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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Protein crystal growth in low gravity

The effect of low gravity on the growth of protein crystals and those parameters which will affect growth and crystal quality was studied. The proper design of the flight hardware and experimental protocols are highly dependent on understanding the factors which influence the nucleation and growth of crystals of biological macromolecules. Thus, those factors are investigated and the body of knowledge which has been built up for small molecule crystallization. These data also provide a basis of comparison for the results obtained from low-g experiments. The flows around growing crystals are detailed. The preliminary study of the growth of isocitrate lyase, the crystal morphologies found and the preliminary x ray results are discussed. The design of two apparatus for protein crystal growth by temperature control are presented along with preliminary results.

Feigelson, Robert S.↗
NASA NTRS1990

Containerless low gravity processing of glass forming and immiscible alloys

Under normal one-g conditions immiscible alloys segregate extensively during solidification due to sedimentation of the more dense of the immiscible liquid phases. Immiscible (hypermonotectic) gold-rhodium alloys were processed in the 100 meter drop tube under low gravity, containerless conditions to determine the feasibility of producing dispersed structures. Three alloy compositions were utilized. Alloys containing 10 percent by volume of the gold-rich hypermonotectic phase exhibited a tendency for the gold-rich liquid to wet the outer surface of the samples. This wetting tendency led to extensive segregation in several cases. Alloys containing 80 and 90 percent by volume of the gold-rich phase possessed completely different microstructures from the 10 percent samples when processed under low-g, containerless conditions. Several samples exhibited microstructures consisting of well dispersed 2 to 3 microns diameter rhodium-rich spheres in a gold-rich matrix.

Andrews, J. Barry↗
NASA NTRS1989

Influence of non steady gravity on natural convection during micro-gravity solidification of semiconductors. I - Time scale analysis. II - Implications for crystal growth experiments

Consideration is given to the influence of temporal variations in the magnitude of gravity on natural convection during unidirectional solidification of semiconductors. It is shown that the response time to step changes in g at low Rayleigh numbers is controlled by the momentum diffusive time scale. At higher Rayleigh numbers, the response time to increases in g is reduced because of inertial effects. The degree of perturbation of flow fields by transients in the gravitational acceleration on the Space Shuttle and the Space Station is determined. The analysis is used to derive the requirements for crystal growth experiments conducted on low duration low-g vehicles. Also, the effectiveness of sounding rockets and KC-135 aircraft for microgravity experiments is examined.

Griffin, P. R.↗
NASA NTRS1990

Influence of low-gravity solidification on heterogeneous nucleation in stable iron-carbon alloys

The effect of gravity on the processes of nucleation and growth of Fe-C alloys during directional solidification was investigated in experiments in which inoculated and uninoculated samples of an alloy of the gray iron type were solidified on ground (1 g) and under the low-gravity (low-g) and high-gravity (high-g) conditions obtained by aircraft parabolic flights. It was found that a higher number of grains was obtained during solidification in high-g condition, due to higher convection in high-g. It was demonstrated that grain multiplication due to convection can contribute up to 23 percent of the total number of grains resulting from heterogeneous nucleation of uninoculated samples. For the case of inoculated samples, it was found that the contribution of the convection-induced nucleation can be as high as 30 percent, but can be zero at very low or very high grain numbers.

Tian, Huameng↗
NASA NTRS1990

Computation of convective flow with gravity modulation in rectangular cavities

In this work, a computational study is presented for the investigation of gravity modulation (g-jitter) effects in thermally driven cavity flows at terrestrial and microgravity environments. The two-dimensional, time-dependent Navier-Stokes equations are numerically integrated by a time-split method using direct matrix solvers. Computations at terrestrial gravity are utilized to assess the effects of adiabatic side-wall boundary conditions as well as the full nonlinearity of the governing equations on the sinusoidally forced Benard problem studied by Gresho and Sani. The low-g calculations focus on the establishment of critical frequency ranges and consider the effects of modulation direction and randomness. The applicability of linear analysis in the excitable frequency range at low g is also discussed.

Biringen, S.↗
NASA NTRS1989

Low frequency vibration isolation technology for microgravity space experiments

The dynamic acceleration environment observed on Space Shuttle flights to date and predicted for the Space Station has complicated the analysis of prior microgravity experiments and prompted concern for the viability of proposed space experiments requiring long-term, low-g environments. Isolation systems capable of providing significant improvements in this environment exist, but have not been demonstrated in flight configurations. This paper presents a summary of the theoretical evaluation for two one degree-of-freedom (DOF) active magnetic isolators and their predicted response to both direct and base excitations, that can be used to isolate acceleration sensitive microgravity space experiments.

