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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Inflight lightning characteristics measurement system

A research data-gathering system being developed for inflight measurement of direct and nearby lightning strike characteristics is described. Wideband analog recorders used to record the lightning scenario are supplemented with high-sample-rate digital transient recorders with augmented memory capacity for increased time resolution of specific times of interest. The endless-loop data storage technique employed by the transient recorders circumvents problems associated with oscilloscopic techniques and allows unattended operation. System integrity and immunity from induced effects is accomplished by fiber-optics signal-transmission links, shielded system enclosures, and the use of a dynamotor for power system isolation.

Pitts, F. L.↗
NASA NTRS1988

Interference effects on the hypersonic, rarefied flow about a flat plate

The Direct Simulation Monte Carlo method is used to study the hypersonic, rarified flow interference effects on a flat plate caused by nearby surfaces. Calculations focus on shock-boundary-layer and shock-lip interactions in hypersonic inlets. Results are presented for geometries consisting of a flat plate with different leading-edge shapes over a flat lower wall and a blunt-edge flat plate over a 5-degree wedge. The problems simulated correspond to a typical entry flight condition of 7.5 km/s at altitudes of 75 to 90 km. The results show increases in predicted local heating rates for shock-boundary-layer and shock-lip interactions that are quantitatively similar to those observed experimentally at much higher densities.

Wilmoth, Richard G.↗
NASA NTRS1987

Ultraviolet observations of starburst systems with Astro and the Hubble Space Telescope

The capabilities of the Astro observatory and the Hubble Space Telescope (HST) for UV astronomical observations are discussed. The advantages of using UV for studying extragalactic problems are reviewed, including sensitivity to hot sources, the rich UV line spectra, sensitivity to interstellar dust, and dark UV sky background. The HST and Astro instrumentation and plans for launching the systems are described. Possibile uses of HST and Astro include the study of massive stars in the Galaxy and nearby galaxies, interstellar medium, the UV excess component in old stellar populations, deep UV surveys (filter imaging and slitless spectroscopy), active galactic nuclei, quasars, and starburst systems.

O'Connell, Robert W.↗
NASA NTRS1989

Interference effects on the hypersonic, rarefied flow about a flat plate

The Direct Simulatiaon Monte Carlo method is used to study the hypersonic, rarefied flow interference effects on a flat plate caused by nearby surfaces. Calculations focus on shock-boundary-layer and shock-lip interactions in hypersonic inlets. Results are presented for geometries consisting of a flat plate with different leading-edge shapes over a flat lower wall and a blunt-edge flat plate over a 5-degree wedge. The problems simulated correspond to a typical entry flight condition of 7.5 km/s at altitudes of 75 to 90 km. The results show increases in predicted local heating rates for shock-boundary-layer and shock-lip interactions that are quantitatively similar to those observed experimentally at much higher densities.

Wilmoth, Richard G.↗
NASA NTRS2006

Asteroid Exploration and Exploitation

John S. Lewis is Professor of Planetary Sciences and Co-Director of the Space Engineering Research Center at the University of Arizona. He was previously a Professor of Planetary Sciences at MIT and Visiting Professor at the California Institute of Technology. Most recently, he was a Visiting Professor at Tsinghua University in Beijing for the 2005-2006 academic year. His research interests are related to the application of chemistry to astronomical problems, including the origin of the Solar System, the evolution of planetary atmospheres, the origin of organic matter in planetary environments, the chemical structure and history of icy satellites, the hazards of comet and asteroid bombardment of Earth, and the extraction, processing, and use of the energy and material resources of nearby space. He has served as member or Chairman of a wide variety of NASA and NAS advisory committees and review panels. He has written 17 books, including undergraduate and graduate level texts and popular science books, and has authored over 150 scientific publications.

