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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Inland and Near-Shore Water Profiles Derived from the High-Altitude Multiple Altimeter Beam Experimental Lidar (MABEL)

The Advanced Topographic Laser Altimeter System (ATLAS) on the Ice, Cloud, and Land Elevation Satellite (ICESat-2) mission is a six beam, low energy, high repetition rate, 532-nanometer laser transmitter with photon counting detectors. Although designed primarily for detecting height changes in ice caps, sea ice, and vegetation, the polar-orbiting satellite will observe global surface water during its designed three-year life span, including inland waterbodies, coasts, and open oceans. In preparation for the mission, an ICESat-2 prototype, the Multiple Altimeter Beam Experimental Lidar (MABEL), was built and flown on high-altitude aircraft experiments over a range of inland and near-shore targets. The purpose was to test the ATLAS concept and to provide a database for developing an algorithm that detects along track surface water height and light penetration under a range of atmospheric and water conditions. The current analysis examines the data sets of three MABEL transects observed from 20 kilometers above ground of coastal and inland waters conducted in 2012 and 2013. Transects ranged from about 2 to 12 kilometers in length and included the middle Chesapeake Bay, the near-shore Atlantic coast at Virginia Beach, and Lake Mead. Results indicate MABEL's high capability for retrieving surface water height statistics with a mean height precision ofapproximately 5-7 centimeters per 100-meter segment length. Profiles of attenuated subsurface backscatter, characterized using a Signal to Background Ratio written in Log10 base, or LSBR (sub 0), were observed over a range of 1.3 to 9.3 meters, depending on water clarity and atmospheric background. Results indicate that observable penetration depth, although primarily dependent on water properties, was greatest when the solar background rate was low. Near-shore bottom reflectance was detected only at the Lake Mead site down to a maximum of 10 meters under a clear night sky and low turbidity of approximately 1.6 Nephelometric Turbidity Units (NTU). The overall results suggest that the feasibility of retrieving operational surface water height statistics from space-based photon counting systems such as ATLAS is very high for resolutions down to about 100 meters, even in partly cloudy conditions. The capability to observe subsurface backscatterprofiles is achievable but requires much longer transects of several hundreds of meters.

inland↗
NASA NTRS1975

Evidence for X-ray emission from flare stars observed by ANS

Observations that detected the first X-ray emission from flare stars are described. An X-ray flare was detected from YZ CMi at 0.28 keV and approximately 1-7 keV, although no optical or radio coverage was available. During a very large optical flare from UV Ceti, X-ray emission at (only) 0.28 keV was detected. Upper limits for X-ray emission from several small optical flares of UV Ceti are presented. Implications for X-ray flare models, the diffuse X-ray background, and low-energy cosmic-ray flux are mentioned.

Heise, J.↗
NASA NTRS1975

Observations of X-rays from flare stars with ANS

Observations during which X-ray emission from flare stars was detected for the first time, are described. An X-ray flare was detected from YZ CMi at 0.28 keV and 1-7 keV, although no optical or radio coverage was available. During a very large optical flare from UV Ceti, X-ray emission at 0.28 keV only was detected. Upper limits for X-ray emission from several small optical flares of UV Ceti are obtained. Implications for X-ray flare models, the diffuse X-ray background, and low-energy cosmic-ray flux are examined.

Grindlay, J.↗
NASA NTRS1976

Large area ion chambers for a high energy cosmic ray experiment

High resolution measurement of the iron group nuclei was performed with the intention of determining individual abundances in the cosmic ray flux at the earth of particles with z = 22 to 30. Of the three types of dE/dx detectors used in the experiment, pulse ion chambers, Cerenkov radiators and scintillators, the first has the best z resolution over a wide range of particle z and energy. The plastic scintillators define the particle acceptance cone of the telescope while the Cerenkov detector aids in rejection of low energy particle background and measurement of particle velocity.

