A final example of what may be anticipated with exploratory missions such as those to Mars is the management of cryogenic liquids such as oxygen. The importance of technologies to manage cryogenic liquids in microgravity has been recognized in previous NRC studies17 and in some NASA exploration planning studies.k Management of a cryogenic liquid involves its storage and transport via ducts. It may be anticipated that the non-venting mode of storage will be used for the long periods of time with exploratory missions. This may require refrigeration to condense the vapor formed if inward heat leaks are sufficiently large. Proper temperature gradients on the condensing surfaces together with their geometry can provide the motion by thermocapillary effects to move the liquid to the inlet of a suitable pump. The necessary temperature gradients can be provided by the refrigeration device. Successful cryo management under such circumstances will require an understanding of multiphase flow and heat transfer issues, and the ISS could serve as a unique testbed if appropriate engineering studies are planned and carried out.
Finding: Multiphase flow and heat transfer systems operating in microgravity environments are profoundly influenced by thermocapillarity effects and may be significant components of exploration missions. Studies aboard the ISS may be the only way to obtain information on temperature and geometry effects on the motion of films and fluid particles at interfaces (with emphasis on thermocapillary effects).
One of the primary justifications for construction of the ISS was that it would allow unique materials to be developed and processed in microgravity. To that end, NASA encouraged and supported a significant research effort in microgravity materials research with the intent of better understanding the effects of gravity on materials processing. With the new vision for the ISS, NASA no longer supports microgravity materials research. The panel is concerned that this wholesale elimination of materials science research has also eliminated consideration of materials processes that might be quite important to exploration missions, such as welding, soldering, and brazingprocesses that rely on poorly understood interfacial effects and thermocapillarity.
1. Friedman, R. 1992-1993. Fire safety practices and needs in human-crew spacecraft. J. Appl. Fire Sci. 2(3): 243-250.
2. Zimmerman, R. 2003. Leaving Earth. Joseph Henry Press, Washington, D.C.
3. National Research Council (NRC). 2003. Factors Affecting the Utilization of the International Space Station for Research in the Biological and Physical Sciences. The National Academies Press, Washington, D.C.
4. NRC. 2000. Microgravity Research in Support of Technologies for the Human Exploration and Development of Space and Planetary Bodies. National Academy Press, Washington, D.C.
5. Ruff, G.A., D.L. Urban, and M.K. King. 2005. A research plan for fire prevention, detection and suppression in crew exploration systems. 43rd AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nev., January 10-13.