Microgravity experiments on ice crystal growth in supercooled water without any effect of convection flow were carried out twice in Kibo of the International Space Station as projects called “Ice Crystal 1” and “Ice Crystal 2”. Many video movies recording the growth process of a single ice crystal were analyzed to clarify the pattern formation processes of single ice crystals and the impurity effect on ice crystal growth kinetics. In the Ice Crystal 1 project, ice crystals were grown in supercooled pure D2O and the pattern formation mechanism for the ice crystal was clarified on the basis of crystal plane-dependent growth kinetics between the basal face and the other crystallographic faces. In the Ice Crystal 2 project, ice crystals were grown in supercooled H2O containing a small amount of an antifreeze glycoprotein as an impurity. Growth enhancement and oscillation for the basal faces were observed for the first time, and their mechanisms were clarified on the basis of the crystal plane-dependent impurity effect of an antifreeze glycoprotein. The origin of the antifreeze function of antifreeze glycoproteins was ultimately explained in connection with the basic criterion for the pattern formation of a polyhedral crystal.
Extending the storage period for cryogenic propellant is necessary for future space exploration, such as Mars transportation. In a space mission, the heat entering from solar induces cryogenic propellant evaporation and generates the boil-off gas (BOG) from the propellant. The BOG causes self-pressurization of the storage and shorten its storage period. Therefore, a pressure regulation system is necessary for extending the storage period. The thermodynamic vent system (TVS) regulates the pressure of the storage tank by reducing BOG with active thermal management. In this study, we did experiments of jet mixing using liquid nitrogen (LN2) against the LN2 self-pressurized tank in ground gravity environment to verify pressure-regulating function by jet mixing, a component of TVS. As a result of the tests, jet mixing reduced the boil-off rate by about 98 %. On the other hand, jet mixing with a smaller supply flow rate could reduce the boil-off rate only slightly. These results showed the effectiveness of jet mixing for reducing BOG and the importance of using appropriate flow rate at actual TVS.
Enzymatic saccharification of cellulose by cellulases is expected to enable energy-efficient production of soluble sugars from biomass, and thus the catalytic mechanisms of cellulases have been intensively studied. We have shown that mutation of non-catalytic cysteine residues of cellobiohydrolase Cel6A from the basidiomycete Phanerochaete chrysosporium improves the thermal stability of the enzyme. To understand why, we considered visualizing the hydrogen bond network within the mutant enzyme by neutron diffraction analysis. In this study, we first examined the optimum concentration ranges of NaCl and polyethylene glycol to produce the required large-volume crystal, and based on the results, we chose nine sets of conditions for crystallization under microgravity at the International Space Station. A large-volume crystal of the mutant enzyme was obtained successfully.