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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 361 records · Page 20
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NASA NTRS1989

Observations of low-frequency radio emissions in the earth's magnetosphere

Electromagnetic radiation in the earth's magnetosphere was investigated for the frequency range between 10 kHz and 80 kHz, using data from the Minnesota Plasma Wave Experiment aboard the IMP 6 spacecraft. Two types of radio emissions were examined, the first being the nonthermal continuum radiation, and the second, much more impulsive, is the radiation which lies between 10 and 60 kHz. The first type of radiation was found to correlate with the enhancements of the magnetic substorm index AE and to follow the onset of the negative bay feature of the AU index by about 20 min. The second radiation was found to correlate with auroral kilometric radiation (AKR) on a time scale of about 1 min; this radiation was found to have a source direction very near that of the coincident AKR.

Filbert, Paul C.↗
NASA NTRS1989

Technical options for high average power free electron milimeter-wave and laser devices

Many of the potential space power beaming applications require the generation of directed energy beams with respectable amounts of average power (MWs). A tutorial summary is provided here on recent advances in the laboratory aimed at producing direct conversion of electrical energy to electromagnetic radiation over a wide spectral regime from microwaves to the ultraviolet.

Swingle, James C.↗
NASA NTRS1989

Structures for remotely deployable precision antennas

Future space missions such as the Earth Science Geostationary Platform (ESGP) will require highly accurate antennas with apertures that cannot be launched fully formed. The operational orbits are often inaccessible to manned flight and will involve expendable launch vehicles such as the Delta or Titan. There is therefore a need for completely deployable antenna reflectors of large size capable of efficiently handling millimeter wave electromagnetic radiation. The parameters for the type of mission are illustrated. The logarithmic plot of frequency versus aperture diameter shows the regions of interest for a large variety of space antenna applications, ranging from a 1500-meter-diameter radio telescope for low frequencies to a 20-meter-diameter infrared telescope. For the ESGP, a major application is the microwave radiometry at high frequencies for atmospheric sounding. Almost all existing large antenna reflectors for space employ a mesh-type reflecting surface. Examples are shown and discussed which deal with the various structural concepts for mesh antennas. Fortunately, those concepts are appropriate for creating the very large apertures required at the lower frequencies for good resolution. The emphasis is on the structural concepts and technologies that are appropriate to fully automated deployment of dish-type antennas with solid reflector surfaces. First the structural requirements are discussed. Existing concepts for fully deployable antennas are then described and assessed relative to the requirements. Finally, several analyses are presented that evaluate the effects of beam steering and segmented reflector design on the accuracy of the antenna.

Hedgepeth, J. M.↗
NASA NTRS1989

Structures for remotely deployable precision antennas

There is a need for completely deployable large antenna reflectors capable of efficiently handling millimeter-wave electromagnetic radiation. The structural concepts and technologies that are appropriate to fully automated deployment of dish-type antennas with solid reflector surfaces were studied. First, the structural requirements are discussed. Then, existing concepts for fully deployable antennas are described and assessed relative to the requirements. Finally, several analyses are presented that evaluate the effects of beam steering and segmented reflector design on the accuracy of the antenna.

Hedgepeth, John M.↗
NASA NTRS1989

Middle Atmosphere Program. Handbook for MAP, volume 29. Part 1: Extended Abstracts, International Symposium on Solar Activity Forcing of the Middle Atmosphere. Part 2: MASH Workshop

The proceedings of the symposium is presented. Eight different sessions were presented: (1) Papers generally related to the subject; (2) Papers on the influence of the Quasi Biennial Oscillation; (3) Papers on the influence of the solar electromagnetic radiation variability; (4) Papers on the solar wind and high energy particle influence; (5) Papers on atmospheric circulation; (6) Papers on atmospheric electricity; (7) Papers on lower ionospheric variability; and (8) Solar posters, which are not included in this compilation.

