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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Optical detector calibrator system

An optical detector calibrator system simulates a source of optical radiation to which a detector to be calibrated is responsive. A light source selected to emit radiation in a range of wavelengths corresponding to the spectral signature of the source is disposed within a housing containing a microprocessor for controlling the light source and other system elements. An adjustable iris and a multiple aperture filter wheel are provided for controlling the intensity of radiation emitted from the housing by the light source to adjust the simulated distance between the light source and the detector to be calibrated. The geared iris has an aperture whose size is adjustable by means of a first stepper motor controlled by the microprocessor. The multiple aperture filter wheel contains neutral density filters of different attenuation levels which are selectively positioned in the path of the emitted radiation by a second stepper motor that is also controlled by the microprocessor. An operator can select a number of detector tests including range, maximum and minimum sensitivity, and basic functionality. During the range test, the geared iris and filter wheel are repeatedly adjusted by the microprocessor as necessary to simulate an incrementally increasing simulated source distance. A light source calibration subsystem is incorporated in the system which insures that the intensity of the light source is maintained at a constant level over time.

Strobel, James P.↗
NASA NTRS1973

White dwarfs as infrared sources in the galactic centre.

It is shown that quantized magnetic bremsstrahlung radiation in intense magnetic fields from the surface layers of white dwarfs could serve as one of the possible explanations for the infrared emission from the center of the galaxy that has been detected by Hoffmann et al. (1971). It is assumed, in particular, that the infrared radiation is from clusters of white dwarfs.

Chow, T. L.↗
NASA NTRS1999

May 4, 1998 Storm: Observations of Energetic Ion Composition by POLAR

A major geomagnetic storm occurred at 5:00-12:05 UT on May 4, 1998. During this period, the magnetosphere was compressed and eroded; POLAR traveled in its outbound orbit from the equatorial radiation belt to the cusp and crossed the magnetopause into the magnetosheath. Two CEP-like (Cusp Energetic Particle) events with two to three orders of magnitudes enhancements of MeV ion fluxes were measured. The first event had a peak flux higher than that of the intense outer radiation belt in the equatorial plane. The shape of the measured energy spectra (in the unit of keV/e) were ion species dependent. For He+/He++ ratio at 18-269 keV/e, the difference between the radiation belt and the magnetosheath can be by a factor of as large as 62. In the magnetosheath, the 18-269 keV/e ion composition are variable, indicating a mass dependent acceleration process. These MeV ions may be energized by a mechanism in the cusp responsible for the CEP events previously reported.

Chen, Jiasheng↗
NASA NTRS1980

Late degeneration in rabbit tissues after irradiation by heavy ions

Results are presented for investigations of the late effects of heavy-ion irradiation on rabbit tissues which were undertaken to assess the hazards associated with the long-term exposure of humans to heavy ions in space during such activities as the construction of solar power stations or voyages to Mars. White rabbits approximately six weeks old were exposed to various doses of collimated beams of 400-MeV/n Ne ions, 570 MeV/n Ar ions and Co-60 gamma rays directed through both eyes, and the responses of the various tissues (hair follicles, skin, cornea, lens, retina, Harderian glands, bone and forebrain) were examined. Proliferating tissues are found to exhibit high damage levels in the early and late periods following irradiation, while terminally differentiating tissues repond to radiation most intensely in the late period, years after irradiation, with no intermediate recovery. The results obtained from rabbits are used to predict the occurrence of late tissue degeneration in the central nervous system, terminally differentiating systems and stem cells of humans one or more decades following exposure to radiation levels anticipated during long-duration space flights. The studies also indicate that tissues may be prematurely aged in the sense that tissue life spans may be shortened without the development of malignancies.

Lett, J. T.↗
NASA NTRS1995

Plume Particle Collection and Sizing from Static Firing of Solid Rocket Motors

Thermal radiation from the plume of any solid rocket motor, containing aluminum as one of the propellant ingredients, is mainly from the microscopic, hot aluminum oxide particles in the plume. The plume radiation to the base components of the flight vehicle is primarily determined by the plume flowfield properties, the size distribution of the plume particles, and their optical properties. The optimum design of a vehicle base thermal protection system is dependent on the ability to accurately predict this intense thermal radiation using validated theoretical models. This article describes a successful effort to collect reasonably clean plume particle samples from the static firing of the flight simulation motor (FSM-4) on March 10, 1994 at the T-24 test bed at the Thiokol space operations facility as well as three 18.3% scaled MNASA motors tested at NASA/MSFC. Prior attempts to collect plume particles from the full-scale motor firings have been unsuccessful due to the extremely hostile thermal and acoustic environment in the vicinity of the motor nozzle.