Lewis, John S.↗
NASA NTRS1982

Steps toward the Hubble constant. VIII - The global value

The problem of determining the global Hubble constant is approached by using two distance indicators whose dispersion in absolute magnitude is small, and hence which are virtually free of the Malmquist bias. New data are presented on the mean absolute-magnitude of the brightest individual red and blue supergiant stars in very nearby galaxies, calibrated relative to the Cepheids. The results are used to calibrate the maximum absolute blue magnitude for two well-observed Type I supernovae (SNe I). The velocity-relative distance diagram for 16 SNe I with known maximum apparent blue magnitudes is then calibrated using distances for IC 4182 and NGC 4214, with the result that the global Hubble constant equals 50 + or - 7 km per second per megaparsec. The result is compared with the known age of globular clusters in the Galaxy to show that the cosmological and the evolutionary time scales now closely agree.

Sandage, A.↗
NASA NTRS2004

A system level testbed for a mid-infrared beam-combiner for Terrestrial Planet Finder

Direct optical detection of earth-like planets orbiting nearby stars is the goal of the Terrestrial Planet Finder project. One instrument which may have the capability to detect such small, faint objects in proximity to the parent star is the infra-red nulling interferometer. A four input beam combiner is being built to test apsects of the beam combination and planet detection problem. This paper describes the design developed for a ground testbed.

Martin, Stefan↗
NASA NTRS2000

Searching for Planets with the Space Interferometry Mission

The Space Interferometry Mission (SIM) will be the first space-based long baseline Michelson interferometer designed for precision astrometry. It will address a wide range of problems in stellar astrophysics and Galactic structure, delivering precision astrometry of stars down to 20 magnitude throughout the entire Galaxy. SIM uses a 10-m Michelson interferometer in Earth-trailing solar orbit to provide 4 microarcsecond (gas) precision astrometry. With a 5-year mission lifetime, SIM will be a powerful tool for discovering planets around nearby stars, through detection of the stellar reflex motion. The astrometric method complements the radial velocity technique which as already yielded many new planets, with an important benefit of directly measuring planetary masses. SIM will have a single-measurement precision of 1 microarcsecond in a frame defined by nearby reference stars, enabling searches for planets with masses as small as a few earth masses around the nearest stars. More massive planets will be detectable to much larger distances. In addition to precision astrometry SIM will also serve an important role as a technology precursor for future astrophysics missions using interferometers. Two technologies demonstrated will be high dynamic-range aperture synthesis imaging at 10-milliarcsec resolution in the optical, and fringe nulling to 10 (exp -4).

Unwin, Stephen↗
NASA NTRSDate not supplied

Suborbital Testing of the OSCAR Trash-to-Gas System

With the sustained human exploration of nearby celestial bodies on the horizon, a renewed outlook on crew waste management must be realized. Current waste management strategies aboard the International Space Station become impractical as we venture beyond low Earth orbit. Furthermore, for future exploration missions, extracting resources from various waste streams becomes increasingly advantageous. One method of combatting the long-duration waste management problem is by thermally degrading solid and liquid crew waste items into a chemically inert, ventable gas stream, a process known as Trash-to-Gas. The Orbital Syngas/Commodity Augmentation Reactor (OSCAR) is the state-of-the-art Trash-to-Gas system which has been designed to explore microgravity Trash-to-Gas concepts for improved mass/volume reduction and resource recovery from waste. OSCAR is a subscale testbed design that supports the NASA Logistics Reduction project under the Advanced Exploration Systems Program and Space Technology Mission Directorate Flight Opportunities Program to determine the feasibility of Trash-to-Gas technology for future use on long duration space missions. OSCAR has flown on two suborbital flight demonstrations aboard Blue Origin’s New Shepard launch vehicle. This paper presents a high-level comparative analysis of these microgravity test campaigns with Earth gravity laboratory experiments. Solid-to-gas conversion, gas production & composition, and reactor temperature & pressure are compared to highlight the operational factors and performance differences within the microgravity environment for future optimization.

Ray P Pitts↗
NASA NTRS1987

Application of the complex cepstrum to the location of acoustic sources near reflective surfaces

The complex cepstrum is used to correct bearing estimations of acoustic sources in the presence of a reflective surface. An automated liftering procedure is used which zeros out a block portion of the cepstrum including the echo information. The problem of the resulting distortion is alleviated by applying a coherence criterion to the recovered direct signals at each microphone. Thus to a large degree the interactive nature of cepstral processing is overcome for this application. For the test signals and geometries considered the cepstrum is shown to accurately correct for bearing errors in acoustic signals contaminated with reflections from nearby surfaces.