Lastovicka, Jan↗
NASA NTRS1989

Comparison of thermal (FLIR) and television images

The human eye is sensitive to electromagnetic radiation in the 0.4 to 0.7 micron band (light). Thermal imaging (TI) systems are sensitive to heat radiation in the infrared band (3-5 or 8-14 microns) and are capable of transforming the distribution of relative temperatures in a scene into a visible TV image. The present experiment was designed to investigate the impact of the difference between TIs and regular TV images on the detection and identification of natural and man-made targets. Parallel TV and TI videotapes were recorded during helicopter flights. Fifteen subjects who viewed both the TV and the TI images (separately), were asked to detect predefined targets and to identify features pointed out to them by the experimenter. In general, performance with TVs was superior to performance with TIs in terms of response times and errors. However, subjects required significantly less time to detect man-made objects with TIs than with TVs. The correlation between the performance of the same task with the two kinds of images was very low. The results are discussed in terms of image quality and in terms of humans' internal representations of natural categories.

Brickner, Michael S.↗
NASA NTRS1990

The effects of the space environment on two aramid materials

Two aramid fibers having closely related chemical structures were chosen for important roles in the first tether to be used to connect pairs of orbiting vehicles. The protective outer jackets of the tethers will consist of woven fibers of poly(m-phenylene isophthalamide), commercially available from du Pont as Nomex. A cylindrical sheath of woven Kevlar 29, whose principal constituent is poly(p-phenylene terephthalamide), will be the load-bearing component for the tethers. Orbiting tethers will be in a hostile environment in which short wavelength electromagnetic radiation and energetic charged particles degrade exposed organic materials. At lower orbiting altitudes atomic oxygen is an especially serious hazard. Studies on the effects of ultraviolet radiation and atomic oxygen on fibers and films of Kevlar and Nomex are in progress. In an experiment to simulate the effects of atomic oxygen in space, small tows of Kevlar and Nomex were mounted in a commercial ashing device filled with oxygen at low pressure. An RF discharge in the instrument dissociated the molecular oxygen producing a strongly oxidizing atmosphere containing O(3P)(sup 4). Erosion was measured in terms of mass loss. Kevlar films were exposed to UV radiation in an apparatus consisting of a small vacuum chamber, 23 cm in diameter, into which a mass spectrometer and a quartz window were incorporated. Samples were exposed under vacuum with a 1000 watt xenon-arc lamp. Volatile products could be monitored with the mass spectrometer during the exposures. Transmission infrared spectra were taken before and after exposure to monitor chemical changes in the films.

Kiefer, Richard L.↗
NASA NTRS1990

Multipurpose hardened spacecraft insulation

A Multipurpose Hardened Spacecraft Multilayer Insulation (MLI) system was developed and implemented to meet diverse survivability and performance requirements. Within the definition and confines of a MLI assembly (blanket), the design: (1) provides environmental protection from natural and induced nuclear, thermal, and electromagnetic radiation; (2) provides adequate electrostatic discharge protection for a geosynchronous satellite; (3) provides adequate shielding to meet radiated emission needs; and (4) will survive ascent differential pressure loads between enclosed volume and space. The MLI design is described which meets these requirements and design evolution and verification is discussed. The application is for MLI blankets which closeout the area between the laser crosslink subsystem (LCS) equipment and the DSP spacecraft cabin. Ancillary needs were implemented to ease installation at launch facility and to survive ascent acoustic and vibration loads. Directional venting accommodations were also incorporated to avoid contamination of LCS telescope, spacecraft sensors, and second surface mirrors (SSMs).

Steimer, Carlos H.↗
NASA NTRS1991

Fiber-optic applications for space-based engines

The use of fiber optic technology is discussed with respect to the instrumentation systems for space based rocket engines. Optical fiber technologies are reviewed with specific attention given to the reliability, light weight, small fiber diameter, and operating life of the components in the space environment. An optical system can facilitate the incorporation of an optical health monitoring system, increase the space available for necessary redundancy, and safe high bandwidth communications that are immune to the effects of electromagnetic radiation.

Sovie, Amy L.↗
NASA NTRS1991

Lightning mapping system

A Lightning Detection and Ranging (LDAR) System is being implemented at KSC in Florida. The first operational use is expected in the late summer of 1991. The system is designed to map the location of in-cloud and cloud-to-ground lightning based on the time of arrival (TOA) of electromagnetic radiation. The system detects very high frequency (VHF) radiation and designed to map the volumetric extent of lightning. The system implements two independent antenna arrays to provide a fast data quality check, as necessary for a real-time warning system. The system performance goals and a comparison with a similar system implemented in the mid-1970's is made.

