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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 73 records · Page 4
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NASA NTRS2000

Mechanisms of the early phases of plant gravitropism

Gravitropism is directed growth of a plant or plant organ in response to gravity and can be divided into the following temporal sequence: perception, transduction, and response. This article is a review of the research on the early events of gravitropism (i.e., phenomena associated with the perception and transduction phases). The two major hypotheses for graviperception are the protoplast-pressure and starch-statolith models. While most researchers support the concept of statoliths, there are suggestions that plants have multiple mechanisms of perception. Evidence supports the hypothesis that the actin cytoskeleton is involved in graviperception/transduction, but the details of these mechanisms remain elusive. A number of recent developments, such as increased use of the molecular genetic approach, magnetophoresis, and laser ablation, have facilitated research in graviperception and have allowed for refinement of the current models. In addition, the entire continuum of acceleration forces from hypo- to hyper-gravity have been useful in studying perception mechanisms. Future interdisciplinary molecular approaches and the availability of sophisticated laboratories on the International Space Station should help to develop new insights into mechanisms of gravitropism in plants.

NASA Discipline Plant Biology↗
NASA NTRS1993

Radiological assessment for Space Station Freedom

Circumstances have made it necessary to reassess the risks to Space Station Freedom crewmembers that arise from exposure to the space radiation environment. An option is being considered to place it in an orbit similar to that of the Russian Mir space station. This means it would be in a 51.6 deg inclination orbit instead of the previously planned 28.5 deg inclination orbit. A broad range of altitudes is still being considered, although the baseline is a 407 km orbit. In addition, recent data from the Japanese A-bomb survivors has made it necessary for NASA to have the exposure limits reviewed. Preliminary findings of the National Council on Radiation Protection and Measurements indicate that the limits must be significantly reduced. Finally, the Space Station will be a laboratory where effects of long-term zero gravity on human physiology will be studied in detail. It is possible that a few crewmembers will be assigned to as many as three 1-year missions. Thus, their accumulated exposure will exceed 1,000 days. Results of this radiation risk assessment for Space Station Freedom crewmembers finds that females less than 35 years old will be confined to mission assignments where the altitude is less than about 400 km. Slight restrictions may also need to be made for male crewmembers less than 35 years old.

Badhwar, Gautam D.↗
NASA NTRS1991

Laboratory and theoretical models of planetary-scale instabilities and waves

Meteorologists and planetary astronomers interested in large-scale planetary and solar circulations recognize the importance of rotation and stratification in determining the character of these flows. The two outstanding problems of interest are: (1) the origins and nature of chaos in baroclinically unstable flows; and (2) the physical mechanisms responsible for high speed zonal winds and banding on the giant planets. The methods used to study these problems, and the insights gained, are useful in more general atmospheric and climate dynamic settings. Because the planetary curvature or beta-effect is crucial in the large scale nonlinear dynamics, the motions of rotating convecting liquids in spherical shells were studied using electrohydrodynamic polarization forces to generate radial gravity and centrally directed buoyancy forces in the laboratory. The Geophysical Fluid Flow Cell (GFFC) experiments performed on Spacelab 3 in 1985 were analyzed. The interpretation and extension of these results have led to the construction of efficient numerical models of rotating convection with an aim to understand the possible generation of zonal banding on Jupiter and the fate of banana cells in rapidly rotating convection as the heating is made strongly supercritical. Efforts to pose baroclinic wave experiments for future space missions using a modified version of the 1985 instrument have led us to develop theoretical and numerical models of baroclinic instability. Some surprising properties of both these models were discovered.

Hart, John E.↗
NASA NTRS2012

Designing Mission Operations for the Gravity Recovery and Interior Laboratory Mission

The Gravity Recovery and Interior Laboratory (GRAIL) mission has placed two orbiters in a low altitude polar orbit around the moon to study its internal structure. GRAIL mission to the Moon offered unique challenges to operatiotn: (1) operate twin-orbiters in parallel, (2) numerous maneuvers, (3) short, compact mission with six unique phases, and (4) detailed contingency planning required.