Sambamurthi, Jay K.↗
NASA NTRS1986

Ground plane interference elimination by passive element

The radiation pattern of a beam at elevation angles near the horizon is improved for phased array antennas by control of the radiation field intensity near the horizon to reduce multipath disturbances, and to improve the axial ratio of a circularly polarized phased array antenna. This is accomplished by placing a parasitic phase shifting element directly below the antenna beam axis. The waveguide section is designed to produce a phase shift in the portion of antenna radiation energy passing through it to cancel some of the radiation energy in the direction of the horizon. The spacing of the waveguide section in front of the antenna is determined empirically for optimum results, i.e., for reduction of beam power below about 20 deg. without affecting beam power at high elevation angles.

Bonebright, Mark E.↗
NASA NTRS1988

Ground plane interference elimination by passive element

The radiation pattern of a beam at elevation angles near the horizon is improved for phased array antennas by control of the radiation field intensity near the horizon to reduce multipath disturbances, and to improve the axial ratio of a circularly polarized phased array antenna. This is accomplished by placing a parasitic phase shifting element directly below the antenna beam axis. The waveguide section is designed to produce a phase shift in the portion of antenna radiation energy passing through it to cancel some of the radiation energy in the direction of the horizon. The spacing of the waveguide section in front of the antenna is determined empirically for optimum results, i.e., for reduction of beam power below about 20.degree. without affecting beam power at high elevation angles.

Bonebright, Mark E.↗
NASA NTRS2012

What Properties of CMEs are Most Important for Space Weather?

Severe space weather is characterized by intense particle radiation from the Sun and major geomagnetic storm caused by magnetized solar plasmas arriving at Earth. Coronal mass ejections (CMEs) are key players in both these aspects. CMEs traveling at super-Alfv nic speeds drive fast-mode MHD shocks that create the high levels of particle radiation. When a CME arrives at Earth, the CME-associated magnetic fields reconnect with Earth s magnetopause fields resulting in solar plasma entry into the magnetosphere and a geomagnetic storm depending on the magnetic structure of the CME. Particle radiation starts affecting geospace as soon as the CMEs leave the Sun and the geospace may be immersed in the radiation for several days. On the other hand, the geomagnetic storm happens only upon CME arrival at Earth. The requirements for the production of particles and magnetic storms by CMEs are different in a number of respects: solar source location, CME magnetic structure, conditions in the ambient solar wind, and shock-driving ability of CMEs. Intense shocks arriving at Earth have additional space weather effects such as sudden impulse that shrinks the magnetosphere often exposing satellites in geosynchronous orbit to the solar wind and energetic storm particle events. This paper highlights these space weather effects using CME observations space and ground based instruments during of solar cycles 23 and 24.

Gopalswamy, Nat↗
NASA NTRS1977

Auroral kilometric radiation as an indicator of auroral magnetic disturbances

Satellite low-frequency radio measurements have shown that auroral kilometric radiation, an intense radio emission from the earth's auroral regions, is closely associated with auroral and magnetic disturbances. In this paper a detailed investigation of this relationship is presented, using the auroral electrojet (AE) index as an indicator of auroral magnetic disturbances and radio measurements from the Imp 6 spacecraft. This study indicates that the mean power flux of the 178-kHz radiation tends to be proportional to the 1.2 power of (AE) for AE more than 100 gamma and, with less certainty, to the square of (AE) for AE less than 100 gamma. The correlation coefficient between log AE and the logarithm of the power flux is 0.514. Occasionally, a kilometric radiation event is detected which is not detected by the ground magnetometer stations, even though an auroral substorm is in progress. This study shows that the remote detection of kilometric radio emissions from the earth can be used as a reasonably reliable indicator of auroral substorm activity.

Voots, G. R.↗
NASA NTRS1982

Absorptivity of water vapor for 10.6 micron radiation

Attention is called to recent measurements of the absorptivity of water vapor to 10.6-micron laser radiation made using shock-heated H2O/H2 and H2O/Ar mixtures and a probe CO2 laser. It is noted that these measurements give values about a factor of 2 lower than Ludwig's (1971) low resolution values. It is also argued that Fowler's (1981) high values are not likely to be caused by excited water molecules. It is shown that very intense laser radiation would be required to obtain any appreciable vibrational nonequilibrium. Within the narrow spectral range of 944-948/cm, no significant variation in absorption coefficient (suitably normalized) is observed as a function of laser line, water vapor concentration, total pressure, or diluent gas.

Pugh, E. R.↗