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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Venus pancake dome formation: Morphologic effects of a cooling-induced variable viscosity during emplacement

The distinctive steep-sided 'pancake' domes discovered in the Magellan images of Venus have morphologies that suggest formation by a single continuous emplacement of a high viscosity magma. A resemblance of the venusian domes to much smaller terrestrial rhyolite and dacite volcanic domes has prompted some authors to suggest that the domes on Venus also have high silica compositions and thus, high viscosities. However, viscosity is a function of crystallinity as well as silica content in a magma, and thus increases as a result of magmatic cooling. To investigate the effect of a cooling-induced viscosity increase on dome morphology, we have modeled the domes as radial viscous gravity currents that cool during emplacement. Various aspects of the investigation are discussed.

Sakimoto, S. E. H.↗
NASA NTRS1993

GMM-1: A 50 degree and order gravitational field model for Mars

Knowledge of the gravitational field, in combination with surface topography, provides one of the principal means of inferring the internal structure of a planetary body. The highest resolution gravitational field for Mars published thus far was derived from Doppler tracking data from the Mariner 9 and Viking 1 and 2 spacecraft and is complete to degree and order 18 corresponding to a half wavelength resolution of approximately 600 km. This field, which is characterized by a spatial resolution that is slightly better than that of the highest resolution (16x16) topographic model, has been utilized extensively in analyses of the state of stress and isostatic compensation of the Martian lithosphere. However, the resolution and quality of current gravity and topographic fields are such that the origin and evolution of even the major physiographic features on Mars, such as the hemispheric dichotomy and Tharsis rise, are not well understood. We have re-analyzed the Viking and Mariner data sets and have derived a new gravitational field, which we designated GMM-1 (Goddard Mars Model-1). This model is complete to spherical harmonic degree and order 50 with a corresponding (half wavelength) spatial resolution of 200-300 km where the data permit. In contrast to previous models, GMM-1 was solved to as high degree and order as necessary to nearly exhaust the attenuated gravitational signal contained in the tracking data.

Smith, D. E.↗
NASA NTRS1995

Observational and numerical studies of extreme frontal scale contraction

The general objective of this effort is to increase understanding of how frontal scale contraction processes may create and sustain intense mesoscale precipitation along intensifying cold fronts. The five-part project (an expansion of the originally proposed two-part project) employed conventional meteorological data, special mesoscale data, remote sensing measurements, and various numerical models. First an idealized hydrostatic modeling study of the scale contraction effects of differential cloud cover on low-level frontal structure and dynamics was completed and published in a peer-reviewed journal. The second objective was to complete and publish the results from a three dimensional numerical model simulation of a cold front in which differential sensible heating related to cloud coverage patterns was apparently crucial in the formation of a severe frontal squall line. The third objective was to use a nonhydrostatic model to examine the nonlinear interactions between the transverse circulation arising from inhomogeneous cloud cover, the adiabatic frontal circulation related to semi-geostrophic forcing, and diabatic effects related to precipitation processes, in the development of a density current-like microstructure at the leading edge of cold fronts. Although the development of a frontal model that could be used to initialize such a primitive equation model was begun, we decided to focus our efforts instead on a project that could be successfully completed in this short time, due to the lack of prospects for continued NASA funding beyond this first year (our proposal was not accepted for future funding). Thus, a fourth task was added, which was to use the nonhydrostatic model to test tentative hypotheses developed from the most detailed observations ever obtained on a density current (primarily sodar and wind profiler data). These simulations were successfully completed, the findings were reported at a scientific conference, and the results have recently been submitted to a peer-reviewed journal. The fifth objective was to complete the analysis of data collected during the Cooperative Oklahoma Profiler Studies (COPS-91) field project, which was supported by NASA. The analysis of the mesoscale surface and sounding data, Doppler radar imagery, and other remote sensing data from multi frequency wind profiler, microwave radiometer, and the Radio Acoustic Sounding System has been completed. This study is a unique investigation of processes that caused the contraction of a cold front to a microscale zone exhibiting an undular bore-like structure. Results were reported at a scientific conference and are being prepared for publication. In summary, considerable progress has been achieved under NASA funding in furthering our understanding of frontal scale contraction and density current - gravity wave interaction processes, and in utilizing models and remotely sensed data in such studies.