Orbital Period Reduction (OPR)↗
NASA NTRS1978

The AFGL absolute gravity program

A brief discussion of the AFGL's (Air Force Geophysics Laboratory) program in absolute gravity is presented. Support of outside work and in-house studies relating to gravity instrumentation are discussed. A description of the current transportable system is included and the latest results are presented. These results show good agreement with measurements at the AFGL site by an Italian system. The accuracy obtained by the transportable apparatus is better than 0.1 microns sq sec 10 microgal and agreement with previous measurements is within the combined uncertainties of the measurements.

Hammond, J. A.↗
NASA NTRS1988

Liquid/vapour phase separation in He-4 using electric fields

In space, a replacement must be found for gravity to physically control and, in certain instances, contain cryogenic liquids. A program has been started at the Jet Propulsion Laboratory to study the use of electric field generated forces to establish the required orienting effects. Measurements which show that it is possible to apply strong enough electric fields to a liquid/vapor interface of He-4 to obtain an orienting force comparable to gravity are presented. Our measurements span the temperature range 1.7-4.2 K and demonstrate the applicability of Pashen's law for maximum attainable field before breakdown occurs. Some advantages of the electric field separator as opposed to passive surface tension devices are identified.

Israelsson, U. E.↗
NASA NTRS2001

Laminar and Turbulent Gaseous Diffusion Flames

Recent measurements and predictions of the properties of homogeneous (gaseous) laminar and turbulent non-premixed (diffusion) flames are discussed, emphasizing results from both ground- and space-based studies at microgravity conditions. Initial considerations show that effects of buoyancy not only complicate the interpretation of observations of diffusion flames but at times mislead when such results are applied to the non-buoyant diffusion flame conditions of greatest practical interest. This behavior motivates consideration of experiments where effects of buoyancy are minimized; therefore, methods of controlling the intrusion of buoyancy during observations of non-premixed flames are described, considering approaches suitable for both normal laboratory conditions as well as classical microgravity techniques. Studies of laminar flames at low-gravity and microgravity conditions are emphasized in view of the computational tractability of such flames for developing methods of predicting flame structure as well as the relevance of such flames to more practical turbulent flames by exploiting laminar flamelet concepts.

Faeth, G. M.↗
NASA NTRS2007

International Space Station Research: Accomplishments and Pathways for Exploration and Fundamental Research

Beginning with the launch of the European Columbus module planned for December 2007, we approach a transition in the assembly of the International Space Station (ISS) that is of great importance for the sciences. During the following 18 months, we will operate the first experiments in Columbus physical science resource facilities and also launch and commission the Japanese Kibo module. In addition, two Multi-purpose Logistics Module (MPLM) flights will deliver the U.S. Combustion Integrated Rack (CIR) and Fluids Integrated Rack (FIR) along with their first science experiments. These facilities provide significant new capabilities for basic and applied physical science research in microgravity. New life support technologies will come online throughout 2008, and we will reach the milestone of a 6-person crew planned for April 2009. A larger crew enables significant more scientific use of all the facilities for the life of ISS. Planning for the use of the International Space Station as a national laboratory is also maturing as we near the completion of assembly, enabling access to ISS as a research platform for other government agencies and the private sector. The latest updates on National Laboratory implementation will also be provided in this presentation. At the same time as these significant increases in scientific capability, there have been significant ongoing accomplishments in NASA's early ISS research both exploration related and fundamental research. These accomplishments will be reviewed in context as harbingers of the capabilities of the International Space Station when assembly is complete. The Vision for Space Exploration serves to focus NASA's applied investigations in the physical sciences. However, the broader capability of the space station as a National Laboratory and as a nexus for international collaboration will also influence the study of gravity-dependent processes by researchers around the world.

