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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Expanding role for autonomy in military space

The Jet Propulsion Laboratory is currently transferring satellite on-board autonomy technology to the USAF for use in military spacecraft as a means of lowering the ground support requirements. The techniques were proven on the Viking and Voyager spacecraft and permitted on-board fault detection and correction. New military satellites will incorporate an autonomous redundancy and maintenance management subsystem in an on-board computer, while the system will still be subject to ground-based safing commands for situations demanding deeper analyses. A level 5 autonomy will need 256 kb memory, 10 Mb nonvolatile data storage and 50 W power and will weigh 20 kg. Systems will be periodically checked and compared with an ideal in the data base. Deviations detected will result in a rollback and redundant examination by two microprocessors, which can initiate correction commands until operational criteria are met. The development of the expert systems to the point that they satisfy military specifications is expected to take 10 yr.

Evans, D. D.↗
NASA NTRS1985

Solar abundances and the role of nucleogenesis in low-to-medium mass stars in the galaxy

The pattern of solar elemental abundances agrees well with that shown by Cl chondrites for nonvolatile elements. For metals of the iron peak, the chief source of uncertainty seems to be the structure of the solar atmosphere. Lines of rare elements are frequently masked by atomic and molecular lines of abundant species. The vast majority of stars (including the sun) will do little to change the bulk composition of the interstellar medium from which new stars are formed. He, C, and N in small quantities are supplied by stars from 1 to 8 solar masses as they evolve and produce nebular envelopes that dissipate into the interstellar medium, but as has long been recognized, oxygen, heavier elements, and all r-process and proton-rich nuclides are made in massive stars.

Aller, L. H.↗
NASA NTRS1985

C2 imagery of the inner coma of Comet IRAS-Araki-Alcock

May 10, 1983 observations of the comet IRAS-Araki-Alcock are analyzed to determine the spatial molecular abundance of C2 in the inner coma, via the Delta-v = +1 Swan band sequence near 4690 A. The observations indicate a deficiency of C2 emission across a projected diameter of about 2000 km that is centered on the peak of continuum emission. Comet imagery indicates a sunward-pointing coma that suggests an outburst of subsurface volatile ices through a nonvolatile surface crust, as predicted for periodic comets. These results are discussed in the framework of instrumental and observational constraints.

Oliversen, R. J.↗
NASA NTRS1985

Photochemical reactions in interstellar grains photolysis of CO, NH3, and H2O

The interstellar grains are currently considered to be the basic building blocks of comets and, possibly, meteorites. To test this theory, a simulation of the organic layer accreted onto interstellar dust particles was prepared by slow deposition of a CO:NH3:H2O gas mixture on an Al block at 10 K, with concomitant irradiation with vacuum UV. The results of the HPLC and IR analyses of the nonvolatile residue formed by photolysis at 10 K are compared with those observed at 77 K and 298 K. Some of the compounds that may be present on the surfaces of interstellar dust particles have been identified, and some specific predictions concerning the types of molecular species present in comets could be drawn. The results also suggest that photochemical reactions may have been important for the formation of meteorite components. The implication of the findings to the questions of the source of organic matter on earth and the origin of life are discussed.

Agarwal, V. K.↗
NASA NTRS1986

First Halley multicolour camera imaging results from Giotto

The Giotto spacecraft's Halley Multicolor Camera imaging results have furnished flyby images that are centered on the brightest part of the inner coma; these show the silouette of a large, solid and irregularly shaped cometary nucleus and jetlike dust activity. The preliminary assessment of these data has yielded information on the dimensions and shape of the nucleus and dust emission activity. It is noted that only minor parts of the surface are active, with most of the surface being covered by a nonvolatile material. Dust jets dominate the inner coma, and are restricted to a subsolar hemisphere.

Keller, H. U.↗
NASA NTRS1986

Hardware requirements: A new generation partial reflection radar for studies of the equatorial mesosphere

A new partial reflection (PR) radar is being developed for operation at the proposed Equatorial Observatory. The system is being designed to make maximum use of recent advances in solid-state technology in order to minimize the power requirements. In particular, it is planned to use a solid-state transmitter in place of the tube transmitters previously used in PR systems. Solid-state transmitters have the advantages that they do not need high voltage supplies, they do not require cathode heaters with a corresponding saving in power consumption and parts are readily available and inexpensive. It should be possible to achieve 15 kW peak powers with recently announced fast switching transistors. Since high mean powers are desirable for obtaining good signal-to-noise ratios, it is also planned to phase code the transmitted pulses and decode after coherent integration. All decoding and signal processing will be carried out in dedicated microprocessors before the signals are passed to a microcomputer for on-line analysis. Recent tests have shown that an Olivetti M24 micro (an IBM compatible) running an 8-MHz clock with a 8087 coprocessor can analyze data at least as fast as the minicomputers presently being used with the Adelaide PR rad ar and at a significantly lower cost. The processed winds data will be stored in nonvolatile CMOS RAM modules; about 0.5 to 1 Mbyte is required to store one week's information.

