capsule will land in the deceleration facility filled with Polystyrene pellets. The maximum deceleration force is less than 25 g over a period of 0.2 seconds. The cylindrical PCM canisters have a diameter in the range of 10 mm and a length of about 20 mm. They are filled with the PCM in vacuum and sealed by electron beam welding. LiF is one of the selected test media. Its high volume contraction will clear up most of the phenomena involved in the shrinking process. Furthermore, its future utilization as a storage medium itself or as a component of a storage eutectic is very likely. Further PCMs under consideration are the eutectics LiF/MgF2, NaF/MgF2 and possibly LiF/LiOH if the melting temperature must be limited. The same PCMs are primary candidates for the ballistic flight experiment and the spacelab experiment described below. Expected Results The cooling rate of the PCM canisters depends on the temperature and the velocity of the nitrogen gas flow. Theoretical estimates show that an optimization of these parameters results in complete solidification of the PCM in the canisters being placed near the gas inlets. To those placed near the outlet—in the middle of the container vessel—the solidification process has just started at the end of free fall. Thus, all stages of the solidification process can be investigated when the PCM canisters are compared with their twins which were solidified in ground experiments. All microgravity-induced phenomena relevant to the TES can be evaluated qualitatively, except those caused by the lack of sedimentation. The main problems to be solved are the fabrication and sealing of the PCM canisters and the development of theoretical models able to describe the solidification
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