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At least 343 records · Page 19

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NASA NTRS1992

Improving survival after tissue vaporization (Ebullism)

Exposure of unprotected humans to altitudes above 63,000 ft results in ebullism. Ebullism occurs when the vapor pressure of tissues is less than the ambient pressure and the tissues spontaneously 'boil'. This may result in rapid unconsciousness, cardiac vaporlock, pulmonary collapse, cerebral anoxia, and sometimes even death. Potential places for this include EVA accidents in space, aircraft experiencing rapid decompression at high altitudes with cabin or pressure suit failure, and accidents during pressure suit training exercises. The pathophysiology of ebullism was studied in the 40's to 60's using animal models. There is one report of a prolonged, unprotected human exposure and several anecdotal of unprotected short term exposures to near vacuum. In addition to pulmonary and neurologic concerns, unprotected exposure of the head may result in freezing of the corneal surface of the eye. Surface eye freezing may impair vision and significantly impact mission completion. At this time, little data are available on the effectiveness of conventional treatment protocols, such as hyperbaric oxygen, for ebullism induced injuries. Research is needed to assess the efficacy of other adjunctive therapies such as high frequency ventilation and cerebral protective drugs that are still under development.

Stegmann, Barbara J.↗

NASA NTRS1992

The Kuwait oil fires as seen by Landsat

A mosaic of two Landsat thematic mapper images acquired May 30, 1991, reveals a dark smoke plume 30-60 km wide extending hundreds of kilometers south of Kuwait City along the Persian Gulf. Smoke coming from the Raudhatain and Sabriyah oil fields blew across the Gulf of Kuwait and over Kuwait City, joined with smoke from the Greater Burgan and Minagish fields, and continued southward over smaller villages and regions of desert agriculture consisting of hundreds of axially irrigated fields in both Kuwait and Saudi Arabia. One agricultural region in Kuwait was completely obscured by the smoke. The light colored limestone gravel and sand surface was darkened by oil lakes near the wells, and by oil drizzling out of the plume downwind of the wells. Most fires produced either a light or dark plume, and the separate plumes mixed to form a combined plume much darker than the land surface, but slightly more reflective than the Gulf waters. A few of the hottest fires had no visible plume, and are presumably associated with methane combustion. The last of the Kuwait fires was reportedly extinguished in November of 1991. Continued monitoring is needed to assess the impact of emissions from both burning and nonburning oil wells on the region's climate, as well as on the agriculture, fishing, and other activities essential to life in the region.

Cahalan, Robert F.↗

NASA NTRS1992

Stochastic sensitivity measure for mistuned high-performance turbines

A stochastic measure of sensitivity is developed in order to predict the effects of small random blade mistuning on the dynamic aeroelastic response of turbomachinery blade assemblies. This sensitivity measure is based solely on the nominal system design (i.e., on tuned system information), which makes it extremely easy and inexpensive to calculate. The measure has the potential to become a valuable design tool that will enable designers to evaluate mistuning effects at a preliminary design stage and thus assess the need for a full mistuned rotor analysis. The predictive capability of the sensitivity measure is illustrated by examining the effects of mistuning on the aeroelastic modes of the first stage of the oxidizer turbopump in the Space Shuttle Main Engine. Results from a full analysis mistuned systems confirm that the simple stochastic sensitivity measure predicts consistently the drastic changes due to misturning and the localization of aeroelastic vibration to a few blades.

Murthy, Durbha V.↗

NASA NTRS1992

Earth science information: Planning for the integration and use of global change information

The Consortium for International Earth Science Information Network (CIESIN) was founded in 1989 as a non-profit corporation dedicated to facilitating access to, use and understanding of global change information worldwide. The Consortium was created to cooperate and coordinate with organizations and researchers throughout the global change community to further access the most advanced technology, the latest scientific research, and the best information available for critical environmental decision making. CIESIN study efforts are guided by Congressional mandates to 'convene key present and potential users to assess the need for investment in integration of earth science information,' to 'outline the desirable pattern of interaction with the scientific and policy community,' and to 'develop recommendations and draft plans to achieve the appropriate level of effort in the use of earth science data for research and public policy purposes.' In addition, CIESIN is tasked by NASA to develop a data center that would extend the benefits of Earth Observing System (EOS) to the users of global change information related to human dimensions issues. For FY 1991, CIESIN focused on two main objectives. The first addressed the identification of information needs of global change research and non-research user groups worldwide. The second focused on an evaluation of the most efficient mechanisms for making this information available in usable forms.

