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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 343 records · Page 19

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NASA NTRS1978

Adiabatic heating in impulsive solar flares

A study is made of adiabatic heating in two impulsive solar flares on the basis of dynamic X-ray spectra in the 28-254 keV range, H-alpha, microwave, and meter-wave radio observations. It is found that the X-ray spectra of the events are like those of thermal bremsstrahlung from single-temperature plasmas in the 10-60 keV range if photospheric albedo is taken into account. The temperature-emission correlation indicates adiabatic compression followed by adiabatic expansion and that the electron distribution remains isotropic. H-alpha data suggest compressive energy transfer. The projected areas and volumes of the flares are estimated assuming that X-ray and microwave emissions are produced in a single thermal plasma. Electron densities of about 10 to the 9th/cu cm are found for homogeneous, spherically symmetric sources. It is noted that the strong self-absorption of hot-plasma gyrosynchrotron radiation reveals low magnetic field strengths.

Maetzler, C.↗

NASA NTRS1984

Thermoelectric temperature control system for the pushbroom microwave radiometer (PBMR)

A closed loop thermoelectric temperature control system is developed for stabilizing sensitive RF integrated circuits within a microwave radiometer to an accuracy of + or - 0.1 C over a range of ambient conditions from -20 C to +45 C. The dual mode (heating and cooling) control concept utilizes partial thermal isolation of the RF units from an instrument deck which is thermally controlled by thermoelectric coolers and thin film heaters. The temperature control concept is simulated with a thermal analyzer program (MITAS) which consists of 37 nodes and 61 conductors. A full scale thermal mockup is tested in the laboratory at temperatures of 0 C, 21 C, and 45 C to confirm the validity of the control concept. A flight radiometer and temperature control system is successfully flight tested on the NASA Skyvan aircraft.

Dillon-Townes, L. A.↗

NASA NTRS1989

Effects of a hot intergalactic medium

One effect a hot intergalactic medium (IGM) would have would be to produce an isotropic X-ray background through thermal bremsstrahlung. Such a background was modeled including both relativistic electron-ion and electron-electron emission; the observed X-ray measurements could be fit with a current temperature of 10.2 keV and Omega (IGM) of 0.27, assuming that the IGM was instantaneously heated at a redshift of 5 and cools by relativistic adiabatic expansion and Compton cooling. Such a hot IGM would also distort the cosmic microwave background spectrum by inverse Compton scattering off relativistic electrons. This distortion was modeled using the relativistic treatment. When including the recent data of Matsumoto et al., an undistorted radiation temperature of 2.86 K and an Omega (IGM) of 0.41 was found.

Taylor, Gregory B.↗

NASA NTRS1991

NASA SBIR product catalog, 1991

This catalog is a partial list of products of NASA SBIR (Small Business Innovation Research) projects that have advanced to some degree into Phase 3. While most of the products evolved from work conducted during SBIR Phase 1 and 2, a few advanced to commercial status solely from Phase 1 activities. The catalog presents information provided to NASA by SBIR contractors who wished to have their products exhibited at Technology 2001, a NASA-sponsored technology transfer conference held in San Jose, California, on December 4, 5, and 6, 1991. The catalog presents the product information in the following technology areas: computer and communication systems; information processing and AI; robotics and automation; signal and image processing; microelectronics; electronic devices and equipment; microwave electronic devices; optical devices and lasers; advanced materials; materials processing; materials testing and NDE; materials instrumentation; aerodynamics and aircraft; fluid mechanics and measurement; heat transfer devices; refrigeration and cryogenics; energy conversion devices; oceanographic instruments; atmosphere monitoring devices; water management; life science instruments; and spacecraft electromechanical systems.