Koch, Steven E.↗
NASA NTRS2011

Developing Tests of Visual Dependency

Astronauts develop neural adaptive responses to microgravity during space flight. Consequently these adaptive responses cause maladaptive disturbances in balance and gait function when astronauts return to Earth and are re-exposed to gravity. Current research in the Neuroscience Laboratories at NASA-JSC is focused on understanding how exposure to space flight produces post-flight disturbances in balance and gait control and developing training programs designed to facilitate the rapid recovery of functional mobility after space flight. In concert with these disturbances, astronauts also often report an increase in their visual dependency during space flight. To better understand this phenomenon, studies were conducted with specially designed training programs focusing on visual dependency with the aim to understand and enhance subjects ability to rapidly adapt to novel sensory situations. The Rod and Frame test (RFT) was used first to assess an individual s visual dependency, using a variety of testing techniques. Once assessed, subjects were asked to perform two novel tasks under transformation (both the Pegboard and Cube Construction tasks). Results indicate that head position cues and initial visual test conditions had no effect on an individual s visual dependency scores. Subjects were also able to adapt to the manual tasks after several trials. Individual visual dependency correlated with ability to adapt manual to a novel visual distortion only for the cube task. Subjects with higher visual dependency showed decreased ability to adapt to this task. Ultimately, it was revealed that the RFT may serve as an effective prediction tool to produce individualized adaptability training prescriptions that target the specific sensory profile of each crewmember.

Kindrat, Alexandra N.↗
NASA NTRS1987

An electric current associated with gravity sensing in maize roots

The study of gravisensing would be greatly enhanced if physiological events associated with gravity sensing could be detected separately from subsequent growth processes. This report presents a means to discriminate sensing from the growth processes. By using a vibrating probe, we have found an electric current generated by the gravity sensing region of the root cap of maize (Zea mays cv Merit) in response to gravistimulation. On the upper surface of the root cap, the change from the endogenous current has a density of 0.55 microampere per square centimeter away from gravity. The onset of the current shift has a characteristic of lag of three to four minutes after gravistimulation, which corresponds to the presentation time for gravity sensing in this tissue. A description of the current provides some information about the sensing mechanism, as well as being a valuable means to detect gravity sensing independently of differential growth.

NASA Discipline Number 40-10↗
NASA NTRS1974

The problem of the influence of ocean currents on free internal gravity waves

The influence of ocean currents on free internal gravity waves is discussed. The dependence of the parameters of gravity waves on the characteristics of stationary marine currents is described. Necessary conditions for existence of these waves are obtained, and the phenomenon of abrupt changes in phase of the internal oscillation with depth is explained.

Savchenko, V. G.↗
NASA NTRS1993

Water Surface Currents, Short Gravity-Capillary Waves and Radar Backscatter

Despite their importance for air-sea interaction and microwave remote sensing of the ocean surface, intrinsic properties of short gravity-capillary waves are not well established. This is largely due to water surface currents and their effects on the direct measurements of wave parameters conducted at a fixed point. Frequencies of small scale waves propagating on a surface which itself is in motion, are subject to Doppler shifts. Hence, the high frequency tail of the wave spectra obtained from such temporal observations is smeared. Conversion of this smeared measured-frequency spectra to intrinsic-frequency (or wavenumber) spectra requires corrections for the Doppler shifts. Such attempts in the past have not been very successful in particular when field data were used. This becomes evident if the amplitude modulation of short waves by underlying long waves is considered. Microwave radar studies show that the amplitude of a short wave component attains its maximum value near the crests and its minimum in the troughs of the long waves. Doppler-shifted wave data yield similar results but much larger in modulation magnitude, as expected. In general, Doppler shift corrections reduce the modulation magnitude. Overcorrection may result in a negligible modulation or even in a strong modulation with the maximum amplitude in the wave troughs. The latter situation is clearly contradictory to our visual observations as well as the radar results and imply that the advection by currents is overestimated. In this study, a differential-advection approach is used in which small scale waves are advected by the currents evaluated not at the free surface, but at a depth proportional to their wavelengths. Applicability of this approach is verified by the excellent agreement in phase and magnitude of short-wave modulation between results based on radar and on wave-gauge measurements conducted on a lake.

