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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 163 records · Page 9

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NASA NTRS1984

Dependence of the spectrum of Pc 3-4 pulsations on the interplanetary magnetic field

Dependence of the power spectrum of Pc 3-4 magnetic pulsations observed at the ATS 6 geosynchronous satellite on the interplanetary magnetic field (IMF) has been studied. Pulsation events that were observed near noon and exhibited harmonic structure are chosen for analysis. Further selected are pulsation events with identical fundamental frequency to study dependence of the power of pulsations at different harmonic bands on the IMF. A weak negative correlation is observed between the IMF cone angle theta-XB and the power of pulsations in the frequency range 20-70 mHz. Also, a positive correlation between the intensity of the IMF B(IMF) and the power of pulsations at 50-70 mHz is found. This B(IMF) control is present at all ranges of the cone angle. A comparison is conducted of this observation with the frequency of bow shock associated upstream waves predicted from a model of wave generation by a cyclotron resonance of ions reflected at the bow shock. The predicted frequency depends on the IMF as B(IMF) (cos theta-XB)-squared. Although this relation gives a proportionality between the frequency and B(IMF) qualitatively consistent with the observation, it does not explain the most obvious IMF control of the spectrum of the pulsations.

Takahashi, K.↗

NASA NTRS1994

A 1- to 10-GHz downconverter for high-resolution microwave survey

A downconverter was designed, built, and tested for the High Resolution Microwave Survey project. The input frequency range is 1 to 10 GHz with instantaneous bandwidth of 350 MHz and dynamic range of 125 dB/Hz. Requirements were derived for the local oscillators and special design techniques were implemented to achieve the high degree of spectral purity required.

Mcwatters, D.↗

NASA NTRS1984

Voyager observations of Jovian millisecond radio bursts

Voyager Planetary Radio Astronomy data collected over 30-day intervals centered on the two close encounters with Jupiter were utilized to study the characteristics of millisecond-duration radio bursts (s-bursts) at frequencies between 5 and 15 MHz. In this frequency range, s-bursts are found to occur almost independently of Central Meridian Longitude and to depend entirely on the phase of Io with respect to the observer's planetocentric line of sight. Individual bursts typically cover a total frequency range of about 1.5 to 3 MHz, and they are usually strongly circularly polarized. Most bursts in a particular s-burst storm will exhibit the same polarization sense (either right-hand or left-hand), and there is some evidence for a systematic pattern in which one polarizations sense is preferred over the other as a function of Io phase and Central Meridian Longitude. These data are all suggestive of a radio source that is located along the instantaneous Io flux tube and that extends over a linear dimension of 5000 km along the field lines in both the northern and southern Hemispheres.

Alexander, J. K.↗

NASA NTRS1984

Voyager observations of Jovian millisecond radio bursts

Alexander, J. K.↗

NASA NTRS1978

Jovian S-burst observations at 32 MHz

Drift rates for S-burst emissions from Jupiter are studied. The burst spectra, recorded in the frequency range near 32 MHz, provide a qualitative illustration of the behavior of electron bunches shortly after injection into the Io-associated magnetic flux tube. The morphology of the spectra may be taken as support for the hypothesis of an ionospheric acceleration mechanism influencing the flow of electrons.

Desch, M. D.↗

DOE OSTI2020

Bulk modulus measurement at mHz frequencies and high-pressure using synchrotron x-ray radiation

We report an experimental protocol for measuring the frequency dependence of the bulk modulus carried out in a synchrotron x-ray facility based multi-anvil high-pressure apparatus. An oscillating pressure perturbation characterized by x-ray diffraction produces a volume strain measured by imaging. Together, these yield the bulk modulus of the sample. In this work, we report data at 3 mHz as an example of the possibility of providing these data for the frequency range of 1 mHz–100 mHz.

47 OTHER INSTRUMENTATION↗

NASA NTRS1980

The microprocessor-based synthesizer controller

Implementation and performance of the microprocessor-based controllers and Dana Digiphase Synthesizer (DCO) installed in the Deep Space Network exciter in the 64-meter and 34-meter subnets to support uplink tuning required for the Voyager-Saturn Encounter is discussed. Test data in tests conducted during the production of the controllers verified the design objective for phase control accuracy of 10 to the - 12 power cycles in eight hours during ramping. Tests conducted require a phase error between a theoretical calculated value and the actual phase of no greater than + or - 1 cycle. Tests included (1) a ramp over a period of eight hours using a ramp rate which covers the synthesizer tuning range (40-51 MHz) and (2) a ramp sequence using the maximum rate (+ or kHz/s) over the tuning range.

