An Initial Review of Microgravity Research in Support of Human Exploration and Development of Space (1997) / Chapter Skim
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3 Science and Technology Needed for HEDS:Examples from an Initial Appraisal
3 Science and Technology Needed for HEDS:Examples from an Initial Appraisal
Pages 16-45
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From page 16... ...
At the same time, however, it should also become clear how crucial the scientific contributions required of MRD will be to meeting the overall goals of the HEDS enterprise. FLUID MANAGEMENT SYSTEMS Fundamental Effects of Microgravity In microgravity, the gravitational body force is reduced by about six orders of magnitude relative to that encountered on Earth.
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From page 17... ...
Microgravity Challenges Many of the issues in fluid management are not unique to HEDS missions but have been of concern to engineers of orbital spacecraft for decades. Some of the engineering solutions implemented for short-duration and near-Earth missions could prove feasible for HEDS missions as well.
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From page 18... ...
There is also the possibility that vibrations or accelerations arising in the course of a mission will cause sloshing modes to develop in fuel tanks, unless care is taken to prevent them. The ability to control and manipulate fluids by use of acoustic or magnetic forces will no doubt be important for management of bulk fluids under microgravity conditions.
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From page 19... ...
, which might be suspended in flowing gases or liquids, will similarly show dynamic effects dependent on the presence or absence of gravity or other body forces. Heat Transfer A thermal management system is necessary to stabilize spacecraft environments during long-duration HEDS missions.
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From page 20... ...
Of particular relevance to HEDS goals are those processes in which the resultant materials properties and behavior exhibit sensitivity to, or modification by, the magnitude and direction of gravity during processing. The response to gravity in materials processing usually arises from the presence of a fluid phase, the transport properties of which become modified by flows induced by the presence of internal density gradients interacting with the molecular and gravitational body forces.
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From page 21... ...
Gravity affects the flow patterns in a welding pool and consequently alters the solidification process and changes the metallurgical structure and mechanical properties of the weld. Another example of a materials processing technique that has been shown to be altered by microgravity processing is liquid phase sintering (LPS)
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From page 22... ...
Welding Welding is an example of a materials processing technique that will be critical to the creation of reliable joints in space. Fusion arc welding, in particular, is an important technique for joining metals and alloys into useful structures and machines.
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From page 23... ...
The interactions of metallurgical variables with the appropriate welding parameters needed for successful welding in space are still poorly understood in general and are not known for specific cases of interest. Microgravity research directed toward this important joining technology would be of value to future HEDS missions that might rely on fusion welding methods for cutting and joining of metallic materials.
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From page 24... ...
Experimental studies of the effects on cell cultures of long-term exposure to microgravity represent a potentially important new area of microgravity research. The medical complications that face astronauts will be caused in large part by alterations in cell and tissue function as a result of the microgravity environment.
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From page 25... ...
Finally, in addition to sources for production of food, nonnutrient biotechnical products such as therapeutic agents with limited shelf life may eventually be required during extended space travel. A significant role for microgravity research may exist in helping to provide the scientific understanding required to learn how to maintain an environment suitable for onboard human activities over the course of extended excursions into deep space.
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From page 26... ...
This redefinition of bioseparation needs represents a change of mind-set for research on microgravity effects on biological separations and, it should be noted, is a redefinition that characterizes research on microgravity effects on cell culture before and after HEDS as well. In sum, although there has been considerable past research on cell culture and bioseparations in microgravity, some key research areas remain to be explored in support of NASA's HEDS goals.
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From page 27... ...
This part of the MRD research program is supported under the first goal of the HEDS enterprise, that is, to increase knowledge of the role of gravity in nature by using the space environment, but it also has applications to other HEDS goals. An example of an important area within the fundamental physics program is that of laser cooling and the development of microgravity atomic clocks.
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From page 28... ...
FIRE SAFETY Fundamental Effects of Low Gravity on Combustion Processes Several important combustion phenomena are influenced strongly by buoyancy because of large density differences that appear at 1 g. These include mixture flammability, combustion instability, gaseous diffusion flames, droplet combustion, particle-cloud combustion, smoldering, and flame spread.18,19,20 The importance of these combustion phenomena to NASA's HEDS missions stems largely either from their importance with respect to fire safety and reliability of systems operations during space travel or from their relevance to the production of chemical species and new materials.
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From page 29... ...
Results to date show that carbon monoxide production in smoldering combustion is enhanced substantially in reduced gravity under suitable conditions.31 Findings of this kind are relevant to determination of fire hazards of many different solid materials and technological components encountered in HEDS. Flame Spreading Flame spreading over solid and liquid surfaces has direct implications with respect to fire safety and materials selection.
