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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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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Blade Displacement Measurements of a Rotor in Forward Flight in the Langley 14-by 22-Foot Wind Tunnel

Stereo photogrammetry was used to measure the elastic bending and twist of a three-bladed rotor in forward flight in the NASA Langley 14-by 22-Ft Subsonic Wind Tunnel. The rotor was imaged from below by two cameras mounted at windows of a large turntable in the floor of the test section. At each test condition, the turntable and cameras were rotated and the cameras were triggered to allow measurements over a range of blade azimuth angles. Retro-reflective targets were applied along the leading and trailing edges of the lower surface of each blade. Image blur due to blade motion was minimized by illuminating the targets with high-intensity LED flash lamps mounted next to each camera. The cameras were re-calibrated at each angular position of the turntable using the positions in each image of retro-reflective targets on the ceiling of the test section whose spatial coordinates had been very accurately measured. The blade displacement measurements yielded elastic bending and twist along each blade as functions of blade azimuth, thrust coefficient, and advance ratio, all at a constant rotor shaft angle. In addition, the measurements produced estimates of the rigid-body blade pitch, flap, and lag angles.

rotor↗
NASA NTRS1989

A useful approximation for the flat surface impulse response

The flat surface impulse response (FSIR) is a very useful quantity in computing the mean return power for near-nadir-oriented short-pulse radar altimeters. However, for very small antenna beamwidths and relatively large pointing angles, previous analytical descriptions become very difficult to compute accurately. An asymptotic approximation is developed to overcome these computational problems. Since accuracy is of key importance, a condition is developed under which this solution is within 2 percent of the exact answer. The asymptotic solution is shown to be in functional agreement with a conventional clutter power result and gives a 1.25-dB correction to this formula to account properly for the antenna-pattern variation over the illuminated area.

Brown, Gary S.↗
NASA NTRS1994

Carbon recombination lines as a diagnostic of photodissociation regions

We have observed the C91 alpha radio recombination line toward the Orion H II region. This narrow (approximately 3-5 km per sec full width at half maximum (FWHM)) line is spatially very extended (approximately 8 arcmin or 1 pc). These charateristics compare well with the observed characteristics of the C II fine structure line at 158 microns. Thus, the C91 alpha line originates in the predominantly neutral photodissociation regions separating the H II region from the molecular cloud. We have developed theoretical models for the C II radio recombination lines from photodissociation regions. The results show that the I(C91 alpha)/I(C158) intensity ratio is a sensitive function of the temperature and density of the emitting gas. We have also extended theoretical models for photodissociation regions to include the C II recombination lines. Comparison with these models show that, in the central portion of the Orion region, the C91 alpha line originates in dense (10(exp 6) per cu cm), warm (500-1000 K) gas. Even at large projected distances (approximately 1 pc), the inferred density is still high (10(exp 5) per cu cm) and implies extremely high thermal pressures. As in the case of the (C II) 158 microns line, the large extent of the C91 alpha line shows that (FUV) photons can penetrate to large distances from the illuminating source. The decline of the intensity of the incident radiation field with distance from Theta(sup 1) C seems to be dominated by geometrical dilution, rather than dust extinction. Finally, we have used our models to calculate the intensity of the 9850 A recombination line of C II. The physical conditions inferred from this line are in good agreement with those determined from the radio recombination and the far-infrared fine-structure lines. We show that the ratio of the 9850 A to the C91 alpha lines is a very good probe of very high density clumps.

Natta, A.↗
NASA NTRS2005

Managing radiation degradation of CCDs on the Chandra X-ray Observatory II

The CCDs on the Chandra X-ray Observatory are vulnerable to radiation damage from low-energy protons scattered off the telescope's mirrors onto the focal plane. Following unexpected damage incurred early in the mission, the Chandra Team developed, implemented, and maintains a radiation-protection program. This program - involving scheduled radiation safing during radiation-belt passes, intervention based upon real-time space-weather conditions and radiation-environment modeling, and on-board radiation monitoring with autonomous radiation safing - has successfully managed the radiation damage to the CCDs. Since implementing the program, the charge-transfer inefficiency (CTI) has increased at an average annual rate of only 2.9x10^-6 (2.3%) for the front- illuminated CCDs and 0.95x10^-6 (6.5%) for the back-illuminated CCDs. This paper describes the current status of Chandra radiation-management program.

O'Dell, Stephen L.↗
NASA NTRS1973

Photoelectrons and solar wind/lunar limb interaction.

