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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

SPS large array simulation

The computer programming efforts were directed primarily to beam pattern analysis. The computer programs used for simulation provide: verification of the reference design; definition of feasible departures such as quantized distributions; the study of far-out sidelobe roll-off characteristics; the analysis of errors and failures; illumination function analysis to develop beam patterns for efficient collection; and beam shaping synthesis to meet environmental constraints.

Rathjen, S.↗
NASA NTRS1982

Radio imaging of solar flares using the very large array - New insights into flare process

An interpretation of VLA observations of microwave bursts is presented in an attempt to distinguish between certain models of flares. The VLA observations provide information about the pre-flare magnetic field topology and the existence of mildly relativistic electrons accelerated during flares. Examples are shown of changes in magnetic field topology in the hour before flares. In one case, new bipolar loops appear to emerge, which is an essential component of the model developed by Heyvaerts et al. (1977). In another case, a quadrupole structure, suggestive of two juxtaposed bipolar loops, appears to trigger the flare. Because of the observed diversity of magnetic field topologies in microwave bursts, it is believed that the magnetic energy must be dissipated in more than one way. The VLA observations are clearly providing means for sorting out the diverse flare models.

Kundu, M. R.↗
NASA NTRS1983

Large array VLSI filter

A 35 by 35 element pipelined convolutional kernel is being fabricated using VLSI chips, each containing a 5 by 1 segment of the kernel. Three levels of printed circuitry are used: the first level is used for the VLSI chips, the second level connects seven chips together on one platform, and the third level connects seven platforms with associated delay lines, all fitting on one board. Therefore, on each board there are seven rows of the kernel containing 245 multipliers and adders, and five such boards complete the kernel array. Each multiplier accepts an 8 bit picture element which is multiplied by a 16 bit weight. A truncated 22 bit product is added to a previously stored product sum and the results are shifted to the following multiplier as the next picture element is read in. The multiplier uses a modified Booth algorithm to reduce the number of shift add operations nearly in half. The filter box is presently configured as an ancillary box to a VAX 11/780, but can be connected to essentially any CPU. The I/O bandwidth is easily compatible with most CPU devices.

Nathan, R.↗
NASA NTRS1984

Very large array observations of Jupiter's nonthermal radiation

The VLA has been used at 18 and 20 cm to obtain observational data on Jupiter at all rotational aspects in all four Stokes parameters, yielding maps of the total, linearly polarized and circularly polarized intensity with a resolution of 0.25 Jupiter radii. These maps reveal such previously undetected phenomena as an emission feature close to the planetary surface north and south of each of the two main radiation peaks. The emission from 1.8 to about 3 Jupiter radii from the planet's center is sharply confined to the magnetic equator.

De Pater, I.↗
NASA NTRS1984

Using the Very Large Array (VLA) and other radio telescopes to perform a parasitic search for extraterrestrial intelligence (SETI)

This paper describes several attempts to utilize various radio telescopes in a manner that is termed 'parasitic', that is in a manner that does not interrupt or seriously impact the standard astronomical observing programs in progress at the radio observatories. In the extreme case, only recorded astronomical data are accessed off-line, after the fact, without any burden on the observatory at all.

Tarter, J. C.↗
NASA NTRS1985

Precise position measurements of Jupiter, Saturn and Uranus systems with the Very Large Array

VLBI observations of the Jovian satellites Europa, Ganymede, and Callisto obtained in 1983, of Titan obtained in 1984, and of Uranus obtained in 1985, all with the VLA at 15 GHz, are used to determine the ephemerides. The results are presented graphically, and it is found that the standard ephemeris reference frame for the outer planets is in error by about -200 marcsec in right ascension.

Muhleman, D. O.↗
NASA NTRS1987

Very-large-array observations of a complex gradual solar burst at 6 cm wavelength

A 6-cm VLA observation of a burst from a solar active region is reported. The burst shows a normal impulsive rise and fall superimposed on a gradual component. The peak brightness temperature of the burst remains relatively constant, and the flux variations are due to changes in the source structure. It appears as though an arcade of loops is gradually heated or filled with hot plasma. The burst is weakly polarized but unipolar; the possible reasons for this structure are considered. Depolarization of optically thin emission due to twisted magnetic fields within the source can produce significant depolarization, but is probably not active in this event. Instead, it is suggested that the flare emission is optically thick, and that hot overlying material preferentially absorbs one polarization.

