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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Interference from the Deep Space Network's 70-m High Power Transmitter in Goldstone, CA to 3G Mobile Users Operating in the Surrounding Area

The International Telecommunications Union (ITU) has allocated 2110-2200 MHz for the third generation (3G) mobile services. Part of the spectrum (2110-2120 MHz) is allocated for space research service and has been used by the DSN for years for sending command uplinks to deep space missions. Due to the extremely high power transmitted, potential interference to 3G users in areas surrounding DSN Goldstone exists. To address this issue, a preliminary analytical study has been performed and computer models have been developed. The goal is to provide theoretical foundation and tools to estimate the strength of interference as a function of distance from the transmitter for various interference mechanisms, (or propagation modes), and then determine the size of the area in which 3G users are susceptible to interference from the 400-kW transmitter in Goldstone. The focus is non-line-of-sight interference, taking into account of terrain shielding, anomalous propagation mechanisms, and technical and operational characteristics of the DSN and the 3G services.

propagation↗
NASA NTRS1982

Mathematical model of the SH-3G helicopter

A mathematical model of the Sikorsky SH-3G helicopter based on classical nonlinear, quasi-steady rotor theory was developed. The model was validated statically and dynamically by comparison with Navy flight-test data. The model incorporates ad hoc revisions which address the ideal assumptions of classical rotor theory and improve the static trim characteristics to provide a more realistic simulation, while retaining the simplicity of the classical model.

Phillips, J. D.↗
NASA NTRS1993

A comparison of VLBI with the ICE-3G glacial rebound model

Crustal motion predicted by the ICE-3G glacial rebound model exhibits a pattern of tangential (horizontal) divergence away from the centers of uplift, which in North America and Europe are located around Hudson Bay and the Gulf of Bothnia. Tangential velocities reach peak magnitudes of 1-2 mm/yr, and must be included when predicting VLBI baseline length change rates due to postglacial rebound. Out of 18 observed VLBI baselines examined three are situated such that their predicted length rates are around their 2 sigma uncertainties or greater. It is encouraging that two of these baselines exhibit predicted length rates within 2 sigma of the observed rates.

James, Thomas S.↗
NASA NTRS2010

SensorWeb 3G: Extending On-Orbit Sensor Capabilities to Enable Near Realtime User Configurability

This research effort prototypes an implementation of a standard interface, Web Coverage Processing Service (WCPS), which is an Open Geospatial Consortium(OGC) standard, to enable users to define, test, upload and execute algorithms for on-orbit sensor systems. The user is able to customize on-orbit data products that result from raw data streaming from an instrument. This extends the SensorWeb 2.0 concept that was developed under a previous Advanced Information System Technology (AIST) effort in which web services wrap sensors and a standardized Extensible Markup Language (XML) based scripting workflow language orchestrates processing steps across multiple domains. SensorWeb 3G extends the concept by providing the user controls into the flight software modules associated with on-orbit sensor and thus provides a degree of flexibility which does not presently exist. The successful demonstrations to date will be presented, which includes a realistic HyspIRI decadal mission testbed. Furthermore, benchmarks that were run will also be presented along with future demonstration and benchmark tests planned. Finally, we conclude with implications for the future and how this concept dovetails into efforts to develop "cloud computing" methods and standards.

Mandl, Daniel↗
NASA NTRS1998

Nonlinear Analysis of the Space Shuttle Superlightweight LO2 Tank: Behavior Under 3g End-of-Flight Loads - Part 2