Source record↗
NASA NTRS1977

Gamma rays from the de-excitation of C-12 resonance 15.11 MeV and C-12 resonance 4.44 MeV as probes of energetic particle spectra

The flux of 15.11 MeV gamma rays relative to the flux 4.44 MeV gamma rays was calculated from measured cross sections for excitation of the corresponding states of C-12 and from experimental determinations of the branching ratios for direct de-excitation of these states to the ground state. Because of the difference in threshold energies for excitation of these two levels, the relative intensities in the two lines are particularly sensitive to the spectral distribution of energetic particles which excite the corresponding nuclear levels. For both solar and cosmic emission, the observability of the 15.11 MeV line is expected to be enhances by low source-background continuum in this energy range.

Crannell, C. J.↗
NASA NTRS1977

Equatorial X-rays and their effect on the lower mesosphere

Equatorial regions are well suited for studies of lower mesospheric response to X-rays because cosmic ray background effects are low there. In a sequence of rocket and balloon-borne observations conducted in Peru (12.5 S, 76.8 W), a direct measurement of a galactic X-ray source was made at an altitude of 65 km. Although no unusual X-ray activity was found above and below the region studied, the 65 km observations were consistent with known data for Sco X-1, i.e., its position and energy spectrum. In addition to showing that stellar X-rays do indeed affect the lower mesosphere, their transient nature leads also to the conclusion that the equatorial energetic electron belt is not a permanent feature of that region.

Goldberg, R. A.↗
NASA NTRS1978

D sub 3 spicules and the lower chromosphere

High resolution filtergrams of the solar limb in D sub 3 and off-band H-alpha have been used to investigate the spatial structure of the D sub 3 chromosphere. It was found that spicules provide the major contribution to the intensity of the D sub 3 emission band observed above the limb, with the remainder of the emission coming from a semi-homogeneous background component at low heights. The observations can be understood on the basis of the photoionization model, whereby it is found that helium is only slightly ionized at the height of peak intensity in the D sub 3 emission band, and that spicules are at least three times denser than their surroundings at this height. In coronal holes, the D sub 3 emission is confined to isolated emission patches, and these patches contain a fine structure resembling normal chromospheric spicules.

Marsh, K. A.↗
NASA NTRS1988

Cosmic-ray detectors on the Moon

The state of cosmic ray physics is reviewed. It is concluded that the nonexistent lunar magnetic field, the low lunar radiation background, and the lack of an atmosphere on the Moon provide an excellent environment for the study of high energy primary cosmic rays.

Linsley, John↗
NASA NTRS1989

Requirements of IR space astronomy

An introduction to a series of infrared detector technology workshops is given. The establishment of goals and new requirements is addressed in a general way. The Shuttle Infrared telescope Facility (SIRIF) goals are listed. Given that the wavelength coverage is established at 2 to 750 microns and the unvignetted field of view is 7 arcmin, the field should be fully utilized at each wavelength, diffraction should be critically sampled, and each detector should be background limited.

Low, Frank J.↗
NASA NTRS1991

Aircraft multifrequency passive microwave observations of light precipitation over the ocean

Aircraft passive microwave observations at 18, 37, 92, and 183 GHz of light oceanic precipitation are studied in conjunction with visible and infrared observations and ground-based radar data. Microwave signatures for clear, cloudy, and precipitating conditions are defined, with results in general agreement with previous theoretical results. Emission signatures are evident at 18, 37, and 92 GHz with clouds and precipitation producing an increase in brightness temperature over that observed over the low-emissivity ocean background. Polarization differences at 18 and 37 GHz also decrease in precipitation areas to minima of 30 K at 18 GHz and 15 K at 37 GHz. The 92-GHz brightness temperature shows a double-valued relationship, with an increase in cloudy and very lightly raining areas and a subsequent decrease for higher rain rates and deeper clouds where the ice scattering process becomes important. The 183-GHz observations display a distinct sensitivity to small amounts of ice. Simple channel differences are shown to compare favorably to the rain field, including polarization differences at 18 and 37 GHz and frequency differences between 92 and 37 GHz and between 183 and 92 GHz.