Fuller, C. R.↗
NASA NTRS1989

A comparison of two neural network schemes for navigation

Neural networks have been applied to tasks in several areas of artificial intelligence, including vision, speech, and language. Relatively little work has been done in the area of problem solving. Two approaches to path-finding are presented, both using neural network techniques. Both techniques require a training period. Training under the back propagation (BPL) method was accomplished by presenting representations of (current position, goal position) pairs as input and appropriate actions as output. The Hebbian/interactive activation (HIA) method uses the Hebbian rule to associate points that are nearby. A path to a goal is found by activating a representation of the goal in the network and processing until the current position is activated above some threshold level. BPL, using back-propagation learning, failed to learn, except in a very trivial fashion, that is equivalent to table lookup techniques. HIA, performed much better, and required storage of fewer weights. In drawing a comparison, it is important to note that back propagation techniques depend critically upon the forms of representation used, and can be sensitive to parameters in the simulations; hence the BPL technique may yet yield strong results.

Munro, Paul W.↗
NASA NTRS1990

A comparison of two neural network schemes for navigation

Neural networks have been applied to tasks in several areas of artificial intelligence, including vision, speech, and language. Relatively little work has been done in the area of problem solving. Two approaches to path-finding are presented, both using neural network techniques. Both techniques require a training period. Training under the back propagation (BPL) method was accomplished by presenting representations of current position, goal position pairs as input and appropriate actions as output. The Hebbian/interactive activation (HIA) method uses the Hebbian rule to associate points that are nearby. A path to a goal is found by activating a representation of the goal in the network and processing until the current position is activated above some threshold level. BPL, using back-propagation learning, failed to learn, except in a very trivial fashion, that is equivalent to table lookup techniques. HIA, performed much better, and required storage of fewer weights. In drawing a comparison, it is important to note that back propagation techniques depend critically upon the forms of representation used, and can be sensitive to parameters in the simulations; hence the BPL technique may yet yield strong results.

Munro, Paul↗
NASA NTRS1998

Multiwavelength Observations of a Dramatic High-Energy Flare in the Blazar 3C 279

The blazar 3C 279, one of the brightest identified extragalactic objects in the gamma-ray sky, underwent a large (factor of approx. 10 in amplitude) flare in gamma-rays toward the end of a 3 week pointing by Compton Gamma Ray Observatory (CGRO), in 1996 January-February. The flare peak represents the highest gamma-ray intensity ever recorded for this object. During the high state, extremely rapid gamma-ray variability was seen, including an increase of a factor of 2.6 in approx. 8 hrs., which strengthens the case for relativistic beaming. Coordinated multifrequency observations were carried out with Rossi X-Ray Timing Explorer (RXTE), Advanced Satellite for Cosmology and Astrophysics (ASCA; or, Astro-D), Roentgen Satellite (ROSAT), and International Ultraviolet Explorer (IUE) and from many ground-based observatories, covering most accessible wavelengths. The well-sampled, simultaneous RXTE light curve shows an outburst of lower amplitude (factor of approx. or equal to 3) well correlated with the gamma-ray flare without any lag larger than the temporal resolution of approx. 1 day. The optical-UV light curves, which are not well sampled during the high-energy flare, exhibit more modest variations (factor of approx. 2) and a lower degree of correlation. The flux at millimetric wavelengths was near a historical maximum during the gamma-ray flare peak, and there is a suggestion of a correlated decay. We present simultaneous spectral energy distributions of 3C 279 prior to and near to the flare peak. The gamma-rays vary by more than the square of the observed IR-optical flux change, which poses some problems for specific blazar emission models. The synchrotron self-Compton (SSC) model would require that the largest synchrotron variability occurred in the mostly unobserved submillimeter/far-infrared region. Alternatively, a large variation in the external photon field could occur over a time scale of a few days. This occurs naturally in the "mirror" model wherein the flaring region in the jet photoionizes nearby broad emission line clouds, which, in turn, provide soft external photons that are Comptonized to gamma-ray energies.

