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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Joint Spectrum Access and Power Control in Air-Air Communications - A Deep Reinforcement Learning Based Approach

This paper considers the dynamic spectrum access and power control problem in a single-hop point-to-point Air-Air Communication Network (AACN). Due to spectrum scarcity, we assume the number of Aircraft-to-Aircraft (A2A) communication links is greater than that of the available channels, such that some communication links need to share the same channel, causing co-channel interference. We formulate the joint channel selection and power control optimization problem to maximize the Weighted Sum Spectral Efficiency (WSSE). A distributed and dynamic deep Q learning-based algorithm is proposed to find the optimal solution. Specifically, we design two different policies that are trained by conducting a trial-and-error scheme. Each communication link can achieve the optimal policy by exploiting the local information from its neighbors, and this distributive approach make it scalable to large networks. Finally, our experimental results demonstrate the effectiveness of the proposed solution in various AACN scenarios.

Zhe Wang↗
NASA NTRSDate not supplied

Joint Spectrum Access and Power Control in Air-Air Communications - A Deep Reinforcement Learning Based Approach

This paper considers the dynamic spectrum access and power control problem in a single-hop point-to-point Air-Air Communication Network (AACN). Due to spectrum scarcity, we assume the number of Aircraft-to-Aircraft (A2A) communication links is greater than that of the available channels, such that some communication links need to share the same channel, causing co-channel interference. We formulate the joint channel selection and power control optimization problem to maximize the Weighted Sum Spectral Efficiency (WSSE). A distributed and dynamic deep Q learning-based algorithm is proposed to find the optimal solution. Specifically, we design two different policies that are trained by conducting a trial-and-error scheme. Each communication link can achieve the optimal policy by exploiting the local information from its neighbors, and this distributive approach make it scalable to large networks. Finally, our experimental results demonstrate the effectiveness of the proposed solution in various AACN scenarios.

Zhe Wang↗
NASA NTRS1985

Time extended production of neutrons during a solar flare

The most energetic neutral emissions expected from solar flares are gamma rays (10 MeV) from relativistic primary and secondary electron bremsstrahlung,from approx 0 meson decay, and from neutrons ( 50 MeV). Bremsstrahlung photon energies extend to that of the highest energy electron present, but the shape of the pi sup 0 gamma ray spectrum, peaking at 69 MeV, does not depend strongly on the proton spectrum above threshold, which is approx. 292 MeV for meson production on protons. The highest energy neutrons observed indicate directly the highest energy ions which interact at the Sun, and the presence or absence of anergy cutoff in the acceleration process. The high-energy proton spectrum shape can be determined from the neutron spectrum.

Chupp, E. L.↗
NASA NTRS2019

Next-Generation Optical Sensing Technologies for Exploring Ocean Worlds - NASA FluidCam, MiDAR, and NeMO-Net

We highlight three emerging NASA optical technologies that enhance our ability to remotely sense, analyze, and explore ocean worlds–FluidCam and fluid lensing, MiDAR, and NeMO-Net. Fluid lensing is the first remote sensing technology capable of imaging through ocean waves without distortions in 3D at sub-cm resolutions. Fluid lensing and the purpose-built FluidCam CubeSat instruments have been used to provide refraction-corrected 3D multispectral imagery of shallow marine systems from unmanned aerial vehicles (UAVs). Results from repeat 2013 and 2016 airborne fluid lensing campaigns over coral reefs in American Samoa present a promising new tool for monitoring fine-scale ecological dynamics in shallow aquatic systems tens of square kilometers in area. MiDAR is a recently-patented active multispectral remote sensing and optical communications instrument which evolved from FluidCam. MiDAR is being tested on UAVs and autonomous underwater vehicles (AUVs) to remotely sense living and non-living structures in light-limited and analog planetary science environments. MiDAR illuminates targets with high-intensity narrowband structured optical radiation to measure an object’s spectral reflectance while simultaneously transmitting data. MiDAR is capable of remotely sensing reflectance at fine spatial and temporal scales, with a signal-to-noise ratio 10-10(exp 3) times higher than passive airborne and spaceborne remote sensing systems, enabling high-framerate multispectral sensing across the ultraviolet, visible, and near-infrared spectrum. Preliminary results from a 2018 mission to Guam show encouraging applications of MiDAR to imaging coral from airborne and underwater platforms whilst transmitting data across the air-water interface. Finally, we share NeMO-Net, the Neural Multi-Modal Observation & Training Network for Global Coral Reef Assessment. NeMO-Net is a machine learning technology under development that exploits high-resolution data from FluidCam and MiDAR for augmentation of low-resolution airborne and satellite remote sensing. NeMO-Net is intended to harmonize the growing diversity of 2D and 3D remote sensing with in situ data into a single open-source platform for assessing shallow marine ecosystems globally using active learning for citizen-science based training. Preliminary results from four-class Q17 coral classification have an accuracy of 94.4%. Together, these maturing technologies present promising scalable, practical, and cost-efficient innovations that address current observational and technological challenges in optical sensing of marine systems.