Adler, Robert F.↗
NASA NTRS1991

Constraints on the optical properties of interstellar dust in the far-ultraviolet - Voyager observations of the diffuse sky background

Four regions of the sky have been observed at various Galactic latitudes and H I column densities, with the ultraviolet spectrometer aboard Voyager 2 finding no evidence for the presence of a diffuse radiation field between 912 and 1100 A at a level of 100-200 photons per sq cm s sr A. As starlight scattered by dust grains may be expected to be a major contributor to the diffuse background, especially at low Galactic latitudes, it is possible to place a very stringent upper limit of less than 0.1 on the reflectivity of the dust in this spectral range. This albedo is much lower than the canonical value of about 0.5 for standard graphite-silicate dust models.

Murthy, Jayant↗
NASA NTRS2000

Design-Filter Selection for H2 Control of Microgravity Isolation Systems: A Single-Degree-of-Freedom Case Study

Many microgravity space-science experiments require active vibration isolation, to attain suitably low levels of background acceleration for useful experimental results. The design of state-space controllers by optimal control methods requires judicious choices of frequency-weighting design filters. Kinematic coupling among states greatly clouds designer intuition in the choices of these filters, and the masking effects of the state observations cloud the process further. Recent research into the practical application of H2 synthesis methods to such problems, indicates that certain steps can lead to state frequency-weighting design-filter choices with substantially improved promise of usefulness, even in the face of these difficulties. In choosing these filters on the states, one considers their relationships to corresponding design filters on appropriate pseudo-sensitivity- and pseudo-complementary-sensitivity functions. This paper investigates the application of these considerations to a single-degree-of-freedom microgravity vibration-isolation test case. Significant observations that were noted during the design process are presented. along with explanations based on the existent theory for such problems.

Hampton, R. David↗
NASA NTRS2005

Going to the Bottom of the Explosion that Formed Cas A

The purpose of this INTEGRAL AO 1 proposal was to observe the gamma-ray lines at 1157 keV, as well as 68 keV and 78 keV of the (44)Ti decay chain from the youngest known galactic supernova remnant Cas A. The radioactive decay of (44)Ti in Cas A was first detected by COMPTEL in the 1157 keV line and later confirmed in the lower energy lines using BeppoSAX data. Despite the second confirming measurement, the flux value still has a considerable error, due to a low signal over background ratio and the poor definition of the continuum background in the range of 70 - 100 keV above the line energies. In addition to improving this flux measurement, INTEGRAL has the unique capability, in principle, to measure the line width of the emission. This type of measurement can further constrain supernova explosion models. Unfortunately, the INTEGRAL instrumental background, especially in the SPI spectrometer, turned out to be significantly higher than estimated at the time of proposal submission before launch. This, and to a smaller extent the reduced effective exposure time of about 1.5 Ms compared to requested 2.5 Ms, has precluded us from reaching the sensitivity necessary for this measurement. Studies of the background variability with the goal of improving background modeling are ongoing, and additional 2.5 Ms observing time has just been approved for the next observing cycle.