Wehrle, A. E.↗
NASA NTRS1998

Multiwavelength Observations of a Dramatic High-Energy Flare in the Blazar 3C 279

The blazar 3C 279, one of the brightest identified extragalactic objects in the gamma-ray sky, underwent a large (factor of approximately 10 in amplitude) flare in gamma-rays toward the end of a 3 week pointing by Compton Gamma Ray Observatory (CGRO), in 1996 January-February. The flare peak represents the highest gamma-ray intensity ever recorded for this object. During the high state, extremely rapid gamma-ray variability was seen, including an increase of a factor of 2.6 in approximately 8 hr, which strengthens the case for relativistic beaming. Coordinated multifrequency observations were carried out with Rossi X-Ray Timing Explorer (RXTE), Advanced Satellite for Cosmology and Astrophysics (ASCA; or, Astro-D), Roentgen Satellite (ROSAT), and International Ultraviolet Explorer (IUE) and from many ground-based observatories, covering most accessible wavelengths. The well-sampled, simultaneous RXTE light curve shows an outburst of lower amplitude (factor of approximately = 3) well correlated with the gamma-ray flare without any lag larger than the temporal resolution of approximately 1 day. The optical-UV light curves, which are not well sampled during the high-energy flare, exhibit more modest variations (factor of approximately 2) and a lower degree of correlation. The flux at millimetric wavelengths was near a historical maximum during the gamma-ray flare peak, and there is a suggestion of a correlated decay. We present simultaneous spectral energy distributions of 3C 279 prior to and near to the flare peak. The gamma-rays vary by more than the square of the observed IR-optical flux change, which poses some problems for specific blazar emission models. The synchrotron self-Compton (SSC) model would require that the largest synchrotron variability occurred in the mostly unobserved submillimeter/far-infrared region. Alternatively, a large variation in the external photon field could occur over a time-scale of a few days. This occurs naturally in the "mirror" model wherein the flaring region in the jet photoionizes nearby broad emission line clouds, which, in turn, provide soft external photons that are Comptonized to gamma-ray energies.

Wehrle, A. E.↗
NASA NTRS1972

Nearest Neighbor Algorithms for Pattern Classification

A solution of the discrimination problem is considered by means of the minimum distance classifier, commonly referred to as the nearest neighbor (NN) rule. The NN rule is nonparametric, or distribution free, in the sense that it does not depend on any assumptions about the underlying statistics for its application. The k-NN rule is a procedure that assigns an observation vector z to a category F if most of the k nearby observations x sub i are elements of F. The condensed nearest neighbor (CNN) rule may be used to reduce the size of the training set required categorize The Bayes risk serves merely as a reference-the limit of excellence beyond which it is not possible to go. The NN rule is bounded below by the Bayes risk and above by twice the Bayes risk.

Barrios, J. O.↗
NASA NTRS1989

The Lunar Configurable Array Telescope (LCAT)

The desire for a much larger space telescope than HST by astronomers is clearly demonstrated by the attendance at this Workshop. The reality is that a much larger space telescope than the HST collides with cost scaling reality. Coupled with this reality is the fact that any multi-billion dollar science project must have broad-based support from the science community and solid political support at both Presidential and Congressional levels. The HST successor is certainly in the same multi-billion dollar class as the Super Collider of the physics community, a project that has finally achieved the broad support base necessary for funding to follow. Advocacy of a bigger HST on the general grounds that 'bigger is better' will not be sufficient. A new concept needs to be developed that clearly diverges from scaling up of a traditional HST-type space telescope. With these realities in mind we have a few comments regarding the nature of a possible space telescope that may depart from what the organizers of this Workshop had in mind. The national goal declared by the President is Space Station, the Moon and Mars, in that order. Space Station is a potential location where a large system could be assembled prior to being sent into a high orbit. It is not a desirable environment for a large space telescope. Mars is not relevant as an observatory site. The Moon is very relevant for reasons we will address. Our comments are based on the premise of a permanent Lunar Outpost. One of the main arguments for a lunar telescope is a degree of permanency, that is, as long as a Lunar Outpost is maintained. In contrast, the relatively short lifetime of an orbiting telescope is a disadvantage, especially as a cost penalty. Access to a telescope in a 100,000 km orbit for refurbishment and resupply is a major problem with no solution in the present NASA planning. A telescope in conjunction with a Lunar Outpost means the possibility for continual upgrading or modifying the telescope to meet changing science objectives. The two main technical disadvantages of the Moon are: 1) its gravity field; and 2) direct Sun and Earth light. The gravity term is manageable. It also appears to be feasible to shield the telescope from direct sun and Earth light and from scattering from nearby lunar terrain. Thermal disturbances to the telescope also appear to be manageable by proper shielding, enabling the telescope to become as cold as if it were at a lunar pole crater. If these conditions are met, the telescope could be at a logistically convenient location near the Lunar Outpost. We want to address a concept that is significantly different from those presented in the preliminary communications from Garth Illingworth in order to help fill in the matrix of possibilities. This option, moreover, is of special interest to JPL and could be an area where JPL can contribute in future studies.

