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At least 973 records · Page 54
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NASA NTRS2008

BRDF of Salt Pan Regolith Samples

Laboratory Bi-directional Reflectance Distribution Function (BRDF) measurements of salt pan regolith samples are presented in this study in an effort to understand the role of spatial and spectral variability of the natural biome. The samples were obtained from Etosha Pan, Namibia (19.20 deg S, 15.93 deg E, alt. 1100 m). It is shown how the BRDF depends on the measurement geometry - incident and scatter angles and on the sample particle sizes. As a demonstration of the application of the results, airborne BRDF measurements acquires with NASA's Cloud Absorption Radiometer (CAR) over the same general site where the regolith samples were collected are compared with the laboratory results. Good agreement between laboratory measured and field measured BRDF is reported.

Georgiev, Georgi T.↗
NASA NTRS2008

NASA Ares I Launch Vehicle Roll and Reaction Control Systems Overview

NASA's Ares I launch vehicle, consisting of a five segment solid rocket booster first stage and a liquid bi-propellant J-2X engine upper stage, is the vehicle that's been chosen to return humans to the moon, mars, and beyond. This paper provides an overview of the work that has taken place on the Ares I launch vehicle roll and reaction control systems. Reaction control systems are found on many launch vehicles and provide a vehicle with a three degree of freedom stabilization during the mission. The Ares I baseline configuration currently consists of a first stage roll control system that will provide the vehicle with a method of counteracting the roll torque that is expected during launch. An upper stage reaction control system will allow the upper stage three degrees of freedom control as needed. Design assessments and trade studies are being conducted on the roll and reaction control systems including: propellant selection, thruster arrangement, pressurization system configuration, and system component trades. Other vehicle considerations and issues include thruster plume impingement, thruster module aerothermal and aerodynamic effects, and system integration. This paper concludes by summarizing the process of down selecting to the current baseline configuration for the Ares I roll and reaction control systems.

Popp, Chris↗
NASA NTRS2008

Performance Increase Verification for a Bipropellant Rocket Engine

Component performance assessment testing for a, pressure-fed earth storable bipropellant rocket engine was successfully completed at Aerojet's Redmond test facility. The primary goal of the this development project is to increase the specific impulse of an apogee class bi-propellant engine to greater than 330 seconds with nitrogen tetroxide and monomethylhydrazine propellants and greater than 335 seconds with nitrogen tetroxide and hydrazine. The secondary goal of the project is to take greater advantage of the high temperature capabilities of iridium/rhenium chambers. In order to achieve these goals, the propellant feed pressures were increased to 400 psia, nominal, which in turn increased the chamber pressure and temperature, allowing for higher c*. The tests article used a 24-on-24 unlike doublet injector design coupled with a copper heat sink chamber to simulate a flight configuration combustion chamber. The injector is designed to produce a nominal 200 lbf of thrust with a specific impulse of 335 seconds (using hydrazine fuel). Effect of Chamber length on engine C* performance was evaluated with the use of modular, bolt-together test hardware and removable chamber inserts. Multiple short duration firings were performed to characterize injector performance across a range of thrust levels, 180 to 220 lbf, and mixture ratios, from 1.1 to 1.3. During firing, ignition transient, chamber pressure, and various temperatures were measured in order to evaluate the performance of the engine and characterize the thermal conditions. The tests successfully demonstrated the stable operation and performance potential of a full scale engine with a measured c* of XXXX ft/sec (XXXX m/s) under nominal operational conditions.

Alexander, Leslie↗
NASA NTRS2008

Improved Determination of Surface and Atmospheric Temperatures Using Only Shortwave AIRS Channels

The Goddard DAAC has been analyzing AIRS/AMSU sounding data using the AIRS Science Team Version 5 retrieval algorithm. The AIRS Version 5 retrieval algorithm produces significantly better temperature profiles under more difficult cloud conditions than does the AIRS Version 4 algorithm, because, following theoretical considerations, it employs 15 micron CO2 tropospheric sounding channels only for the purpose of generating cloud cleared radiances for all AIRS channels, and determines temperature profiles using only 4.2 micron AIRS observations. This approach works equally well during both daytime and night time conditions. The AIRS Version 6 retrieval algorithm takes this approach one step further, and now also determines surface skin temperatures over both land and ocean, using only shortwave AIRS window channel cloud cleared radiances. Shortwave surface spectral emissivity and spectral bi-directional reflectance are solved for simultaneously along with the surface skin temperature. Longwave surface spectral emissivity is determined in a subsequent step using only AIRS longwave window channels, using the previously determined surface skin temperature. The methodology to do this will be described, and results will be presented demonstrating significant improvement in retrieved surface skin temperatures and surface spectral emissivities compared to those obtained using Version 5, both day and night.