Vincent, R. A.↗
NASA NTRS1987

Comet thermal modeling

The past year was one of tremendous activity because of the appearance of Halley's Comet. Observations of the comet were collected from a number of sources and compared with the detailed predictions of the comet thermal modeling program. Spacecraft observations of key physical parameters for cometary nucleus were incorporated into the thermal model and new cases run. These results have led to a much better understanding of physical processes on the nucleus and have pointed the way for further improvements to the modeling program. A model for the large-scale structure of cometary nuclei was proposed in which comets were envisioned as loosely bound agglomerations of smaller icy planetesimals, essentially a rubble pile of primordial dirty snowballs. In addition, a study of the physical history of comets was begun, concentrating on processes during formation and in the Oort cloud which would alter the volatile and nonvolatile materials in cometary nuclei from their pristine state before formation.

Weissman, Paul R.↗
NASA NTRS1986

Thermal emission from the dust coma of Comet Bowell and a model for the grains

An analysis of the physical characteristics of Comet Bowell is presented based on 10 and 20 microns emissions observed with the NASA 3 m IR telescope during 1981-82. Numerical models are defined for quantifying the number of dust particles at a given radius and at a given angular distance from the nucleus, the contribution of icy grains to the 20 microns flux and the average albedo, and the dust distribution in the coma. Large, dirty ice grains are judged to be responsible for production of OH at a rate of about 10 to the 29th mol/sec during the spring of 1981. The total surface area of the dirty ice grains is projected to be 10 to the 15th sq cm. The coma in 1982 would therefore have consisted of nonvolatile grains, i.e., old dirty ice grains. Further observations of other, similar comets are needed to identify the composition of the emitted grains and the heliocentric distance at which high water production is initiated.

Hanner, M. S.↗
NASA NTRS1988

Programmable Synaptic Arrays For Electronic Neural Networks

High resistances prevent hotspots in parallel input and output operation. Nonvolatile computer memory combines ultrahigh storage density with extremely-low power dissipation. Accommodates about 1 billion bits in square centimeter of surface area. Bit written with expenditure of less than 1 nanojoule of energy and read with even lower energy. Developed for parallel input and output operation.

Thakoor, Anilkumar P.↗
NASA NTRS1988

An automated ozone photometer

A photometer capable of automatically measuring ozone concentration data to very high resolution during scientific research flights in the Earth's atmosphere was developed at NASA Ames Research Center. This instrument was recently deployed to study the ozone hole over Antarctica. Ozone is detected by absorbing 253.7-nm radiation from an ultraviolet lamp which shines through the sample of air and impinges on a vacuum phototube. A lower output from the phototube indicates more ozone present in the air sample. The photometer employs a CMOS Z80 microprocessor with an STD bus system for experiment control, data collection, and storage. Data are collected and stored in nonvolatile memory for experiments lasting up to 8 hr. Data are downloaded to a portable ground-support computer and processed after the aircraft lands. An independent single-board computer in the STD bus also calculates ozone concentration in real time with less resolution than the CMOS Z80 system, and sends this value to a cockpit meter to aid the pilot in navigation.

Lavelle, Joseph R.↗
NASA NTRS1987

Optoelectronic analogs of self-programming neural nets - Architecture and methodologies for implementing fast stochastic learning by simulated annealing

Self-organization and learning is a distinctive feature of neural nets and processors that sets them apart from conventional approaches to signal processing. It leads to self-programmability which alleviates the problem of programming complexity in artificial neural nets. In this paper architectures for partitioning an optoelectronic analog of a neural net into distinct layers with prescribed interconnectivity pattern to enable stochastic learning by simulated annealing in the context of a Boltzmann machine are presented. Stochastic learning is of interest because of its relevance to the role of noise in biological neural nets. Practical considerations and methodologies for appreciably accelerating stochastic learning in such a multilayered net are described. These include the use of parallel optical computing of the global energy of the net, the use of fast nonvolatile programmable spatial light modulators to realize fast plasticity, optical generation of random number arrays, and an adaptive noisy thresholding scheme that also makes stochastic learning more biologically plausible. The findings reported predict optoelectronic chips that can be used in the realization of optical learning machines.

