Showing papers on "TEC published in 1977"

Measurements of the Neutron-Induced Fission Cross Sections of 234U, 236U, and 238U Relative to 235U from 0.1 to 30 MeV

Abstract: We have measured the fission cross-section ratios 234U:235U, 236U:235U, and 238U:235U as a function of neutron energy from 0.1 to 30 MeV using ionization fission chambers and the time-of-flight tec...

Effect of electrojet on the total electron content of the ionosphere over the Indian subcontinent

Abstract: THE radio beacon method of measuring TEC along a chain of optimally spaced stations near the equatorial anomaly has been used to monitor continuously the latitudinal extent of the anomaly. Comparisons with the magnitude of the electrojet show a clear dependence of anomaly strength upon the electrojet intensity with an approximate two-hour time delay.

Correlation Distance of Mean Daytime Electron Content

Abstract: : In the total electron content (TEC) monitoring station network, an important parameter is the required number of stations for a given percentage improvement over the use of monthly median predicted values. Using data from nine TEC stations, taken a pair at a time, values are computed for the correlation coefficient for the 10 to 16 hour local time period when the diurnal values of TEC are generally highest. Little consistent seasonal differences were found in the correlation coefficient values. Thus simple linear relations between station separation and correlation coefficient were chosen for stations having approximate north-south and east-west spacings. For a 50 percent improvement in TEC prediction over a monthly median value, TEC monitoring stations must be spaced approximately 2400 km in longitude and 1600 km in latitude. These values agree reasonably well with previous studies of the correlation distance of the ionospheric parameter foF2.

Summary of the CTS Transient Event Counter Data after One Year of Operation

Abstract: A spacecraft electrical system transient detector has been operating on the joint Canadian-American Communications Technology Satellite (CTS), now called Hermes, since January 31, 1976. This detector, called the transient event counter (TEC), senses and counts transients having a minimum amplitude of 5 volts and a rise time of less than 0.3 ?sec. The transients in three separate wiring harnesses are counted: the attitude control harness, the solar array instrumentation harness and the solar array power harness. Recently, anomalous behavior of geosynchronous satellites has been attributed to the electrostatic charging of spacecraft surfaces by the environment during geomagnetic substorms. Insulating surface materials subjected to high electrical stress by such charging can discharge through electrical arcing. It is believed that the electromagnetic pulses from such discharges can couple into the spacecraft wiring harnesses and result in uncommanded switching of logic circuits, which in turn is responsible for the observed anomalies. The function of the TEC is to count such transients. This report describes the TEC and presents the flight data for a year of operation. A large number of transients have occurred but these have not caused any anomalous electronic switching events in the satellite systems. The character of the transients seems to imply that additional sensors are required to understand the discharge phenomenon on large satellites. The results of this experiment indicate that satellite system immunity to discharge-related electronic switching anomalies can be obtained by filtering out the harness transients.

On the Installation, Operation, Data Reduction, and Maintenance of VHF Electronic Polarimeters for Total Electron Content Measurements.

Abstract: : This report gives practical, explanatory information on the installation, operation, and maintenance of VHF Electronic Polarimeters and on the reduction of data for computations of ionospheric total electron content (TEC). It should be used by Air Weather Service maintenance and observer personnel engaged in making real-time TEC measurements, and it can also be used by personnel engaged in making TEC measurements for scientific studies. Many aspects of the experimental problems associated with TEC measurements are presented in this report. (Author)

The NASA thermionic-conversion /TEC-ART/ program

Abstract: The current emphasis is on out-of-core thermionic conversion (TEC). The additional degrees of freedom offer new potentialities, but high-temperature material effects determine the level and lifetime of TEC performance: New electrodes not only raise power outputs but also maintain them regardless of emitter-vapor deposition on collectors. In addition, effective electrodes serve compatibly with hot-shell alloys. Space TEC withstands external and internal high-temperature vaporization problems, and terrestrial TEC tolerates hot corrosive atmospheres outside and near-vacuum inside. Finally, reduction of losses between converter electrodes is essential even though rather demanding geometries appear to be required for some modes of enhanced operation.

Distortions of the winter nighttime ionosphere at L = 4

Abstract: The winter nighttime ionosphere at L = 4 reveals frequent increases in F region peak density (Nmax) accompanied by a constant or declining total electron content (TEC). This effect is examined statistically by using two winter periods of simultaneous TEC and Nmax data and 24 years of December foF2 observations. The month of December 1971 was chosen for a detailed analysis. Two nights, December 9 and 15, were used in simulation attempts to identify the conditions needed to account for the increasing Nmax-constant TEC effect. For each case study, Isis 2 topside sounder Ne(h) interpolated data and Ne(h) profiles from ground-based ionosondes were combined with simultaneous TEC measurements to form a semiempirical computer model for Ne(h) versus latitude from h = 0 to geostationary satellite height. The results indicate that vertical distortions of the Ne(h) profile over a wide latitude range are needed to reproduce the increasing Nmax-constant TEC effect. The mechanism causing these distortions is still poorly understood. It is suggested that substorm-enhanced westward electric fields induce a lowering of the F layer during which air drag effects may permit a buildup of plasma at hmax before enhanced loss processes take over.