Susskind, Joel↗
NASA NTRS2008

Reconfigurable L-Band Radar

The reconfigurable L-Band radar is an ongoing development at NASA/GSFC that exploits the capability inherently in phased array radar systems with a state-of-the-art data acquisition and real-time processor in order to enable multi-mode measurement techniques in a single radar architecture. The development leverages on the L-Band Imaging Scatterometer, a radar system designed for the development and testing of new radar techniques; and the custom-built DBSAR processor, a highly reconfigurable, high speed data acquisition and processing system. The radar modes currently implemented include scatterometer, synthetic aperture radar, and altimetry; and plans to add new modes such as radiometry and bi-static GNSS signals are being formulated. This development is aimed at enhancing the radar remote sensing capabilities for airborne and spaceborne applications in support of Earth Science and planetary exploration This paper describes the design of the radar and processor systems, explains the operational modes, and discusses preliminary measurements and future plans.

Rincon, Rafael F.↗
NASA NTRS2008

MODIS Solar Diffuser On-orbit Performance

MODIS is a key instrument for the NASA Earth Observing System (EOS), currently operated on both the Terra and Aqua missions. Each MODIS instrument has 20 reflective solar bands (RSBs) and 16 thermal emissive bands (TEBs). MODIS RSB on-orbit calibration is reflectance based using an on-board solar diffuser (SD). The SD bi-directional reflectance factors (BRFs) were characterized pre-launch using reference diffuser samples, which are traceable to NIST reflectance standards. The SD BRF on-orbit degradation (or change) is tracked by another onboard device, called the solar diffuser stability monitor (SDSM). The SDSM is operated during each scheduled SD calibration event, making alternate observations of direct sunlight and the diffusely reflected sunlight from the SD. The time series of the ratios of SDSM's SD view to its Sun view provide SD degradation information. This paper presents and compares the Terra and Aqua MODIS SD on-orbit performance. Results show that the SD on-orbit degradation depends on the amount of solar exposure of the SD plate. In addition, it is strongly wavelengthdependent, with a larger degradation rate at shorter wavelengths. For Terra MODIS, an SD door anomaly occurred in May 2003 that led to a decision to fix the door permanently at an "open" position. Since then, the SD degradation rate has significantly increased due to more frequent solar exposure. As expected, the SD on-orbit performance directly impacts the RSB calibration performance. The lessons learned from MODIS on-orbit calibration will provide useful insights into the development and operation of future SD calibration systems.

Xiong, Xiaoxiong↗
NASA NTRS2006

Using Thermoelectric Converters for Loop Heat Pipe Operating Temperature Control

This paper describes an experimental study to investigate the effectiveness of using thermoelectric converters (TECs) to control the loop heat pipe (LHP) operating temperature. Tests were conducted on an LHP having two evaporators and two condensers. Each evaporator has its own integral compensation chamber (CC). One side of the TEC is attached to the CC, and the other side is connected to the evaporator through a copper thermal strap. A bi-polar power supply is used to provide the power for the operation of each TEC. The bipolar supply will automatic change the direction of the current to the TEC depending on whether the CC requires heating or cooling in order to maintain its temperature at the desired set point. When cooling the CC, the heat pumped by the TEC plus the power needed to operate the TEC is dissipated to the evaporator, and is ultimately transmitted to the condenser. When heating the CC, the TEC can draw heat from the evaporator to supplement the required control heater power. Test results showed that the TEC could control the LHP operating temperature within h1K of the set point temperature. The control heater power required for TEC operation was also much less than that of using electrical heaters.

Ku, Jentung↗
NASA NTRS2007

CMEs and Low Density Events in the Solar Wind

From time to time the density of the Solar Wind falls below unity for a day or so. Despite studies of these events, their cause has not been established. In the solar wind there are frequent rarefactions but these are much shallower than the ones we are discussing here. In particular any role that CMEs might play in forming more extreme rarefactions is not clear . We discuss 9 cases of extreme events, leading to sub-alfvenic flow and well observed by Wind, which occurred between 1999 and 2002, and look for corresponding CME events in the LASCO cotalog. The catalog gives a fitted speed , good out to 20 Rs ,as well as a speed lower down in the corona, and this is used to distinguish between a CME and an ICME. We find one of the events ,which was simulated by Usmanov et al.,cannot be associated with an ICME. The other eight events can plausibly be associated with fast ICMEs, identified by the prescence of bi-streaming electrons also seen by Wind SWE, and by other phenomena The implications of these observations are discussed but do not seem to be conclusive as to the cause of the extreme rarefactions.