Lousma, Jack R.↗

NASA NTRS1992

Lunar resource evaluation and mine site selection

Two scenarios in this evaluation of lunar mineral resources and the selection of possible mining and processing sites are considered. The first scenario assumes that no new surface or near-surface data will be available before site selection (presumably one of the Apollo sites). The second scenario assumes that additional surface geology data will have been obtained by a lunar orbiter mission, an unmanned sample return mission (or missions), and followup manned missions. Regardless of the scenario, once a potentially favorable mine site has been identified, a minimum amount of fundamental data is needed to assess the resources at that site and to evaluate its suitability for mining and downstream processing. Since much of the required data depends on the target mineral(s), information on the resource, its beneficiation, and the refining, smelting, and fabricating processes must be factored into the evaluation. The annual capacity and producing lifetime of the mine and its associated processing plant must be estimated before the resource reserves can be assessed. The available market for the product largely determines the capacity and lifetime of the mine. The Apollo 17 site is described as a possible mining site. The use of new sites is briefly addressed.

Bence, A. Edward↗

NASA NTRS1993

Life cycles of transient planetary waves

In recent years there has been an increasing effort devoted to understanding the physical and dynamical processes that govern the global-scale circulation of the atmosphere. This effort has been motivated, in part, from: (1) a wealth of new satellite data; (2) an urgent need to assess the potential impact of chlorofluorocarbons on our climate; (3) an inadequate understanding of the interactions between the troposphere and stratosphere and the role that such interactions play in short and long-term climate variability; and (4) the realization that addressing changes in our global climate requires understanding the interactions among various components of the earth system. The research currently being carried out represents an effort to address some of these issues by carrying out studies that combine radiation, ozone, seasonal thermal forcing and dynamics. Satellite and ground-based data that is already available is being used to construct basic states for our analytical and numerical models. Significant accomplishments from 1991-1992 are presented and include the following: ozone-dynamics interaction; (2) periodic local forcing and low frequency variability; and (3) steady forcing and low frequency variability.

Nathan, Terrence↗

NASA NTRS1993

Entry Systems Panel deliberations

The Entry Systems Panel was chaired by Don Rummler, LaRC and Dan Rasky, ARC. As requested, each panel participant prior to the workshop prepared and delivered presentations to: (1) identify technology needs; (2) assess current programs; (3) identify technology gaps; and (4) identify highest payoff areas R&D. Participants presented background on the entry systems R&D efforts and operations experiences for the Space Shuttle Orbiter. These participants represented NASA Centers involved in research (Ames Research Center), development (Johnson Space Center) and operations (Kennedy Space Center) and the Shuttle Orbiter prime contractor. The presentations lead to the discovery of several lessons learned.

Rasky, Daniel J.↗

NASA NTRS1992

Near-Earth asteroids: Observer alert network and physical observations

This project strives to obtain physical observations on newly discovered Near-Earth Objects (NEO's) in order to provide fundamental data needed to assess the resources available in the population. The goal is acquiring data on all objects brighter than magnitude V= 17.0. To accomplish this, an electronic mail alert and observer information service that informs observers around the world as to the status of physical observations on currently observable NEO's was established. Such data is also acquired ourselves through a cooperative program with European colleagues that uses telescopes on La Palma to obtain spectra of NEO's and through observations made from a local telescope on Tumamoc Hill. This latter telescope has the advantage that large amounts of observing time are available, so that whenever a new NEO's discovered, we can be assured of getting time to observe it.

Davis, Donald R.↗

NASA NTRS1993

SWIRL as a means of liquid management in low gravity

Swirling of a liquid in a container may prove to be a more desirable method of managing liquids in low gravity (space) environments than by rotating the entire container. By injecting a relatively high velocity liquid tangentially into the body of the fluid, swirl can best be started rapidly, however an estimate of the quantity and velocity of jetflow, or mechanical power of a pump impeller required to maintain a given radial acceleration (G force) is needed to assess the feasibility of such a method. While the key aspect of the problem is determining the rate of rotational energy dissipation by wall friction in the container, there are other considerations, and the present study investigates the possible additional effects of axial variation of tangential velocity and secondary (radial and axial) flow components within the rotating fluid.

