Microgravity Research in Support of Technologies for the Human Exploration and Development of Space and Planetary Bodies (2000) / Chapter Skim
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V Other Concerns
V Other Concerns
Pages 167-178
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From page 167... ...
Another such indirect effect concerns the products of wear and decay, which are presumably less easily collected and managed in reduced gravity than in Earth gravity. There can be no confidence in the success and safety of long-duration crowed missions unless such indirect effects are well identified, understood, and managed.
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From page 168... ...
One may conclude that careful analysis should be made of the system dynamics of entire fluid networks for HEDS applications in reduced gravity, including structural effects as well as the multiphase fluid flow phenomena treated in Section IV.C. Bearings It has been pointed out that many HEDS systems and components will have rotating machinery, and these will require bearings to maintain shaft positions and to bear loads under various speed requirements.
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From page 169... ...
However, the dynamic behavior of mechanical devices in microgravity certainly merits ongoing, device-specific research for HEDS. It must be borne in mind that HEDS missions will typically impose a significant range of gravity levels, and all spacecraft elements will be expected to function in variable gravity.
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From page 170... ...
During a typical HEDS mission, the gravity level will vary from zero to near-Earth values; this variability of gravity is itself a problem, because a design suited to one gravity level may be quite inappropriate for other levels that are encountered in the course of the mission. Artificial gravity could eliminate this variability by making possible the continuous adjustment of effective gravity level during the course of a mission.
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From page 171... ...
The most familiar and, presumably, reliable method is to impose rotation in order to provide a centrifugal force that mimics gravity, subject to certain limitations (to be discussed)
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From page 172... ...
Because an adjustable level of effective gravity achievable by spacecraft rotation could be beneficial for both crew health and component performance, microgravity research should take account of the following: · Physical effects should be studied as functions of gravity level. That is, it should be recognized that gravity level is not necessarily "given" but might be "designed." For example, above what gravity level will a two-phase heat transfer loop be preferred to a single-phase device?
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From page 173... ...
The approach used may be the direct one of mechanical rotation (the so-called rotary fluid management device) , or a more indirect, passive one that induces swirl by tangential flow injection.
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From page 174... ...
In microgravity, the purpose might be to separate phases, as in the case of the RFMD, or to mix phases. The reversal of force direction implicit in oscillations suggests that oscillations would be especially useful when mixing is the purpose, perhaps to enhance heat transfer or increase combustion rates.
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From page 175... ...
Flow Deflection as a Microgravity Countermeasure Sinuous steady flow can also be a means of phase management. A natural example is river meander, which increases with time by continuous transport of soil from the outer bank of a river bend to the inner bank, as a result of secondary (viscous)
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From page 176... ...
It should also be made clear to the HEDS community how m~crogravity research can explain the need for, and the value of, artificial gravity, especially for long missions; in other words, the m~crogravity research community should provide the motivation for NASA to solve perceived problems, using spacecraft rotation or other appropriate and feasible means. NASA should consider planning in-space research on partial gravity using rotational or other means to achieve desired gravity levels for HEDS systems or their components.
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From page 177... ...
In particular, a better understanding of scaling-law boundaries and multiphase flow and heat transfer phenomena is needed. There is, clearly, a logical path leading from microgravity research to modeling, to risk assessment, and, finally, to reliability.
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