Ogilvie, K. W.↗
NASA NTRS2008

Civil Service Workforce Market Supply and the Effect on Cost Estimating Relationship (CERS) that May Effect the Productivity Factors for Future NASA Missions

The upcoming retirement of the Baby Boomers will leave a workforce age gap between the younger generation (the future NASA decision makers) and the gray beards. This paper will reflect on the average age of the workforce across NASA Centers, the Aerospace Industry and other Government Agencies, like DoD. This paper will dig into Productivity and Realization Factors and how they get applied to bi-monthly (payroll) data for true full-time equivalent (FTE) calculations that could be used at each of the NASA Centers and other business systems that are on the forefront in being implemented. This paper offers some comparative costs analysis/solutions, from simple FTE cost-estimating relationships (CERs) versus CERs for monthly time-phasing activities for small research projects that start and get completed within a government fiscal year. This paper will present the results of a parametric study investigating the cost-effectiveness of alternative performance-based CERs and how they get applied into the Center's forward pricing rate proposals (FPRP). True CERs based on the relationship of a younger aged workforce will have some effects on labor rates used in both commercial cost models and other internal home-grown cost models which may impact the productivity factors for future NASA missions.

Sterk, Steve↗
NASA NTRS2007

Characterization of MODIS Solar Diffuser On-orbit Degradation

MODIS reflective solar bands (RSB) are calibrated on-orbit by a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). The SD bi-directional reflectance factor (BRF) was characterized pre-launch by the instrument vendor using reference samples traceable to NIST reflectance standards. Its on-orbit degradation is regularly monitored by the SDSM. It consists of a solar integration sphere (SIS) with 9 filtered detectors with wavelengths ranging from 0.41 to 0.94 micrometer, a rotating mirror assembly, and an electronics module. During each SD/SDSM calibration, the SDSM views the sunlight directly and the sunlight diffusely reflected from the SD panel. The time series of SDSM measurements (ratio of the SD view response to the Sun view response) is used to compute the SD BRF degradation at each SDSM detector wavelength. Since launch Terra MODIS has operated for more than seven years and Aqua for nearly five years. The SD panel on each MODIS instrument has experienced noticeable degradation with the largest changes observed in the VIS spectral region. Following a brief description of the MODIS RSB calibration methodology and SD/SDSM operational activities, this paper illustrates the SD on-orbit degradation results for both Terra and Aqua MODIS. It discusses the impacts on the SD RF degradation due to sensor operational conditions and SD solar exposure time. For Aqua MODIS, operated under the same conditions, the SD annual degradation rate is approximately 2.9% at 0.41 micrometers, 1.6% at 0.47 micrometers, and less than 1.1% at wavelengths above 0.53 micrometers. For Terra MODIS, however, an SD door (SDD) related anomaly in May 2003 had led to a decision to keep the SDD permanently at its open position. Since then its SD has experienced a much faster SD degradation rate.

Xiong, X.↗
NASA NTRS2007

The Impacts of Bowtie Effect and View Angle Discontinuity on MODIS Swath Data Gridding

We have analyzed two effects of the MODIS viewing geometry on the quality of gridded imagery. First, the fact that the MODIS scans a swath of the Earth 10 km wide at nadir, causes abrupt change of the view azimuth angle at the boundary of adjacent scans. This discontinuity appears as striping of the image clearly visible in certain cases with viewing geometry close to principle plane over the snow of the glint area of water. The striping is a true surface Bi-directional Reflectance Factor (BRF) effect and should be preserved during gridding. Second, due to bowtie effect, the observations in adjacent scans overlap each other. Commonly used method of calculating grid cell value by averaging all overlapping observations may result in smearing of the image. This paper describes a refined gridding algorithm that takes the above two effects into account. By calculating the grid cell value by averaging the overlapping observations from a single scan, the new algorithm preserves the measured BRF signal and enhances sharpness of the image.