Steward, W. Gene↗

NASA NTRS1993

Monitoring cognitive function and need with the automated neuropsychological assessment metrics in Decompression Sickness (DCS) research

Hypobaric decompression sickness (DCS) research presents the medical monitor with the difficult task of assessing the onset and progression of DCS largely on the basis of subjective symptoms. Even with the introduction of precordial Doppler ultrasound techniques for the detection of venous gas emboli (VGE), correct prediction of DCS can be made only about 65 percent of the time according to data from the Armstrong Laboratory's (AL's) hypobaric DCS database. An AL research protocol concerned with exercise and its effects on denitrogenation efficiency includes implementation of a performance assessment test battery to evaluate cognitive functioning during a 4-h simulated 30,000 ft (9144 m) exposure. Information gained from such a test battery may assist the medical monitor in identifying early signs of DCS and subtle neurologic dysfunction related to cases of asymptomatic, but advanced, DCS. This presentation concerns the selection and integration of a test battery and the timely graphic display of subject test results for the principal investigator and medical monitor. A subset of the Automated Neuropsychological Assessment Metrics (ANAM) developed through the Office of Military Performance Assessment Technology (OMPAT) was selected. The ANAM software provides a library of simple tests designed for precise measurement of processing efficiency in a variety of cognitive domains. For our application and time constraints, two tests requiring high levels of cognitive processing and memory were chosen along with one test requiring fine psychomotor performance. Accuracy, speed, and processing throughout variables as well as RMS error were collected. An automated mood survey provided 'state' information on six scales including anger, happiness, fear, depression, activity, and fatigue. An integrated and interactive LOTUS 1-2-3 macro was developed to import and display past and present task performance and mood-change information.

Nesthus, Thomas E.↗

NASA NTRS1993

Driving terrestrial ecosystem models from space

Regional air pollution, land-use conversion, and projected climate change all affect ecosystem processes at large scales. Changes in vegetation cover and growth dynamics can impact the functioning of ecosystems, carbon fluxes, and climate. As a result, there is a need to assess and monitor vegetation structure and function comprehensively at regional to global scales. To provide a test of our present understanding of how ecosystems operate at large scales we can compare model predictions of CO2, O2, and methane exchange with the atmosphere against regional measurements of interannual variation in the atmospheric concentration of these gases. Recent advances in remote sensing of the Earth's surface are beginning to provide methods for estimating important ecosystem variables at large scales. Ecologists attempting to generalize across landscapes have made extensive use of models and remote sensing technology. The success of such ventures is dependent on merging insights and expertise from two distinct fields. Ecologists must provide the understanding of how well models emulate important biological variables and their interactions; experts in remote sensing must provide the biophysical interpretation of complex optical reflectance and radar backscatter data.

Waring, R. H.↗

NASA NTRS1993

Global coverage Mobile Satellite Systems: System availability versus channel propagation impairments

Mobile Satellite Systems (MSS) in Highly Elliptical (HEO) and circular Earth orbits at Medium (MEO) and Low (LEO) altitudes have been intensively studied in the last few years as an effective means of providing global communication services. Such global coverage MSS networks are also expected to mitigate typical channel impairments usually encountered in geostationary Land Mobile Satellite (LMS) systems. In the design stages of these satellite networks, information regarding the mobile propagation channel is needed to assess the overall link availability versus elevation angle and environmental scenarios. For multisatellite LMS configurations, the mobile user on the Earth surface sees, at any given time, more than one satellite of the constellation. In our paper, it is shown that, under certain working assumptions regarding the statistics of the propagation channel, an improvement of the link availability may be achieved through the use of a multisatellite constellation. The analyses have been carried out using the European Space Agency (ESA) LMS propagation data base which presently covers a wide range of elevation angles and environmental scenarios.

Sforza, M.↗

NASA NTRS1994

Stationary Plasma Thruster Plume Characteristics

Stationary Plasma Thrusters (SPT's) are being investigated for application to a variety of near-term missions. This paper presents the results of a preliminary study of the thruster plume characteristics which are needed to assess spacecraft integration requirements. Langmuir probes, planar probes, Faraday cups, and a retarding potential analyzer were used to measure plume properties. For the design operating voltage of 300 V the centerline electron density was found to decrease from approximately 1.8 x 10 exp 17 cubic meters at a distance of 0.3 m to 1.8 X 10 exp 14 cubic meters at a distance of 4 m from the thruster. The electron temperature over the same region was between 1.7 and 3.5 eV. Ion current density measurements showed that the plume was sharply peaked, dropping by a factor of 2.6 within 22 degrees of centerline. The ion energy 4 m from the thruster and 15 degrees off-centerline was approximately 270 V. The thruster cathode flow rate and facility pressure were found to strongly affect the plume properties. In addition to the plume measurements, the data from the various probe types were used to assess the impact of probe design criteria

