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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The NASA SETI sky survey - Recent developments

NASA's Search for Extraterrestrial Intelligence (SETI) project utilizes two complimentary search strategies: a sky survey and a targeted search. The SETI team at the Jet Propulsion Laboratory have primary responsibility to develop and carry out the sky survey part of the Microwave Observing Project. The paper describes progress that has been made to develop the major elements of the survey including a two-million channel wideband spectrum analyzer system that is being developed and constructed by JPL for the Deep Space Network. The new system will be a multiuser instrument that will serve as a prototype for the SETI Sky Survey processor. This system will be used to test the signal detection and observational strategies on deep-space network antennas in the near future.

Klein, Michael J.↗
NASA NTRS1989

Experimental limits on the radiative decay of SN 1987A neutrinos

SMM gamma-ray spectrometer data are examined to look for gamma-ray emission coincident with the about-10-s neutrino burst from SN 1987A. The absence of a detectable signal suggests that the energy radiated into MeV gamma rays by neutrino decay (or any other process) is less than 10 to the -10th of that in supernova neutrinos above 9 MeV. The results are used to set a direct limit on the lifetime of any massive neutrino type generated in the core collapse leading to SN 1987A.

Chupp, Edward L.↗
NASA NTRS1988

Information processing

Theoretical models of sensory-information processing by the human brain are reviewed from a human-factors perspective, with a focus on their implications for aircraft and avionics design. The topics addressed include perception (signal detection and selection), linguistic factors in perception (context provision, logical reversals, absence of cues, and order reversals), mental models, and working and long-term memory. Particular attention is given to decision-making problems such as situation assessment, decision formulation, decision quality, selection of action, the speed-accuracy tradeoff, stimulus-response compatibility, stimulus sequencing, dual-task performance, task difficulty and structure, and factors affecting multiple task performance (processing modalities, codes, and stages).

Wickens, Christopher D.↗
NASA NTRS1988

The U.S. Sarsat geosynchronous experiment - Ground processor description and test results

The development of a specialized digital signal processor, the Geosynchronous Signal Processor (GSP), for short beacon burst signal detection and demodulation is described. The processing is based on fast Fourier Transform techniques for detection and message integration on the respective message bursts for demodulation. The GSP is based on array processor technology; it is designed to yield an ultimate capacity of 50-75 simultaneous beacon transmissions within the nominal 20 KHz bandwidth centered at 406.025 MHz.

Flikkema, P. G.↗
NASA NTRS1988

Further analysis of the results from a series of tethered rocket experiments

The data obtained in the most recent Japan-US tether rocket experiment CHARGE 2 have been further analyzed. The interaction of the moving tether system across the geomagnetic field with the ionospheric plasma can be explained by a simple model of the current through a plasma. The response of the tether system when a high voltage is applied is studied and 500 volts could be applied without any appreciable discharge. The detected signal of the wave excited by an application of high voltage between the mother and daughter rocket and by a pulse modulated electron beam is also studied.

Kawashima, N.↗
NASA NTRS1989

The NASA SETI sky survey: Recent developments

NASA's Search for Extraterrestrial Intelligence (SETI) project utilizes two complementary search strategies: a sky survey and a targeted search. The SETI team at the Jet Propulsion Laboratory (JPL) in Pasadena, California, has primary responsibility to develop and carry out the sky survey part. Described here is progress that has been made developing the major elements of the survey including a 2-million channel wideband spectrum analyzer system that is being designed and constructed by JPL for the Deep Space Network (DSN). The system will be a multiuser instrument; it will serve as a prototype for the SETI sky survey processor. This prototype system will be used to test the signal detection and observational strategies on DSN antennas in the near future.

Klein, M. J.↗
NASA NTRS1990

A two-telescope receiver design for deep space optical communications

A two-telescope system for a deep space optical communication receiver is proposed. To substantially improve the overall receiver efficiency, the design reserves the large telescope for signal-detection purposes only. A small diffraction-limited telescope is introduced to accomplish the task of navigational tracking.

Shaik, K.↗
NASA NTRS1990

Codeless GPS Applications to Multi-Path: CGAMP

Cordless Global Positioning System (GPS) Applications to Multi-Path (CGAMP) is meeting the challenge of exploiting the L-band signals from the Global Positioning System (GPS) satellites for the measurement of the impulse response of radio transmission channels over space-Earth paths. This approach was originally suggested by E. K. Smith and has been pursued by J. Lemmon, without an affordable implementation being identifiable. In addition to the high cost of a suitable P code correlating GPS receiver, there is also the major impediment of the often announced Department of Defense policy of selective availability/anti-spoof (SA/AS) that clouds reliable access to the wideband (20 MHz) P channel of the GPS signals without cryptographic access. A technique proposed by MacDoran utilizes codeless methods for exploiting the P channel signals implemented by the use of a pair of antennas and cross correlation signal detection.

