid from collecting in the extensions, a porous body is positioned in the cavity.

Baker, Karl W.↗

NASA NTRS1992

Lidar receivers for picosecond remote sensing

The lidars of picosecond resolution are an attractive tool for remote probing of some highly dynamic objects like sea subsurface waters, small-scale turbulences in the atmosphere, etc. The picosecond lasers are suitable illuminating sources, but the main restrictions are due to the lack of proper receiving methods, combining the both high temporal and amplitude resolution, good sensitivity, short integration time, and wide dynamic range. The methods for short pulse measurements are not suitable for picosecond lidars, operating at low level, with highly dynamic signals. The streak-cameras are of high cost, lower sensitivity, and lower dynamic range (approximately 10(exp 3)). Because of the background, the single quantum regime in photomultipliers (PMT) is ineffective. The sampling of highly dynamic optical signals with resolution less than or equal to 1ns is a serious problem, limiting the application of the high speed PMT-MCP (microchannel plate) in the picosecond lidar systems. The goal of this work is to describe the use of a new photodetection technique which combines the picosecond resolution with the high amplitude resolution, dynamic range, and sensitivity.

Stoyanov, D. V.↗

NASA NTRS1991

Gravity field error analysis - Applications of Global Positioning System receivers and gradiometers on low orbiting platforms

The concept of a Global Positioning System (GPS) receiver as a tracking facility and a gradiometer as a separate instrument on a low-orbiting platform offers a unique tool to map the earth's gravitational field with unprecedented accuracies. The former technique allows determination of the spacecraft's ephemeris at any epoch to within 3-10 cm, the latter permits the measurement of the tensor of second order derivatives of the gravity field to within 0.01 to 0.0001 Eotvos units depending on the type of gradiometer. First, a variety of error sources in gradiometry where emphasis is placed on the rotational problem pursuing as well a static as a dynamic approach is described. Next, an analytical technique is described and applied for an error analysis of gravity field parameters from gradiometer and GPS observation types. Results are discussed for various configurations proposed on Topex/Poseidon, Gravity Probe-B, and Aristoteles, indicating that GPS only solutions may be computed up to degree and order 35, 55, and 85, respectively, whereas a combined GPS/gradiometer experiment on Aristoteles may result in an acceptable solution up to degree and order 240.

Schrama, Ernst J. O.↗

NASA NTRS1990

Availability of positioning and receiver autonomous integrity monitoring for the global positioning system

Receiver-autonomous integrity monitoring (RAIM) of GPS data is examined by means of a simulation of the availability of a RAIM system that can provide both a GPS coverage model and a Markov reliability model. State probabilities of GPS failure scenarios are assigned with the Markov model with a maximum of 6 simultaneous satellite failures. The parametric analysis of the failures on GPS RAIM availability includes the maximum allowable value of the horizontal dilution of precision (HDOP), the mean time to repair, and the efficacy of incorporating altimeter measurements. When the HDOP requirement is relaxed the number of RAIM outages is minimized, and poor satellite geometry can lead to a large HDOP. The use of an altimeter can also reduce outages, and RAIM availability increases with optimistic values for the mean time to repair.

Kline, Paul A.↗

NASA NTRS1992

Low earth orbit durability evaluation of Haynes 188 solar receiver material

The effects of elevated-temperature vacuum and elevated-temperature atomic oxygen exposure on the mass, surface chemistry, surface morphology, and optical properties of Haynes 188, a possible heat receiver material for space-based solar dynamic power systems, have been studied. Pristine and surface modified Haynes 188 were exposed to vacuum less than or equal to 10 exp -6 torr at 820 C for 5215.5 h, and to atomic oxygen in an air plasma asher at 34 and 827 C for fluences up to 5.6 x 10 exp 21 atoms/sq cm. Results obtained indicate that vacuum heat treatment caused surface morphology and chemistry changes with corresponding optical property changes. Atomic oxygen exposure caused optical property changes which diminished with time. Mass changes are considered to be negligible for both exposures.

De Groh, Kim K.↗

NASA NTRS1991

Receiver autonomous integrity monitoring (RAIM) - Techniques, performance and potential

The goal of receiver autonomous integrity monitoring (RAIM) for the Global Positioning System (GPS) is to provide a sufficient level of navigation integrity for all phases of flight based on the signals transmitted by the GPS satellites only. Integrity requirements for airborne use of GPS are reviewed. This is followed by the description of a baseline fault detection algorithm which is shown to be capable of satisfying tentative integrity requirements. The related issue of testing the fault detection algorithm is also briefly addressed. Preliminary performance results for the baseline fault detection algorithm are presented, along with the potential of RAIM techniques for achieving GPS integrity.