Ved Chirayath↗
NASA NTRS1991

NASA Report to Education, Volume 9

This is an edition of 'NASA Report to Education' covering NASA's Educational Workshop, Lewis Research Center's T-34 and the Space Exploration Initiative. The first segment shows NASA Education Workshop program (NEWEST - NASA Educational Workshops for Elementary School Teachers). Highlights of the 14 days of intense training, lectures, fieldtrips and simple projects that the educators went through to teach the program are included. Participants are shown working on various projects such as the electromagnetic spectrum, living in Space Station Freedom, experience in T-34, tour of tower at the Federal Aviation Administrative Facilities, conducting an egg survival system and an interactive video conference with astronaut Story Musgrave. Participants share impressions of the workshop. The second segment tells how Lewis Research Center's T-34 aircraft is used to promote aerospace education in several Cleveland schools and excite students.

Source record↗
NASA NTRS1981

Sunshade/radiative cooler for IRAS infrared astronomical satellite

The Infrared Astronomical Satellite (IRAS) is a joint project shared by the United States and the Netherlands with the United Kingdom providing tracking and ground support services. IRAS features a cryogenically cooled telescope designed to perform an unbiased all-sky survey of the far infrared spectrum from 8 to 120 microns and to observe objects of special interest. The sunshade is designed to protect the telescope aperture and sunshade radiators from: direct solar radiation; direct earth radiation; radiation exchange with satellite structures; excessive aperture heating caused by sunshade inner cone emission. The sunshade three-stage radiative cooler design meets the listed requirements and, in addition, provides some contamination protection for the telescope aperture and optical surfaces during pointing maneuvers when the telescope is tilted in the direction of the velocity vector. Unless protected by the sunshade, the ram effect can cause molecules to enter the aperture and deposit on the cooled optical surfaces. This paper describes the sunshade design, the thermal analyses, and the results of thermal balance testing of the flight hardware.

Anderson, R. R.↗
NASA NTRS1980

X-ray observations of the supernova remnant MSH 11-54

Soft X-ray observations of the X-ray source H1122-59 in the 0.4-2 keV band made with the low-energy detector 1 of the HEAO A-2 experiment are described. Based on positional coincidence, the source is identified with the supernova remnant MSH-11-54, thus confirming the report of Share et al. (1980). The object is a bright source in the 0.4-2 keV band with an X-ray flux of 9 x 10 to the -11th ergs/sq cm s near the earth. The measured source spectrum implies a plasma temperature of 4 million K and X-ray luminosity in the 0.4-2 keV band of 10 to the 37th ergs/s using a distance of 10 kpc for MSH 11-54. The X-ray observations, interpreted in terms of an adiabatic shock wave model, give a shock velocity of about 560 km/s and a supernova age of about 2300 yr, in good agreement with the age derived from the radio observations.

Agrawal, P. C.↗
NASA NTRS2012

The Dust Properties of Hot R Coronae Borealis Stars and a Wolf-Rayet Central Star of a Planetary Nebula: In Search of the Missing Link

We present new Spitzer IIRS spectra of two hot R Coronae Borealis (RCB) stars, one in the Galaxy,V348 Sgr, and one lying in the Large Magellanic Cloud, HV 2671. These two objects constitute a link between the RCB stars and the [WCL] class of central stars of planetary nebula (CSPNe) that has little or no hydrogen in their atmospheres such as CPD -560 8032. HV 2671 and V348 Sgr are members of a rare subclass that has significantly higher effective temperatures than most RCB stars, but sharing the traits of hydrogen deficiency and dust formation that define the cooler RCB stars. The [WC] CSPNe star, CPD -560 8032, displays evidence for dual-dust chemistry showing both PAHs and crystalline silicates in its mid-IR spectrum. HV 2671 shows strong PAH emission but shows no sign of having crystalline silicates. The spectrum of V348 Sgr is very different from those of CPD -56deg 8032 and HV 2671. The PAH emission seen strongly in the other two stars is only weakly present. Instead, the spectrum is dominated by a broad emission centered at about 8.5 microns. This feature is not identified with either PAHs or silicates. Several other novae and post-asymptotic giant branch stars show similar features in their IR spectra. The mid-IR spectrum of CPD -56deg 8032 shows emission features associated with C60 . The other two stars do not show evidence for C60. The nature of the dust around these stars does not help us in establishing further links that may indicate a common origin.