Robinson, Julie A.↗
NASA NTRS2004

Reduced Gravity Studies of Soret Transport Effects in Liquid Fuel Combustion

Soret transport, which is mass transport driven by thermal gradients, can be important in practical flames as well as laboratory flames by influencing transport of low molecular weight species (e.g., monatomic and diatomic hydrogen). In addition, gas-phase Soret transport of high molecular weight fuel species that are present in practical liquid fuels (e.g., octane or methanol) can be significant in practical flames (Rosner et al., 2000; Dakhlia et al., 2002) and in high pressure droplet evaporation (Curtis and Farrell, 1992), and it has also been shown that Soret transport effects can be important in determining oxygen diffusion rates in certain classes of microgravity droplet combustion experiments (Aharon and Shaw, 1998). It is thus useful to obtain information on flames under conditions where Soret effects can be clearly observed. This research is concerned with investigating effects of Soret transport on combustion of liquid fuels, in particular liquid fuel droplets. Reduced-gravity is employed to provide an ideal (spherically-symmetrical) experimental model with which to investigate effects of Soret transport on combustion. The research will involve performing reduced-gravity experiments on combustion of liquid fuel droplets in environments where Soret effects significantly influence transport of fuel and oxygen to flame zones. Experiments will also be performed where Soret effects are not expected to be important. Droplets initially in the 0.5 to 1 mm size range will be burned. Data will be obtained on influences of Soret transport on combustion characteristics (e.g., droplet burning rates, droplet lifetimes, gas-phase extinction, and transient flame behaviors) under simplified geometrical conditions that are most amenable to theoretical modeling (i.e., spherical symmetry). The experiments will be compared with existing theoretical models as well as new models that will be developed. Normal gravity experiments will also be performed.

Shaw, Benjamin D.↗
NASA NTRS1972

Study of the production of unique new glasses

A number of high new oxide glasses have been prepared by a laser-spin melting technique where droplets are ejected from a molten mass. Techniques have been developed for measuring the optical properties of most of the new glasses so produced. A preliminary study of processing equipment for producing new glasses in a zero gravity environment onboard manned space laboratory is reported. Induction and laser melting emerge as preferred techniques for melting spheroids of new glass compositions in space. Sample calculations for power required to induction melt new glass compositions are presented. Cooling rate calculations show that radiation cooling of the high melting materials results in very short cooling times for 1/2 inch diameters to temperatures where the spheroids can be handled.

Happe, R. A.↗
NASA NTRS1985

Ignition and Flame Spread Above Liquid Fuel Pools

Phenomena of ignition and flame spread above liquid fuel pools are studied and factors that can improve fire safety are determined. Dominant mechanisms for convective heat transfer and impact on ignition and flame spread above liquid fuel pools will be determined from these efforts. The approach is: (1) analytical and computational studies to evaluate scaling factors; (2) experimental design, development, and operation in laboratory at Earth's gravity; (3) experimental design for drop towers at NASA Lewis Research Center; (4) development and operation of drop tower experiments together with NASA Lewis Research personnel and; (5) develop recommendations for Lear Jet and/or Space Shuttle experiments. Through this research, a mathematical model of two-phase systems is formulated and is being coded for the computer.

Sirignano, W. A.↗
NASA NTRS1999

Instrumentation and Methods to Measure Dynamic Forces During Exercise Using the Horizontal Exercise Machine

It is hypothesized that bone loss experienced by astronauts in zero gravity conditions may be curtailed by appropriate exercise. According to Wolf's law, bone regenerates when muscles produce stresses by pulling on the bone during daily activity and/or exercise on Earth. To use this theory to prevent or decrease bone loss, one needs to quantify musculoskeletal loads and relate them to bone density changes. In the context of the space program, it is desirable to determine musculoskeletal loads during exercise so that one may make similar measurements on Earth and in space. In this manner, load measurements on Earth may be used as reference to generate similar loads during exercise in space. A research project to investigate the effects of high-resistive exercise to decrease bone density loss underzero-gravity conditions is being carried out in Life Sciences Research Laboratories at NASA JSC. The project consists of a bed-rest study whereby subjects remain in horizontal position for seventeen weeks. During the study, a subset of those subjects executes a regime of resistive exercises in the horizontal exercise machine (HEM). The HEM was designed so that subjects remain horizontal while exercising to minimize gravity loading even during exercise. Bone density of each subject is measured throughout the duration of their participation. The objective of the study is to determine if the resistive exercises are effective in diminishing or eliminating bone loss. My participation in this project relates to instrumentation, measurement, and processing of signals from displacement sensors (optical encoders) and load-cells. Measurement of displacements will be used to determine the motion of the body during exercise, and load measurements will be used (along with displacement data) to determine forces and torques exerted on each section of the body during exercise. Further, I have assisted in specifying new sensors to be added to the HEM and to a new prototype resistive exercise machine called the Interim Resistive Exercise Device (IRED). New load cells and encoders should be mounted in these devices to obtain more complete kineto-dynamic information. This report includes a description of the instrumentation that was built to perform measurements in the HEM and the IRED, along with the software that was developed to collect the measurements. It also includes examples of measurements taken in the HEM. Finally, a plan is laid out that describes how these measurements may be used to determine forces exerted by muscles for each exercise.

