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                    Microsystems in Spacecraft Thermal Control                      201


                    low heat capacity, and low thermal conductivity heat transport paths, they can
                    exceed their survival temperatures very easily in a short time.
                       MEMS thermal control devices need to be properly protected for physical
                    damages. Sensors and actuators coming into contact with the environment
                    must be protected against adverse affects, especially if the devices are subject to
                    long-term reliability concerns. Careful procedures need to be considered during
                    design and handling of MEMS TCS to prevent potential threat of humidity,
                    contamination, and charging. Ground handling is as much of a concern as in-
                    space operations.
                       Similar to other components on a spacecraft, MEMS thermal control devices
                    are susceptible to space environment induced damages. Therefore, ground-based
                    environmental tests must be conducted on the final flight design to verify surviv-
                    ability of MEMS thermal control devices. Based on mission conditions, a list of
                    environmental test requirements will typically be established for the MEMS de-
                    vices.


                    9.5 CONCLUSION

                    Spacecraft TCS use both passive and active thermal control devices to maintain
                    spacecraft systems within allowable temperature ranges. Passive thermal control is
                    the most commonly used, while active thermal control is employed to accommodate
                    stringent temperature control requirements, high power dissipation, and to provide
                    design flexibility. Passive thermal control devices do not contain either moving
                    parts or fluids. Based on these distinct characteristics, MEMS TCS are categorized
                    as mainly an active thermal control concept.
                       Future space missions require complex spacecraft design, operation scenarios,
                    and flight configurations. The push for low-cost and short-assembly schedules
                    increases the demand for nano- or microsatellites. MEMS thermal control devices
                    may become a critical element in such applications as they offer some unique
                    advantages, especially for small spacecraft. Although the development of MEMS-
                    based technology is still in its infancy, the advancement in MEMS thermal control
                    devices is moving forward.



                    REFERENCES
                     1. Birur, G., G. Siebes, and T.D. Swanson, Spacecraft thermal control, in Encyclopedia of
                       Physical Science and Technology. 2002.
                     2. Incropera, F.P. and D.P. DeWitt, Introduction to Heat Transfer. Third ed. 1996, John
                       Wiley and Sons, Inc., New York, NY.
                     3. Wingate, C.A., Spacecraft thermal control, in Fundamentals of Space Systems, Pisacane,
                       V.L. and R.D. Moore, Editors, 1994, Oxford University Press, New York, NY, p. 443.
                     4. Biter, W., S. Oh, and S. Hess, Electrostatic switched radiator for space based thermal
                       control, in Space Technology and Applications International Forum — STAIF 2002.
                       2002, Albuquerque, NM.





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