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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Solution growth of Triglycine Sulfate (TGS) crystals on the International Microgravity Laboratory (IML-1)

An experiment was planned for the International Microgravity Laboratory (IML-1) to be launched around Feb. 1991. Crystals of triglycine sulfate (TGS) will be grown by low temperature solution crystal growth technique using a multiuser facility called Fluid Experiment System (FES). A special cooled sting technique of solution crystal growth will be used where heat is extracted from the seed crystal through a semi-insulating sting, thereby creating the desired supersaturation near the growing crystal. Also, a holocamera will be used to provide tomography of the three dimensional flow field and particle image displacement velocimetry to monitor the convective flows.

Lal, Ravi B.↗
NASA NTRS1991

Minor surgery in microgravity

The purpose is to investigate and demonstrate equipment and techniques proposed for minor surgery on Space Station Freedom (SSF). The objectives are: (1) to test and evaluate methods of surgical instrument packaging and deployment; (2) to test and evaluate methods of surgical site preparation and draping; (3) to evaluate techniques of sterile procedure and maintaining sterile field; (4) to evaluate methods of trash management during medical/surgical procedures; and (4) to gain experience in techniques for performing surgery in microgravity. A KC-135 parabolic flight test was performed on March 30, 1990 with the goal of investigating and demonstrating surgical equipment and techniques under consideration for use on SSF. The flight followed the standard 40 parabola profile with 20 to 25 seconds of near-zero gravity in each parabola.

Billica, Roger↗
NASA NTRS1990

Microgravity laboratory simulations of planetary and stellar circulations

This paper summarizes experiments on thermal convection in a rotating differentially heated spherical shell of liquid that were carried out in the microgravity laboratory of Spacelab III. In these experiments, dielectric polarization forces were used to generate a radially-directed buoyancy force. This enabled the simulation of a number of geophysically and astrophysically important situations in which sphericity and rotation both impose strong constraints on the global scale fluid dynamics. Recent theoretical and numerical interpretations of the original data are discussed. Further laboratory experiments in the areas of geophysical and g-jitter fluid dynamics are suggested.

Hart, John E.↗
NASA NTRS1991

Instability of multi-layer fluid configurations in the presence of time-dependent accelerations in a microgravity environment

The increasing number of research opportunities in a microgravity environment will benefit not only fundamental studies in fluid dynamics, but also technological applications such as those involving materials processing. In particular, fluid configurations which involve fluid-fluid interfaces would occur in a variety of experimental investigations. This work investigates the stability of a configuration involving fluid-fluid interfaces in the presence of a time-dependent forcing. Both periodic (g-jitter) and nonperiodic accelerations are considered. The fluid configuration is multilayered, and infinite in extent. The analysis is linear and inviscid, and the acceleration vector is oriented perpendicular to each interface. A Floquet analysis is employed in the case of the periodic forcing. In the problem of nonperiodic forcing, the resulting system of equations are integrated in time. Specific nondimensional parameters appear in each problem. The configuration behavior is investigated for a range of parameter values.

Lyell, M. J.↗
NASA NTRS1991

Programmable multi-zone furnace for microgravity research

In order to provide new furnace technology to accommodate microgravity research studies and commercial applications in material processes, research has been initiated on the development of the Programmable-Multi-zone Furnace (PMZF). The PMZF is described as a multi-user materials processing furnace facility that is composed of thirty or more heater elements in series on a muffle tube or in a stacked ring-type configuration and independently controlled by a computer. One of the aims of the PMZF project is to allow furnace thermal gradient profiles to be reconfigured without physical modification of the hardware by creating the capability of reconfiguring thermal profiles in response to investigators' requests. The future location of the PMZF facility is discussed; the preliminary science survey results and preliminary conceptual designs for the PMZF are presented; and a review of multi-zone furnace technology is given.

Rosenthal, Bruce N.↗
NASA NTRS1991

Ground based preparation for microgravity growth of alloy semiconductors

Ground-based research conducted in order to prepare a microgravity space flight experiment is presented. The thermophysical properties of a PbSnTe alloy used for semiconductors are investigated, and furnace calibration and fluid-flow measurements are performed. The alloy has a zero energy crossing at approximately 40 percent SnTe in its band-gap vs composition diagram, which facilitates the design of long-wavelength IR detectors and lasers. The uniformity of devices made from this material depends on the ratio of PbTe and SnTe and requires the composition of the crystal growth to be closely controlled. The main obstacle to such control is the fact that liquid of this material is always solutally or thermally unstable, and, in a high-temperature gradient, the double convective instability cannot be made stable by balancing thermal and solutal expansion. In order to extend the science of crystal growth, the limits of suppression of convection have to be tested in low earth orbit.

