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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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NASA NTRS2008

Status of Terra and Aqua MODIS Instruments

Currently, two nearly identical MODIS instruments are operating in space: one on the Terra spacecraft launched in December 1999 and another on the Aqua spacecraft launched in May 2002. MODIS has 36 spectral bands with wavelengths covering from visible (VIS) to long-wave infrared (LWIR). Since launch, MODIS observations and data products have contributed significantly to studies of changes in the Earth system of land, oceans, and atmosphere. To maintain its on-orbit calibration and data product quality, MODIS was built with a comprehensive set of on-board calibrators, consisting of a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the reflective solar bands (RSB) and an on-board blackbody (BB) for the thermal emissive bands (TEB). Both instruments have demonstrated good performance. The primary Level 1 B (LIB) data products are top of the atmosphere (TOA) reflectance for RSB and radiance for TEB This paper provides an overview of MODIS calibration methodologies, activities, lifetime on-orbit performance and challenging issues for each MODIS, the impact on LIB product quality, and lessons learned for future sensors such as the NPOESS VIIRS.

Xiong, Xiaoxiong↗
NASA NTRS1986

Time-dependent coronal shock acceleration of energetic solar flare particles

A global time-dependent model is presented for the coronal and interplanetary shock acceleration and propagation of energetic solar flare particles. The calculations are carried out to help prove that coronal shock acceleration of solar flare particles is responsible for energetic solar flare event data gathered in interplanetary space. The model is based on the theory of diffusive shock acceleration, and requires particle speeds to be much greater than bulk velocities. Also, sufficient scattering must occur upstream and downstream of the shock for the particle scattering mean free path to be smaller than the characteristic scale lengths, which causes the same particles to encounter the shock repeatedly. A spherically symmetric shock wave is assumed, which leads to the same emission configuration for impulsively and monoenergetically emitted particles. Consideration is given to acceleration by compression at the shock front, adiabatic deceleration in the divergent downstream flow, the temporal evolution of the shock and the three-dimensional geometry of the corona. The model is used to generate normalized proton omnidirectional distributions at 1 AU and at the shock front. The spectral exhibit trends similar to those in observational data, especially proton acceleration times and the proton distribution profiles at 1 AU.

Lee, M. A.↗
NASA NTRS1987

Numerical methods for one-dimensional reaction-diffusion equations arising in combustion theory

A review of numerical methods for one-dimensional reaction-diffusion equations arising in combustion theory is presented. The methods reviewed include explicit, implicit, quasi-linearization, time linearization, operator-splitting, random walk and finite-element techniques and methods of lines. Adaptive and nonadaptive procedures are also reviewed. These techniques are applied first to solve two model problems which have exact traveling wave solutions with which the numerical results can be compared. This comparison is performed in terms of both the wave profile and computed wave speed. It is shown that the computed wave speed is not a good indicator of the accuracy of a particular method. A fourth-order time-linearized, Hermitian compact operator technique is found to be the most accurate method for a variety of time and space sizes.

Ramos, J. I.↗
NASA NTRS1993

Comment on 'Comparison of observed and calculated implanted ion distributions outside Comet Halley's bow shock' by T. I. Gombosi, M. Neugebauer, A. D. Johnstone, A. J. Coates, and D. E. Huddleston

It is argued that the formulation used by Gombosi (1991) does not distinguish between two fundamental types of resonant interactions (those between cometary pickup ions and LF electromagnetic waves). Two problems arise from using their overly simplified expressions. The wave polarization of the solar wind Alfven wave is not purely right-handed, and values from alpha sub com and alpha sub sw are not well known, nor are the 'polarizations' of the 'backward'-going waves in either case. Gombosi et al. discuss the antisunward vs the sunward propagating solar wind Alfven wave, and assume a reasonable value of 0.2 for alpha sub sw. However, alpha sub com is totally unknown. It is concluded that a more correct analysis of wave polarization can lead to significant changes in the formulation and results from Gombosi et al. In his reply Gombosi argues that his simplified wave-particle interaction model is consistent with Giotto observations and plasma kinetic simulations and it leads to a reasonable approximation of the implanted ion transport coefficients. The more complicated approach suggested by Tsurutani & Thorne (1993) requires the introduction of several ad hoc parameters and it does not lead to any change of the energy diffusion coefficient.