Wick, M. R.↗

NASA NTRS2007

Switched Band-Pass Filters for Adaptive Transceivers

Switched band-pass filters are key components of proposed adaptive, software- defined radio transceivers that would be parts of envisioned digital-data-communication networks that would enable real-time acquisition and monitoring of data from geographically distributed sensors. Examples of sensors to be connected to such networks include security cameras, radio-frequency identification units, and geolocation units based on the Global Positioning System. Through suitable software configuration and without changing hardware, these transceivers could be made to operate according to any of a number of complex wireless-communication standards that could be characterized by diverse modulation schemes, bandwidths, and data-handling protocols. The adaptive transceivers would include field-programmable gate arrays (FPGAs) and digital signal-processing hardware. In the receiving path of a transceiver, the incoming signal would be amplified by a low-noise amplifier (LNA). The output spectrum of the LNA would be processed by a band-pass filter operating in the frequency range between 900 MHz and 2.4 GHz. Then a down-converter would translate the signal to a lower frequency range to facilitate analog-to-digital conversion, which would be followed by baseband processing by one or more FPGAs. In the transmitting path, a digital stream would first be converted to an analog signal, which would then be up-converted to a selected frequency band before being applied to a transmitting power amplifier. The aforementioned band-pass filter in the receiving path would be a combination of resonant inductor-and-capacitor filters and switched band-pass filters. The overall combination would implement a switch function designed mathematically to exhibit desired frequency responses and to switch the signal in each frequency band to an analog-to-digital converter appropriate for that band to produce a digital intermediate-frequency signal for digital signal processing.

Wang, Ray↗

NASA NTRS1988

High-speed analog fiber optic links for satellite communication

Large-aperture phased array antennas operating at millimeter wave frequencies are designed for space-based communications and imaging. Array elements are comprised of active transmit/receive (T/R) modules which are linked to the central processing unit through a high-speed fiberoptic network. This paper demonstrates optical control of active modules for satellite communication at 24 GHz. An approach called T/R level data mixing, which utilizes fiberoptic transmission of a data signal to individual T/R modules to be upconverted by an optically synchronized local oscillator, is demonstrated at 24 GHz. A free-running HEMT oscillator, used as local oscillator at 24 GHz, is synchronized using indirect subharmonic optical injection locking over a locking range of 14 MHz. Results of data link performance over 500-1000 MHz is also reported in terms of gain-bandwidth, linearity and third-order intercept, sensitivity, and dynamic range.

Daryoush, A. S.↗

DOE OSTI2024

Gravitational wave measurement in the mid-band with atom interferometers

Abstract Gravitational Waves (GWs) have been detected in the ∼ 100 Hz and nHz bands, but most of the gravitational spectrum remains unobserved. A variety of detector concepts have been proposed to expand the range of observable frequencies. In this work, we study the capability of GW detectors in the “mid-band”, the ∼ 30 mHz– 10 Hz range between LISA and LIGO, to measure the signals from and constrain the properties of ∼ 1 – 100M ⊙ compact binaries. We focus on atom-interferometer-based detectors. We describe a Fisher matrix code,AIMforGW, which we created to evaluate their capabilities, and present numerical results for two benchmarks: terrestrial km-scale detectors, and satellite-borne detectors in medium Earth orbit. Mid-band GW detectors are particularly well-suited to pinpointing the location of GW sources on the sky. We demonstrate that a satellite-borne detector could achieve sub-degree sky localization for any detectable source with chirp mass ℳ c ≲ 50M ⊙ . We also compare different detector configurations, including different locations of terrestrial detectors and various choices of the orbit of a satellite-borne detector. As we show, a network of only two terrestrial single-baseline detectors or one single-baseline satellite-borne detector would each provide close-to-uniform sky-coverage, with signal-to-noise ratios varying by less than a factor of two across the entire sky. We hope that this work contributes to the efforts of the GW community to assess the merits of different detector proposals.

Astronomy & Astrophysics↗

NASA NTRS1993

Frequency Swept Diode-pumped Single Frequency TM,Ho:YLiF Laser for spaceborne Doppler Lidar

Optical heterodyne experiments involving the photomixing of two single frequency, deode-pumped thulium holmium yttrium lithium flouride lasers are described. Operated in external frquency stabilization loops, the lasers exhibit 1MHz short term stability, and are photomixed and offset-locked at 140 MHz. Summation of sine wave modulation onto the PZT control voltage on one laser results in frequency swept operation over a continuous tuning range of 160 MHz.