Farrell, James L.↗

NASA NTRS1992

Nb/Al-Al2O3/Nb junctions with inductive tuning elements for a very low noise 205-250 GHz heterodyne receiver

The superconductor-insulator-superconductor (SIS) junction is the most sensitive nonlinear element for millimeter-wave heterodyne detection. An Nb/Al-Al203/Nb junction fabrication process has been developed which allows the use of planar tuning circuits integrated with the junctions. These tuning elements permit the use of junctions with relatively large areas and small current densities with excellent results. Recent measurements have yielded a double sideband receiver noise temperature less than 50 K from 205 to 240 GHz and 44 K at 230 GHz. This Nb/Al-Al203/Nb trilayer technology is also being extended to the fabrication of sub-square-micron area planar junctions for submillimeter-wavelengths.

Lichtenberger, Arthur W.↗

NASA NTRS1992

Solar wind thermal electrons in the ecliptic plane between 1 and 4 AU - Preliminary results from the Ulysses radio receiver

The radio receiver of the Unified Radio and Plasma experiment aboard the Ulysses spacecraft records spectra of the quasi-thermal plasma noise. The interpretation of these spectra allows the determination of the total electron density Ne and of the cold (core) electron temperature Tc in the solar wind. A single power law does not fit the variations of Ne which result from the contribution from different solar wind structures. The distribution of the values of Tc suggests that, on the average, the solar wind is nearly isothermal.

Hoang, S.↗

NASA NTRS1991

Critical technology experiment results for lightweight space heat receiver

Critical technology experiments have been performed on thermal energy storage modules in support of the NASA Advanced Solar Dynamic Brayton Heat Receiver Program. The modules, wedge-shaped canisters containing lithium fluoride (LiF), were designed to minimize the mechanical stresses that occur during the phase change of the LiF. Nickel foam inserts were placed in two of the test canisters to provide thermal conductivity enhancement and to distribute the void volume throughout the canister. A procedure was developed for reducing the nickel oxides on the nickel foam to enhance the wicking ability of the foam. The canisters were filled with LiF and closure-welded at the NASA Lewis Research Center. Two canisters, one with a nickel foam insert, the other without an insert, were thermally cycled in various orientations in a fluidized bed furnace. Computer-aided tomography was successfully used to nondestructively determine void locations in the canisters. Finally, canister dimensional stability was measured after thermal cycling with an inspection fixture.

Schneider, Michael G.↗

NASA NTRS1992

Useful receiver telescope diameter of ground-based and airborne 1-, 2-, and 10-micron coherent lidars in the presence of atmospheric refractive turbulence

Calculations of the integrated effect of atmospheric refractive turbulence on 1-, 2-, and 10-micron coherent lidar performance are presented for a series of different lidar propagation geometries. The effective lidar receiver telescope diameter is evaluated for each case. The results indicate that atmospheric turbulence should not be a significant factor in the performance of a downward-looking high-altitude or satellite-borne coherent lidar system. It is also shown that ground-based 1-2-micron coherent lidars may be limited in their useful telescope aperture, especially for horizontal or nearly horizontal path measurements near the ground.

Chan, Kin P.↗

NASA NTRS1991

Photovoltaic receivers for laser beamed power in space

Landis, Geoffrey A.↗

NASA NTRS1993

MMIC Receiver For Water-Vapor Radiometer

MMIC receiver puts out signal, frequency of which proportioned to brightness temperature of sky at input frequency of 31 GHz. Miniaturization enhances thermal stability and stability of calibration of water-vapor radiometer. Potential for mass production at relatively low cost. Facilitating widespread use of MMIC water vapor radiometers in meteorology and aviation, deployed at several global sites to improve capability of general circulation models and at airports to monitor icing conditions by measuring supercooled liquid water in clouds.

Sukamto, Lin M.↗

NASA NTRS1992

Tracking performance and cycle slipping in the all-digital symbol synchronizer loop of the block 5 receiver

Computer simulated noise performance of the symbol synchronizer loop (SSL) in the Block 5 receiver is compared with the theoretical noise performance. Good agreement is seen at the higher loop SNR's (SNR(sub L)'s), with gradual degradation as the SNR(sub L) is decreased. For the different cases simulated, cycle slipping is observed (within the simulation time of 10(exp 4) seconds) at SNR(sub L)'s below different thresholds, ranging from 6 to 8.5 dB, comparable to that of a classical phase-locked loop. An important point, however, is that to achieve the desired loop SNR above the seemingly low threshold to avoid cycle slipping, a large data-to-loop-noise power ratio, P(sub D)/(N(sub 0)B(sub L)), is necessary (at least 13 dB larger than the desired SNR(sub L) in the optimum case and larger otherwise). This is due to the large squaring loss (greater than or equal to 13 dB) inherent in the SSL. For the special case of symbol rates approximately equaling the loop update rate, a more accurate equivalent model accounting for an extra loop update period delay (characteristic of the SSL phase detector design) is derived. This model results in a more accurate estimation of the noise-equivalent bandwidth of the loop.

Aung, M.↗