Fripp, Archibald L.↗
NASA NTRS1991

A preview of a microgravity laser light scattering instrument

The development of a versatile, miniature, modular light scattering instrument to be used in microgravity is described. The instrument will measure microscopic particles in the size range of thirty angstroms to above three microns. This modular instrument permits several configurations, each optimized for a particular experiment. In particular, a multiangle instrument will probably be mounted in a rack in the Space Shuttle and on the Space Station. It is possible that a Space Shuttle glove-box and a lap-top computer containing a correlator card can be used to perform a number of experiments and to demonstrate the technology needed for more elaborate investigations.

Meyer, W. V.↗
NASA NTRS1990

Thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity

Computer simulation of steady-state axisymmetrical heat transfer and fluid flow was conducted to study thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity. The effects of key variables on the extent of thermocapillary flow in the melt zone, the shapes of melt/solid interfaces and the length of the melt zone were discussed. These variables are: (1) the temperature coefficient of surface tension (or the Marangoni number), (2) the pulling speed (or the Peclet number), (3) the feed rod radius, (4) the ambient temperature distribution, (5) the heat transfer coefficient (or the Biot number), and (6) the thermal diffusivity of the material (or the Prandtl number).

Lan, C. W.↗
NASA NTRS1990

A half-zone study of Marangoni convection in floating-zone crystal growth under microgravity

Floating-zone crystal growth under microgravity, though free from natural convection, can still be susceptible to Marangoni convection. The use of a ring heater in contact with most of the surface of the melt zone, has recently been considered as one way of reducing Marangoni convection in the melt zone. In order to study Marangoni convection in the melt zone in this modified floating-zone crystal growth process, a half-zone system was adopted. Computer simulation and direct observation of Marangoni convection in the half-zone system were carried out for two different cases. In the first case, the surface of the melt zone was completely free, while in the second it was mostly in contact with a quartz ring. The results of computer simulation and direct observation both indicated that in the second case Marangoni convection was significantly reduced near the melt/solid interface as well as in the bulk melt.

Lan, C. W.↗
NASA NTRS1990

A new approach to controller design for microgravity isolation systems

A new method has been developed to design an active vibration isolation system for microgravity space experiments. This method yields the required controller transfer functions for a specified transmissibility. Hence, it is a straightforward task to guarantee that the desired vibration isolation performance is achieved at each frequency. The theory for such a controller design has been presented by considering a single degree of freedom system. The magnitude of the control force required by the new method has been found to be less than that used by a standard phase lead/lag compensator.

Sinha, A.↗
NASA NTRS1990

Limitations on vibration isolation for microgravity space experiments

The vibration-isolation limitations of spaceborne microgravity experiments are largely due to isolation-system volume restrictions. In the present one-degree-of-freedom representation of an experimental aircraft, assuming an ideal vibration actuator, wall motion is characterized as sinusoidal at a single frequency. The result is a kinematic representation which poses the problem of the minimum acceleration trajectory within a pair of moving walls; analysis then yields a simple condition under which a closed-form solution is available. The results obtained demonstrate that isolation from low-frequency vibration requires more interior space than is available for vibration isolation on manned orbiters.

Knospe, C.↗
NASA NTRS1991

Decreased susceptibility to motion sickness during exposure to visual inversion in microgravity

Head and body movements made in microgravity tend to bring on symptoms of motion sickness. Such head movements, relative to comparable ones made on earth, are accompanied by unusual combinations of semicircular canal and otolith activity owing to the unloading of the otoliths in 0G. Head movements also bring on symptoms of motion sickness during exposure to visual inversion (or reversal) on earth because the vestibulo-ocular reflex is rendered anti-compensatory. Here, evidence is presented that susceptibility to motion sickness during exposure to visual inversion is decreased in a 0G relative to 1G force background. This difference in susceptibility appears related to the alteration in otolith function in 0G. Some implications of this finding for the etiology of space motion sickness are described.

