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Smith, J. G.

Publications and source records attributed to Smith, J. G..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Thermal Conductivity of Polyimide/Carbon Nanofiller Blends

Ultem(TM) was mixed with three different carbon-based nanofillers in efforts to increase the thermal conductivity of the polymer. After initial mixing, the nanocomposites were extruded or processed via the Laboratory Mixing Molder (LMM) process. High resolution scanning electron microscopy (HRSEM) revealed significant alignment of the nanofillers in the extruded samples. Thermal conductivity measurements were made both in the direction and perpendicular to the direction of alignment of nanofillers as well as for unaligned samples. It was found that the largest improvement in thermal conductivity was achieved in the case of aligned samples when the measurement was performed in the direction of alignment. Unaligned samples also showed a significant improvement in thermal conductivity and may be useful in applications when it is not possible to align the nanofiller. However the improvements in thermal conductivity did not approach those expected based on a rule of mixtures. This is likely due to poor phonon transfer through the matrix.

Delozier, D. M.↗
NASA NTRS2006

Thermal Conductivity of Polyimide/Nanofiller Blends

In efforts to improve the thermal conductivity of Ultem(TM) 1000, it was compounded with three carbon based nano-fillers. Multiwalled carbon nanotubes (MWCNT), vapor grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. Ribbons were extruded to form samples in which the nano-fillers were aligned. Samples were also fabricated by compression molding in which the nano-fillers were randomly oriented. The thermal properties were evaluated by DSC and TGA, and the mechanical properties of the aligned samples were determined by tensile testing. The degree of dispersion and alignment of the nanoparticles were investigated with high-resolution scanning electron microscopy. The thermal conductivity of the samples was measured in both the direction of alignment as well as perpendicular to that direction using the Nanoflash technique. The results of this study will be presented.

Ghose, S.↗
NASA NTRS2005

Flammability of Epoxy Resins Containing Phosphorus

As part of a program to develop fire-resistant exterior composite structures for future subsonic commercial and general aviation aircraft, flame-retardant epoxy resins are under investigation. Epoxies and their curing agents (aromatic diamines) containing phosphorus were synthesized and used to prepare epoxy formulations. Phosphorus was incorporated within the backbone of the epoxy resin and not used as an additive. The resulting cured neat epoxy formulations were characterized by thermogravimetric analysis, propane torch test, elemental analysis, microscale combustion calorimetry, and fire calorimetry. Several formulations showed excellent flame retardation with phosphorous contents as low as 1.5% by weight. The fracture toughness and compressive strength of several cured formulations showed no detrimental effect due to phosphorus content. The chemistry and properties of these new epoxy formulations are discussed.

Flammability studies↗
NASA NTRS2003

Preparation and Characterization of Space Durable Polymer Nanocomposite Films from Functionalized Carbon Nanotubes

Low color, flexible, space durable polyimide films with inherent, robust electrical conductivity have been under investigation as part of a continuing materials development activity for future NASA space missions involving Gossamer structures. Electrical conductivity is needed in these films to dissipate electrostatic charge build-up that occurs due to the orbital environment. One method of imparting conductivity is through the use of single walled carbon nanotubes (SWNTs). However, the incompatibility and insolubility of the SWNTs severely hampers their dispersion in polymeric matrices. In an attempt to improve their dispersability, SWNTs were functionalized by the reaction with an alkyl hydrazone. After this functionalization, the SWNTs were soluble in select solvents and dispersed more readily in the polymer matrix. The functionalized SWNTs were characterized by Raman spectroscopy and thermogravimetric analysis (TGA). The functionalized nanotubes were dispersed in the bulk of the films using a solution technique. The functionalized nanotubes were also applied to the surface of polyimide films using a spray coating technique. The resultant polyimide nanocomposite films were evaluated for nanotube dispersion, electrical conductivity, mechanical, and optical properties and compared with previously prepared polyimide-SWNT samples to assess the effects of SWNT functionalization.