Myers, Roger M.↗

NASA NTRS1993

Flight-vehicle materials, structures, and dynamics - Assessment and future directions. Vol. 5 - Structural dynamics and aeroelasticity

Various papers on flight vehicle materials, structures, and dynamics are presented. Individual topics addressed include: general modeling methods, component modeling techniques, time-domain computational techniques, dynamics of articulated structures, structural dynamics in rotating systems, structural dynamics in rotorcraft, damping in structures, structural acoustics, structural design for control, structural modeling for control, control strategies for structures, system identification, overall assessment of needs and benefits in structural dynamics and controlled structures. Also discussed are: experimental aeroelasticity in wind tunnels, aeroservoelasticity, nonlinear aeroelasticity, aeroelasticity problems in turbomachines, rotary-wing aeroelasticity with application to VTOL vehicles, computational aeroelasticity, structural dynamic testing and instrumentation.

Noor, Ahmed K.↗

NASA NTRS1994

Radar altimeter calibration using SLR

Clearly a calibration of the TOPEX altimeter (and future TOPEX-class altimeters) which is more accurate and better prepared to meet the demands of global sea level trend monitoring is warranted. TOPEX/Posideon (T/P) is in its second year of data acquisition. If it survives or surpasses the two to five year projected baseline, an unprecedented opportunity for monitoring global sea level trends at mm/y levels will have been lost due to insufficient accuracy in its altimeter calibration. It is therefore paramount to revisit the design of the T/P calibration experiment and implement a more direct approach which better utilizes the accuracy of SLR to perform this needed bias assessment.

Klosko, Steven M.↗

NASA NTRS1994

Acoustic properties and durability of liner materials at non-standard atmospheric conditions

This report documents the results of an experimental study on how acoustic properties of certain absorbing liner materials are affected by nonstandard atmospheric conditions. This study was motivated by the need to assess risks associated with incorporating acoustic testing capability in wind tunnels with semicryogenic high Reynolds number aerodynamic and/or low pressure capabilities. The study consisted of three phases: 1) measurement of acoustic properties of selected liner materials at subatmospheric pressure conditions, 2) periodic cold soak and high pressure exposure of liner materials for 250 cycles, and 3) determination of the effect of periodic cold soak on the acoustic properties of the liner materials at subatmospheric conditions and the effect on mechanical resiliency. The selected liner materials were Pyrell foam, Fiberglass, and Kevlar. A vacuum facility was used to create the subatmospheric environment in which an impedance tube was placed to measure acoustic properties of the test materials. An automated cryogenic cooling system was used to simulate periodic cold soak and high pressure exposure. It was found that lower ambient pressure reduced the absorption effectiveness of the liner materials to varying degrees. Also no significant change in the acoustic properties occurred after the periodic cold soak. Furthermore, mechanical resiliency tests indicated no noticeable change.

Ahuja, K. K.↗

NASA NTRS1995

Category 5 problem solution using an unstructured finite volume algorithm

For the simulation of flows with complex geometries, unstructured finite volume methods have proven to be very popular, and simulations of a large number of flows have been done with good results using this approach. Since most of the simulations to date were done for steady flows, it is not clear that present unstructured finite volume algorithms can accurately track the unsteady propagation of acoustic waves in a computation. Therefore, there is a need to assess the accuracy of these methods for acoustic calculations. In this paper, we perform the numerical simulation of a very small amplitude acoustic wave incident on the non-uniform steady flow in a quasi- 1 D convergent-divergent nozzle using an unstructured finite volume algorithm with piece-wise linear, least square reconstruction, Roe flux difference splitting, and second-order MacCormack time marching. First, the spatial accuracy of the algorithm is evaluated for the steady flow by running the simulation with a sequence of successively finer meshes. Then the unsteady numerical solution with the acoustic perturbation is presented.

Bui, Trong T.↗

NASA NTRS1995

Low acid producing solid propellants

The potential environmental effects of the exhaust products of conventional rocket propellants have been assessed by various groups. Areas of concern have included stratospheric ozone, acid rain, toxicity, air quality and global warming. Some of the studies which have been performed on this subject have concluded that while the impacts of rocket use are extremely small, there are propellant development options which have the potential to reduce those impacts even further. This paper discusses the various solid propellant options which have been proposed as being more environmentally benign than current systems by reducing HCI emissions. These options include acid neutralized, acid scavenged, and nonchlorine propellants. An assessment of the acid reducing potential and the viability of each of these options is made, based on current information. Such an assessment is needed in order to judge whether the potential improvements justify the expenditures of developing the new propellant systems.

Bennett, Robert R.↗