Clayton, Geoffrey C.↗
NASA NTRS2016

Solar Coronal Jets: Observations, Theory, and Modeling

Coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of significant mass and energy input to the upper solar atmosphere and the solar wind. While the energy involved in a jet-like event is smaller than that of "nominal" solar flares and coronal mass ejections (CMEs), jets share many common properties with these phenomena, in particular, the explosive magnetically driven dynamics. Studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. On the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients close or at the limit of the current spatial resolution such as spicules. Furthermore, jet phenomena may hint to basic process for heating the corona and accelerating the solar wind; consequently their study gives us the opportunity to attack a broad range of solar-heliospheric problems.

Raouafi, N. E.↗
NASA NTRS1992

Reflectance spectroscopy and GEX simulation of palagonite and iron-rich montmorillonite clay mixtures: Implications for the surface composition of Mars

Because of the power of remote sensing reflectance spectroscopy in determining mineralogy, it has been used as the major method of identifying a possible mineral analogue of the martian surface. A summary of proposed martian surface compositions from reflectance spectroscopy before 1979 was presented by Singer et al. Since that time, iron-rich montmorillonite clay, nanocrystalline or nanophase hematite, and palagonite have been suggested as Mars soil analogue materials. Palagonite in petrological terms is best described as an amorphous, hydrated, ferric iron, silica gel. Montmorillonite is a member of the smectite clay group, and its structure is characterized by an octahedral sheet in coordination with two tetrahedral sheets in which oxygen atoms are shared. The crystal unity of montmorillonite is well defined in contrast to palagonite where it is considered amorphous or poorly crystalline at best. Because of the absence of the diagnostic strong 2.2-micron reflectance band characteristic of clays in the near-infrared (NIR) spectrum of Mars and palagonite and based upon a consideration of wide wavelength coverage (0.3-50 microns), Roush et al. concluded that palagonite is a more likely Mars surface analogue. In spite of the spectral agreement of palagonite and the Mars reflectance spectrum in the 2.2-micron region, palagonite shows poor correspondence with the results of the Viking LR experiment. In contrast, iron-rich montmorillonite clays show relatively good agreement with the results of the Viking LR experiment. This spectral study was undertaken to evaluate the spectral properties of mixtures of palagonite and Mars analogue iron-rich montmorillonite clay (16-18 wt. percent Fe as Fe2O3) as a Mars surface mineralogical model. Mixtures of minerals as Mars surface analogue materials have been studied before, but the mixtures were restricted to crystalline clays and iron oxides.

Orenberg, J. B.↗
NASA NTRS2003

Biosignatures of early earths

A major goal of NASA's Origins Program is to find habitable planets around other stars and determine which might harbor life. Determining whether or not an extrasolar planet harbors life requires an understanding of what spectral features (i.e., biosignatures) might result from life's presence. Consideration of potential biosignatures has tended to focus on spectral features of gases in Earth's modern atmosphere, particularly ozone, the photolytic product of biogenically produced molecular oxygen. But life existed on Earth for about 1(1/2) billion years before the buildup of atmospheric oxygen. Inferred characteristics of Earth's earliest biosphere and studies of modern microbial ecosystems that share some of those characteristics suggest that organosulfur compounds, particularly methanethiol (CH(3)SH, the sulfur analog of methanol), may have been biogenic products on early Earth. Similar production could take place on extrasolar Earth-like planets whose biota share functional chemical characteristics with Earth life. Since methanethiol and related organosulfur compounds (as well as carbon dioxide) absorb at wavelengths near or overlapping the 9.6-microm band of ozone, there is potential ambiguity in interpreting a feature around this wavelength in an extrasolar planet spectrum.