Oberlack, Uwe↗
NASA NTRS2005

High-Power Radar Sounders for the Investigation of Jupiter Icy Moons

The high power and high data rate capability made available by a Prometheus class spacecraft could significantly enhance our ability to probe the subsurface of the planets/moons and asteroid/comets. The main technology development driver for our radar is the proposed Jupiter Icy Moon Orbiter (or JIMO) mission due to its harsh radiation environment. We plan to develop a dual-band radar at 5 and 50 MHz in response to the two major science requirements identified by the JIMO Science Definition Team: studying the near subsurface (less than 2 km) at high resolution and detection of the ice/ocean interface for Europa (depth up to 30 km). The 50-MHz band is necessary to provide high spatial resolution (footprint and depth) as required by the JIMO mission science requirements as currently defined. Our preliminary assessment indicates that the 50-MHz system is not required to be as high-power as the 5-MHz system since it will be more limited by the surface clutter than the Jupiter or galactic background noise. The low frequency band (e.g. 5 MHz), which is the focus of this effort, would be necessary to mitigate the performance risks posed by the unknown subsurface structure both in terms of unknown attenuation due to volumetric scattering and also the detection of the interface through the attenuative transition region at the ice/ocean interface. Additionally, the 5-MHz band is less affected by the surface roughness that can cause loss of coherence and clutter noise. However, since the Signal-to-Noise-Ratio (SNR) of the 5-MHz radar band is reduced due to Jupiter noise when operating in the Jupiter side of the moon, it is necessary to increase the radiated power. Our challenge is to design a high-power HF radar that can hnction in Jupiter's high radiation environment, yet be able to fit into spacecraft resource constraints such as mass and thermal limits. Our effort to develop the JIMO radar sounder will rely on our team's experience with planetary radar sounder design gained during our participation in the MARSIS radar sounder implementation.

Safaeinili, A.↗
NASA NTRS2005

MIT Participation in the Data Analysis of the XRS and XIS Instruments on the Astro-E2 Mission

Since the inception of this grant six weeks ago, we have completed the initial activation of the Suzaku X-ray Imaging Spectrometer (XIS) (on 13 August) and we have supported initial calibration observations. The instrument is performing very well in all respects. We have characterized the spectral resolution and effective area of each XIS sensor. We are especially excited about the scientific opportunities provided by the XIS'S back- illuminated sensor, which exhibits spectral resolution in the sub-keV band unmatched by any X-ray CCD currently in orbit. As specified in our proposal, we have established a web site (http://space.mit.edu/XIS) on which we maintain an up-to-date summary of instrument performance characteristics. Gain, spectral resolution and system noise, as well as residual background rates, are currently available on this site. Although the particle background level is low compared with Chandra and XMM, we are currently evaluating methods to reduce it still further. Techniques under study include use of 5x5 mode information and alternative grade selection methods. Although the primary responsibility for development of instrument response functions rests with our Japanese colleagues, we are incorporating our latest measurements of spectral resolution into some temporary response functions which we hope to make available to the Suzaku General Observer Facility and the Science Working Group(SWG). We are also preparing proposals for use of SWG observing time.

Bautz, Mark↗
NASA NTRS2010

Contributions to Future Stratospheric Climate Change: An Idealized Chemistry-Climate Model Sensitivity Study

Within the framework of an idealized model sensitivity study, three of the main contributors to future stratospheric climate change are evaluated: increases in greenhouse gas concentrations, ozone recovery, and changing sea surface temperatures (SSTs). These three contributors are explored in combination and separately, to test the interactions between ozone and climate; the linearity of their contributions to stratospheric climate change is also assessed. In a simplified chemistry-climate model, stratospheric global mean temperature is most sensitive to CO2 doubling, followed by ozone depletion, then by increased SSTs. At polar latitudes, the Northern Hemisphere (NH) stratosphere is more sensitive to changes in CO2, SSTs and O3 than is the Southern Hemisphere (SH); the opposing responses to ozone depletion under low or high background CO2 concentrations, as seen with present-day SSTs, are much weaker and are not statistically significant under enhanced SSTs. Consistent with previous studies, the strength of the Brewer-Dobson circulation is found to increase in an idealized future climate; SSTs contribute most to this increase in the upper troposphere/lower stratosphere (UT/LS) region, while CO2 and ozone changes contribute most in the stratosphere and mesosphere.