Grodsinsky, C. M.↗
NASA NTRS1990

Prediction and reconstruction of on-orbit acceleration

As the number of acceleration sensitive experiments to be carried on each Shuttle or Space Station mission increases, the requirement for either low-g environment or for accelerometry at each experiment location also increases. Preflight planning of such experiments in the past has not always included detailed analyses of the acceleration environment at the experiment location that had a serious impact on the experiment. Careful modeling of the mission activities and their effect on the experiment in many cases would have been beneficial to these experiments. In some cases, the experiment was not comprised, but insufficient instrumentation was available onboard to directly measure accelerations at the experiment location. The type of preflight modeling available to assist in experiment design and mission integration is described, as well as the use of that tool postflight to enhance flight data when sensors are not ideally suited to experiment analysis. Examples of recent shuttle flight experiments are presented.

Bergmann, Edward↗
NASA NTRS1989

Integrated Cryogenic Experiment (ICE) microsphere investigation

The main objective is to determine the performance of microsphere insulation in a 0-g environment and compare its performance to reference insulations such as multilayer insulation. The Lockheed Helium Extended-Life Dewar (HELD) is used to provide superfluid-helium cold sink for the experiment. The use of HELD allows the low-g dynamic properties of Passive Orbital Disconnect Struts (PODS) to be characterized and provides a flight demonstration of the PODS system. The thermal performance of microspheres in 1 and 0 g was predicted, a flight experiment was designed to determine microsphere thermal performance, and the interface was also designed between the experimental package and the shuttle through HELD and the Hitchhiker-M carrier. A single test cell was designed and fabricated. The cell was filled with uncoated glass microspheres and tested with a liquid-nitrogen cold sink. The data were found to agree with predictions of microsphere performance in 1 g.

Spradley, I.↗
NASA NTRS1991

Influence of a magnetic field during directional solidification of MAR-M 246 + Hf superalloy

An area that has been almost totally overlooked in the optimization of properties in directionally solidified superalloys is the control of microstructural features through the application of a magnetic field during solidification. The influence of a magnetic field on the microstructural features of a nickel-base superalloys is investigated. Studies were performed on the dendritic MAR-M 246+Hf alloy, which was solidified under both a 5 K gauss magnetic field and under no-applied-field conditions. The possible influences of the magnetic field on the solidification process were observed by studying variations in microstructural features including volume fraction, surface area, number, and shape of the carbide particles. Stereological factors analyzed also included primary and secondary dendrite arm spacing and the volume fraction of the interdendritic eutectic constituent. Microprobe analysis was performed to determine the chemistry of the carbides, dendrites, and interdendritic constituents, and how it varied between field and no-field solidification samples. Experiments involving periodic application and removal of the magnetic field were also performed in order to permit a comparison with structural variations observed in a MAR-M 246+Hf alloy solidified during KC-135 high-g, low-g maneuvers.

Andrews, J. Barry↗
NASA NTRS1991

Analysis of cryogenic propellant behavior in microgravity and low thrust environments

Predictions of a CFD program calculating a fluid-free surface shape and motion as a function of imposed acceleration are validated against the drop-tower test data collected to support design and performance assessments of the Saturn S-IVB stage liquid-hydrogen tank. The drop-tower facility, experimental package, and experiment procedures are outlined, and the program is described. It is noted that the validation analysis confirms the program's suitability for predicting low-g fluid slosh behavior, and that a similar analysis could examine the effect of incorporating baffles and screens to impede initiation of any unwanted side loads due to slosh. It is concluded that in actual vehicle applications, the engine thrust tailoff profile should be included in computer simulations if the precise interface versus time definition is needed.

Fisher, Mark F.↗
NASA NTRS1991

Directional solidification in immiscible systems - The influence of gravity

The possibility of producing aligned fibrous composite microstructures with a high volume fraction of the immiscible phase, L2, through the directional solidification of hypermonotectic alloys is examined. Early work suggests that low gravity conditions are necessary to prevent sedimentation of the more dense L2 phase. However, if convective flows result, they disrupt the formation of the desired fibrous microstructure and produce a disperse structure. The need for long-duration low-g experiments is emphasized.

