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At least 811 records · Page 45

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NASA NTRS1980

Interferometric locating system

A system is described for determining the position of a vehicle or other target that emits radio waves and which is of the type that senses the difference in time of arrival at spaced ground stations of signals from the vehicle to locate the vehicle on a set of intersecting hyperbolas. A network of four ground stations detects the radio emissions from the vehicle and by means of cross correlation derives the relative signal delay at the ground stations from which the vehicle position is deduced. Because the signal detection is by cross correlation, no knowledge of the emission is needed, which makes even unintentional radio noise emissions usable as a locator beacon. By positioning one of the four ground stations at an elevation significantly above the plane of the other three stations, a three dimensional fix on the vehicle is possible.

Macdoran, P. F.↗

NASA NTRS1980

System for plotting subsoil structure and method therefor

Data for use in producing a tomograph of subsoil structure between boreholes is derived by pacing spaced geophones in one borehole, on the Earth surface if desired, and by producing a sequence of shots at spaced apart locations in the other borehole. The signals, detected by each of the geophones from the various shots, are processed either on a time of arrival basis, or on the basis of signal amplitude, to provide information of the characteristics of a large number of incremental areas between the boreholes. Such information is useable to produce a tomograph of the subsoil structure between the boreholes. By processing signals of relatively high frequencies, e.g., up to 100 Hz, and by closely spacing the geophones, a high resolution tomograph can be produced.

Narasimhan, K. Y.↗

NASA NTRS1980

Comparison of ISEE-1 and -3 interplanetary magnetic field observations

Three hourly correlation coefficients and the lag at maximum correlation are computed using one minute averages of ISEE-1 and -3 magnetometer data during the period in which ISEE-3 moved from the earth to its halo orbit around the libration point. The maximum correlation coefficients are highly variable ranging from close to zero to almost unity. The lags, while on the average approximating the expected corotation delay, have very large departures from this value. These results suggest that the normals to the planes separating fields of differing orientation often make large angles to the ecliptic plane and/or that the interplanetary magnetic field has a significant amount of bending on a scale length the order of 200 earth radii. Furthermore, there often appears to be a significant amount of propagating structure in the IMF. Thus, ISEE-3 magnetic field measurements should be used with caution if precise timing of arrival at the earth or precise directions of the field upon arrival are important.

Russell, C. T.↗

NASA NTRS1980

Observing lightning from ground-based and airborne stations

The operational designs and performance capabilities of ground-based and airborne lightning detection systems are reviewed. The airborne Stormscope system is described and compared with onboard radar and the lightning detection and ranging system (LDAR). Two examples of difference-in-time-of-arrival systems for detecting spherics from discharges in electrified clouds are described: (1) The LDAR system and (2) Taylor's lightning mapping system. Next, an interferometric system adapted to lightning location is discussed. Finally, systems that are based upon crossed-loop magnetic direction finding principles but which have been refined and improved to accurately locate lightning discharges to ground are reviewed.

Corbin, J. C., Jr.↗

NASA NTRS1981

Pilot guidance and display considerations for energy efficient flight profiles

Two computer programs are applied to energy efficient flight operation in order to minimize aircraft operating costs. One algorithm (OPTIM) computes vertical flight profiles which optimize direct operating costs, including fuel and time costs, for an aircraft flying over a fixed range and with a fixed time-of-arrival. The second program (TRAGEN) simulates an aircraft steered to fly along a specified vertical flight trajectory, in order to examine fuel and cost penalties involved in flying nonoptimal trajectories. Constraints such as air traffic control procedures, and atmospheric and weight conditions are considered and supported by graphs and diagrams. The use of the algorithms as preflight planning tools is discussed, emphasizing OPTIM's future application for on-board energy management. Finally, research questions concerning pilot guidance and display considerations for advanced energy/flight management systems are addressed.

Samms, K. H.↗

NASA NTRS1980

Water vapor - The wet blanket of microwave interferometry

The various techniques that utilize microwave interferometry could be employed to determine distances of several thousand kilometers with an accuracy of 1 cm or 2 cm. Such measurements would be useful to obtain new knowledge of earth dynamics, greater insight into fundamental astronomical constants, and the ability to accurately navigate a spacecraft in interplanetary flight. There is, however, a basic problem, related to the presence of tropospheric water vapor, which has to be overcome before such measurements can be realized. Differing amounts of water vapor over the interferometer stations cause errors in the differential time of arrival which is the principal observable quantity. Approaches for overcoming this problem are considered, taking into account requirements for water vapor calibration to support interferometric techniques.

