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At least 163 records · Page 9

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NASA NTRS1994

Study of cosmic-ray H and He isotopes at 23 AU

We have measured the spectra of H and He isotopes during the 1987 solar minimum with the cosmic-ray detector system (CRS) on the Voyager 2 spacecraft. By carrying out the measurement near solar minimum and at large heliospheric distances, the effects of solar modulations were reduced. In particular, the adiabatic energy losses were smaller, and these results from 23 AU over the solar minimum period of cycle 21 represent observations at energies not accessible from previous measurements near 1 AU. The modulated spectra with the diffusion coefficient constant k(sub 0) = 3.15 x 10(exp 22) sq cm/s (which corresponds to a solar modulation parameter of 360 MV at 23 AU and 500 MV at 1 AU) agree well with both our data at 23 AU and the previous solar minimum measurements at 1 AU. The measured H-1 and H-2 spectra are both consistent with the calculated spectra, using standard Galactic and heliospheric propagation models without invoking an anomalous hydrogen component. With the fixed modulation parameter of 360 MV, the mean pathlengths, source spectra, and cross sections were varied to study the effects of different input parameters on the spectra and relative abundances. At this stage of our work, we have not found any strong evidence from the low-energy H-2 and He-3 data that H-1 and He-4 should have a different propagation history, or different types of source spectra from the heavier cosmic-ray nuclei.

Seo, E. S.↗

NASA NTRS2003

Simple gain probability functions for large reflector antennas of JPL/NASA

Simple models for the patterns as well as their cumulative gain probability and probability density functions of the Deep Space Network antennas are developed. These are needed for the study and evaluation of interference from unwanted sources such as the emerging terrestrial system, High Density Fixed Service, with the Ka-band receiving antenna systems in Goldstone Station of the Deep Space Network.

large reflector antenna probability density functi↗

NASA NTRS2008

Mass Spectrometer Containing Multiple Fixed Collectors

A miniature mass spectrometer that incorporates features not typically found in prior mass spectrometers is undergoing development. This mass spectrometer is designed to simultaneously measure the relative concentrations of five gases (H2, He, N2, O2, and Ar) in air, over the relative-concentration range from 10(exp -6) to 1, during a sampling time as short as 1 second. It is intended to serve as a prototype of a product line of easy-to-use, portable, lightweight, highspeed, relatively inexpensive instruments for measuring concentrations of multiple chemical species in such diverse applications as detecting explosive or toxic chemicals in air, monitoring and controlling industrial processes, measuring concentrations of deliberately introduced isotopes in medical and biological investigations, and general environmental monitoring. The heart of this mass spectrometer is an integral combination of a circular cycloidal mass analyzer, multiple fixed ion collectors, and two mass-selective ion sources. By circular cycloidal mass analyzer is meant an analyzer that includes (1) two concentric circular cylindrical electrodes for applying a radial electric field and (2) a magnet arranged to impose a magnetic flux aligned predominantly along the cylindrical axis, so that ions, once accelerated into the annulus between the electrodes, move along circular cycloidal trajectories. As in other mass analyzers, trajectory of each ion is determined by its mass-to-charge ratio, and so ions of different species can be collected simultaneously by collectors (Faraday cups) at different locations intersected by the corresponding trajectories (see figure). Unlike in other mass analyzers, the installation of additional collectors to detect additional species does not necessitate increasing the overall size of the analyzer assembly.