Optimize out-of-core thermionic energy conversion for nuclear electric propulsion

Abstract: Current designs for out of core thermionic energy conversion (TEC) to power nuclear electric propulsion (NEP) were evaluated Approaches to improve out of core TEC are emphasized and probabilities for success are indicated TEC gains are available with higher emitter temperatures and greater power densities Good potentialities for accommodating external high temperature, high power density TEC with heat pipe cooled reactors exist

Ionospheric Total Electron Content Measurements from Turkey during the Solar Eclipse of 29 April 1976

Abstract: Total ionospheric electron content (TEC) has been determined from the measurements of the Faraday rotation of a plane polarized wave that have been returned from the geostationary satellite ATS 6 transmitting at a frequency of 140 MHz. The results of the computations have been presented in the form of diurnal curves in order to investigate the effect of the solar eclipse of 29 April 1976 on the TEC over Ankara longitudes.

Reduction of the Uncertainty of Radar Range Correction.

Abstract: : A correction for the range error induced by the ionosphere is examined for a representative 425 Mhz radar. A technique has been developed to update the basic prediction of the median so that the residual day-to-day variability of the range correction is reduced. This technique is examined over a descending phase of a solar cycle using measurements of total electron content from Hamilton, Massachusetts. The results show that hourly updating can reduce the residual error in range correction by 60 percent, and three-hourly updating will provide a 30 percent reduction in day-time when the absolute error in range correction is greatest. During periods of rapid changes in TEC such as, sunrise and sunset, and periods of sever magnetic disturbance updating in 15-30 minute intervals is recommended to significantly reduce error. (Author)

High-temperature, high-power-density thermionic energy conversion for space

Abstract: Theoretic converter outputs and efficiencies indicate the need to consider thermionic energy conversion (TEC) with greater power densities and higher temperatures within reasonable limits for space missions. Converter-output power density, voltage, and efficiency as functions of current density were determined for 1400-to-2000 K emitters with 725-to-1000 K collectors. The results encourage utilization of TEC with hotter-than-1650 K emitters and greater-than-6W sq cm outputs to attain better efficiencies, greater voltages, and higher waste-heat-rejection temperatures for multihundred-kilowatt space-power applications. For example, 1800 K, 30 A sq cm TEC operation for NEP compared with the 1650 K, 5 A/sq cm case should allow much lower radiation weights, substantially fewer and/or smaller emitter heat pipes, significantly reduced reactor and shield-related weights, many fewer converters and associated current-collecting bus bars, less power conditioning, and lower transmission losses. Integration of these effects should yield considerably reduced NEP specific weights.

Spatial correlation of transionospheric signal-time-delays

Abstract: Excess time delays of transionospheric radio signals introduce ranging errors in satellite-navigation and radar systems, which are directly proportional to the total electron content (TEC) along the propagation path. Correlation between TEC at Fort Monmouth, NJ ( 40.18\deg N, 74.06\deg W) and Richmond, FL ( 25.60\deg N, 80.40\deg W) was determined. The correlation analysis was performed at monthly and daily intervals for the equinoctial and winter periods during the quiet phase of the solar cycle. Positive maxima of monthly correlation coefficients were \gsim 0.9 for data comparisons at identical or nearly identical times, and decreased when the data sets were shifted in time with respect to each other. Positive maxima of daily correlation coefficients were, in general, \gsim 0.9 . Seasonal variations were noticeable.

Correlation distance of mean daytime electron content. Air force surveys in geophysics

Abstract: In the total electron content (TEC) monitoring station network, an important parameter is the required number of stations for a given percentage improvement over the use of monthly median predicted values. With data from nine TEC stations, taken a pair at a time, values are computed for the correlation coefficient for the 10 to 16 hour local time period when the diurnal values of TEC are generally highest. Little consistent seasonal differences were found in the correlation coefficient values. Thus simple linear relations between station separation and correlation coefficient were chosen for stations having approximate north-south and east-west spacings. For a 50 percent improvement in TEC prediction over a monthly median value, TEC monitoring stations must be spaced approximately 2400 km in longitude and 1600 km in latitude. These values agree reasonably well with previous studies of the correlation distance of the ionospheric parameter foF2.

Midlatitude Total Electron Content and Slab Thickness-A Summary of Seasonal, Solar Cycle, and Magnetically Disturbed Behavior.

Abstract: : This paper is a summary of the results of nearly a full solar cycle of recordings of Total Electron Content, TEC, taken from Hamilton, Massachusetts, a northern midlatitude station. While many of the aspects of TEC behavior from this station have been published separately, the completion of a nearly full solar cycle of data recordings provides a convenient time to compile a summary of the conclusions drawn from this work. The major features of diurnal, seasonal, and solar-cycle dependence of TEC and equivalent slab thickness are described. The seasonal anomaly in daily maximum TEC has a pronounced peak during equinoxes, as does N(max) from a nearby ionosonde. Daytime equivalent slab thickness, however, has no seasonal anomaly and a negligible semiannual component. Slab thickness is also shown not to be a useful measure of daytime neutral temperature. Average changes in TEC, N(max) and slab thickness during magnetic storms are summarized as well. (Author)