Results of linear bifurcation and nonlinear analyses of the Space Shuttle super lightweight (SLWT) external liquid-oxygen (LO2) tank are presented for an important end-of-flight loading condition. These results illustrate an important type of response mode for thin-walled shells, that are subjected to combined mechanical and thermal loads, that may be encountered in the design of other liquid-fuel launch vehicles. Linear bifurcation analyses are presented that predict several nearly equal eigenvalues that correspond to local buckling modes in the aft dome of the LO2 tank. In contrast, the nonlinear response phenomenon is shown to consist of a short-wavelength bending deformation in the aft elliptical dome of the LO2 tank that grows in amplitude in a stable manner with increasing load. Imperfection sensitivity analyses are presented that show that the presence of several nearly equal eigenvalues does not lead to a premature general instability mode for the aft dome. For the linear bifurcation and nonlinear analyses, the results show that accurate predictions of the response of the shell generally require a large-scale, high fidelity finite-element model. Results are also presented that show that the SLWT LO2 tank can support loads in excess of approximately 1.9 times the values of the operational loads considered.

Nemeth, Michael P.↗
NASA NTRS2001

D1((2)B2g) to D0((2)Au) Fluorescence from the Matrix-Isolated Perylene Cation Following Laser Excitation into the D5(2)B3g) and D2 ((2)B3g) Electronic States

Fluorescence spectra of the perylene cation, pumped by direct laser excitation via the D(sub 2)((2)B(sub 3g)) (left arrow) D(sub 0)((2)A(sub u)) and D(sub 5)(2)B(sub 3g)) (left arrow) D(sub 0)((2)A(sub u)) transitions, are presented. Direct excitation into the D5 or D2 states is followed by rapid non-radiative relaxation to D1 that, in turn,relaxes radiatively. Excitation spectroscopy across the D(sub 2)((2)B(sub 3g)) (left arrow) D(sub 0)((2)A(sub u)) transition near 730 nm shows that site splitting plays little or no role in determining the spectral substructure in the ion spectra. Tentative assignments for ground state vibrational frequencies are made by comparison of spectral intervals with calculated normal mode frequencies.

Chillier, Xavier D. F.↗
NASA NTRS2013

Re-Greening Sahel: 30 Years of Remote Sensing Data and Field Observations (Mali, Niger)

Desertification of the Sahel region has been debated for decades, while the concept of a "re-greening" Sahel appeared with satellite remote sensing data that allowed vegetation monitoring across wide regions and over increasingly long series of years (nowadays 30 years with the GIMMS-3g dataset). However, the scarcity of long-term field observations of vegetation in the Sahel prevents ground validation and deeper analysis of such trends. After assessing the consistency of the new GIMMS-3g NDVI product by comparison to three other AVHRR-NDVI datasets and MODIS NDVI, regional GIMMS-3g NDVI trends over 1981-2011 are analyzed. Trends are found positive and statistically significant almost everywhere in Sahel over the 1981-2011 period. Long-term field observations of the aboveground herbaceous layer mass have been collected within the Gourma region in Mali (1984-2011) and within the Fakara region in western Niger (1994-2011). These observations sample ecosystem and soil diversity, thus enabling estimation of averaged values representative of the Gourma and Fakara. NDVI measurements are found in good agreement with field observations, both over the Gourma and Fakara regions where re-greening and negative trends are observed respectively. A linear regression analysis performed between spatially averaged seasonal NDVI and a weighted average of field measurements explains 59% of the variability for the Gourma region over 1984-2011, and 38% for the Fakara region over 1994-2011. In the Gourma, which is a pastoral region, the re-greening trend is mainly observed over sandy soils, and attests for the ecosystem's resilience to the 1980s' drought, able to react to the more favorable rainfall of the 1990s and 2000s. However, contrasted changes in the landscape's functioning have occurred locally. An increase in erosion and run-off processes in association with decreasing or stable vegetation cover was observed over shallow soils, which occupy 30% of the area. In the agro-pastoral Fakara, the decreasing trends observed both from satellite NDVI and field assessments of herbaceous mass are hardly explained by rainfall. These results give confidence in the dominant positive trends in Sahelian greenness, but indicate that degradation trends can also be observed, both in situ and from satellite time series.