Figueroa, Fernando↗
NASA NTRS1996

Experiments on Thermal Convection in Rotating Spherical Shells With Radial Gravity: The Geophysical Fluid Flow Cell

Experiments designed to study the fluid dynamics of buoyancy driven circulations in rotating spherical shells were conducted on the United States Microgravity Laboratory 2 spacelab mission. These experiments address several aspects of prototypical global convection relevant to large scale motions on the Sun, Earth, and on the giant planets. The key feature is the consistent modeling of radially directed gravity in spherical geometry by using dielectric polarization forces. Imagery of the planforms of thermally driven flows for rapidly-rotating regimes shows an initial separation and eventual merger of equatorial and polar convection as the heating (i.e. the Rayleigh number) is increased. At low rotation rates, multiple-states of motion for the same external parameters were observed.

Hart, John E.↗
NASA NTRS2009

Extravehicular Activity Testing in Analog Environments: Evaluating the Effects of Center of Gravity and Environment on Human Performance

The EVA Physiology, Systems and Performance (EPSP) Project is performing tests in different analog environments to understand human performance during Extravehicular Activity (EVA) with the aim of developing more safe and efficient systems for lunar exploration missions and the Constellation Program. The project is characterizing human EVA performance in studies using several test beds, including the underwater NASA Extreme Environment Mission Operations (NEEMO) and Neutral Buoyancy Laboratory (NBL) facilities, JSC fs Partial Gravity Simulator (POGO), and the NASA Reduced Gravity Office (RGO) parabolic flight aircraft. Using these varied testing environments, NASA can gain a more complete understanding of human performance issues related to EVA and the limitations of each testing environment. Tests are focused on identifying and understanding the EVA system factors that affect human performance such as center of gravity (CG), inertial mass, ground reaction forces (GRF), suit weight, and suit pressure. The test results will lead to the development of lunar EVA systems operations concepts and design requirements that optimize human performance and exploration capabilities. METHODS: Tests were conducted in the NBL and during NEEMO missions in the NOAA Aquarius Habitat. A reconfigurable back pack with repositionable mass was used to simulate Perfect, Low, Forward, High, Aft and NASA Baseline CG locations. Subjects performed simulated exploration tasks that included ambulation, kneel and recovery, rock pick-up, and shoveling. Testing using POGO, that simulates partial gravity via pneumatic weight offload system and a similar reconfigurable rig, is underway for a subset of the same tasks. Additionally, test trials are being performed on the RGO parabolic flight aircraft. Subject performance was assessed using a modified Cooper-Harper scale to assess operator compensation required to achieve desired performance. All CG locations are based on the assumption of a standardized 6 ft 180 lb subject. RESULTS: The modified Cooper-Harper Scale assesses desired task performance described as performance in a reduced gravity environment as compared to a 1G environment. Modified Cooper-Harper ratings of . 3 indicate no improvements are needed, ratings of 4-6 indicate improvements are desirable, and ratings . 7 indicate improvements are mandatory. DISCUSSION: Differences were noted in suited CH results based on environment at the same CG and suit pressure. Additionally, results suggest that CG location affects unsuited human performance. Subjects preferred locations near their natural CG over those that are high, aft, or a combination of high and aft. Further testing and analyses are planned to compare these unsuited results to suited performance.