Source record↗

NASA NTRS1994

The Soft X-Ray/Microwave Ratio of Solar and Stellar Flares and Coronae

We have carried out plasma diagnostics of solar flares using soft X-ray (SXR) and simultaneous microwave observations and have compared the ratio of X-ray to microwave luminosities of solar flares with various active late-type stars available in the published literature. Both the SXR low-level ('quiescent') emission from stellar coronae and the flaring emission from the Sun and stars are generally interpreted as thermal radiations of coronal plasmas. On the other hand, the microwave emission of stars and solar flares is generally attributed to an extremely hot or nonthermal population of electrons. Solar flare SXR are conventionally measured in a narrower and harder passband than the stellar sources. Observations of the GOES-2 satellite in two energy channels have been used to estimate the luminosity of solar flares as it would appear in the ROSAT satellite passband. The solar and stellar flare luminosities fit well at the lower end of the active stellar coronae. The flare SXR/microwave ratio is similar to the ratio for stellar coronae. The average ratio follows a power-law relation L(sub X) varies as L(sub R)(sup 0.73 +/- 0.03) over 10 orders of magnitude from solar microflares to RS CVn and FK Com-type coronae. Dwarf Me and Ke stars, and RS CVn stars are also compatible with a linear SXR/microwave relation, but the ratio is slightly different for each type of star. Considering the differences between solar flares, stellar flares and the various active stellar coronae, the similarity of the SXR/microwave ratios is surprising. It suggests that the energetic electrons in low-level stellar coronae observed in microwaves are related in a similar way to the coronal thermal plasma as flare electrons to the flare thermal plasma, and, consequently, that the heating mechanism of active stellar coronae is a flare-like process.

Benz, A. O.↗

NASA NTRS1987

A review of research and development on the microwave-plasma electrothermal rocket

The microwave-plasma electrothermal rocket (MWPETR) shows promise for spacecraft propulsion and maneuvering, without some of the drawbacks of competitive electric propulsion systems. In the MWPETR, the electric power is first converted to microwave-frequency radiation. In a specially-designed microwave cavity system, the electromagnetic energy of the radiation is transferred to the electrons in a plasma sustained in the working fluid. The resulting high-energy electrons transfer their energy to the atoms and molecules of the working fluid by collisions. The working fluid, thus heated, expands through a nozzle to generate thrust. In the MWPETR, no electrodes are in contact with the working fluid, the energy is transferred into the working fluid by nonthermal mechanisms, and the main requirement for the materials of construction is that the walls of the plasma chamber be insulating and transparent to microwave radiation at operating conditions. In this survey of work on the MWPETR, several experimental configurations are described and compared. Diagnostic methods used in the study are described and compared, including titration, spectroscopy, calorimetry, electric field measurements, gas-dynamic methods, and thrust measurements. Measured and estimated performance efficiencies are reported. Results of computer modeling of the plasma and of the gas flowing from the plasma are summarized.

Hawley, Martin C.↗

NASA NTRS1976

Satellite-observed latent heat release in a tropical cyclone

Earlier observational estimates of storm latent heat release (LHR) have been made using a moisture budget approach. The present paper summarizes results for the tropical cyclone Nora, using the electrically scanning microwave radiometer (ESMR) on Nimbus 5, on the basis of the theoretical brightness temperature/rainfall rate relationship for an assumed freezing level of 5 km. The LHR of the storm as a function of time for a circular area of radius 4 deg latitude positioned on the circulation center is discussed along with the calculated mean rain rate as a function of distance from the storm center. The contribution of the various magnitudes of rain rates to the total LHR of the storm is examined. It is concluded that the Nimbus 5 ESMR data can be used to determine the LHR characteristics of tropical cyclones and are potentially useful in the monitoring of such storms. The calculations for Typhoon Nora indicate that the LHR for the storm increases as the storm intensifies from a tropical disturbance to a typhoon.

Adler, R. F.↗

NASA NTRS1992

Structure, processing, and properties of potatoes

The objective of this experiment and lesson intended for high school students in an engineering or materials science course or college freshmen is to demonstrate the relation between processing, structure, and thermodynamic and physical properties. The specific objectives are to show the effect of structure and structural changes on thermodynamic properties (specific heat) and physical properties (compressive strength); to illustrate the first law of thermodynamics; to compare boiling a potato in water with cooking it in a microwave in terms of the rate of structural change and the energy consumed to 'process' the potato; and to demonstrate compression testing.