Tsurutani, Bruce T.↗
NASA NTRS1995

A ROSAT observation of the supernova remnant Kes 79

Kes 79 was observed with the ROSAT Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI). Some X-ray emission comes from a faint outer region, well correlated with the outer shell. Most emission is from a bright diffuse inner region where there are also bright radio filaments. The X-ray spectrum is fitted with a thermal model with temperature 1.3 keV. Variations in spectra from different regions arew small. There is no X-ray evidence for an internal neutron star. Remnant characteristics are derived using a simple blast-wave model. The observed X-ray absorption is less than expected. It is possible that the remnant is closer than the published distance of 10 kpc.

Seward, F. D.↗
NASA NTRS1998

Coupling Processes between Atmospheric Chemistry and Climate

This is the fourth semi-annual report for NAS5-97039, covering the time period July through December 1998. The overall objective of this project is to improve the understanding of coupling processes between atmospheric chemistry and climate. Model predictions of the future distributions of trace gases in the atmosphere constitute an important component of the input necessary for quantitative assessments of global change. We will concentrate on the changes in ozone and stratospheric sulfate aerosol, with emphasis on how ozone in the lower stratosphere would respond to natural or anthropogenic changes. The key modeling tools for this work are the Atmospheric and Environmental Research (AER) two-dimensional chemistry-transport model, the AER two-dimensional stratospheric sulfate model, and the AER three-wave interactive model with full chemistry. For this six month period, we report on a modeling study of new rate constant which modify the NOx/NOy ratio in the lower stratosphere; sensitivity to changes in stratospheric water vapor in the future atmosphere; a study of N2O and CH4 observations which has allowed us to adjust diffusion in the 2-D CTM in order to obtain appropriate polar vortex isolation; a study of SF6 and age of air with comparisons of models and measurements; and a report on the Models and Measurements II effort.

Ko, Malcolm K. W.↗
NASA NTRS2017

Metallized Nanotube Polymer Composite (MNPC) and Methods for Making Same

A novel method to develop highly conductive functional materials which can effectively shield various electromagnetic effects (EMEs) and harmful radiations. Metallized nanotube polymer composites (MNPC) are composed of a lightweight polymer matrix, superstrong nanotubes (NT), and functional nanoparticle inclusions. MNPC is prepared by supercritical fluid infusion of various metal precursors (Au, Pt, Fe, and Ni salts), incorporated simultaneously or sequentially, into a solid NT-polymer composite followed by thermal reduction. The infused metal precursor tends to diffuse toward the nanotube surface preferentially as well as the surfaces of the NT-polymer matrix, and is reduced to form nanometer-scale metal particles or metal coatings. The conductivity of the MNPC increases with the metallization, which provides better shielding capabilities against various EMEs and radiations by reflecting and absorbing EM waves more efficiently. Furthermore, the supercritical fluid infusion process aids to improve the toughness of the composite films significantly regardless of the existence of metal.

Park, Cheol↗
NASA NTRS2021

The First Widespread Solar Energetic Particle Event Observed By Solar Orbiter on 2020 November 29