Moskala, Robert↗

NASA NTRS2012

Real-Time Distributed Embedded Oscillator Operating Frequency Monitoring

A document discusses the utilization of embedded clocks inside of operating network data links as an auxiliary clock source to satisfy local oscillator monitoring requirements. Modem network interfaces, typically serial network links, often contain embedded clocking information of very tight precision to recover data from the link. This embedded clocking data can be utilized by the receiving device to monitor the local oscillator for tolerance to required specifications, often important in high-integrity fault-tolerant applications. A device can utilize a received embedded clock to determine if the local or the remote device is out of tolerance by using a single link. The local device can determine if it is failing, assuming a single fault model, with two or more active links. Network fabric components, containing many operational links, can potentially determine faulty remote or local devices in the presence of multiple faults. Two methods of implementation are described. In one method, a recovered clock can be directly used to monitor the local clock as a direct replacement of an external local oscillator. This scheme is consistent with a general clock monitoring function whereby clock sources are clocking two counters and compared over a fixed interval of time. In another method, overflow/underflow conditions can be used to detect clock relationships for monitoring. These network interfaces often provide clock compensation circuitry to allow data to be transferred from the received (network) clock domain to the internal clock domain. This circuit could be modified to detect overflow/underflow conditions of the buffering required and report a fast or slow receive clock, respectively.

Pollock, Julie↗

NASA NTRS2021

Starshade Rendezvous: Exoplanet Sensitivity and Observing Strategy

Launching a starshade to rendezvous with the Nancy Grace Roman Space Telescope (Roman) would provide the first opportunity to directly image the habitable zones (HZs) of nearby sunlike stars in the coming decade. A report on the science and feasibility of such a mission was recently submitted to NASA as a probe study concept. The driving objective of the concept is to determine whether Earth-like exoplanets exist in the HZs of the nearest sunlike stars and have biosignature gases in their atmospheres. With the sensitivity provided by this telescope, it is possible to measure the brightness of zodiacal dust disks around the nearest sunlike stars and establish how their population compares with our own. In addition, known gas-giant exoplanets can be targeted to measure their atmospheric metallicity and thereby determine if the correlation with planet mass follows the trend observed in the Solar System and hinted at by exoplanet transit spectroscopy data. We provide the details of the calculations used to estimate the sensitivity of Roman with a starshade and describe the publicly available Python-based source code used to make these calculations. Given the fixed capability of Roman and the constrained observing windows inherent for the starshade, we calculate the sensitivity of the combined observatory to detect these three types of targets, and we present an overall observing strategy that enables us to achieve these objectives.

Andrew Frederic Romero-wolf↗

NASA NTRS1978

Soft X-ray structure of the Perseus cluster of galaxies

A 0.5-1.5-keV X-ray image of the Perseus cluster of galaxies was obtained with a focusing telescope system aboard a sounding rocket. The source consists of a region of diffuse emission plus a superposed central source in the vicinity of NGC 1275 smaller than 4 arcmin in diameter that accounts for one-quarter of the total intensity within a radius of 25 arcmin. The results for the diffuse source are consistent with the isothermal-hydrostatic picture in which the hot gas has a core radius of 17 arcmin and is approximately symmetric about NGC 1275. Several isothermal-hydrostatic models are considered which relate the size and temperature of the diffuse X-ray source with the core radius of the galaxies and their velocity dispersion. Fixing the velocity dispersion at values measured by Chincarini and Rood (1971) requires the core radius of the galaxies to be 28 + or - 9 arcmin, which is larger than present measurements. Conversely, fixing the core radius of the galaxies at 8 arcmin requires a smaller velocity dispersion or a condition in which the velocity distribution is anisotropic. Upper limits on the intrinsic X-ray absorption of the central source place the bulk of its X-ray emission beyond the nuclear region of NGC 1275.

Gorenstein, P.↗

NASA NTRS2016

Discovery and Modelling of a Flattening of the Positive Cyclotron Line/luminosity Relation in GX 304-1 with RXTE

The Rossi X-ray Timing Explorer (RXTE) observed four outbursts of the accreting Xray binary transient source, GX 304−1 in 2010 and 2011. We present results of detailed 3-100 keV spectral analysis of 69 separate observations, and report a positive correlation between cyclotron line parameters, as well as other spectral parameters, with power-law flux. The cyclotron line energy, width and depth versus flux, and thus luminosity, correlations show a flattening of the relationships with increasing luminosity, which are well described by quasi-spherical or disc accretion that yield the surface magnetic field to be ∼5 × 1012 Gauss. Since HEXTE (High Energy X-ray Timing Experiment) cluster A was fixed aligned with the Proportional Counter Array field of view and cluster B was fixed viewing a background region 1. ◦ 5 off of the source direction during these observations near the end of the RXTE mission, the cluster A background was estimated from cluster B events using HEXTEBACKEST. This made possible the detection of the ∼55 keV cyclotron line and an accurate measurement of the continuum. Correlations of all spectral parameters with the primary 2-10 keV power-law flux reveal it to be the primary driver of the spectral shape. The accretion is found to be in the collisionless shock braking regime.