Lloyd, Isabel K.↗

NASA NTRS2013

An Ultra-Wideband, Microwave Radar for Measuring Snow Thickness on Sea Ice and Mapping Near-Surface Internal Layers in Polar Firn

Sea ice is generally covered with snow, which can vary in thickness from a few centimeters to >1 m. Snow cover acts as a thermal insulator modulating the heat exchange between the ocean and the atmosphere, and it impacts sea-ice growth rates and overall thickness, a key indicator of climate change in polar regions. Snow depth is required to estimate sea-ice thickness using freeboard measurements made with satellite altimeters. The snow cover also acts as a mechanical load that depresses ice freeboard (snow and ice above sea level). Freeboard depression can result in flooding of the snow/ice interface and the formation of a thick slush layer, particularly in the Antarctic sea-ice cover. The Center for Remote Sensing of Ice Sheets (CReSIS) has developed an ultra-wideband, microwave radar capable of operation on long-endurance aircraft to characterize the thickness of snow over sea ice. The low-power, 100mW signal is swept from 2 to 8GHz allowing the air/snow and snow/ ice interfaces to be mapped with 5 c range resolution in snow; this is an improvement over the original system that worked from 2 to 6.5 GHz. From 2009 to 2012, CReSIS successfully operated the radar on the NASA P-3B and DC-8 aircraft to collect data on snow-covered sea ice in the Arctic and Antarctic for NASA Operation IceBridge. The radar was found capable of snow depth retrievals ranging from 10cm to >1 m. We also demonstrated that this radar can be used to map near-surface internal layers in polar firn with fine range resolution. Here we describe the instrument design, characteristics and performance of the radar.

Snow Cover↗

NASA NTRS1986

Electron-cyclotron maser emission during flares: Emission in various modes and temporal variations

Absorption of radiation at the electron-cyclotron frequency, OMEGA sub e, generated by the electron-cyclotron maser instability was proposed as a possible mechanism for transporting energy and heating of the corona during flares. Radiation from the same instability but at harmonics of OMEGA sub e is believed to be the source of solar microwave spike bursts. The actual mode and frequency of the dominant emission from the maser instability is shown to be dependent on: (1) the plasma temperature, (2) the form of the energetic electron distribution, and (3) on the ratio of the plasma frequency omega sub p to OMEGA sub e. As a result, the emission along a flux tube can vary, with emission at harmonics being favored in regions where omega sub p/OMEGA sub e approx. equal to or greater than 1. Changes in the plasma density and temperature in the source region associated with the flare can also cause the characteristics of the emission to change in time.

Winglee, R. M.↗

NASA NTRS1990

The universe in a box - Thermal effects in the standard cold dark matter scenario

An attempt is made to compute the evolution of a representative piece of the universe at a minimal resolution of a flux-based mesh code coupled with a standard particle-mesh dark matter code. It is found that, on scales greater than 1/h Mpc, dark matter is more clumped than gas. Bremsstrahlung and Compton cooling are unimportant on scales of 1 Mpc or greater. Shocks gradually heat the gas, leaving most of it in voids at T = 10 exp 3.5 K or less, but with a small fraction reaching T = 10 million K or more. Ultraviolet and soft X-ray emission from the heated gas is significant, providing an important part of the background radiation field and significant ionizing of the intergalactic medium. The mean induced Delta T/T for microwave background radiation in the Rayleigh-Jeans part of the spectrum is 1.1 x 10 to the -6th with fluctuation of 5.6 x 10 to the -7th on arcmin scales and a mean y parameter of 5.5 x 10 to the -7th, which is potentially detectable by the COBE satellite.

Cen, R. Y.↗

NASA NTRS1992

Air-sea interaction and remote sensing

The first part of the proposed research was a joint effort between our group and the Applied Physics Laboratory (APL), University of Washington. Our own research goal is to investigate the relation between the air-sea exchange processes and the sea state over the open ocean and to compare these findings with our previous results obtained over a small body of water namely, Lake Washington. The goals of the APL researchers are to study (1) the infrared sea surface temperature (SST) signature of breaking waves and surface slicks, and (2) microwave and acoustic scattering from water surface. The task of our group in this joint effort is to conduct measurements of surface fluxes (of momentum, sensible heat, and water vapor) and atmospheric radiation (longwave and shortwave) to achieve our research goal as well as to provide crucial complementary data for the APL studies. The progress of the project is summarized.

Katsaros, Kristina B.↗

NASA NTRS1977

Ionosphere/microwave beam interaction study

A solar power satellite microwave power density of 20mw sq cm was confirmed as the level where nonlinear interactions may occur in the ionosphere, particularly at 100 km altitude. Radio wave heating at this altitude, produced at the Arecibo Observatory, yielded negative results for radio wave heating of an underdense ionosphere. Overdense heating produced striations in the ionosphere which may cause severe radio frequency interference problems under certain conditions. The effects of thermal self-focusing are shown to be limited severely geographically. The aspect sensitivity of field-aligned striations makes interference-free regions above magnetic latitude about 60 deg. A test program is proposed to simulate the interaction of the SPS beam with the ionosphere, to measure the effects of the interaction on the ionosphere and on communication and navigation systems, and to interpret the results.