It is suggested that boundary conditions for solar wind/lunar limb interactions are active. The 'whole-moon' limb does not evoke a shock cone, because warm (approximately equal 13 eV/electron) solar wind electrons are replaced by cool (less than or equal to 2 eV/electron) photoelectrons that are ejected from the generally smooth areas of the lunar terminator illuminated at glazing angles by the sun. A localized volume of low thermal pressure is created in the solar wind by these cool photoelectrons. The solar wind expands into this turbulence-suppressive volume without shock production. Conversely, directly illuminated highland areas exchange hot photoelectrons (greater than 20 eV/electron) for warm solar wind electrons. The hot electrons generate a localized pressure increase in the adjacent solar wind flow which evokes a shock streamer in the solar wind. Shock streamers are identifiable by a coincident increase in the magnitude of the solar wind magnetic field immediately external to the lunar wake. Shock occurrence is controlled by lunar topography, solar activity in the hard ultraviolet (greater than 20 eV), solar wind electron density and thermal velocity, and the intensity of the solar wind magnetic field.

Criswell, D. R.↗
NASA NTRS1990

Vega balloon meteorological measurements

The Vega balloons obtained in situ measurements of pressure, temperature, vertical winds, cloud density, ambient illumination, and the frequency of lightning during their flights in the Venus middle cloud layer. The Vega measurements were used to develop a comprehensive description of the meteorology of the Venus middle cloud layer. The Vega measurements provide the following picture: large horizontal temperature gradients near the equator, vigorous convection, and weather conditions that can change dramatically on time scales as short as one hour.

Crisp, D.↗
NASA NTRSDate not supplied

Spectral Characterization of Modern Spacecraft Materials

One of the observational parameters of interest in ground-based optical measurements is ascertaining material properties using broadband filter photometry and spectroscopy for orbiting targets. Broadband photometry can provide reflectance measurements that can aid in color-color indices and assess if objects can be classified into families or taxonomies. However, these reflectance properties can vary due to aspect angle, phase angle, and general degradation of the target’s exterior material. Spectral characterization can aid in material characterization utilizing known absorption bands and spectra signatures, but these signatures are affected by the same conditions described for remote observations. When utilizing ground-based measurements, it is well understood that material characterization is subject to variability due to space weathering and/or other external events (i.e., collision or explosion). The focus of this study is on space weathering effects on spacecraft materials in low Earth orbit. To better assess how materials are affected by the harsh space environment, specifically modern materials, a collection of materials was analyzed in both its pristine condition and after electron bombardment. This sample collection is part of an upcoming mission with the Materials International Space Station Experiment Flight Facility (MISSE-FF) that will be launched in 2022. These laboratory analyses on the samples will provide a ground truth to compare with the in-situ collected data. The data will also be stored in the NASA Johnson Space Center’s Spacecraft Materials Spectral Database that is available to U. S. citizens and maintained by the Orbital Debris Program Office. The following paper provides an overview of the materials investigated, laboratory and database overview, and spectral results for both pristine and post-electron exposed conditions. The spectral signature data highlights which materials are stable, or remain relatively unchanged, and which materials vary significantly due to exposure and material configuration (variations due to rotation of the sample on a flat surface). Initial results on changes in spectral directional reflectance of the materials as a function of incident illumination direction are also presented. This data also will benefit the space situational awareness community with spectral characterization of novel materials that can support their respective optical measurements focused on material identification.

Heather M Cowardin↗
NASA NTRSDate not supplied

Spectral Characterization of Modern Spacecraft Materials

One of the observational parameters of interest in ground-based optical measurements is ascertaining material properties using broadband filter photometry and spectroscopy for orbiting targets. Broadband photometry can provide reflectance measurements that can aid in producing color-color indices and assess if objects can be classified into families or taxonomies. However, these reflectance properties can vary due to aspect angle, phase angle, and general degradation of the target’s exterior material. Spectral characterization can aid in material characterization utilizing known absorption bands and spectral signatures, but these signatures are affected by the same conditions described for remote observations.When utilizing ground-based measurements, it is well understood that material characterization is subject to variability due to space weathering and/or other external events (i.e., collision or explosion). The focus of this study is on space weathering effects on spacecraft materials in low Earth orbit. To better assess how materials are affected by the harsh space environment, specifically modern materials, a collection of materials were analyzed in both their pristine condition and after electron bombardment. This sample collection is part of an upcoming mission with the Materials International Space Station Experiment Flight Facility (MISSE-FF) that will be launched in 2022. These laboratory analyses on the samples will provide a ground-truth to compare with the insitu collected data. The data will also be stored in the NASA Johnson Space Center’s Spacecraft Materials Spectral Database that is available to U.S. citizens and maintained by the Orbital Debris Program Office. The following paper provides an overview of the materials investigated, laboratory, and database overview, and spectral results for both pristine and post-electron exposed conditions. The spectral signature data highlights which materials are stable, or remain relatively unchanged, and which materials vary significantly due to exposure and material configuration (variations due to rotation of the sample on a flat surface).Initial results on changes in spectral directional reflectance of the materials as a function of incident illumination direction are also presented.This data also will benefit the space situational awareness community with spectral characterization of novel materials that can support their respective optical measurements focused on material identification.