Earth (Planet)↗
NASA NTRS1980

WARC and CCIR support for spectrum-orbit planning

Papers prepared for the use of the U.S. delegation to the 1979 World Administrative Radio Conference; papers contributed to the National CCIR study groups on broadcasting satellites and spectrum-orbit utilization; responses to specific requests for technical analyses and evaluations; and papers presented at technical conferences on related topics are presented. Nonlinear optimization methods for finding optimum positions of satellites in the fixed satellite service; the effects of geography on the use of the geostationary orbit; intercontinental orbit sharing; traffic coordination in interfering satellites operating in the fixed satellite service; and domestic fixed and broadcasting satellite systems are covered. A possible channel orbit plan for broadcasting satellite service in the U.S. and Canada; polarization for broadcasting satellite systems; and the communication capacity of the geostationary satellite orbit are also examined.

Sawitz, P. H.↗
NASA NTRS2004

Mineralogical Variations Among High Albedo E-Type Asteroids: Implications for Asteroid Igneous Processes

The link between the E-type asteroids and the enstatite achondrites (aubrites) was first proposed for the original E-asteroid, 44 Nysa. The association was based on the high albedos and the featureless spectra shared by the E-asteroids and the aubrites. Among the plausible geologic and meteoritic materials, only enstatite (the magnesium end-member of the pyroxene solid solution series) is sufficiently abundant to comprise asteroid-sized bodies. However, the presence of a weak 0.89 m absorption feature in the spectrum of 44 Nysa indicates that its pyroxene contains a small amount of Fe(2+) but still substantially more than any aubrite present in the meteorite collection. The original E-class was defined based on its high albedo and flat to slightly reddish spectrum. In the absence of albedo data, the E-type was degenerate with the M- and P-types, and together these were designated as X-types. Recently, a taxonomy has been proposed to identify E-types in the absence of albedo data. In this newer classification system three subdivisions of the X-type have been proposed, including Xc, Xe and Xk. Of nine albedo-defined E-types [d], this newer non-albedo based taxonomy produced the following classifications: X-1 asteroid; Xc-2 asteroids; Xe-5 asteroids; and Xk-1 asteroid. Although the Xe subtype includes the largest number of albedo-defined E-types, most of the remaining 24 Xe-types can be excluded based on their low measured IRAS albedos, ranging from 0.116 to 0.329, which are below the lower albedo limit of the E-class (0.34) and substantially below that of the lowest albedo an actual E-type asteroid (0.41). The present discussion will be limited to unambiguous E-type asteroids determined on albedo criteria.

Gaffey, Michael J.↗
NASA NTRS2012

Temporal Variability of Observed and Simulated Hyperspectral Earth Reflectance

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a climate observation system designed to study Earth's climate variability with unprecedented absolute radiometric accuracy and SI traceability. Observation System Simulation Experiments (OSSEs) were developed using GCM output and MODTRAN to simulate CLARREO reflectance measurements during the 21st century as a design tool for the CLARREO hyperspectral shortwave imager. With OSSE simulations of hyperspectral reflectance, Feldman et al. [2011a,b] found that shortwave reflectance is able to detect changes in climate variables during the 21st century and improve time-to-detection compared to broadband measurements. The OSSE has been a powerful tool in the design of the CLARREO imager and for understanding the effect of climate change on the spectral variability of reflectance, but it is important to evaluate how well the OSSE simulates the Earth's present-day spectral variability. For this evaluation we have used hyperspectral reflectance measurements from the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY), a shortwave spectrometer that was operational between March 2002 and April 2012. To study the spectral variability of SCIAMACHY-measured and OSSE-simulated reflectance, we used principal component analysis (PCA), a spectral decomposition technique that identifies dominant modes of variability in a multivariate data set. Using quantitative comparisons of the OSSE and SCIAMACHY PCs, we have quantified how well the OSSE captures the spectral variability of Earth?s climate system at the beginning of the 21st century relative to SCIAMACHY measurements. These results showed that the OSSE and SCIAMACHY data sets share over 99% of their total variance in 2004. Using the PCs and the temporally distributed reflectance spectra projected onto the PCs (PC scores), we can study the temporal variability of the observed and simulated reflectance spectra. Multivariate time series analysis of the PC scores using techniques such as Singular Spectrum Analysis (SSA) and Multichannel SSA will provide information about the temporal variability of the dominant variables. Quantitative comparison techniques can evaluate how well the OSSE reproduces the temporal variability observed by SCIAMACHY spectral reflectance measurements during the first decade of the 21st century. PCA of OSSE-simulated reflectance can also be used to study how the dominant spectral variables change on centennial scales for forced and unforced climate change scenarios. To have confidence in OSSE predictions of the spectral variability of hyperspectral reflectance, it is first necessary for us to evaluate the degree to which the OSSE simulations are able to reproduce the Earth?s present-day spectral variability.