Rothschild, Richard E.↗

NASA NTRS1980

On source radiation

The power output from given sources is usually ascertained via an energy flux integral over the normal directions to a remote (far field) surface; an alternative procedure, which utilizes an integral that specifies the direct rate of working by the source on the resultant field, is described and illustrated for both point and continuous source distribution. A comparison between the respective procedures is made in the analysis of sound radiated from a periodic dipole source whose axis performs a periodic plane angular movement about a fixed direction. Thus, adopting a conventional approach, Sretenskii (1956) characterizes the rotating dipole in terms of an infinite number of stationary ones along a pari of orthogonal directions in the plane, and through the far field representation of the latter, arrives at a series development for the instantaneous radiated power, whereas the local manner of power calculation dispenses with the equivalent infinite aggregate of sources and yields a compact analytical result.

Levine, H.↗

NASA NTRS1993

Cryogenic Fluid Film Bearing Tester Development Study

Conceptual designs were developed for the determination of rotordynamic coefficients of cryogenic fluid film bearings. The designs encompassed the use of magnetic and conventional excitation sources as well as the use of magnetic bearings as support bearings. Test article configurations reviewed included overhung, floating housing, and fixed housing. Uncertainty and forced response analyses were performed to assess quality of data and suitability of each for testing a variety of fluid film bearing designs. Development cost and schedule estimates were developed for each design. Facility requirements were reviewed and compared with existing MSFC capability. The recommended configuration consisted of a fixed test article housing centrally located between two magnetic bearings. The magnetic bearings would also serve as the excitation source.

Scharrer, Joseph K.↗

NASA NTRS1975

Random coding strategies for minimum entropy

This paper proves that there exists a fixed random coding strategy for block coding a memoryless information source to achieve the absolute epsilon entropy of the source. That is, the strategy can be chosen independent of the block length. The principal new tool is an easy result on the semicontinuity of the relative entropy functional of one probability distribution with respect to another. The theorem generalizes a result from rate-distortion theory to the 'zero-infinity' case.

Posner, E. C.↗

NASA NTRS1975

Process description

The production of hydrogen from coal by hydrogasification and subsequent steam hydrocarbon reforming was studied. Process heat and power requirements are supplied by an HTGR. The process is examined as a function of a maximum reforming (process) temperature of 922 K (1200 F) to 1367 K (2000 F). The major parameters for the five cases selected are summarized in a table. A fixed thermal capacity of 3000 MW for the HTGR heat source was used as a basis. The resulting hydrogen production rates and the corresponding hydrogen purity are also given in a table.

Source record↗

NASA NTRS1980

Mechanism associated with the Space Shuttle main engine oxidizer valve/duct system anomalous high amplitude discrete acoustical excitation

Anomalous high frequency pressure fluctuations in the Space Shuttle main engine have been experienced during hot firings. Through diagnostic analysis of hot firing engine data, it was determined that this excitation originated at the main oxidizer valve. The intensity of these fluctuations was such that the main oxidizer valve was partially consumed in fire, experienced fretting, and had seal damage. Delineated in this paper are the associated dynamical phenomena and the methodologies leading toward understanding the excitation mechanism. The results presented demonstrate that the source of the anomalous frequencies was suppressed by a simple fix and all main oxidizer valve damage was terminated.