Heather M. Cowardin↗
NASA NTRS1993

A model for the selective amplification of spatially coherent waves in a centrifugal compressor on the verge of rotating stall

A simple model for the stability zones of a low speed centrifugal compressor is developed, with the goal of understanding the driving mechanism for the changes in stalling behavior predicted for, and observed in, the Purdue Low Speed Centrifugal Research Compressor Facility. To this end, earlier analyses of rotating stall suppression in centrifugal compressors are presented in a reduced form that preserves the essential parameters of the model that affect the stalling behavior of the compressor. The model is then used to illuminate the relationship between compressor geometry, expected mode shape, and regions of amplification for weak waves which are indicative of the susceptibility of the system to rotating stall. The results demonstrate that increasing the stagger angle of the diffuser vanes, and consequently the diffusion path length, results in the compressor moving towards a condition where higher-order spatial modes are excited during stall initiation. Similarly, flow acceleration in the diffuser section caused by an increase in the number of diffuser vanes also results in the excitation of higher modes.

Lawless, Patrick B.↗
NASA NTRS2008

Orbital Express Advanced Video Guidance Sensor

In May 2007 the first US fully autonomous rendezvous and capture was successfully performed by DARPA's Orbital Express (OE) mission. Since then, the Boeing ASTRO spacecraft and the Ball Aerospace NEXTSat have performed multiple rendezvous and docking maneuvers to demonstrate the technologies needed for satellite servicing. MSFC's Advanced Video Guidance Sensor (AVGS) is a primary near-field proximity operations sensor integrated into ASTRO's Autonomous Rendezvous and Capture Sensor System (ARCSS), which provides relative state knowledge to the ASTRO GN&C system. This paper provides an overview of the AVGS sensor flying on Orbital Express, and a summary of the ground testing and on-orbit performance of the AVGS for OE. The AVGS is a laser-based system that is capable of providing range and bearing at midrange distances and full six degree-of-freedom (6DOF) knowledge at near fields. The sensor fires lasers at two different frequencies to illuminate the Long Range Targets (LRTs) and the Short Range Targets (SRTs) on NEXTSat. Subtraction of one image from the other image removes extraneous light sources and reflections from anything other than the corner cubes on the LRTs and SRTs. This feature has played a significant role for Orbital Express in poor lighting conditions. The very bright spots that remain in the subtracted image are processed by the target recognition algorithms and the inverse-perspective algorithms, to provide 3DOF or 6DOF relative state information. Although Orbital Express has configured the ASTRO ARCSS system to only use AVGS at ranges of 120 m or less, some OE scenarios have provided opportunities for AVGS to acquire and track NEXTSat at greater distances. Orbital Express scenarios to date that have utilized AVGS include a berthing operation performed by the ASTRO robotic arm, sensor checkout maneuvers performed by the ASTRO robotic arm, 10-m unmated operations, 30-m unmated operations, and Scenario 3-1 anomaly recovery. The AVGS performed very well during the pre-unmated operations, effectively tracking beyond its 10-degree Pitch and Yaw limit-specifications, and did not require I-LOAD adjustments before unmated operations. AVGS provided excellent performance in the 10-m unmated operations, effectively tracking and maintaining lock for the duration of this scenario, and showing good agreement between the short and long range targets. During the 30-m unmated operations, the AVGS continuously tracked the SRT to 31.6 m, exceeding expectations, and continuously tracked the LRT from 8.8 m out to 31.6 m, with good agreement between these two target solutions. After this scenario was aborted at a 10-m separation during remate operations, the AVGS tracked the LRT out 54.3 m, until the relative attitude between the vehicles was too large. The vehicles remained apart for eight days, at ranges from 1 km to 6 km. During the approach to remate in this recovery operation, the AVGS began tracking the LRT at 150 m, well beyond the OE planned limits for AVGS ranges, and functioned as the primary sensor for the autonomous rendezvous and docking.