Atakturk, Serhad S.↗
NASA NTRS1989

The use of bioelectric currents to study gravity perception in roots

Inhibitor-based studies of gravity perception in plants have yielded ambiguous results because gravitropism consists of many steps in series. Inhibiting any step eliminates gravicurvature; it cannot be shown whether gravity perception and transduction are affected by the inhibitory treatment. The use of the vibrating probe has allowed detection of a response that is measurable independent of stimulus transmission and growth, two post-transduction steps of gravitropism. This application of the vibrating probe requires particular attention to artifacts. Calmodulin action and auxin transport are both believed to be components of gravitropism and specific roles have been proposed for them in graviperception. The perception-dependent current measured with the vibrating probe is eliminated by inhibitors of calmodulin, but not by auxin inhibitors. Thus, the vibrating probe has made it possible to offer more direct evidence for a role of calmodulin in transduction, and to reject one for auxin transport in perception and transduction.

Non-NASA Center↗
NASA NTRS1984

Spaceborne Gravity Gradiometers

The current status of gravity gradiometers and technology that could be available in the 1990's for the GRAVSAT-B mission are assessed. Problems associated with sensors, testing, spacecraft, and data processing are explored as well as critical steps, schedule, and cost factors in the development plan.

Wells, W. C.↗
NASA NTRS1973

The nature of circular maria based on gravity studies.

Current thinking on the evolution of major lunar morphological features, i.e., large lunar circular basins, and on the nature and origin of surface structures observed in the fill deposits is summarized. The great lunar circular basins must result from high-velocity impact of large bodies with the moon. A hydrostatic mechanism is outlined, and a working hypothesis is presented for the evolution of lunar circular basins subsequent to their origin by impact. In the main appeal is made to Doppler gravity data to support the hypothesis, although photographic and altimetric information is also used. It is considered that all large ringed circular basins follow a common evolutionary path of superisostatic volcanic flooding followed by partial and variable isostatic adjustment. The difference between basins is the amount of flooding, which in turn may be related to the center of figure-center of mass offset of the moon.

Phillips, R. J.↗
NASA NTRS1988

Droplet combustion at reduced gravity

The current work involves theoretical analyses of the effects identified, experiments in the NASA Lewis drop towers performed in the middeck areas of the Space Shuttle. In addition, there is laboratory work associated with the design of the flight apparatus. Calculations have shown that some of the test-matrix data can be obtained in drop towers, and some are achievable only in the space experiments. The apparatus consists of a droplet dispensing device (syringes), a droplet positioning device (opposing, retractable, hollow needles), a droplet ignition device (two matched pairs of retractable spark electrodes), gas and liquid handling systems, a data acquisition system (mainly giving motion-picture records of the combustion in two orthogonal views, one with backlighting for droplet resolution), and associated electronics.

Dryer, F. L.↗
NASA NTRS2005

EXERCISE WITHIN LOWER BODY NEGATIVE PRESSURE AS AN ARTIFICIAL GRAVITY COUNTERMEASURE

Current exercise systems for space, which attempt to maintain performance, are unable to generate cardiovascular and musculoskeletal loads similar to those on Earth [1, 2]. The purpose of our research is to evaluate the use of lower body negative pressure (LBNP) treadmill exercise to prevent deconditioning during simulated microgravity.