Sahel↗
NASA NTRS1980

Thermoregulation in rats: Effects of varying duration of hypergravic fields

The effects of hypergravitational fields on the thermoregulatory system of the rat are examined. The question underlying the investigation was whether the response of the rat to the one hour cold exposure depends only upon the amplitude of the hypergravic field during the period of cold exposure or whether the response is also dependent on the amplitude and duration of the hypergravic field prior to cold exposure. One hour of cold exposure applied over the last hour of either a 1, 4, 7, 13, 19, 25, or 37 hr period of 3G evoked a decrease in core temperature (T sub c) of about 3 C. However, when rats were subjected concurrently to cold and acceleration following 8 days at 3G, they exhibited a smaller fall in T sub c, suggesting partial recovery of the acceleration induced impairment of temperature regulation. In another series of experiments, the gravitational field profile was changed in amplitude in 3 different ways. Despite the different gravitational field profiles used prior to cold, the magnitude of the fall in T sub c over the 1 hr period of cold exposure was the same in all cases. These results suggest that the thermoregulatory impairment has a rapid onset, is a manifestation of an ongoing effect of hypergravity, and is not dependent upon the prior G profile.

Horowitz, J. M.↗
NASA NTRS1990

Reach performance while wearing the Space Shuttle launch and entry suit during exposure to launch accelerations

A crew of four veteran astronaut/pilots were subjected to sustained linear accelerations of up to 3G(x) in order to quantify crew reach performance while wearing the currently used Launch and Entry Suit (LES). Photogrammetric techniques were used to quantify magnitudes of reach in any direction while subjects rode a centrifuge. Subjects exhibited small changes of reach capability in the +x (forward) direction which ranged from an improvement of 2.04 cm to a decrease of 14.4 cm while reach performance in the +z (overhead) direction was improved in three of four subjects, indicating that any task which could be accomplished under exposure to 1G(x) could definitely be done at 3G(x). The data from this experiment demonstrated that Shuttle crews in training can expect to maintain all of the overhead reach capability evident in good simulator runs and suffer only moderate degradation in the forward reach performance during the launch phase of an actual Shuttle mission.

Bagian, James P.↗
NASA NTRS1995

Present-day Antarctic ice mass changes and crustal motion

The peak vertical velocities predicted by three realistic, but contrasting, present-day scenarios of Antarctic ice sheet mass balance are found to be of the order of several mm/a. One scenario predicts local uplift rates in excess of 5 mm/a. These rates are small compared to the peak Antarctic vertical velocities of the ICE-3G glacial rebound model, which are in excess of 20 mm/a. If the Holocene Antarctic deglaciation history protrayed in ICE-3G is realistic, and if regional upper mantle viscosity is not an order of magnitude below 10(exp 21) Pa(dot)s, then a vast geographical region in West Antarctica is uplifting at a rate that could be detected by a future Global Positioning System (GPS) campaign. While present-day scenarios predict small vertical crustal velocities, their overall continent-ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion (omega m(arrow dot)) and time-varying zonal gravity field.

James, Thomas S.↗
NASA NTRS1995

Present-day Antarctic Ice Mass Changes and Crustal Motion

The peak vertical velocities predicted by three realistic, but contrasting, present-day scenarios of Antarctic ice sheet mass balance are found to be of the order of several mm/a. One scenario predicts local uplift rates in excess of 5 mm/a. These rates are small compared to the peak Antarctic vertical velocities of the ICE-3G glacial rebound model, which are in excess of 20 mm/a. If the Holocene Antarctic deglaciation history portrayed in ICE-3G is realistic, and if regional upper mantle viscosity is not an order of magnitude below 10(exp 21) pa s, then a vast geographical region in West Antarctica is uplifting at a rate that could be detected by a future Global Positioning System (GPS) campaign. While present-day scenarios predict small vertical crustal velocities, their overall continent-ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion ((Omega)m(bar)) and time-varying zonal gravity field J(sub 1).