Context. On 2020 November 29, the first widespread solar energetic particle (SEP) event of solar cycle 25 was observed at four widely separated locations in the inner (. 1AU) heliosphere. Relativistic electrons as well as protons with energies > 50MeV were observed by Solar Orbiter (SolO), Parker Solar Probe (PSP), the Solar Terrestrial Relations Observatory (STEREO)-A and multiple near-Earth spacecraft. The SEP event was associated with an M4.4 class X-ray flare and accompanied by a coronal mass ejection (CME) and an extreme ultraviolet (EUV) wave as well as a type II radio burst and multiple type III radio bursts. Aims. We present multi-spacecraft particle observations and place them in context with source observations from remote sensing instruments and discuss how such observations may further our understanding of particle acceleration and transport in this widespread event. Methods. Velocity dispersion analysis (VDA) and time shift analysis (TSA) were used to infer the particle release times at the Sun. Solar wind plasma and magnetic field measurements were examined to identify structures that influence the properties of the energetic particles such as their intensity. Pitch angle distributions and first-order anisotropies were analyzed in order to characterize the particle propagation in the interplanetary medium. Results. We find that during the 2020 November 29 SEP event, particles spread over more than 230° in longitude close to 1AU. The particle onset delays observed at the different spacecraft are larger as the flare–footpoint angle increases and are consistent with those from previous STEREO observations. Comparing the timing when the EUV wave intersects the estimated magnetic footpoints of each spacecraft with particle release times from TSA and VDA, we conclude that a simple scenario where the particle release is only determined by the EUV wave propagation is unlikely for this event. Observations of anisotropic particle distributions at SolO, Wind, and STEREO-A do not rule out that particles are injected over a wide longitudinal range close to the Sun. However, the low values of the first-order anisotropy observed by near-Earth spacecraft suggest that diffusive propagation processes are likely involved.

A Kollhoff↗
NASA NTRS2018

MODIS Solar Diffuser Degradation Determination and Its Spectral Dependency

This study presents a modeling approach to improve solar diffuser (SD) degradation determination from SD stability monitor (SDSM) measurements. The MODIS instrument uses a SDto calibrate its reflective solar bands (RSBs) on-orbit. Due to the imperfectly designed SDSM sun view screen, the SD reflectance tracked by SDSM has large noise. The SDSM measurements noise is spectrally coherent and can be minimized by normalizing measurements to the least degradeddetector 9 (936 nm). In this study, a SD degradation model is used to determine the SDdegradation's wavelength dependency and the detector 9 degradation is estimated by the model solution.The results show the SD degradations measured at 6 SDSM detectors (554 _ 936 nm) have stable relationships, where the degradation is inversely proportion to 1/wavelength^4. The model estimated SD degradation at SDSM detector 9 wavelength (936 nm) is ~0.9% from 2002 to 2018.Based on the SD degradation model solution, the SD degradation at short/mid wave bands are estimated to improve short/mid wave bands calibration. The model can also be used to improve interpolating SD degradation at SDSM detectors to RSB wavelengths. Compared to linear interpolation, bands 9 and 10 show the largest differences of up to 0.3 and 0.4% respectively. These differences directly impact the calibration coefficients of these bands.

radiometric calibration↗
NASA NTRS1999

Noise and Bandwidth Measurements of Diffusion-Cooled Nb Hot-Electron Bolometer Mixers at Frequencies Above the Superconductive Energy Gap

Diffusion-cooled Nb hot-electron bolometer (HEB) mixers have the potential to simultaneously achieve high intermediate frequency (IF) bandwidths and low mixer noise temperatures for operation at THz frequencies (above the superconductive gap energy). We have measured the IF signal bandwidth at 630 GHz of Nb devices with lengths L = 0.3, 0.2, and 0.1 micrometer in a quasioptical mixer configuration employing twin-slot antennas. The 3-dB EF bandwidth increased from 1.2 GHz for the 0.3 gm long device to 9.2 GHz for the 0.1 gm long device. These results demonstrate the expected 1/L squared dependence of the IF bandwidth at submillimeter wave frequencies for the first time, as well as the largest EF bandwidth obtained to date. For the 0.1 gm device, which had the largest bandwidth, the double sideband (DSB) noise temperature of the receiver was 320-470 K at 630 GHz with an absorbed LO power of 35 nW, estimated using the isothermal method. A version of this mixer with the antenna length scaled for operation at 2.5 THz has also been tested. A DSB receiver noise temperature of 1800 plus or minus 100 K was achieved, which is about 1,000 K lower than our previously reported results. These results demonstrate that large EF bandwidth and low-noise operation of a diffusion-cooled HEB mixer is possible at THz frequencies with the same device geometry.