Andrews, J. B.↗
NASA NTRS1992

Determination of the natural convection coefficient in low-gravity

Fire safety is an important issue in the current space program; ignition in low-g needs to be studied. The reduction in the gravitational acceleration causes changes in the ignition process. This paper examines the effect of gravity on natural convection, which is one of the important parameters in the ignition process. The NASA-Lewis 2.2 Second Drop Tower provided the low-gravity environment for the experiments. A series of experiments was conducted to measure the temperature of a small copper plate which was heated by a high intensity lamp. These experiments verified that in low-gravity the plate temperature increased faster than in the corresponding 1-g cases, and that the natural convection coefficient rapidly decreased in the low-gravity environment.

Goldmeer, J.↗
NASA NTRS1991

International manned lunar base - Beginning the 21st century in space

An evaluation is made of requirements for, and advantages in, the creation of a manned lunar base whose functions emphasize astronomical investigations. These astronomical studies would be able to capitalize on the lunar environment's ultrahigh vacuum, highly stable surface, dark and cold sky, low-G, absence of wind, isolation from terrestrial 'noise', locally usable ceramic raw materials, and large radiotelescope dish-supporting hemispherical craters. Large telescope structures would be nearly free of the gravity and wind loads that complicate their design on earth.

Smith, Harlan J.↗
NASA NTRS1989

Fluid management in space construction

The low-g fluids management group with the Center for Space Construction is engaged in active research on the following topics: gauging; venting; controlling contamination; sloshing; transfer; acquisition; and two-phase flow. Our basic understanding of each of these topics at present is inadequate to design space structures optimally. A brief report is presented on each topic showing the present status, recent accomplishings by our group and our plans for future research. Reports are presented in graphic and outline form.

Snyder, Howard↗
NASA NTRS1990

Cryogenic On-Orbit Liquid Depot Storage, Acquisition, and Transfer satellite (COLD-SAT) feasibility study

The Cryogenic On-Orbit Liquid Depot Storage, Acquisition, and Transfer Satellite (COLD-SAT) is an experimental spacecraft launched from an expendable launch vehicle which is designed to investigate the systems and technologies required for efficient, effective, and reliable management of cryogenic fluid in the reduced gravity space environment. The COLD-SAT program will provide the necessary data base and provide low-g proving of fluid and thermal models of cryogenic storage, transfer, and resupply concepts and processes. A conceptual approach was developed and an overview of the results of the 24 month COLD-SAT Phase A feasibility is described which includes: (1) a definition of the technology needs and the accompanying experimental 3 month baseline mission; (2) a description of the experiment subsystem, major features and rationale for satisfaction of primary and secondary experiment requirements using liquid hydrogen as the test fluid; and (3) a presentation of the conceptual design of the COLD-SAT spacecraft subsystems which support the on-orbit experiment with emphasis on areas of greatest challenge.

Bailey, William J.↗
NASA NTRS1990

Feasibility study for a Cryogenic On-Orbit Liquid Depot-Storage, Acquisition and Transfer (COLD-SAT) satellite

This feasibility study presents the conceptual design of a spacecraft for performing a series of cryogenic fluid management flight experiments. This spacecraft, the Cryogenic On-Orbit Liquid Depot-Storage, Acquisition, and Transfer (COLD-SAT) satellite, will use liquid hydrogen as the test fluid, be launched on a Delta expendable launch vehicle, and conduct a series of experiments over a two to three month period. These experiments will investigate the physics of subcritical cryogens in the low gravity space environment to characterize their behavior and to correlate the data with analytical and numerical models of in-space cryogenic fluid management systems. Primary technologies addressed by COLD-SAT are: (1) pressure control; (2) chilldown; (3) no-vent fill; (4) liquid acquisition device fill; (5) pressurization; (6) low-g fill and drain; (7) liquid acquisition device expulsion; (8) line chilldown; (9) thermodynamic state control; and (10) fluid dumping.

Rybak, S. C.↗
NASA NTRS1992

Low gravity quenching of hot tubes with cryogens

An experimental proceedure for examining flow boiling in low gravity environment is presented. The proceedure involves both ground based and KC-135 flight experiments. Two experimental apparati were employed, one for studying subcooled liquid boiling and another for examining saturated liquid boiling. For the saturated flow experiments, liquid nitrogen was used while freon 113 was used for the subcooled flow experiments. The boiling phenomenon was investigated in both cases using flow visualization techniques as well as tube wall temperature measurements. The flow field in both cases was established by injecting cold liquid in a heated tube whose temperature was set above the saturation values. The tubes were both vertically and horizontally supported with the liquid injected from the lower end of the tube. The results indicate substantial differences in the flow patterns established during boiling between the ground based, (1-g), experiments and the flight experiments, (low-g). These differences in the flow patterns will be discussed and some explanations will be offered.

Antar, Basil N.↗