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From page 30... ...
Continuing microgravity combustion investigations can provide added information relevant to such selections and to general improvement of fire safety for HEDS. IN SITU RESOURCE UTILIZATION Fundamental Effects of Low Gravity on Materials and Chemical Processing In the absence of large pumping systems, gravity controls the maximum transport rates in fluids, even though its influence on chemical thermodynamic properties is negligible.
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From page 31... ...
The near elimination of such flows severely diminishes convective momentum and any associated heat and mass transport and thereby restricts the process of energy transport and mixing in fluids to molecular diffusion, thereby limiting the useful energy transfer modes to pure thermal conduction and radiation. The large reduction of buoyancy forces experienced in microgravity environments can also cause fluid systems to exhibit unusual behaviors governed by the emergence, and even dominance, of weak "secondary" molecular forces, such as the surface tension, thermo-capillary, or Marangoni forces, and van der Waals interactions.
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From page 32... ...
The ability to store and recover energy efficiently, in response to actual power requirements, is an important concern for HEDS missions. Chemical batteries are used to store energy in the kilowatt-hour range, but they are supplanted by fuel cells and other devices when the energy storage requirements go much beyond a few kilowatt-hours.
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From page 33... ...
Impacts on HEDS Goals The process for extracting oxygen from the Martian atmosphere is now understood sufficiently well to have been demonstrated in terrestrial laboratories.35 The converting of locally available atmospheric carbon dioxide into oxygen, for example, depends on an overall process design that is beginning to be shaped by higher-order questions related to the influence on thermal and chemical processes of the reduced gravity encountered on the Martian surface. The extraction of carbon monoxide from the Martian atmosphere, the production of methane using the Martian atmosphere, and in situ water recovery are less well developed chemical processes but are still well within current technological capabilities.
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From page 34... ...
Furthermore, in support of the HEDS enterprise, it must be recognized that a crewed mission to Mars will occur primarily in the microgravity environment imposed during the long journeys from Earth to Mars. Hence, the ability to use ISS as a test bed to develop extremely reliable autonomous systems for processing or recovering simple molecules represents a unique opportunity to develop advanced waste recycling and life-support systems that translate directly into early resource utilization systems.
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From page 35... ...
In fact, MRD has recently recognized the importance of this area by calling for proposals on in situ resource development as part of the materials science NRA.47 Some elements of that research, especially those associated with solidification and transport processes, could be used directly in the design of in situ resource processing systems associated with microgravity environments -- particularly for the production of materials for use in orbit. Near-term ISRU systems are also being addressed, to a limited extent, via the systematic study of fundamental fluid synthesis and transport processes in fractional and microgravity environments.
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From page 36... ...
Analysis and experiments concerning the thermal behavior in realistic microgravity environments of bearing designs will clearly be needed. The matter of bearings for space machinery provides an example of research and development that is needed because of microgravity effects, even though the device using the bearing itself may not require microgravity research.
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From page 37... ...
Presumably, robots will be especially well adapted for operations in microgravity, and they should be designed for the longest possible endurance. Therefore, how to design failure-proof joint bearings for robots and how to provide appropriate dynamic controls for robots are important topics for future microgravity research.
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From page 38... ...
This system would doubtless encounter many microgravity-related problems, including evaporation of the working fluid in a boiler, its passage through a vapor turbine, and its condensation back to a liquid metal, with heat rejection, to complete the cycle. In the evaporator56 and associated pumps and piping operating in a reduced or microgravity environment, capillary forces will become important in the process of liquid-vapor separation.
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From page 39... ...
With the new HEDS goals in mind, NASA should allow for the possibility that provision of a body force substitute for gravity may prove to be an absolute necessity for ambitious manned space missions of the future.
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From page 40... ...
1995. Liquid-phase sintering under microgravity conditions.
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From page 41... ...
1995. Microgravity Research Opportunities for the 1990s.
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From page 42... ...
1990. Radiation-controlled opposed-flow flame spread in a microgravity environment.
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P 11 in Proceedings of the Second Annual Symposium, University of Arizona NASA Space Engineering Research Center, Tucson, Ariz.; Lynch, D.C.
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From page 44... ...
1996. Thermohydrodynamic Analysis of Cryogenic Liquid Turbulent Flow Fluid Film Bearings.
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From page 45... ...
1990. Thermal Hydraulics for Space Power, Propulsion, and Thermal Management System Design, Progress in Astronautics and Aeronautics, Vol.
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