Wyss, R. A.↗
NASA NTRS1987

Ti:LiNbO3 components for a fiber gyroscope

It is maintained that integrated optics will play a major role in the next generation of fiber gyros since the potential exists for mass producing low-cost integrated gyro front-end circuits. Ti:LiNbO3 wave guide technology has been used to demonstrate all the necessary components. The combined use of the 3dB splitter and polarizer functions in a 3 x 3 directional coupler is considered. Such a device was designed for operation at lambda = 1.3 microns and fabricated with 6.5-micron Ti strip widths, and a 1050 C/6 hr diffusion.

Minford, W. J.↗
NASA NTRS1988

Development of a 39.5 GHz Karp traveling wave tube for use in space

A millimeter-wave TWT was developed using a dispersive, high-impedance forward wave interaction structure based on a ladder, with non-space-harmonic interaction, for a tube with high gain per inch and high efficiency. The 'Tunneladder' interaction structure combines ladder properties modified to accommodate Pierce gun beam optics on a radially magnetized PM focusing structure. The development involved the fabrication of chemically milled, shaped ladders diffusion brazed to each ridge of a double ridged waveguide. Cold-test data are presented, representing the omega-Beta and impedance characteristics of the modified ladder circuit These results were used in small and large-signal computer programs to predict TWT gain and efficiency. A laboratory model tube was designed and fabricated, including all major subassemblies.

Jacquez, A.↗
NASA NTRS1988

A millimeter-wave tunneladder TWT

A millimeter-wave traveling wave tube (TWT) was developed using a dispersive, high-impedance forward wave interaction structure based on a ladder, with non-space-harmonic interaction, for a tube with high gain per inch and high efficiency. The 'TunneLadder' interaction structure combines ladder properties modified to accommodate Pierce gun beam optics in a radially magnetized PM focusing structure. The development involved the fabrication of chemically milled, shaped ladders diffusion brazed to diamond cubes which are in turn active diffusion brazed to each ridge of a doubly ridged waveguide. Cold-test data, representing the (omega)(beta) and and impedance characteristics of the modified ladder circuit, were used in small and large-signal computer programs to predict TWT gain and efficiency. The structural design emphasizes ruggedness and reliability. Actual data from tested tubes verify the predicted performance while providing broader bandwidth than expected.

Wilson, D.↗
NASA NTRS2011

MODIS On-Orbit Performance and Lessons Learned

MODIS is a key instrument for the NASA's Earth Observing System (EOS) and has successfully operated for more than 11 and 9 years, respectively, on-board the Terra and Aqua spacecraft. MODIS collects data in 36 spectral bands, covering wavelengths from visible (VIS) to long-wave infrared (LWIR). To date, both Terra and Aqua MODIS have produced an unprecedented amount of data products and significantly contributed to the earth remote sensing studies and applications. MODIS was developed with stringent calibration requirements and was, consequently, designed and built with a set of on-board calibrators (OBC), which include a solar diffuser (SD), a solar diffuser stability monitor (SDSM), a blackbody (BB), and a spectroradiometric calibration assembly (SRCA). This presentation briefly reviews MODIS instrument operation and various calibration and characterization activities, It demonstrates both the instrument and the OBC on-orbit performance and discusses lessons learned, particularly focusing on on-orbit changes in sensor responses, optics degradation, and major challenging issues. As expected, Terra and Aqua MODIS on-orbit performance and lessons learned will continue to benefit the operation and calibration of future sensors, such as NPP/JPSS VIIRS and GOES-R ABI.