Resch, G. M.↗

NASA NTRS1982

Ultrasonic input-output for transmitting and receiving longitudinal transducers coupled to same face of isotropic elastic plate

The quantitative understanding of ultrasonic nondestructive evaluation parameters such as the stress wave factor were studied. Ultrasonic input/output characteristics for an isotropic elastic plate with transmitting and receiving longitudinal transducers coupled to the same face were analyzed. The asymptotic normal stress is calculated for an isotropic elastic half space subjected to a uniform harmonic normal stress applied to a circular region at the surface. The radiated stress waves are traced within the plate by considering wave reflections at the top and bottom faces. The output voltage amplitude of the receiving transducer is estimated by considering only longitudinal waves. Agreement is found between the output voltage wave packet amplitudes and times of arrival due to multiple reflections of the longitudinal waves.

Williams, J. H., Jr.↗

NASA NTRS1982

Lightning detection and ranging

A lightning detector and ranging (LDAR) system developed at the Kennedy Space Center and recently transferred to Wallops Island is described. The system detects pulsed VHF signals due to electrical discharges occurring in a thunderstorm by means of 56-75 MHz receivers located at the hub and at the tips of 8 km radial lines. Incoming signals are transmitted by wideband links to a central computing facility which processes the times of arrival, using two independent calculations to determine position in order to guard against false data. The results are plotted on a CRT display, and an example of a thunderstorm lightning strike detection near Kennedy Space Center is outlined. The LDAR correctly identified potential ground strike zones and additionally provided a high correlation between updrafts and ground strikes.

Lennon, C. L.↗

NASA NTRS1980

Charge distribution in lightning flashes

Four VHF receivers about 10 km apart were used to detect three-dimensional lightning VHF sources during active thunderstorms. A computer implemented algorithm was used to determine the difference in the time of arrival (DTOA) between the VHF pulses. The three-dimensional source locations determined from the DTOA were correlated with ground electric field measurements (0.1 Hz to 1.5 MHz). Four cloud to ground (CG) and three intracloud (IC) flashes, selected randomly, were studied. A point charge model was used to determine the charge being removed during the different phases of CG and IC flashes. It was determined that return strokes lowered between 24.1 and 3.6 coulombs of negative charge to ground from heights between 10.5 and 5.8 km above MSL. The interstroke process after the first return stroke in a CG flash lowered between 3.4 and 0.9 coulombs of negative charge between the heights of 14.2 (near the cloud tops) to heights of 5.8 km (near the beginning of the leader-return stroke process).

Rustan, P. L.↗

NASA NTRS1984

Laser pulse detection method and apparatus

A sensor is described for detecting the difference in phase of a pair of returned light pulse components, such as two components of a light pulse of an optical gyro. In an optic gyro, the two light components have passed in opposite directions through a coil of optical fiber, with the difference in phase of the returned light components determining the intensity of light shining on the sensor. The sensor includes a CCD (charge coupled device) that receives the pair of returned light components to generate a charge proportional to the number of photons in the received light. The amount of the charge represents the phase difference between the two light components. At a time after the transmission of the light pulse and before the expected time of arrival of the interfering light components, charge accumulating in the CCD as a result of reflections from components in the system, are repeatedly removed from the CCD, by transferring out charges in the CCD and dumping these charges.

Goss, W.↗

NASA NTRS1985

Limits on monopole fluxes from KFG experiment

The nucleon decay experiment at KGF at a depth of 2.3 Km is eminently suited for the search of Grand Unified theory (GUT) monopoles, whose velocities at the present epoch are predicted to be around 0.001C. At this depth the cosmic ray background is at a level 2/day in the detector of size 4m x 6m x 3.7m and one can look for monopoles traversing the detector in all directions, using three methods, i.e., (1) dE/dx (ionization); (2) time of flight and (3) catalysis of nucleon decay. The detector is composed of 34 layers of proportional counters arranged in horizontal planes one above the other in an orthogonal maxtrix. Each of the 1594 counters are instrumented to measure ionization in the gas (90% Argon + 10% Methane) as well as the time of arrival of particles.

Krishnaswamy, M. R.↗

NASA NTRS1985

Design of an advanced flight planning system

The demand for both fuel conservation and four-dimensional traffic management require that the preflight planning process be designed to account for advances in airborne flight management and weather forecasting. The steps and issues in designing such an advanced flight planning system are presented. Focus is placed on the different optimization options for generating the three-dimensional reference path. For the cruise phase, one can use predefined jet routes, direct routes based on a network of evenly spaced grid points, or a network where the grid points are existing navaid locations. Each choice has its own problem in determining an optimum solution. Finding the reference path is further complicated by choice of cruise altitude levels, use of a time-varying weather field, and requiring a fixed time-of-arrival (four-dimensional problem).