Roberts, Yolanda↗
NASA NTRS1982

A new strategy for efficient solar energy conversion: Parallel-processing with surface plasmons

This paper introduces an advanced concept for direct conversion of sunlight to electricity, which aims at high efficiency by tailoring the conversion process to separate energy bands within the broad solar spectrum. The objective is to obtain a high level of spectrum-splitting without sequential losses or unique materials for each frequency band. In this concept, sunlight excites a spectrum of surface plasma waves which are processed in parallel on the same metal film. The surface plasmons transport energy to an array of metal-barrier-semiconductor diodes, where energy is extracted by inelastic tunneling. Diodes are tuned to different frequency bands by selecting the operating voltage and geometry, but all diodes share the same materials.

Anderson, L. M.↗
NASA NTRS2008

ART-XC: A Medium-energy X-ray Telescope System for the Spectrum-R-Gamma Mission

The ART-XC instrument is an X-ray grazing-incidence telescope system in an ABRIXAS-type optical configuration optimized for the survey observational mode of the Spectrum-RG astrophysical mission which is scheduled to be launched in 2011. ART-XC has two units, each equipped with four identical X-ray multi-shell mirror modules. The optical axes of the individual mirror modules are not parallel but are separated by several degrees to permit the four modules to share a single CCD focal plane detector, 1/4 of the area each. The 450-micron-thick pnCCD (similar to the adjacent eROSITA telescope detector) will allow detection of X-ray photons up to 15 keV. The field of view of the individual mirror module is about 18 x 18 arcminutes(exp 2) and the sensitivity of the ART-XC system for 4 years of survey will be better than 10(exp -12) erg s(exp -1) cm(exp -2) over the 4-12 keV energy band. This will allow the ART-XC instrument to discover several thousand new AGNs.

Arefiev, V.↗
NASA NTRS1998

NASA Technology Plan 1998

This NASA Strategic Plan describes an ambitious, exciting vision for the Agency across all its Strategic Enterprises that addresses a series of fundamental questions of science and research. This vision is so challenging that it literally depends on the success of an aggressive, cutting-edge advanced technology development program. The objective of this plan is to describe the NASA-wide technology program in a manner that provides not only the content of ongoing and planned activities, but also the rationale and justification for these activities in the context of NASA's future needs. The scope of this plan is Agencywide, and it includes technology investments to support all major space and aeronautics program areas, but particular emphasis is placed on longer term strategic technology efforts that will have broad impact across the spectrum of NASA activities and perhaps beyond. Our goal is to broaden the understanding of NASA technology programs and to encourage greater participation from outside the Agency. By relating technology goals to anticipated mission needs, we hope to stimulate additional innovative approaches to technology challenges and promote more cooperative programs with partners outside NASA who share common goals. We also believe that this will increase the transfer of NASA-sponsored technology into nonaerospace applications, resulting in an even greater return on the investment in NASA.

Source record↗
NASA NTRS1987

Concurrent communication among multi-transceiver stations over shared media

In order to increase a local-area network's throughput beyond a single bus data rate without using dedicated switching nodes, multiple buses and multitransceiver stations are required. The design space of single-hop interconnections is explored among such stations. Interconnections are presented whose throughput can grow quadratically with the number of transmitters and receivers per station. These are referred to as selective broadcast interconnections (SBIs). The performance of various SBIs are studied. A spread-spectrum channel can accommodate several current successful transmission, and a single-transceiver node can thus utilize only a small fraction of the channel capacity. In order to allocate the appropriate fraction of capacity to a busy node, it is proposed to equip it with several transmitters and receivers, thereby turning it into a supernode. Several architectures and operation policies for supernodes are suggested and compared. It is shown that a supernode can significantly outperform a collection of independent conventional nodes with the same total numbers of transmitters and receivers. Packet-radio networks with half-duplex nodes, as well as networks with full-duplex nodes, are considered.

Birk, Yitzhak↗