Schutzenhofer, L. A.↗

NASA NTRS1991

In situ measurements of light extinction of stratospheric aerosols

The extinction coefficient of ambient aerosol particles was measured using a multiple transverse cell (White Cell) with an effective path length of 100 m. Measurements were performed at seven fixed wavelengths in the visible region using a white light source and an interference filter set with 2 nm bandwidth and center wavelengths of 405.5, 450, 500, 550, 600, 650, and 692.5 nm. The total air flow in the system was 16.7 1/min; the volume of the chamber is close to 10 liters. It takes about one minute to fill the chamber with particles homogeneously, but it needs up to five minutes to get the chamber particle-free. Before measuring the aerosol, the transmission of the particle-free air is determined; then the aerosol passes through the chamber for a period of ten minutes; after this the transmission of particle-free ambient air is measured again for eight minutes. All times are subject to change. At present the measurements are done with a frequency of 1 Hz, but an increase of up to 30 Hz is possible. The lower detection limit of the used White Cell is 3.4 by 10(exp -06) per m. This is sufficient for measuring the extinction coefficient during most tropospheric and some stratospheric conditions. It will be necessary to increase the sensitivity by a factor of ten when measurements under the clearest stratospheric conditions take place.

Metzig, Gunthard↗

NASA NTRS1994

Personal cooling systems: Possibilities and limitations

Personal thermal control by means of gas- or liquid-conditioned garments was developed during the 1960s and has been applied in a variety of aerospace and industrial settings. Both USAF fighter pilots and astronauts are required to wear heavy protective clothing which insulates them from the environment and thus creates stress through storage of metabolic heat. The problem is particularly severe in astronauts who perform heavy physical work during extra-vehicular activity (EVA); without artificial cooling they could reach incapacitating hyperthermia in a matter of minutes. This paper reviews the factors which influence the design of personal cooling systems. An important early step is determination of acceptable heat stress level, taking into account possible interactions of heat stress with other physiological problems such as motion sickness, diminished plasma volume, decompression sickness and acceleration tolerance. Other factors which require consideration include the work schedule, the area to be covered by the cooling garment, and the practicalities of a fixed or body-mounted heat sink and its power source. Nearly every imaginable heat sink has been proposed or tried over the past 30 years, including direct gas systems, phase-change systems with open or closed loops and thermoelectric heat sinks. The latter are now the system of choice for aircraft.

Nunneley, Sarah A.↗

NASA NTRS2011

Fast Plasma Investigation for MMS: Simulation of the Burst Triggering System

The Magnetospheric Multiscale (MMS) mission will study small-scale reconnection structures and their rapid motions from closely spaced platforms using instruments capable of high angular, energy, and time resolution measurements. To meet these requirements, the Fast Plasma Instrument (FPI) consists of eight (8) identical half top-hat electron sensors and eight (8) identical ion sensors and an Instrument Data Processing Unit (IDPU). The sensors (electron or ion) are grouped into pairs whose 6 degree x 180 degree fields-of-view (FOV) are set 90 degrees apart. Each sensor is equipped with electrostatic aperture steering to allow the sensor to scan a 45 degree x 180 degree fan about the its nominal viewing (0 deflection) direction. Each pair of sensors, known as the Dual Electron Spectrometer (DES) and the Dual Ion Spectrometer (DIS), occupies a quadrant on the MMS spacecraft and the combination of the eight electron/ion sensors, employing aperture steering, image the full-sky every 30-ms (electrons) and 150-ms (ions), respectively. To probe the diffusion regions of reconnection, the highest temporal/spatial resolution mode of FPI results in the DES complement of a given spacecraft generating 6.5-Mb (raised dot) per second of electron data while the DIS generates 1.1-Mb (raised dot) per second of ion data yielding an FPI total data rate of 6.6-Mb (raised dot) per second. The FPI electron/ion data is collected by the IDPU then transmitted to the Central Data Instrument Processor (CIDP) on the spacecraft for science interest ranking. Only data sequences that contain the greatest amount of temporal/spatial structure will be intelligently down-linked by the spacecraft. This requires a data ranking process known as the burst trigger system. The burst trigger system uses pseudo physical quantities to approximate the local plasma environments. As each pseudo quantity will have a different value, a set of two scaling factors is employed for each pseudo term. These pseudo quantities are then combined at the instrument, spacecraft, and observatory level leading to a final ranking of data based on expected scientific interest. Here, we present simulations of the fixed point burst trigger system for the FPI. A variety of data sets based on previous mission data as well as analytical formulations are tested. Comparisons of floating point calculations versus the fixed point hardware simulation are shown. Analysis of the potential sources of error from overflows, quantization, etc. are examined and mitigation methods are presented. Finally a series of calibration curves are presented, showing the expected error in pseudo quantities based solely on the scale parameters chosen and the expected data range. We conclude with a presentation of the current base-lined FPI burst trigger approach.