Macdoran, P. F.↗
NASA NTRS1990

Characteristic microwave-background distortions from collapsing spherical domain walls

The redshift distortion induced by collapsing spherical domain walls is calculated. The most frequent microwave background distortions are found to occur at large angles in the form of blue disks. This is the angular region currently measured by the COBE satellite. COBE could therefore detect signals predicted here for domain walls with surface energy density of the order of MeV. Such values for sigma are proposed in the late-time phase-transition scenario of Hill et al. (1989).

Goetz, Guenter↗
NASA NTRS1989

Sparse distributed memory: Principles and operation

Sparse distributed memory is a generalized random access memory (RAM) for long (1000 bit) binary words. Such words can be written into and read from the memory, and they can also be used to address the memory. The main attribute of the memory is sensitivity to similarity, meaning that a word can be read back not only by giving the original write address but also by giving one close to it as measured by the Hamming distance between addresses. Large memories of this kind are expected to have wide use in speech recognition and scene analysis, in signal detection and verification, and in adaptive control of automated equipment, in general, in dealing with real world information in real time. The memory can be realized as a simple, massively parallel computer. Digital technology has reached a point where building large memories is becoming practical. Major design issues were resolved which were faced in building the memories. The design is described of a prototype memory with 256 bit addresses and from 8 to 128 K locations for 256 bit words. A key aspect of the design is extensive use of dynamic RAM and other standard components.

Flynn, M. J.↗
NASA NTRS1991

The fractional Fourier transform and applications

This paper describes the 'fractional Fourier transform', which admits computation by an algorithm that has complexity proportional to the fast Fourier transform algorithm. Whereas the discrete Fourier transform (DFT) is based on integral roots of unity e exp -2(pi)i/n, the fractional Fourier transform is based on fractional roots of unity e exp -2(pi)i(alpha), where alpha is arbitrary. The fractional Fourier transform and the corresponding fast algorithm are useful for such applications as computing DFTs of sequences with prime lengths, computing DFTs of sparse sequences, analyzing sequences with noninteger periodicities, performing high-resolution trigonometric interpolation, detecting lines in noisy images, and detecting signals with linearly drifting frequencies. In many cases, the resulting algorithms are faster by arbitrarily large factors than conventional techniques.

Bailey, David H.↗
NASA NTRS1992

Status of the NASA SETI Sky Survey microwave observing project

The Sky Survey observing program is one of two complementary strategies that NASA plans to use in its microwave Search for Extraterrestrial Intelligence (SETI). The primary objective of the Sky Survey is to search the entire sky over the frequency range 1000-10,000 MHz for evidence of narrow band signals of extraterrestrial, intelligent origin. Spectrum analyzers with upwards of 10 million channels and data rates in excess of 10 gigabits per second are required to complete the survey in less than 7 years. To lay the foundation for the operational SETI Sky Survey, a prototype system has been built to test and refine real time signal detection algorithms, to test scan strategies and observatory control functions, and to test algorithms designed to reject radio frequency interference. This paper presents a high level description of the prototype hardware and reports on the preparations to deploy the system to the 34-m antenna at the research and development station of NASA's Deep Space Communication Complex, Goldstone, California.

Klein, M. J.↗
NASA NTRS1992

Ultrasonic Imaging Of Bond Layers Through Bond Layers

Combination of hardware and software helps ultrasonic C-scan inspection system create images of bond layer in laminated composite material, even when obscured by another bond layer. Produces image of both layers in single scan. Includes ultrasonic transducer, pulser/receiver, mechanical scanner, personal computer as controller, and electronic circuitry that gates first and second peak signals, detects peaks, and feeds resulting amplitude data to computer.

Chern, E. James↗
NASA NTRS1992

An analysis of I/O efficient order-statistic-based techniques for noise power estimation in the HRMS sky survey's operational system

Noise power estimation in the High-Resolution Microwave Survey (HRMS) sky survey element is considered as an example of a constant false alarm rate (CFAR) signal detection problem. Order-statistic-based noise power estimators for CFAR detection are considered in terms of required estimator accuracy and estimator dynamic range. By limiting the dynamic range of the value to be estimated, the performance of an order-statistic estimator can be achieved by simpler techniques requiring only a single pass of the data. Simple threshold-and-count techniques are examined, and it is shown how several parallel threshold-and-count estimation devices can be used to expand the dynamic range to meet HRMS system requirements with minimal hardware complexity. An input/output (I/O) efficient limited-precision order-statistic estimator with wide but limited dynamic range is also examined.