James, Thomas S.↗
NASA NTRS2003

Hypergravity-Induced Changes in Hematological and Lymphocyte Function Parameters in a Mouse Model

The purpose of this study was to quantify hypergravity-induced changes in hematological and lymphocyte characteristics. Mice were subjected to 1, 2, and 3G and euthanized on days 1 , 4, 7, 10, and 21. The data show that increased gravitational force resulted in persistent hypothermia. Red blood cell (RBC) counts, hematocrit, and hemoglobin were reduced by day 21, whereas hemoglobin and RBC volume were low at most times of measurement. A transient increase was noted in platelet numbers in the 3G group. Fluctuations in spontaneous blastogenesis of lymphocytes were dependent upon centrifugation time and not gravity. Changes in splenocyte responses to T and B cell mitogens due to gravity were also noted. Cytokine production was primarily affected during the first week; IL-2, IL-4 and TNF-alpha were increased, whereas IFN-gamma was decreased. These findings indicate that altered gravity can influence both hematological and functional variables that may translate into serious health consequences.

Gridley, Daila S.↗
NASA NTRS2017

Chronic Hypergravity Induces Changes in the Dopaminergic Neuronal System in Drosophila Melanogaster

Upon atmospheric exitre-entry and during training, astronauts are subjected to temporary periods of hypergravity, which has been implicated in the activation of oxidative stress pathways contributing to mitochondrial dysfunction and neuronal degeneration. The pathogenesis of Parkinsons disease and other neurodegenerative disorders is associated with oxidative damage to neurons involved in dopamine systems of the brain. Our study aims to examine the effects of a hypergravitational developmental environment on the degeneration of dopaminergic systems in Drosophila melanogaster. Male and female flies (Gal4-UAS transgenic line) were hatched and raised to adulthood in centrifugal hypergravity (97rpm, 3g). The nuclear expression of the reporter, Green Fluorescent Protein (GFP) is driven by the dopaminergic enzyme tyrosine hydroxylase (TH) promoter, allowing for the targeted visualization of dopamine producing neurons. After being raised to adulthood and kept in hypergravity until 18 days of age, flies were dissected and the expression of TH was measured by fluorescence confocal microscopy. TH expression in the fly brains was used to obtain counts of healthy dopaminergic neurons for flies raised in chronic hypergravity and control groups. Dopaminergic neuron expression data were compared with those of previous studies that limited hypergravity exposure to late life in order to determine the flies adaptability to the gravitational environment when raised from hatching through adulthood. Overall, we observed a significant effect of chronic hypergravity exposure contributing to deficits in dopaminergic neuron expression (p 0.003). Flies raised in 3g had on average lower dopaminergic neuron counts (mean 97.7) when compared with flies raised in 1g (mean 122.8). We suspect these lower levels of TH expression are a result of oxidative dopaminergic cell loss in flies raised in hypergravity. In future studies, we hope to further elucidate the mechanism by which hypergravity-induced oxidative stress damages the dopaminergic neuronal system, as well as examining possible chemical countermeasures to the hypergravity-induced oxidative stress response in dopaminergic neurons in order to combat cell death and consequent mental and behavioral deficits.

Parkinson's Disorder↗
NASA NTRS2017

Effects of Chronic Hypergravity on the Dopaminergic Neuronal System in Drosophila Melanogaster