Lackner, James R.↗
NASA NTRS1990

An approach to counteracting long-term microgravity-induced muscle atrophy

To find means of alleviating muscle atrophy induced by long-term microgravity, the effects of a 19-week-long heavy-resistance training regime (using either concentric muscle actions only or concentric and eccentric muscle actions) on the strengths of the exercised knee extensor muscle group were investigated in two groups of male human subjects performing two types of training exercises: supine leg press or/and seated knee extension. Results show that a training program in which both the concentric and the eccentric muscle action was performed led to substantially greater increases in maximal muscle strength than when only concentric exercises were performed.

Tesch, P. A.↗
NASA NTRS1991

Maximum expiratory flow-volume curves during short periods of microgravity

Nine normal subjects were studied in a NASA microgravity research aircraft to elucidate the effect of normal gravitation on the shape of the maximum expiratory flow-volume (MEFV). They performed multiple MEFV maneuvers at 0, 1, and approximately 2 G. The MEFV curves for each subject were filtered, aligned at residual volume, and ensemble-averaged to produce an average MEFV curve for each state, allowing differences to be studied. Most subjects showed a decrease in the forced vital capacity at 0 G. The mean lung volume associated with a given flow was lower at 0 G over about the upper half of the vital capacity. There were consistent but highly individual changes in the position and magnitude of detailed features of the curve. This supports the concept that the location and motion of choke points that determine the detailed individual configuration of MEFG curves can be significantly influenced by gravitational forces, presumably via the effects of change in longitudinal tension on local airway pressure-diameter behavior and thus wave speed.

Guy, H. J. B.↗
NASA NTRS1991

Microgravity testing a surgical isolation containment system for Space Station use

Anticipated hazards for crewmembers in future long term space flights may result in a variety of injuries including trauma and burns. Management of these injuries will require special techniques because of the lack of gravity, limitations of space and environmental restrictions. A small surgical isolation containment system was developed and tested in microgravity. The chamber provided both protection of the injury and of the cabin environment and is felt to be the most effective means of trauma and burn care in future Health Maintenance Facilities planned for prolonged space exposure.

Markham, Sanford M.↗
NASA NTRS1991

High resolution synchrotron X-radiation diffraction imaging of crystals grown in microgravity and closely related terrestrial crystals

Irregularities in three crystals grown in space and in four terrestrial crystals grown under otherwise comparable conditions have been observed in high resolution diffraction imaging. The images provide important new clues to the nature and origins of irregularities in each crystal. For two of the materials, mercuric iodide and lead tin telluride, more than one phase (an array of non-diffracting inclusions) was observed in terrestrial samples; but the formation of these multiple phases appears to have been suppressed in directly comparable crystals grown in microgravity. The terrestrial seed crystal of triglycine sulfate displayed an unexpected layered structure, which propagated during directly comparable space growth. Terrestrial Bridgman regrowth of gallium arsenide revealed a mesoscopic structure substantially different from that of the original Czochralski material. A directly comparable crystal is to be grown shortly in space.

Steiner, Bruce↗
NASA NTRS1991

Heat Transfer to a Thin Solid Combustible in Flame Spreading at Microgravity

The heat transfer rate to a thin solid combustible from an attached diffusion flame, spreading across the surface of the combustible in a quiescent, microgravity environment, was determined from measurements made in the drop tower facility at NASA-Lewis Research Center. With first-order Arrhenius pyrolysis kinetics, the solid-phase mass and energy equations along with the measured spread rate and surface temperature profiles were used to calculate the net heat flux to the surface. Results of the measurements are compared to the numerical solution of the complete set of coupled differential equations that describes the temperature, species, and velocity fields in the gas and solid phases. The theory and experiment agree on the major qualitative features of the heat transfer. Some fundamental differences are attributed to the neglect of radiation in the theoretical model.

Bhattacharjee, S.↗
NASA NTRS1991

Discharge rate of cryogens in microgravity - What ground based experimentation cannot resolve

The discharge of cryogenic vapor and liquid from tanks to a vacuum is examined and the effects of the mass quality, length/diameter ratio, supply tank transient and gravitational environment are discussed. Existing model results and normal gravity experiments are presented which indicate that the homogeneous equilibrium model provides an accurate description of two-phase critical flow for a number of conditions likely to be encountered in practical microgravity systems. Nonequilibrium effects are shown to produce flow rates greater than homogeneous equilibrium model predictions for long tubes with low inlet pressure and short tubes with high inlet pressure.

Purwin, T. P.↗