Zimmerman, G. A.↗
NASA NTRS1992

Novel position sensor technologies for microaccelerometers

An important new approach for vehicle guidance and control is based on the use of compact, low-mass, low-cost sensors integrated with the vehicle structure. Many advantages of this approach lead to new capabilities. However, the development of compact guidance and control sensors leads to a variety of fundamental physical problems associated with sensor sensitivity and noise. For example, as sensor size is reduced, it becomes necessary to improve the sensitivity of the sensor signal detection mechanism. These challenges to sensor development will be described. Recent developments at JPL, based on new position sensor principles such as electron tunneling, have produced a series of novel, ultra-high sensitivity micro-sensors and micro-instruments. Included among the applications demonstrated, are a high sensitivity micro-accelerometer and micro-seismometer. In this paper, the fundamental limits of conventional position sensors will be discussed and a new position sensor for advanced accelerometers will be described.

Vanzandt, T. R.↗
NASA NTRS1990

Supply Current Diagnosis in VLSI

This paper presents a technique based upon the power supply current signature (cd) which allows for the testing of mixed-signal systems, in situ. Through experiments with a microprocessor, the cd is shown to contain important information concerning the operational status of the system which may be easily extracted using approaches based on statistical signal detection theory. The fault-detection performance of these techniques is compared to that achieved through auto-regressive modeling of the cd.

Frenzel, J. F.↗
NASA NTRS1992

Environmental projects. Volume 15: Environmental assessment: Proposed 1-megawatt radar transmitter at the Mars site

The Goldstone Deep Space Communications Complex (GDSCC), located in the Mojave Desert about 64.5 km (40 mi) north of Barstow, California. and about 258 km (160 mi) northeast of Pasadena, California, is part of the National Aeronautics and Space Administration's (NASA's) Deep Space Network (DSN), one of the world's larger and more sensitive scientific telecommunications and radio navigation networks. The Goldstone Complex is managed, technically directed, and operated for NASA by the Jet Propulsion Laboratory (JPL) of the California Institute of Technology in Pasadena, California. Activities at the GDSCC support the operation of six parabolic dish antennas located at five separate sites called Deep Space Stations (DSS's). Four sites, named Echo, Mars, Uranus, and Apollo, are operational for space missions, while the remaining Venus Site is devoted to research and development activities. The Mars Site at the GDSCC contains two antennas: the Uranus antenna (DSS 15, 34 m) and the Mars antenna (DSS 14, 70 m). This present volume deals solely with the DSS-14 Mars antenna. The Mars antenna not only can act as a sensitive receiver to detect signals from spacecraft, but it also can be used in radar astronomy as a powerful transmitter to send out signals to probe the solar system. At present, the Mars antenna operates as a continuous-wave microwave system at a frequency of 8.51 GHz at a power level of 0.5 MW. JPL has plans to upgrade the Mars antenna to a power level of 1 MW. Because of the anticipated increase in the ambient levels of radio frequency radiation (RFR), JPL retained Battelle Pacific Northwest Laboratories (BPNL), Richland, Washington, to conduct an environmental assessment with respect to this increased RFR. This present volume is a JPL-expanded version of the BPNL report titled Environmental Assessment of the Goldstone Solar System Radar, which was submitted to JPL in Nov. 1991. This BPNL report concluded that the operation of the upgraded Mars antenna at the GDSCC, with its increased potential electromagnetic radiation hazards and interferences, would have no significantly adverse biological, physical, or socioeconomic effects on the environment. Thus, a Finding of No Significant Impact (FONSI) is appropriate in accordance with local, State, Federal, and NASA environmental rules and regulations.

Source record↗
NASA NTRS1993

New methods of generation of ultrashort laser pulses for ranging

To reach the millimeter satellite laser ranging accuracy, the goal for nineties, new laser ranging techniques have to be applied. To increase the laser ranging precision, the application of the ultrashort laser pulses in connection with the new signal detection and processing techniques, is inevitable. The two wavelength laser ranging is one of the ways to measure the atmospheric dispersion to improve the existing atmospheric correction models and hence, to increase the overall system ranging accuracy to the desired value. We are presenting a review of several nonstandard techniques of ultrashort laser pulses generation, which may be utilized for laser ranging: compression of the nanosecond pulses using stimulated Brillouin and Raman backscattering; compression of the mode-locked pulses using Raman backscattering; passive mode-locking technique with nonlinear mirror; and passive mode-locking technique with the negative feedback.

Jelinkova, Helena↗