Upon atmospheric exitre-entry and during training, astronauts are subjected to temporary periods of hypergravity, which has been implicated in the activation of oxidative stress pathways contributing to mitochondrial dysfunction and neuronal degeneration. The pathogenesis of Parkinsons disease and other neurodegenerative disorders is associated with oxidative damage to neurons involved in dopamine systems of the brain. Our study aims to examine the effects of a hypergravitational developmental environment on the degeneration of dopaminergic systems in Drosophila melanogaster. Male and female flies (Gal4-UAS transgenic line) were hatched and raised to adulthood in centrifugal hypergravity (97rpm, 3g). The nuclear expression of the reporter, Green Fluorescent Protein (GFP) is driven by the dopaminergic enzyme tyrosine hydroxylase (TH) promoter, allowing for the targeted visualization of dopamine producing neurons. After being raised to adulthood and kept in hypergravity until 18 days of age, flies were dissected and the expression of TH was measured by fluorescence confocal microscopy. TH expression in the fly brains was used to obtain counts of healthy dopaminergic neurons for flies raised in chronic hypergravity and control groups. Dopaminergic neuron expression data were compared with those of previous studies that limited hypergravity exposure to late life in order to determine the flies adaptability to the gravitational environment when raised from hatching through adulthood. Overall, we observed a significant effect of chronic hypergravity exposure contributing to deficits in dopaminergic neuron expression (p 0.003). Flies raised in 3g had on average lower dopaminergic neuron counts (mean 97.7) when compared with flies raised in 1g (mean 122.8). We suspect these lower levels of TH expression are a result of oxidative dopaminergic cell loss in flies raised in hypergravity. In future studies, we hope to further elucidate the mechanism by which hypergravity-induced oxidative stress damages the dopaminergic neuronal system, as well as examining possible chemical countermeasures to the hypergravity-induced oxidative stress response in dopaminergic neurons in order to combat cell death and consequent mental and behavioral deficits.

Pelos, Andrew↗
NASA NTRS2021

Fe xvii 2p–3s Line Ratio Diagnostic of Shock Formation Radius in O Stars

The 2p–3s lines of Fe xvii in the X-ray spectrum of the O-type star ζ Puppis exhibit an anomalous (3G + M2)/(3F) line ratio of ∼1.4, in comparison with ∼2.4 for almost all other collisionally excited astrophysical spectra. Based on the work of Mauche et al., we conjectured that the strong UV field of ζ Puppis produces the observed ratio by depopulation of metastable 3s excited states, and that the ratio can potentially be used as an independent diagnostic of plasma formation radius. We used the Flexible Atomic Code collisional-radiative model to model the effect of UV photoexcitation from O stars on the Fe xvii lines. We compared our model calculations to archival spectra of coronal and hot stars from the Chandra HETGS and XMM-Newton RGS to benchmark our calculations for various electron densities and UV field intensities. Our calculations show that UV photoexcitation does not produce a sufficiently large dynamic range in the 3F / (3F + 3G + M2) fraction to explain the difference in the observed ratio between coronal stars and ζ Pup. Thus, this effect likely cannot explain the observed line ratio of ζ Pup, and its origin is still unexplained.

Gabriel J. Grell↗
NASA NTRS2021

Fe XVII 2p–3s Line Ratio Diagnostic of Shock Formation Radius in O Stars

The 2p–3s lines of Fe xvii in the X-ray spectrum of the O-type star ζ Puppis exhibit an anomalous (3G + M2)/(3F) line ratio of ∼1.4, in comparison with ∼2.4 for almost all other collisionally excited astrophysical spectra. Based on the work of Mauche et al., we conjectured that the strong UV field of ζ Puppis produces the observed ratio by depopulation of metastable 3s excited states, and that the ratio can potentially be used as an independent diagnostic of plasma formation radius. We used the Flexible Atomic Code collisional-radiative model to model the effect of UV photoexcitation from O stars on the Fe xvii lines. We compared our model calculations to archival spectra of coronal and hot stars from the Chandra HETGS and XMM-Newton RGS to benchmark our calculations for various electron densities and UV field intensities. Our calculations show that UV photoexcitation does not produce a sufficiently large dynamic range in the 3F / (3F + 3G + M2) fraction to explain the difference in the observed ratio between coronal stars and ζ Pup. Thus, this effect likely cannot explain the observed line ratio of ζ Pup, and its origin is still unexplained.

Gabriel Grell↗