Duncan, L. M.↗

NASA NTRS1981

High frequency plasma generators for ion thruster applications

Two concepts for high frequency discharge ion thrusters are described. Both sources are designed for use with 30 cm grid sets and argon propellant and utilize multi-cusp permanent magnet geometries for plasma confinement. The RF induction source is a conventional design representing a synthesis of the RIT and multi-cusp concepts. The preliminary data (without system optimization) indicate a discharge efficiency comparable to that obtained in 30 cm hollow cathode multi-cusp argon thrusters. The electron cyclotron heating source is electrodeless and exhibits plasma characteristics which should lead to greatly reduced discharge chamber and screen sputter rates with the optimization of the magnetic fields, microwave frequency, and feed configuration.

Divergilio, W. F.↗

NASA NTRS1985

Dual frequency observations of solar microwave bursts using the VLA

Simultaneous VLA observations of microwave bursts at 6 and 2 cm in a solar active region are presented and discussed. Using the full-day synthesis, I and V maps of the active region are produced. The radiation mechanisms at these wavelengths are discussed and the upper and lower bounds on the magnetic field of the active region are derived. The magnetic fields in the microwave burst source are estimated from the brightness temperature and the degree of circular polarization. It is concluded that the 6 cm radiation originates from the bulk heated plasma, whereas the 2 cm radiation is due to the nonthermal particles generated in the energy-release process. The delay between the peaks of emission at the two wavelengths is interpreted using a dc electric field model of flares. Depending on the strength of the electric field and the density in the flaring region, delays in either sense can be observed.

Shevgaonkar, R. K.↗

NASA NTRS1986

Simultaneous Solar Maximum Mission (SMM) and very large array observations of solar active regions

The research deals mainly with Very Large Array and Solar Maximum Mission observations of the ubiquitous coronal loops that dominate the structure of the low corona. As illustrated, the observations of thermal cyclotron lines at microwave wavelengths provide a powerful new method of accurately specifying the coronal magnetic field strength. Processes are delineated that trigger solar eruptions from coronal loops, including preburst heating and the magnetic interaction of coronal loops. Evidence for coherent burst mechanisms is provided for both the Sun and nearby stars, while other observations suggest the presence of currents that may amplify the coronal magnetic field to unexpectedly high levels. The existence is reported of a new class of compact, variable moving sources in regions of apparently weak photospheric field.

Lang, K. R.↗

NASA NTRS1987

Tropical rainfall measuring mission (TRMM)

By measuring rainfall in the tropics, the Tropical Rainfall Measuring Mission (TRMM) will make possible the understanding of the heat engine that drives the global weather. The TRMM mission parameters are given, and the spacecraft is described. The instruments are examined, including the precipitation radar, TRMM microwave radiometer, and Advanced Very High Frequency Radiometer. The mission life is addressed, including atmospheric data, fuel consumption, and life extension methods. The spacecraft interfaces, payload configuration, and deployment sequence are considered. The subsystems are described, including propulsion, power, command, data handling, and tracking. A Japanese Experimental Data Relay Tracking Satellite experimental package working with TRMM is briefly addressed.

Keating, Thomas↗

NASA NTRS1989

Global atmospheric moisture variability

Research efforts during FY-88 have focused on completion of several projects relating to analysis of FGGE data during SOP-1 and on expanded studies of global atmospheric moisture. In particular, a revised paper on the relationship between diabatic heating and baroclinicity in the South Pacific Convergence Zone (SPCZ) was submitted. A summary of completed studies on diagnostic convective parameterization was presented at the Satellite Meteorology and Oceanography Convergence last February. These investigations of diabatic heating in the SPCZ have demonstrated the requirement for a more quantitative description of atmospheric moisture. As a result, efforts were directed toward use of passive remote microwave measurements from the Nimbus-7 SMMR and the DOD's Special Sensor Microwave Imager (SSMI/I) as critical sources of moisture data. Activities this year are summarized.

Robertson, Franklin R.↗