Delozier, D. M.↗
NASA NTRS1987

Ka-band (32-GHz) downlink capability for deep space communications

The first quarter century of U.S. solar system exploration using unmanned spacecraft has involved progressively higher operating frequencies for deep space telemetry: L-band (960 MHz) in 1962 to S-band (2.3 GHz) in 1964 to X-band (8.4 GHZ) in 1977. The next logical frequency to develop for deep space is the Ka-band (32 GHz) for which a primary deep space allocation of 500 MHz between 31.8 to 32.3 GHz was established in 1979. The telecommunications capability was improved by a factor of 77 (18.9 dB) through the frequency changes from L-band to X-band. Another improvement factor of 14.5 (11.6 dB) can be achieved by going to Ka-band. Plans to develop and demonstrate Ka-band capability include the continued measurement of weather effects at Deep Space Network (DSN) sites, development of a prototype DSN ground antenna and supporting subsystems, augmentation of planned spacecraft with Ka-band beacons, and development of spacecraft prototype modules for future Ka-band transmitters. Plans for augmenting the DSN with Ka-band capability by 1995 were also developed. A companion set of articles describes the Ka-band performance and technology in greater detail.

Smith, J. G.↗
NASA NTRS1987

A growth path for deep space communications

Increased Deep Space Network (DPN) receiving capability far beyond that now available for Voyager is achievable through a mix of increased antenna aperture and increased frequency of operation. In this note a sequence of options are considered: adding midsized antennas for arraying with the existing network at X-band; converting to Ka-band and adding array elements; augmenting the DSN with an orbiting Ka-band station; and augmenting the DSN with an optical receiving capability, either on the ground or in space. Costs of these options are compared as means of achieving significantly increased receiving capability. The envelope of lowest costs projects a possible path for moving from X-band to Ka-band and thence to optical frequencies, and potentially for moving from ground-based to space-based apertures. The move to Ka-band is clearly of value now, with development of optical communications technology a good investment for the future.

Layland, J. W.↗
NASA NTRS1987

Beam waveguides in the Deep Space Network

A beam waveguide is a mechanism for guiding electromagnetic radiation from one part of an antenna to another through a series of reflectors. Appropriate placement of reflectors on an antenna allows a beam to be guided around the elevation axis and/or below the alidade. The beam waveguide permits placement of all electronics in a room on the alidade below the elevation axis, or below the alidade; feed horn covers to be protected from the weather; and feed electronics to be in spacious rooms rather than in crowded cones, and always level rather than tipping with change in elevation angle. These factors can lead to lower costs in implementation such as Ka-band, better antenna performance at X-band, more efficient and stable performance of transmitters and receivers, and lower maintenance and operating costs. Studies are underway to determine methods for converting the major antennas of the Deep Space Network (DSN) to beam waveguide operations by 1995.

Clauss, R. C.↗
NASA NTRS1985

Communicating through deep space

NASA's Deep Space Network (DSN) consists of a worldwide set of communication stations and a central control facility in California, enabling communication with spacecraft thousands of millions of miles from earth. The stations have gone from 26 m diameter antennas operating at 960 MHz to 70 m diameter (by 1988) at 8400 MHz. The DSN provides exceptional performance in high gain steerable antennas, ultra-low noise receivers, high power transmitters, frequency and time standards, and precise radio metric data. Spacecraft missions envisaged in the 1990's for the continuing exploration of the Solar System include an array of increasingly complex visits to the inner planets, asteroids and comets and the outer planets. The Deep Space Network planned for the mid-1980s may not meet all the needs of these missions without substantial change. Deep space stations may require conversion to operation with beam waveguides, higher frequency and relative frequency stability of 10 to the -16th. A deep space relay station in earth orbit could permit operation at higher frequencies, with attendant higher performance. Long range planning to select the appropriate future network configurations and develop the technologies essential to their implementation is underway.

Smith, J. G.↗
NASA NTRS1983

How to protect a wind turbine from lightning

Techniques for reducing the chances of lightning damage to wind turbines are discussed. The methods of providing a ground for a lightning strike are discussed. Then details are given on ways to protect electronic systems, generating and power equipment, blades, and mechanical components from direct and nearby lightning strikes.