Hargens, Alan R.↗
NASA NTRS2009

Space Systems - Safety and Compatibility of Materials - Method to Determine the Flammability Thresholds of Materials

Spacecraft fire safety emphasizes fire prevention, which is achieved primarily through the use of fire-resistant materials. Materials selection for spacecraft is based on conventional flammability acceptance tests, along with prescribed quantity limitations and configuration control for items that are non-pass or questionable. ISO 14624-1 and -2 are the major methods used to evaluate flammability of polymeric materials intended for use in the habitable environments of spacecraft. The methods are upward flame-propagation tests initiated in static environments and using a well-defined igniter flame at the bottom of the sample. The tests are conducted in the most severe flaming combustion environment expected in the spacecraft. The pass/fail test logic of ISO 14624-1 and -2 does not allow a quantitative comparison with reduced gravity or microgravity test results; therefore their use is limited, and possibilities for in-depth theoretical analyses and realistic estimates of spacecraft fire extinguishment requirements are practically eliminated. To better understand the applicability of laboratory test data to actual spacecraft environments, a modified ISO 14624 protocol has been proposed that, as an alternative to qualifying materials as pass/fail in the worst-expected environments, measures the actual upward flammability limit for the material. A working group established by NASA to provide recommendations for exploration spacecraft internal atmospheres realized the importance of correlating laboratory data with real-life environments and recommended NASA to develop a flammability threshold test method. The working group indicated that for the Constellation Program, the flammability threshold information will allow NASA to identify materials with increased flammability risk from oxygen concentration and total pressure changes, minimize potential impacts, and allow for development of sound requirements for new spacecraft and extravehicular landers and habitats. Furthermore, recent research has shown that current normal gravity materials flammability tests do not correlate with flammability in ventilated, micro- or reduced-gravity conditions. Currently, the materials selection for spacecraft is based on the assumption of commonality between ground flammability test results and spacecraft environments, which does not appear to be valid. Materials flammability threshold data acquired in normal gravity can be correlated with data obtained in microgravity or reduced-gravity experiments, and consequently a more accurate assessment of the margin of safety of the material in the real environment can be made. In addition, the method allows the option of selecting better or best space system materials, as opposed to what would be considered just acceptable from a flammability point of view and realistic assessment of spacecraft fire extinguishment needs, which could result in significant weight savings. The knowledge afforded by this technique allows for limited extrapolations of flammability behavior to conditions not specifically tested and that could potentially result in significant cost and time savings. The intent of this Technical Specification is to bring to the attention of International Aerospace Community the importance of correlating laboratory test data with real-life space systems applications. The method presented is just one of the possibilities that are believed will lead to better understanding the applicability of laboratory aerospace materials flammability test data. International feedback on improving the proposed method, as well as suggestions for correlating other laboratory aerospace test data with real-life applications relevant to space systems are being sought.

Hirsch, David↗
NASA NTRS1983

Mapping the earth's magnetic and gravity fields from space Current status and future prospects

The principal magnetic fields encountered by earth orbiting spacecraft include the main (core) field, external fields produced by electrical currents within the ionosphere and magnetosphere, and the crustal (anomaly) field generated by variations in the magnetization of the outermost portions of the earth. The first orbital field measurements which proved to be of use for global studies of crustal magnetization were obtained by a series of three satellites launched and operated from 1965 to 1971. Each of the satellites, known as a Polar Orbiting Geophysical Observatory (POGO), carried a rubidium vapor magnetometer. Attention is also given to Magsat launched in 1979, the scalar anomaly field derived from the Magsat measurements, satellite tracking studies in connection with gravity field surveys, radar altimetry, the belt of positive free air gravity anomalies situated along the edge of the Pacific Ocean basin, future technological capabilities, and information concerning data availability.

Settle, M.↗