Wang, Yujie↗
NASA NTRS2008

Understanding Black Hole X-ray Binaries: The Case of Cygnus X-1

Black Hole X-ray Binaries are known to display distinct emission states that differ in their X-ray spectra, their X-ray timing properties (on times scales less than 1 s) and their radio emission. In recent years monitoring observations, specially with NASA's Rossi X-ray Timing Explorer (RXTE), have provided us with detailed empirical modeling of the phenomenology of the different states as well as a unification scheme of the long term evolution of black holes, transient and persistent, in terms of these states. Observations of the persistent High Mass X-ray Binary (HMXB) Cygnus X-l have been at the forefront of learning about black hole states since its optical identification through a state transition in 1973. In this talk I will present in depth studies of several different aspects of the accretion process in this system. The main data base for these studies is an ongoing RXTE and Ryle radio telescope bi-weekly monitoring campaign that started in 1997. I will discuss high-resolution timing results, especially power spectra, which first gave rise to the Lorentzian description now widely used for black hole and neutron star binaries, and time lags, which we found to be especially well suited to identify state transitions. The evolution of spectral, timing, and radio parameters over years will be shown, including the rms-flux relation and the observation of a clearly correlated radio/x-ray flare. We also observed Cygnus X-1 with INTEGRAL, which allowed us to extend timing and spectral studies to higher energies, with XMM, which provided strong constraints on the parameters of the 6.4 keV iron fluorescence line, and with Chandra, which provided the most in depth study to date of the stellar wind in this system. Models based on the physical conditions in the accretion region are still mainly concentrated on the one or other of the observational areas but they are expanding: as an example I will review results from a jet model for the quantitative description of the radio through X-ray spectra. I will conclude with an outlook on a truly multi-instrument observing campaign of Cygnus X-1 that was performed in 2008 April in order to better constrain the jet models mentioned above (and provide a unique data set for cross-calibration).

Pottschmidt, Katja↗
NASA NTRS2008

Dielectric Elastomer Actuated Systems and Methods

The system of the present invention includes an actuator having at least two electrodes, an elastomeric dielectric film disposed between the two electrodes, and a frame attached to the elastomeric dielectric film. The frame provides a linear actuation force characteristic over a displacement range. The displacement range is preferably the stroke of the actuator. The displacement range can be about 5 mm and greater. Further, the frame can include a plurality of configurations, for example, at least a rigid members coupled to a flexible member wherein the frame provides an elastic restoring force. In preferred embodiments, the rigid member can be, but is not limited to, curved beams, parallel beams, rods and plates. In a preferred embodiment the actuator can further include a passive element disposed between two flexible members such as, for example, links to tune a stiffness characteristic of the actuator. The passive element can be a bi-stable element. Further, the actuator can include a plurality of layers of the elastomeric dielectric film integrated into the frame. The elastomeric film can be made of different materials such as, for example, acrylic, silicone and latex.

Dubowsky, Steven↗
NASA NTRS2008

NASA Tech Briefs, July 2008

Topics covered include: Torque Sensor Based on Tunnel-Diode Oscillator; Shaft-Angle Sensor Based on Tunnel-Diode Oscillator; Ground Facility for Vicarious Calibration of Skyborne Sensors; Optical Pressure-Temperature Sensor for a Combustion Chamber; Impact-Locator Sensor Panels; Low-Loss Waveguides for Terahertz Frequencies; MEMS/ECD Method for Making Bi(2-x)Sb(x)Te3 Thermoelectric Devices; Low-Temperature Supercapacitors; Making a Back-Illuminated Imager with Back-Side Contact and Alignment Markers; Compact, Single-Stage MMIC InP HEMT Amplifier; Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors; Improved Sand-Compaction Method for Lost-Foam Metal Casting; Improved Probe for Evaluating Compaction of Mold Sand; Polymer-Based Composite Catholytes for Li Thin-Film Cells; Using ALD To Bond CNTs to Substrates and Matrices; Alternating-Composition Layered Ceramic Barrier Coatings; Variable-Structure Control of a Model Glider Airplane; Axial Halbach Magnetic Bearings; Compact, Non-Pneumatic Rock-Powder Samplers; Biochips Containing Arrays of Carbon-Nanotube Electrodes; Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors; Neon as a Buffer Gas for a Mercury-Ion Clock; Miniature Incandescent Lamps as Fiber-Optic Light Sources; Bidirectional Pressure-Regulator System; and Prism Window for Optical Alignment. Single-Grid-Pair Fourier Telescope for Imaging in Hard-X Rays and gamma Rays Range-Gated Metrology with Compact Optical Head Lossless, Multi-Spectral Data Compressor for Improved Compression for Pushbroom-Typetruments.