Farhat, Nabil H.↗
NASA NTRS1987

Compositional evidence regarding the origins of rims on Semarkona chondrules

This paper presents results on neutron activation analyses of the interiors and the abraded surfaces of seven chondrules from Semarkona chondrite. The results showed that six of seven chondrule rims have enhanced contents of siderophiles and chalcophiles relative to chondrule interiors, indicating that, during chondrule formation, metal/sulfide melts migrated to the exterior of the chondrule; later reheating caused this material to spread out into fine-grained rim material. For nonvolatile elements, the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors, indicating that the surface and the interior metal might have originated from a single precursor. The volatile to moderately-volatile elements K, As, and Zn tend to be enriched in the surface, compared with other elements of similar mineral affinity.

Grossman, Jeffrey N.↗
NASA NTRS1988

An investigation of the nucleus and coma of Comet P/Arend-Rigaux

Narrow-band photometry of Comet P/Arend-Rigaux in the visible and near-ultraviolet are presented for six nights during the 1884/1985 apparition, including three nights of simultaneous observations in the thermal infrared made with the NASA IRTF. The results indicate a period of rotation of 13.47 hr, dimensions for the nucleus of 13 x 8 x 8 km (under the assumption of prolate spheroid shape), and a steady decrease in the comet's gas production from a month before perihelion to more that two months after perihelion. Results for the nucleus and the coma suggest that the nucleus is totally covered with a nonvolatile mantle.

Millis, Robert L.↗
NASA NTRS1987

Binary synaptic connections based on memory switching in a-Si:H for artificial neural networks

A scheme for nonvolatile associative electronic memory storage with high information storage density is proposed which is based on neural network models and which uses a matrix of two-terminal passive interconnections (synapses). It is noted that the massive parallelism in the architecture would require the ON state of a synaptic connection to be unusually weak (highly resistive). Memory switching using a-Si:H along with ballast resistors patterned from amorphous Ge-metal alloys is investigated for a binary programmable read only memory matrix. The fabrication of a 1600 synapse test array of uniform connection strengths and a-Si:H switching elements is discussed.

Thakoor, A. P.↗
NASA NTRS1989

Variable-Resistivity Material For Memory Circuits

Nonvolatile memory elements packed densely. Electrically-erasable, programmable, read-only memory matrices made with newly-synthesized organic material of variable electrical resistivity. Material, polypyrrole doped with tetracyanoquinhydrone (TCNQ), changes reversibly between insulating or higher-resistivity state and conducting or low-resistivity state. Thin film of conductive polymer separates layer of row conductors from layer of column conductors. Resistivity of film at each intersection and, therefore, resistance of memory element defined by row and column, increased or decreased by application of suitable switching voltage. Matrix circuits made with this material useful for experiments in associative electronic memories based on models of neural networks.

Nagasubramanian, Ganesan↗
NASA NTRS1989

Memory Switches Based On MnO2-x Thin Films

Thin films of Mn02-x at intersections between metallic row and column conductors serve as switching elements for nonvolatile electronic memories. "On"-state resistance adjustable, and on-to-off transition irreversible. Elements electrically programmable and especially suitable for use in associative electronic memories based on neural-network concepts.

Ramesham, Rajeshuni↗
NASA NTRS1988

Precision cleaning methods for spacecraft applications

A small CO2 snow cleaning apparatus to clean both molecular films and particles from small and large components and surfaces was constructed. Various types of surfaces were cleaned using the CO2 technique. Vacuum deposited and sputtered metallic coatings such as germanium, aluminum, and silver and silicon wafers, and polished copper conical mirrors were purposely contaminated with everyday aerospace contaminants, including particle fallout and fingerprints. Precleaning characterization by Bidirectional Reflectance Distribution Function (BRDF), ellipsometry, nonvolatile residue, and microscopic particle evaluation served as evaluation of cleaning efficiency. Good results were obtained in trial application.

Ryan, L. E.↗
NASA NTRS1988

Comet Halley's colorful outbursts

Two preperihelion outbursts by Comet Halley were observed, each showing different brightness changes at 2.3, 3.6, 4.6 and 10.3 micrometers. Neither event was observed from beginning to end. The first observation on 8 Nov. 1985 lasted on the order of a day and was accompanied by a tail-like appendage recorded photographically. During the outburst the IR colors changed dramatically, showing no significant change at 10.3 micrometers but showing progressively more change at shorter wavelengths over a time scale of a few hours. The second outburst measurement extended over several days (10 to 13 Jan. 1986) during which time the intensities at the four wavelengths increased by roughly the same amount. Although the outbursts were of different duration, the IR measurements suggest that the first event involved volatile ice particles that evaporated, while the second was associated with long lived nonvolatile dust grains.

Lynch, David K.↗