Meinel, Aden B.↗
NASA NTRS1999

Statistical Quality Control of Moisture Data in GEOS DAS

A new statistical quality control algorithm was recently implemented in the Goddard Earth Observing System Data Assimilation System (GEOS DAS). The final step in the algorithm consists of an adaptive buddy check that either accepts or rejects outlier observations based on a local statistical analysis of nearby data. A basic assumption in any such test is that the observed field is spatially coherent, in the sense that nearby data can be expected to confirm each other. However, the buddy check resulted in excessive rejection of moisture data, especially during the Northern Hemisphere summer. The analysis moisture variable in GEOS DAS is water vapor mixing ratio. Observational evidence shows that the distribution of mixing ratio errors is far from normal. Furthermore, spatial correlations among mixing ratio errors are highly anisotropic and difficult to identify. Both factors contribute to the poor performance of the statistical quality control algorithm. To alleviate the problem, we applied the buddy check to relative humidity data instead. This variable explicitly depends on temperature and therefore exhibits a much greater spatial coherence. As a result, reject rates of moisture data are much more reasonable and homogeneous in time and space.

Dee, D. P.↗
NASA NTRS1998

The Space Interferometry Mission

The Space Interferometry Mission (SIM) is the next major space mission in NASA's Origins program after SIRTF. The SIM architecture uses three Michelson interferometers in low-earth orbit to provide 4 microarcsecond precision absolute astrometric measurements on approx. 40,000 stars. SIM will also provide synthesis imaging in the visible waveband to a resolution of 10 milliarcsecond, and interferometric nulling to a depth of 10(exp -4). A near-IR (1-2 micron) capability is being considered. Many key technologies will be demonstrated by SIM that will be carried over directly or can be readily scaled to future Origins missions such as TPF. The SIM spacecraft will carry a triple Michelson interferometer with baselines in the 10 meter range. Two interferometers act as high precision trackers, providing attitude information at all time, while the third one conducts the science observations. Ultra-accurate laser metrology and active systems monitor the systematic errors and to control the instrument vibrations in order to reach the 4 microarcsecond level on wide-angle measurements. SIM will produce a wealth of new astronomical data. With an absolute positional precision of 4 microarcsecond, SIM will improve on the best currently available measures (the Hipparcos catalog) by 2 or 3 orders of magnitude, providing parallaxes accurate to 10% and transverse velocities to 0.2 km/s anywhere in the Galaxy, to stars as faint as 20th magnitude. With the addition of radial velocities, knowledge of the 6-dimension phase space for objects of interest will allow us to attack a wide array of previously inaccessible problems such as: search for planets down to few earth masses; calibration of stellar luminosities and by means of standard candles, calibration of the cosmic distance scale; detecting perturbations due to spiral arms, disk warps and central bar in our galaxy; probe of the gravitational potential of the Galaxy, several kiloparsecs out of the galactic plane; synthesis imaging of circumstellar disks around young stellar objects; imaging the narrow-line regions of AGNs in the optical; direct distance determination of a half dozen nearby spiral galaxies using rotational kinematics, thereby sidestepping reddening and metallicity issues in the calibration of distance estimators like Tully-Fisher; imaging exozodiacal dust disks (when operating in its nulling mode, SIM will be sensitive, at a distance of (beta) Pic (20 pc), to scales ranging from 0.2 to 5 AU).

Unwin, Stephen C.↗