Source record↗
NASA NTRS2009

Regenerative Performance of the NASA Symmetrical Solid Oxide Fuel Cell Design

The NASA Glenn Research Center is developing both a novel cell design (BSC) and a novel ceramic fabrication technique to produce fuel cells predicted to exceed a specific power density of 1.0 kW/kg. The NASA Glenn cell design has taken a completely different approach among planar designs by removing the metal interconnect and returning to the use of a thin, doped LaCrO3 interconnect. The cell is structurally symmetrical. Both electrodes support the thin electrolyte and contain micro-channels for gas flow-- a geometry referred to as a bi-electrode supported cell or BSC. The cell characteristics have been demonstrated under both SOFC and SOE conditions. Electrolysis tests verify that this cell design operates at very high electrochemical voltage efficiencies (EVE) and high H2O conversion percentages, even at the low flow rates predicted for closed loop systems encountered in unmanned aerial vehicle (UAV) applications. For UAVs the volume, weight and the efficiency are critical as they determine the size of the water tank, the solar panel size, and other system requirements. For UAVs, regenerative solid oxide fuel cell stacks (RSOFC) use solar panels during daylight to generate power for electrolysis and then operate in fuel cell mode during the night to power the UAV and electronics. Recent studies, performed by NASA for a more electric commercial aircraft, evaluated SOFCs for auxiliary power units (APUs). System studies were also conducted for regenerative RSOFC systems. One common requirement for aerospace SOFCs and RSOFCs, determined independently in each application study, was the need for high specific power density and volume density, on the order of 1.0 kW/kg and greater than 1.0 kW/L. Until recently the best reported performance for SOFCs was 0.2 kW/kg or less for stacks. NASA Glenn is working to prototype the light weight, low volume BSC design for such high specific power aerospace applications.

Cable, Thomas L.↗
NASA NTRS2008

Microstructure Evolution in Cut Metal Chips of Ti-6Al-4V

The microstructural evolution following metal cutting was investigated within metal chips of Ti-6Al-4V. Metal cutting was used to impose a high strain rate on the order of approx.10(exp 5)/s within the primary shear zone as the metal was removed from the workpiece. The initial microstructure of the parent material (PM) was composed of a bi-modal microstructure with coarse prior beta grains and equiaxed primary alpha located at the boundaries. After metal cutting, the microstructure of the metal chips showed coarsening of the equiaxed primary alpha grains and beta lamellar. These metallographic findings suggest that the metal chips experienced high temperatures which remained below the beta transus temperature.

Dong, L.↗
NASA NTRS2009

Cytogenetic Response to Ionizing Radiation Exposure in Human Fibroblasts with Suppressed Expression of Non-DSB Repair Genes

Changes of gene expression profile are one of the most important biological responses in living cells after ionizing radiation (IR) exposure. Although some studies have shown that genes up-regulated by IR may play important roles in DNA damage repair, the relationship between the regulation of gene expression by IR, particularly genes not known for their roles in double-strand break (DSB) repair, and its impact on cytogenetic responses has not been well studied. The purpose of this study is to identify new roles of IR inducible genes in radiation-induced chromosome aberrations and micronuclei formation. In the study, the expression of 25 genes selected on the basis of their transcriptional changes in response to IR was individually knocked down by small interfering RNA in human fibroblast cells. Frequencies of micronuclei (MN) formation and chromosome aberrations were measured to determine the efficiency of cytogenetic repair, and the fraction of bi-nucleated cells in the MN analysis was used as a marker for cell cycle progression. In response to gamma radiation, the formation of MN was significantly increased by suppressed expression of five genes: Ku70 (DSB repair pathway), XPA (nucleotide excision repair pathway), RPA1 (mismatch repair pathway), RAD17 and RBBP8 (cell cycle control). Knocked-down expression of four genes (MRE11A, RAD51 in the DSB pathway, SESN1, and SUMO1) significantly inhibited cell cycle progression, possibly because of severe impairment of DNA damage repair. Moreover, decreased XPA, p21, or MLH1 expression resulted in both significantly enhanced cell cycle progression and increased yields of chromosome aberrations, indicating that these gene products modulate both cell cycle control and DNA damage repair. Nine of these eleven genes, whose knock-down expression affected cytogenetic repair, were up-regulated in cells exposed to gamma radiation, suggesting that genes transcriptionally modulated by IR were critical to regulate IR-induced biological consequences. Furthermore, eight non-DBS repair genes showed involvement in regulating DSB repair, indicating that successful DSB repair requires both DSB repair mechanisms and non-DSB repair systems.

Zhang, Ye↗
NASA NTRS2009

Microstructural Evolution of Ti-6Al-4V during High Strain Rate Conditions of Metal Cutting

The microstructural evolution following metal cutting was investigated within the metal chips of Ti-6Al-4V. Metal cutting was used to impose a high strain rate on the order of approx.10(exp 5)/s within the primary shear zone as the metal was removed from the workpiece. The initial microstructure of the parent material (PM) was composed of a bi-modal microstructure with coarse prior grains and equiaxed primary located at the boundaries. After metal cutting, the microstructure of the metal chips showed coarsening of the equiaxed primary grains and lamellar. These metallographic findings suggest that the metal chips experienced high temperatures which remained below the transus temperature.

Dong, Lei↗