Kundu, M. R.↗
NASA NTRS1987

Simultaneous SMM flat crystal spectrometer and Very Large Array observations of solar active regions

High-resolution images of the quiescent emission from two solar active regions at 20 cm (VLA) and soft X-ray (SMM FCS) wavelengths are compared. There are regions where the X-ray coronal loops have been completely imaged at 20 cm wavelength. In other regions, the X-ray radiation was detected without detectable 20 cm radiation, and vice versa. The X-ray data were used to infer average electron temperatures of about 3-million K and average electron densities of about 2.5 x 10 to the 9th/cu cm for the X-ray emitting plasma in the two active regions. The thermal bremsstrahlung of the X-ray emitting plasma is optically thin at 20 cm wavelength. The 20 cm brightness temperatures were always less than T(e), which is consistent with optically thin bremsstrahlung. The low T(B) can be explained if a higher, cooler plasma covers the hotter X-ray emitting plasma. Thermal gyroresonance radiation must account for the intense 20 cm radiation near and above sunspots where no X-ray radiation is detected.

Lang, Kenneth R.↗
NASA NTRS1988

Very Large Array observations of Uranus at 2.0 cm

Radio observations of Uranus obtained at 2.0 cm with the B configuration of the VLA during April 1985 are reported. The calibration and data-reduction procedures are described in detail, and the results are presented in tables, maps, and graphs and compared with IRIS 44-micron observations (Hanel et al., 1986). Features discussed include highest brightness centered on the pole rather than on the subearth point, a decrease in brightness temperature (by up to 9 K) at latitudes between -20 and -50 deg (well correlated with the IRIS data), and disk-center position (corrected for the observed radio asymmetry) in good agreement with that found on the basis of the outer contours of the image.

Berge, G. L.↗
NASA NTRS1991

A flat array large telescope concept for use on the moon, earth, and in space

An astronomical optical telescope concept is described which can provide very large collecting areas, of order 1000 sq m. This is an order of magnitude larger than the new generation of telescopes now being designed and built. Multiple gimballed flat mirrors direct the beams from a celestial source into a single telescope of the same aperture as each flat mirror. Multiple images of the same source are formed at the telescope focal plane. A beam combiner collects these images and superimposes them into a single image, onto a detector or spectrograph aperture. This telescope could be used on the earth, the moon, or in space.

Woodgate, Bruce E.↗
NASA NTRS1999

The "Water-Fountain Nebula" IRAS 16342-3814: Hubble Space Telescope/Very Large Array Study of a Bipolar Protoplanetary Nebula

We present Hubble Space Telescope (HST) Wide-Field Planetary Camera 2 images and VLA OH maser emission-line maps of the cold infrared object IRAS 16342-3814, believed to be a protoplanetary nebula. The HST images show an asymmetrical bipolar nebula, with the lobes separated by a dark equatorial waist. The two bright lobes and the dark waist are simply interpreted as bubble-like reflection nebulae illuminated by starlight escaping through polar holes in a dense, flattened, optically thick cocoon of dust, which completely obscures the central star. A faint halo can be seen surrounding each of the lobes. The bubbles are likely to have been created by a fast outflow (evidenced by H2O emission) plowing into a surrounding dense, more slowly expanding, circumstellar envelope of the progenitor asymptotic giant-branch (AGB) star (evidenced by the halo). The IRAS fluxes indicate a circumstellar mass of about 0.7 solar mass (D/2 kpc) and an AGB mass-loss rate of about 10(exp -4) solar mass/yr (V(sub exp)/15 km/s)(D/2 kpc)(sup 2) (assuming a gas-to-dust ratio of 200). OH features with the largest redshifted and blueshifted velocities are concentrated around the bright eastern and western polar lobes, respectively, whereas intermediate-velocity features generally occur at low latitudes, in the dark waist region. We critically examine evidence for the post-AGB classification of IRAS 16342-3814.

Sahal, Raghvendra↗
NASA NTRS1985

Using the Very Large Array (VLA) and other radio telescopes to perform a parasitic Search for Extraterrestrial Intelligence (SETI)

This paper describes several attempts to utilize various radio telescopes in a manner that we term "parasitic," that is in a manner that does not interrupt or seriously impact the standard astronomical observing programs in progress at the radio observatories. In the extreme case, only recorded astronomical data are accessed off-line, after the fact, without any burden on the observatory at all.

Extraterrestrial Environment↗