Hurwitz, M. M.↗
NASA NTRS2013

Herschel Observations of the Debris Disc Around HIP 92043

Context: Typical debris discs are composed of particles ranging from several micron sized dust grains to kilometer-sized asteroidal bodies, and their infrared emission peaks at wavelengths 60-100 microns. Recent Herschel DUNES (Dust Around Nearby Stars) observations have identified several debris discs around nearby Sun-like stars (F, G and K spectral type) with significant excess emission only at 160 microns. Aims: We observed HIP 92043 (110 Her, HD 173667) at far-infrared and sub-millimetre wavelengths with Herschel PACS (Photodetector Array Camera and Spectrometer) and SPIRE (Spectral and Photometric Imaging Receiver).Identification of the presence of excess emission from HIP 92043 and the origin and physical properties of any excess was undertaken through analysis of its spectral energy distribution (SED) and the PACS images. Methods: The PACS and SPIRE images were produced using the HIPE (Herschel Interactive Processing Environment) photProject map maker routine. Fluxes were measured using aperture photometry. A stellar photosphere model was scaled to optical and near infrared photometry and subtracted from the far-infared and sub-mm fluxes to determine the presence of excess emission. Source radial profiles were fitted using a 2D Gaussian and compared to a PSF (Point Spread Function) model based on Herschel observations of alpha Boo to check for extended emission. Results: Clear excess emission from HIP 92043 was observed at 70 and 100 microns. Marginal excess was observed at 160 and 250 microns.Analysis of the images reveals that the source is extended at 160 microns. A fit to the source SED is inconsistent with a photosphere and single temperature black body. Conclusions: The excess emission from HIP 92043 is consistent with the presence of an unresolved circumstellar debris disc at 70and 100 microns, with low probability of background contamination. The extended 160 micron emission may be interpreted as an additional cold component to the debris disc or as the result of background contamination along the line of sight. The nature of the 160 micron excess cannot be determined absolutely from the available data, but we favour a debris disc interpretation, drawing parallels with previously identified cold disc sources in the DUNES sample.

debris discs↗
NASA NTRSDate not supplied

Developing Methods for Exercise System Kinematic Tracking

BACKGROUND How to quantify the load and forces produced by exercise equipment and their Vibration Isolation and Stabilization (VIS) platforms in-flight is an active area of investigation. Kinematic tracking paired with system modeling can provide insights as well as verification and validation of simulations used for system design and development. Traditional motion capture methods can require significant cost in equipment procurement and crew-time, but newer lessons learned can be leveraged [1]. The VIS systems of current and future exercise hardware on the International Space Station (ISS) such as the Cycle Ergometer with Vibration Isolation System (CEVIS) and the European Enhanced Exploration Exercise Device (E4D) are not currently outfitted with IMUs or similar measurement devices. Video-based methods would enable use of multi-purpose, crew-familiar flight equipment. An initial exploration of video-based solutions was performed utilizing 2-camera video from crew cycling on Teal-CEVIS on the ISS. METHODS AND RESULTS Our group has scoped a variety of video-based object tracking methods. To date, we have primarily investigated computer vision toolkits such as open CV. Techniques explored include key-point detection, background subtraction, region-of interest tracking, color-based tracking, tag masking and tracking, and corner detection. Although object-tracking and 6D pose estimation is a rich field, space applications are a unique problem that are challenging for existing software and toolkits. The majority of the existing object-tracking applications involve vehicles/pedestrians and household objects with simple backgrounds. We have identified the following features which pose particular challenges for on-station exercise equipment tracking: 1. Busy and visually cluttered background 2. Low-textured tracking object with relatively small motions 3. Occlusions and motion by human subject and loose, floating objects 4. Limited number of video cameras with no fixed global references 5. Limited ability to add tags, markers, or visual references to the tracking object 6. Lack of training data for Machine Learning (ML) algorithms CONCLUSION We will summarize the efficacy of techniques tested for a ground mock-trial and the on-station exercise trial. It is likely that human-in-loop feedback or a conglomerate of methods is required. ML-based methods, like those implemented for human body tracking [2], may still be a viable option, but more training data and validation is needed.

L Nilsson↗