Howard, Ricky↗
NASA NTRS1975

Instruction manual, Optical Effects Module, Model OEM

The Optical Effects Module Model OEM-1, a laboratory prototype instrument designed for the automated measurement of radiation transmission and scattering through optical samples, is described. The system comprises two main components: the Optical Effects Module Enclosure (OEME) and the Optical Effects Module Electronic Controller and Processor (OEMCP). The OEM is designed for operation in the near UV at approximately 2540A, corresponding to the most intense spectral line activated by the mercury discharge lamp used for illumination. The radiation from this source is detected in transmission and reflection through a number of selectable samples. The basic objective of this operation is to monitor in real time the accretion of possible contamination on the surface of these samples. The optical samples are exposed outside of the OEME proper to define exposure conditions and to separate exposure and measurement environments. Changes in the transmissivity of the sample are attributable to surface contamination or to bulk effects due to radiation. Surface contamination will increase radiation scattering due to Rayleigh-Gans effect or to other phenomena, depending on the characteristics size of the particulate contaminants. Thus, also scattering from the samples becomes a part of the measurement program.

Source record↗
NASA NTRS1980

Efficient ionisation of calcium, strontium and barium by resonant laser pumping

Efficient ionization has been observed when an atomic vapor of strontium, barium or calcium was illuminated with a long pulse tunable laser at the frequency of the atomic resonance line. The variation in the degree of ionization with neutral density and laser intensity has been measured using the 'hook' method. The maximum ionization observed was 94%. Excited state populations were measured yielding an excitation temperature (depending on exact experimental conditions) in the region of 0.4 eV. The decay of ion density after the laser pulse was monitored and the recombination coefficients determined. The results are interpreted in terms of an electron heating model.

Skinner, C. H.↗
NASA NTRS1992

Radar-anomalous, high-altitude features on Venus

Over nearly all of the surface of Venus the reflectivity and emissivity at centimeter wavelengths are about 0.15 and 0.85 respectively. These values are consistent with moderately dense soils and rock populations, but the mean reflectivity is about a factor of 2 greater than that for the Moon and other terrestrial planets. Pettingill and Ford, using Pioneer Venus reflectivities and emissivities, found a number of anomalous features on Venus that showed much higher reflectivities and much lower emissivities with both values approaching 0.5. These include Maxwell Montes, a number of high regions in Aphrodite Terra and Beta Regio, and several isolated mountain peaks. Most of the features are at altitudes above the mean radius by 2 to 3 km or more. However, such features have been found in the Magellan data at low altitudes and the anomalies do not exist on all high structures, Maat Mons being the most outstanding example. A number of papers have been written that attempt to explain the phenomena in terms of the geochemistry balance of weathering effects on likely surface minerals. The geochemists have shown that the fundamentally basaltic surface would be stable at the temperatures and pressures of the mean radius in the form of magnetite, but would evolve to pyrite and/or pyrrhotite in the presence of sulfur-bearing compounds such as SO2. Pyrite will be stable at altitudes above 4 or 5 km on Venus. Although the geochemical arguments are rather compelling, it is vitally important to rationally look at other explanations for radar and radio emission measurements such as that presented by Tryka and Muhleman. The radar reflectivity values are retrieved from the raw Magellan backscatter measurements by fitting the Hagfors' radar scattering model in which a surface roughness parameters and a normal incidence electrical reflectivity are estimated. The assumptions of the theory behind the model must be considered carefully before the results can be believed. These include that the surface roughness exists only at horizontal scales large compared to the wavelength, the vertical deviations are gaussianly distributed, there is no shadowing, and that the reflection occurs at the interface of two homogeneous dielectric half-spaces. Probably all these conditions are violated at the anomalous features under discussion. The most important of these is the homogeneity of the near surface of Venus, particularly in highlands. Under the assumptions of the theory, all of the radio energy is reflected by the impedance jump at the very boundary. However, in heterogeneous soil some fraction of the illuminating energy is propagated into the soil and then scattered back out by impedance discontinuities such as rock, voids, and cracks. In light soils, the latter effect can overwhelm the scattering effects of the true surface and greatly enhance the backscatter power, suggesting a much higher value of an effective dielectric constant that would be estimated from Hagfors' model.

Muhleman, Duane O.↗
NASA NTRS2007

Managing Radiation Degradation of CCDs on the Chandra X-Ray Observatory--III

The CCDs on the Chandra X-ray Observatory are vulnerable to radiation damage from low-energy protons scattered off the telescope's mirrors onto the focal plane. Following unexpected damage incurred early in the mission, the Chandra team developed, implemented, and maintains a radiation-protection program. This program--involving scheduled radiation safing during radiation-belt passes, intervention based upon real-time space-weather conditions and radiation-environment modeling, and on-board radiation monitoring with autonomous radiation safing--has successfully managed the radiation damage to the CCDs. Since implementing the program, the charge-transfer inefficiency (CTI) has increased at an average annual rate of only 3.2x 10(exp -6) (2.3 percent) for the front-illuminated CCDs and 1.0x10(exp -6) (6.7 percent) for the back-illuminated CCDs. This paper describes the current status of the Chandra radiation-management program, emphasizing enhancements implemented since the previous papers.