Gernhardt, M.L.↗
NASA NTRS1991

Progress in the development of an artificial gravity simulator (AGS)

The paper describes the short-arm centrifuge for studying the effects of acceleration on human subjects which was built at the Artificial Gravity Simulator (AGS) laboratory at Woodlands, Texas. The AGS centrifuge comprises a turntable, a traction system, a platform, four beds, and a data-communication system. Schematic diagrams are presented of the AGS laboratory layout, the centrifuge turntable, the tiltable (up to 6 deg) bed frame, and of the data collection multiplexer (master switch) for physiological data communications.

Cardus, David↗
NASA NTRS2011

The Regolith of 4 Vesta: Perspectives from Howardite Meteorites and Dawn Mission Observations

4 Vesta is the largest asteroid with a basaltic surface, the only surviving differentiated asteroid recording igneous processes from the earliest phase of solar system history. The Dawn spacecraft is in orbit about Vesta pursuing a campaign of high resolution imaging and visible and infrared spectrometry of the surface; compositional mapping by gamma-ray and neutron spectrometry will follow. Vesta is heavily cratered with a surface covered by impact debris, a regolith. One important goal of the Dawn mission is to develop an understanding of regolith processes that are affecting this surface debris. Regolith characteristics are a record of interaction with the environment (e.g., impactors, dust, solar wind, galactic cosmic-rays) and give evidence of surface processes (down-gravity movement, etc.). Regolith mineralogy and composition reflect the local bedrock, with influences from regional and global mixing. Understanding regolith processes will aid in determining the lithology of underlying crust. Vesta is most likely the parent asteroid of the howardite, eucrite and diogenite meteorites. Eucrites are intrusive and extrusive mafic rocks composed mostly of ferroan low-Ca clinopyroxene and calcic plagioclase, while diogenites are cumulate magnesian orthopyroxenites. Magmatism occurred within a few million years of the formation of the solar system and then ceased. Impacts into the igneous crust produced the howardites - polymict breccias composed of mineral and lithic debris derived mostly from eucrites and diogenites. Some howardites are true regolith breccias formed by lithification of extensively impact-gardened surface debris. However, howardites have a number of significant petrologic and compositional differences from mature lunar regolith breccias and soils reflecting the different environment around Vesta compared to that at 1 AU. The most significant differences are the higher impactor flux with a lower mean impact velocity and the lower gravity. As a result, regolith processes on Vesta differ in detail from those on the Moon. Laboratory study of howardites and orbital investigation of Vesta will allow for development of robust models of regolith formation on hand sample to multi-kilometer scales.

Mittlefehldt, David W.↗
NASA NTRS1996

Microgravity Turbulent Gas-Jet Diffusion Flames

A gas-jet diffusion flame is similar to the flame on a Bunsen burner, where a gaseous fuel (e.g., propane) flows from a nozzle into an oxygen-containing atmosphere (e.g., air). The difference is that a Bunsen burner allows for (partial) premixing of the fuel and the air, whereas a diffusion flame is not premixed and gets its oxygen (principally) by diffusion from the atmosphere around the flame. Simple gas-jet diffusion flames are often used for combustion studies because they embody the mechanisms operating in accidental fires and in practical combustion systems. However, most practical combustion is turbulent (i.e., with random flow vortices), which enhances the fuel/air mixing. These turbulent flames are not well understood because their random and transient nature complicates analysis. Normal gravity studies of turbulence in gas-jet diffusion flames can be impeded by buoyancy-induced instabilities. These gravitycaused instabilities, which are evident in the flickering of a candle flame in normal gravity, interfere with the study of turbulent gas-jet diffusion flames. By conducting experiments in microgravity, where buoyant instabilities are avoided, we at the NASA Lewis Research Center hope to improve our understanding of turbulent combustion. Ultimately, this could lead to improvements in combustor design, yielding higher efficiency and lower pollutant emissions. Gas-jet diffusion flames are often researched as model flames, because they embody mechanisms operating in both accidental fires and practical combustion systems (see the first figure). In normal gravity laboratory research, buoyant air flows, which are often negligible in practical situations, dominate the heat and mass transfer processes. Microgravity research studies, however, are not constrained by buoyant air flows, and new, unique information on the behavior of gas-jet diffusion flames has been obtained.

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