Sorensen, J. A.↗

NASA NTRS1988

Charge states of substorm particle injections

The charge states of ions injected during substorms are discussed. Observations from the Medium Energy Particle Analyzer (McEntire et al., 1985) are used to time the arrival of peak proton, helium, and oxygen fluxes at the Charge Composition Explorer satellite. In addition, the dominant ion charge states of these species in the energy range 72-1000 keV are determined. It is found that the freshly-injected heluim (72-240 keV) and oxygen (137-365 keV) are singly ionized, but that more energetic oxygen (greater than 365 keV) is multiply charged. It is suggested that this result implies either a dominant ionospheric source at the lower energies with a solar-wind source at the higher energies, or an energization of the preexisting ring-current population.

Sibeck, D. G.↗

NASA NTRS1989

Time analysis of polydisperse sprays in complex turbulent environments

The two-phase flow field of a small swirl-stabilized burner has been investigated, using a phase Doppler particle analyzer to obtain the velocity, drop size, and time of arrival components. Water/kerosene comparisons were made for the case of nonreacting flow. It is found that the spray flow field is strongly influenced by the aerodynamic flow field and by the reaction and fluid properties. It is noted that vortex shedding produces clusters of drops.

Rudoff, R. C.↗

NASA NTRS1990

Planar double delay-line readout technique for microchannel plate detectors

A two-dimensional position-sensitive electrical readout system for microchannel plate detectors in spectroscopic applications has been devised. Two adjacent parallel coplanar delay lines are used. The difference in time of arrival of the electron event signal between the ends of the delay lines gives one coordinate of the centroid of each event pulse. The ratio of the event amplitudes on the two delay lines gives the orthogonal coordinate by means of charge partitioning. The performance characteristics of operational double delay lines for systems of this type are presented.

Lampton, M.↗

NASA NTRS1991

A system for mapping sources of VHF and electric field pulses from in-cloud lightning at KSC

The literature concerning VHF radiation and wideband electric fields from in-cloud lightning is reviewed. VHF location systems give impressive radio images of lightning in clouds with high spatial and temporal resolution. Using systems based on long and short baseline time-or-arrival and interferometry, workers have detected VHF sources that move at speeds of 10(exp 5) to 10(exp 8) m/s. The more slowly moving sources appear to be associated with channel formation but the physical basis for the higher speeds is not clear. In contrast, wideband electric fields are directly related to physical parameters such as current and tortuosity. A long baseline system is described to measure simultaneously VHF radiation and wideband electric fields at five stations at Kennedy Space Center. All signals are detected over remote, isolated ground planes with fiber optics for data transmission. The modification of this system to map rapidly varying dE/dt pulses is discussed.

Thomson, Ewen M.↗

NASA NTRS1992

Air-Traffic Controllers Evaluate The Descent Advisor

Report describes study of Descent Advisor algorithm: software automation aid intended to assist air-traffic controllers in spacing traffic and meeting specified times or arrival. Based partly on mathematical models of weather conditions and performances of aircraft, it generates suggested clearances, including top-of-descent points and speed-profile data to attain objectives. Study focused on operational characteristics with specific attention to how it can be used for prediction, spacing, and metering.

Tobias, Leonard↗

NASA NTRS1992

Constraints on the putative companions to PSR1257+12

The radio pulsar PSR1257+12 was first observed about two years ago at the Arecibo radio telescope. It has a pulse period of 6.2 milliseconds which makes it one of only a handful of known objects of this type that spin at a dizzying rate of several hundred times per second. Routine follow-up monitoring of this object has continued since its discovery. The pulsar's discoverer has recently reported that a standard analysis of the time-of-arrival measurements of the radio pulses from PSR1257+12 showed that after accounting for the usual features of millisecond pulsars, there remained a residual in the signal which appeared to be a superposition of two components, one with a period of 98 days and the other with a period of 66 days. This was interpreted as being due to the presence of two low mass companions in orbit about the pulsar. The amplitude of the individual components in the residuals then gives a measure of the masses of the companions, up to a factor 1/sin i where i is the inclination of the orbital plane to the plane of the sky, so that a lower limit of the companion masses is well defined. The work reported in this paper tests the validity of this interpretation through orbital dynamics.

Malhotra, R.↗