O'Dell, Stephen L.↗
NASA NTRS2012

Galactic Cosmic Rays: From Earth to Sources

For nearly 100 years we have known that cosmic rays come from outer space, yet proof of their origin, as well as a comprehensive understanding of their acceleration, remains elusive. Direct detection of high energy (up to 10(exp 15)eV), charged nuclei with experiments such as the balloon-born, antarctic Trans-Iron Galactic Element Recorder (TIGER) have provided insight into these mysteries through measurements of cosmic ray abundances. The abundance of these rare elements with respect to certain intrinsic properties suggests that cosmic rays include a component of massive star ejecta. Supernovae and their remnants (SNe & SNRs), often occurring at the end of a massive star's life or in an environment including massive star material, are one of the most likely candidates for sources accelerating galactic comic ray nuclei up to the requisite high energies. The Fermi Gamma-ray Space Telescope Large Area Detector (Fermi LAT) has improved our understanding of such sources by widening the window of observable energies and thus into potential sources' energetic processes. In combination with multiwavelength observations, we are now better able to constrain particle populations (often hadron-dominated at GeV energies) and environmental conditions, such as the magnetic field strength. The SNR CTB 37A is one such source which could contribute to the observed galactic cosmic rays. By assembling populations of SNRs, we will be able to more definitively define their contribution to the observed galactic cosmic rays, as well as better understand SNRs themselves. Such multimessenger studies will thus illuminate the long-standing cosmic ray mysteries, shedding light on potential sources, acceleration mechanisms, and cosmic ray propagation.

Brandt, Theresa J.↗
NASA NTRS2013

Time-Dependent Photoionization of Gaseous Nebulae: The Pure Hydrogen Case

We study the problem of time-dependent photoionization of low density gaseous nebulae subjected to sudden changes in the intensity of ionizing radiation. To this end, we write a computer code that solves the full timedependent energy balance, ionization balance, and radiation transfer equations in a self-consistent fashion for a simplified pure hydrogen case. It is shown that changes in the ionizing radiation yield ionizationthermal fronts that propagate through the cloud, but the propagation times and response times to such fronts vary widely and nonlinearly from the illuminated face of the cloud to the ionization front (IF). IFthermal fronts are often supersonic, and in slabs initially in pressure equilibrium such fronts yield large pressure imbalances that are likely to produce important dynamical effects in the cloud. Further, we studied the case of periodic variations in the ionizing flux. It is found that the physical conditions of the plasma have complex behaviors that differ from any steady-state solution. Moreover, even the time average of ionization and temperature is different from any steady-state case. This time average is characterized by overionization and a broader IF with respect to the steady-state solution for a mean value of the radiation flux. Around the time average of physical conditions there is a large dispersion in instantaneous conditions, particularly across the IF, which increases with the period of radiation flux variations. Moreover, the variations in physical conditions are asynchronous along the slab due to the combination of nonlinear propagation times for thermal frontsIFs and equilibration times.

Seyfert↗
NASA NTRS1971

Goggle device for measuring the visually perceived direction of space

A detailed description is given of a miniature line-target system that is illuminated by a radioactive source, collimated, and provided with suitable scales to indicate its position within the roll and pitch planes. These components are assembled in a lightweight, goggle that can be precisely positioned by means of a biteboard attachment. Uses of the goggle in the measurements of the perceived direction of space under ordinary and extraordinary test conditions are illustrated. Modifications are suggested that can extend its usefulness.

Miller, E. F., II↗
NASA NTRS1974

Observations of artificially produced scintillations using satellite transmissions

The ionospheric modification experiment, utilizing a high-powered transmitter, provides an opportunity to study ionospheric irregularities under relatively known conditions. The irregularities were studied by means of transionospheric signals from the polar-orbiting satellite ESSA 8 transmitting at 137 MHz. These observations show that scintillations occur when the satellite to ground station geometry is such that the ray from the satellite passes through the region in the ionosphere under modification. In general, a cut across the illuminated volume is obtained; thus an active region of about 100 km in diameter is indicated. For the most part, the artificial scintillations appear to be similar to those obtained from naturally occurring irregularities, but a systematic change from 3 to 1 sec in the fluctuation period is usually observed as the satellite traverses from the northern to the southern portions of the active region. The change in period appears to be produced by a systematic change in irregularity scale size from about 4 to about 1 km.

Pope, J. H.↗