Dodd, C. W.↗
NASA NTRS1982

Deep space communication - A one billion mile noisy channel

Deep space exploration is concerned with the study of natural phenomena in the solar system with the aid of measurements made at spacecraft on deep space missions. Deep space communication refers to communication between earth and spacecraft in deep space. The Deep Space Network is an earth-based facility employed for deep space communication. It includes a network of large tracking antennas located at various positions around the earth. The goals and achievements of deep space exploration over the past 20 years are discussed along with the broad functional requirements of deep space missions. Attention is given to the differences in space loss between communication satellites and deep space vehicles, effects of the long round-trip light time on spacecraft autonomy, requirements for the use of massive nuclear power plants on spacecraft at large distances from the sun, and the kinds of scientific return provided by a deep space mission. Problems concerning a deep space link of one billion miles are also explored.

Smith, J. G.↗
NASA NTRS1981

NASA tracking and data acquisition in the 1990s - High earth orbit and planetary spacecraft support

It is pointed out that during the decade of the 1980's the Deep Space Network (DSN) and the ground stations of the Ground Spaceflight Tracking Data Network (GSTDN) will have been consolidated into one ground-based network to provide services for tracking and data acquisition for NASA deep space probes and highly elliptical earth orbiters. The Tracking and Data Relay Satellite System (TDRSS) will have been implemented to handle low earth orbiters. Anticipated solar system exploration missions of the 1990's are discussed, and a description is presented of the new tracking and data acquisition requirements for supporting these missions. The technology options needed to meet these new requirements are identified, and the impact of these technology options on the consolidated DSN is discussed. Attention is given to the evolution of the DSN of the 1980's into the DSN of the year 2000.

Smith, J. G.↗
NASA NTRS1980

Satellite personal communications system

Voice channel communication between low power mobile stations dispersed over a large area is provided by a system which includes a geostationary satellite utilizing a large UHF antenna that can receive a transmission from a caller and retransmit it over any one beam of a matrix of narrow beams, so the chosen beam covers an area in which a designated called party is located. A single up-link control channel occupying a narrow frequency band, can be utilized to receive dial up signals from a caller, and another single down link control channel can be utilized to ring up the called party located anywhere within the continental United States. The satellite antenna includes a matrix of feed horns that not only direct the beams in a controlled matrix onto the area of the continental United States, but also permit detection of the region from which the caller's signal is transmitted and the region from which the called party's answer is received, to enable the interconnection of signals received from these two regions. The system is particularly useful for rural areas.

Reilly, N. B.↗
NASA NTRS1980

Alternate symbol inversion for improved symbol synchronization in convolutionally coded systems

Inverting alternate symbols of the encoder output of a convolutionally coded system provides sufficient density of symbol transitions to guarantee adequate symbol synchronizer performance, a guarantee otherwise lacking. Although alternate symbol inversion may increase or decrease the average transition density, depending on the data source model, it produces a maximum number of contiguous symbols without transition for a particular class of convolutional codes, independent of the data source model. Further, this maximum is sufficiently small to guarantee acceptable symbol synchronizer performance for typical applications. Subsequent inversion of alternate detected symbols permits proper decoding.

Simon, M. K.↗
NASA NTRS1978

A national voice network with satellite and small transceivers

A geostationary satellite utilizing a large multiple-beam UHF antenna is shown to be potentially capable of providing tens of thousands of voice channels for hundreds of thousands of mobile ground terminals using hand-held or vehicular-mounted transceivers with whip antennas. Inclusion of on-board network switching facilities permits full interconnection between any terminal pair within the continental United States (CONUS). Configuration tradeoff studies at selected frequencies from 150 to 1500 MHz, with antenna diameters ranging from 20 to 200 m, and CONUS-coverage multiple beams down to 0.3 deg beamwidth, establish that monthly system user costs in the range of $90 to $150, including leased and maintained ground equipment, are feasible.

Reilly, N. B.↗
NASA NTRS1977

Inclusive gamma-ray spectra from psi/3095/ and psi-prime/3684/ decays

Inclusive gamma-ray experiments were carried out in a e(+)e(-) colliding-beam apparatus with NaI(Tl) arrays as detectors. The inclusive gamma-ray spectra, after cosmic-ray background subtraction, are shown as histograms for the decays of the psi(3095) and psi-prime(3684). The psi spectrum has no significant narrow structure, while the psi-prime spectrum shows at least four peaks. Three major radiative decays of the psi-prime(3684) are found, and their respective branching fractions are computed.

Biddick, C. J.↗