Barrie, A. C.↗

NASA NTRS2013

The GLAS Science Algorithm Software (GSAS) Detailed Design Document Version 6

The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document describes the detailed design of GLAS Science Algorithm Software (GSAS). The GSAS is used to create the ICESat GLAS standard data products. The National Snow and Ice Data Center (NSDIC) distribute these products. The document contains descriptions, flow charts, data flow diagrams, and structure charts for each major component of the GSAS. The purpose of this document is to present the detailed design of the GSAS. It is intended as a reference source to assist the maintenance programmer in making changes that fix or enhance the documented software.

Lee, Jeffrey E.↗

NASA NTRS2022

The impacts of immersion ice nucleation parameterizations on Arctic mixed-phase stratiform cloud properties and the Arctic radiation budget in GEOS-5

The influence of four different immersion freezing parameterizations on Arctic clouds and the top-of-the atmosphere (TOA) and surface radiation fluxes is investigated in the fifth version of the National Aeronautics and Space Administration (NASA) Goddard Earth Observing System (GEOS-5) with sea surface temperature, sea ice fraction and aerosol emissions held fixed. The different parameterizations were derived from a variety of sources, including classical nucleation theory, field and laboratory measurements. Despite the large spread in the ice-nucleating particle (INP) concentrations in the parameterizations, the cloud properties and radiative fluxes had a tendency to form two groups, with the lower INP concentration category producing larger water path and low-level cloud fraction during winter and early spring, whereas the opposite occurred during the summer season. The stability of the lower troposphere was found to strongly correlate with low-cloud fraction, and along with the effect of ice nucleation, ice sedimentation and melting rates, appears to explain the spring-to-summer reversal pattern in the relative magnitude of the cloud properties between the two categories of simulations. The strong modulation effect of the liquid phase on immersion freezing led to the successful simulation of the characteristic Arctic cloud structure, with a layer rich in supercooled water near cloud top and ice and snow at lower levels. Comparison with satellite retrievals and in situ data suggest that simulations with low INP concentrations more realistically represent Arctic clouds and radiation.

Arctic↗

NASA NTRS2014

Aviation Trends Related to Atmospheric Environment Safety Technologies Project Technical Challenges

Current and future aviation safety trends related to the National Aeronautics and Space Administration's Atmospheric Environment Safety Technologies Project's three technical challenges (engine icing characterization and simulation capability; airframe icing simulation and engineering tool capability; and atmospheric hazard sensing and mitigation technology capability) were assessed by examining the National Transportation Safety Board (NTSB) accident database (1989 to 2008), incidents from the Federal Aviation Administration (FAA) accident/incident database (1989 to 2006), and literature from various industry and government sources. The accident and incident data were examined for events involving fixed-wing airplanes operating under Federal Aviation Regulation (FAR) Parts 121, 135, and 91 for atmospheric conditions related to airframe icing, ice-crystal engine icing, turbulence, clear air turbulence, wake vortex, lightning, and low visibility (fog, low ceiling, clouds, precipitation, and low lighting). Five future aviation safety risk areas associated with the three AEST technical challenges were identified after an exhaustive survey of a variety of sources and include: approach and landing accident reduction, icing/ice detection, loss of control in flight, super density operations, and runway safety.

Reveley, Mary S.↗