Lennon, C.↗
NASA NTRS1990

A mechanism for bursty radio emission in planetary magnetospheres

Bursty radio emissions are often observed from the polar magnetospheres of the earth, Jupiter, Saturn, and Uranus in addition to the smooth radio emissions commonly detected. It is shown that in plasma regimes in which the electron plasma frequency is less than the electron cyclotron frequency, anisotropic electron beams or gyrating electron beams can excite directly broadband electromagnetic radiation. The largest growth is for right-hand X-mode radiation with frequencies above the electron cyclotron frequency. This instability can produce bursty, broadband emission, consistent with some of the properties of the radiation observed from the magnetized planets.

Wong, H. K.↗
NASA NTRS1991

Multipolar magnetic fields in neutron stars

The small periods and period derivatives of millisecond pulsars permit interesting upper bounds to be placed on the strength of multipole components in their magnetic fields if the loss of rotational energy may be approximated by vacuum electromagnetic radiation formulas. The surface field strength of millisecond pulsars may be as high as about 10 to the 12th G if the dominant multipole component is l not less than 3. Significant multipole moments may help explain the unusual pulse morphology of millisecond pulsars. If the magnetic fields in gamma-ray burst sources (old neutron stars?) have the same evolutionary history as in millisecond pulsars, the about 10 to the 12th G local fields observed in several gamma-ray bursts must be due to multipole moments with l not less than 3.

Krolik, Julian H.↗
NASA NTRS1990

Low energy gamma ray attenuation in multiphase water

A gauging system is proposed to enable monitoring of slush density, solid-liquid interface, and slush level as well as its flow rate. It is based on the principle that the electromagnetic radiation mass attenuation coefficient of a multiphase chemical compound is constant for all relative phase concentrations. Results showing the essential constancy of mass attenuation coefficients for single-phase water vapor, liquid water, ice, and multiphase mixtures of water/ice are described.

Singh, Jag J.↗
NASA NTRS1991

Fiber-optic applications for space-based rocket engines

The use of fiber-optic technology is discussed with respect to the instrumentation systems for space-based rocket engines. Optical fiber technologies are reviewed with specific attention given to the reliability, light weight, small fiber diameter, and operating life of the components in the space environment. An optical system can facilitate the incorporation of an optical health-monitoring system, increase the space available for necessary redundancy, and safe high-bandwidth communications that are immune to the effects of electromagnetic radiation.

Sovie, Amy L.↗
NASA NTRS1992

Photofabricated Wire-Grid Polarizers

Freestanding metallic grids for use as polarizers for electromagnetic radiation at millimeter and submillimeter wavelengths made by simple modification of designs of freestanding square- and nearly-square cell metallic grids, according to proposal. Cross wires provide mechanical support, but distance between cross wires made greater than one wavelength so cross wires have little effect on polarizing characteristics of grid. Possible to fabricate grids commercially for frequencies up to several terahertz.

Siegel, Peter H.↗
NASA NTRS1991

Photonics

Optoelectronic materials and devices are examined. Optoelectronic devices, which generate, detect, modulate, or switch electromagnetic radiation are being developed for a variety of space applications. The program includes spatial light modulators, solid state lasers, optoelectronic integrated circuits, nonlinear optical materials and devices, fiber optics, and optical networking photovoltaic technology and optical processing.

Source record↗
NASA NTRS1991

Sensor technology workshop: Structure and goals

The Astrotech 21 charter for the second of three workshops is described. The purpose was to identify technology needs in the areas of electromagnetic radiation sensors, and to recommend a plan to develop the required capabilities that are not currently available. The panels chosen for this workshop focused specifically on those technologies needed for the Astrotech 21 Program including: gamma ray and x ray sensors, ultraviolet and visible sensors, direct infrared sensors, and heterodyne submillimeter wave sensors.

Wilson, Barbara A.↗
NASA NTRS1993

Treating Surfaces To Obtain Narrowband Thermal Emission

Surfaces emitting electromagnetic radiation predominantly in desired narrow spectral bands when heated made more durable, and fabricated less expensively, according to proposal. Narrowband thermal emitters made by polishing metal substrates to specularity, then coating specular surfaces with films of rare-earth oxides approximately less than 1 micrometer thick. Metal substrates inherently resistant to mechanical shock. Resistance to thermal shock achieved by choosing metals and rare-earth oxides having equal or nearly equal coefficients of thermal expansion.

Burger, Dale R.↗