Xiong, Xiaoxiong↗
NASA NTRS1969

Lidar

Lidar is an optical radar technique employing laser energy. Variations in signal intensity as a function of range provide information on atmospheric constituents, even when these are too tenuous to be normally visible. The theoretical and technical basis of the technique is described and typical values of the atmospheric optical parameters given. The significance of these parameters to atmospheric and meteorological problems is discussed. While the basic technique can provide valuable information about clouds and other material in the atmosphere, it is not possible to determine particle size and number concentrations precisely. There are also inherent difficulties in evaluating lidar observations. Nevertheless, lidar can provide much useful information as is shown by illustrations. These include lidar observations of: cirrus cloud, showing mountain wave motions; stratification in clear air due to the thermal profile near the ground; determinations of low cloud and visibility along an air-field approach path; and finally the motion and internal structure of clouds of tracer materials (insecticide spray and explosion-caused dust) which demonstrate the use of lidar for studying transport and diffusion processes.

Collis, R. T. H.↗
NASA NTRS1978

Whistler mode noise in Jupiter's inner magnetosphere

A study is made of the amplitude and spectral extent of whistler mode noise in the inner magnetosphere of Jupiter. It is found that the 'hat-shaped' pitch angle distributions of energetic electrons (21 and 31 MeV at L=3) are consistent with those predicted in the presence of a band-limited spectrum of whistler mode noise. The equatorial maximum linear growth rate of parallel propagating whistlers are consistent with those necessary to limit the energetic electron intensities by the whistler mode instability. It is noted that the wave phase speeds before wave reflection can occur at high latitudes and that wave growth is limited to a disk-like region centered around the magnetic equator. The frequency extent of the whistler mode noise spectrum may be estimated by the range of frequencies maximally unstable to equatorial linear growth. A value is found for the spectral density of the broadband whistler mode noise necessary to balance radial diffusion of energetic electrons above the critical range, and an expression is derived for the energetic electron system response to fluctuations about the limiting flux value.

Sentman, D. D.↗
NASA NTRS1986

Scene simulation for passive IR systems

The development of large mosaic detector arrays will allow for the construction of staring long wave infrared (LWIR) sensors which can observe large fields of view instantaneously and continuously. In order to evaluate and exercise these new systems, it will be necessary to provide simulated scenes of many moving targets against an infrared clutter background. Researchers are currently developing a projector/screen system. This system is comprised of a mechanical scanner, a diffuse screen, and a miniature blackbody. A prototype of the mechanical scanner, which is comprised of four independently driven scanners, has been designed, fabricated, and evaluated under room and cryogenic vacuum conditions. A large diffuse screen has been constructed and tested for structural integrity under cryogenic/vacuum thermal cycling. Construction techniques have been developed for the fabrication of miniature high-temperature blackbody sources. Finally, a concept has been developed to use this miniature blackbody to produce a spectrally tailorable source.

Holt, J. D.↗
NASA NTRS1990

Review of acousto-ultrasonic NDE for composites

Acousto-ultrasonics utilizes simulated stress waves to detect and quantify defect states, damage conditions, and variations of mechanical properties in fiber reinforced composites. The term acousto-ultrasonics denotes a combination of aspects of acoustic emission methodology with ultrasonic materials characterization. The acousto-ultrasonic approach was developed to deal primarily with evaluation of the integrated effect of minor flaws and diffuse flaw populations of subcritical flaws in composite and bonded structures. These factors singly and collectively also influence acousto-ultrasonic measurements that, in turn, correlate with dynamic response and mechanical property variations. Since it was first introduced, the acousto-ultrasonic approach was successfully applied to a variety of materials, including polymeric, metallic, and ceramic matrix composites; adhesively bonded materials; paper and wood products; cable and rope; and also human bone. Examples of applications and limitations of the approach are reviewed. Basic methods and guidelines are discussed. The underlying hypothesis and theory development needs are indicated.

Vary, Alex↗