Doppler Lidar Optical heterodyne experiments↗

NASA NTRS1983

First results from the Clark Lake Multifrequency Radioheliograph

The characteristics of the Clark Lake Multifrequency Radioheliograph, which is presently being used for solar research in the frequency range 20-125 MHz, are examined and several solar maps obtained with this instrument are presented. Two-dimensional images of the sun's corona at several frequencies within this range are examined, which were obtained with time resolution as good as 1.28 s. It is found that the shape of the sun's outer corona as observed at meter-decameter wavelengths appears to change in time periods as short as a few seconds.

Kundu, M. R.↗

NASA NTRS1984

Rotational frequency splitting of solar oscillations

Prograde and retrograde sectoral oscillations of the sun have been observed so as to determine frequency differences produced by rotation. Oscillations in the frequency range 2.1-3.7 mHz and with spherical harmonic degrees from 1 to 100 have been identified. Average frequency shifts due to rotation in a sidereal reference frame are found to range from a high of about 660 nHz at degree 1 to a low of about 423 nHz at degree 6, rising to about 471 nHz at degree 100. These results indicate that most of the sun's volume rotates at a rate close to that of the surface, but also that the energy-generating core may rotate more rapidly than the surface.

Duvall, T. L., Jr.↗

NASA NTRS1995

A Low-Frequency Radio Sky Survey from Space

The frequency range below 30 MHz has not been explored with high angular resolution due to the opacity and refraction of the Earth's ionosphere. An interferometer array in space could provide high dynamic range images of the entire sky with arcminute angular resolution.

interferometer array space survey low frequency ap↗

NASA NTRS1981

The plasma wave and quasi-static electric field instrument /PWI/ for dynamics Explorer-A

It is explained that the Plasma Wave Instrument (PWI) on Dynamics Explorer-A measures both plasma wave phenomena and quasi-static electric fields. The quasi-static electric fields are measured parallel to the spin axis of the spacecraft in a range of 2 mV/m to 2 V/m and perpendicular to the spin axis 0.5 mV/m to 2 V/m at 16 samples/s. The ac electric field sensors include a 200-m tip-to-tip long wire antenna and a 0.6-m short electric antenna, both of which are perpendicular to the spin axis, and a 9-m tip-to-tip tubular antenna parallel to the spin axis. AC electric wave fields are measured over a frequency range of 1 Hz to 2 MHz and over an amplitude range of 0.03 microvolt/m to 100 mV/m.

Shawhan, S. D.↗

NASA NTRS1995

Cheap, Easy-To-Read Frequency Monitor For Pulsed Laser

Electronic circuit provides bar-graph display of difference between carrier frequency of pulsed laser transmitter and frequency of another laser serving as local oscillator in receiver. Display device linear array of light-emitting diodes (LED's), each representing 1-MHz portion of beat-frequency range from 20 to 40 MHz. Middle LED and neighbors green; LED's representing edges of passband yellow; LED's of frequencies outside passband red. Operator determines approximate relative frequency of transmitter at a glance by observing color and position of illuminated LED.

Esporoles, Carlos↗

DOE OSTI2020

Broadband fibre-pigtailed acousto-optic frequency shifter

A two-crystal fibre-pigtailed acousto-optic frequency shifter has been developed and investigated. An optimal configuration of acousto-optic cells is chosen. A two-crystal acousto-optic frequency shifter of 785-nm laser radiation in the range from 156 to 196 MHz, with single-mode polarisation maintaining fibres at the input and output, is described. Some recommendations are given how to improve the shifter transmission coefficient and increase the frequency shift range. (acousto-optic modulation of light)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1973

The prevalence of second harmonic radiation in type III bursts observed at kilometric wavelengths.

We present the analysis of 64 type III solar bursts that drifted from 3.5 MHz down to the range 350-50 kHz between March 1968 and February 1970. Bursts arrival times were predicted by a simple model and then compared with observations. The results show that, as the bursts drift, the fundamental often disappears below a certain frequency range while the second harmonic remains. Below about 1 MHz, the second harmonic occurrence predominates. Recognizing this fact we deduce a mean velocity of 0.32c plus or minus 0.02c for the exciter particles, where the uncertainty is the standard error and c the velocity of light in vacuum; the electron density model used is comparable to a solar wind model.

Haddock, F. T.↗