Plants play an important role in bio-regenerative life support systems (BLSSs) for long-term manned space missions. During parabolic airplane flights, we investigated stem sap flow without forced air movement and water vapor conductance with forced air movement using sweetpotato plants. Stem sap flow was promoted under microgravity, but only when forced air movement was applied to the plants. The water vapor conductance of the plant leaves increased under microgravity at an air velocity of 0.25 m∙s－1. Leaf temperatures also increased under microgravity at an air velocity of 0.02 m∙s－1. This suggests that forced air movement is important in maintaining long-term, healthy plant growth in BLSSs.

View full abstract

We studied crystallization process of charged colloids under microgravity (µG) by performing time resolved reflection spectroscopy, during aircraft parabolic flight experiments. We used dilute colloidal silica samples (specific gravity of the particles = 2.1, the particle concentration = 1 – 2 vol.%) that crystallized from shear-melt colloids, within the duration time of µG (approximately 20 seconds). An influence of µG was found to be less significant for the heterogeneous nucleation process with the aid of the cell walls. The incubation times of the homogeneous nucleation, τ, at µG was longer than that at 1G. Furthermore, the half-widths of the Bragg diffraction peaks from the crystals were narrower by 30% at the largest, under µG. This suggests that the crystal grain size (cross-sectional area) became larger under µG environment, according to the Scherrer’s relation.

View full abstract

Convection flows induced by formation of solute depletion zone around growing protein crystals are visualized to confirm whether growth of crystals at a ceiling position (top wall of a growth container) can really suppress this convection flow effectively or not. First, we observed the convection flows around the crystal at the ceiling position at 1.0 G. Second, parabolic flight experiments revealed that flow rates of polystyrene particles (as marker particles, 500 nm in diameter) around a crystal at the ceiling position did not indicate zero at high-gravity conditions, and the particles almost stop at zero gravity. Thus, stable microgravity experiments are still indispensable to attain complete convection-free conditions.

View full abstract

Cosmic dust, which is composed of nanometer-sized particles and is ubiquitously distributed in the universe, is formed in a gas outflow from evolved stars under a microgravity environment. Its formation processes have been studied on the basis of knowledge obtained under the 1 G environment on Earth and is thus not fully understood under realistic conditions. To better understand the process, here, we performed nucleation experiments of dust analogs under a microgravity environment. We show the details of our experiments using an aircraft including results of in-situ observation employing an interferometer and ex-situ transmission electron microscopy to reveal the difficulty of nucleation and variability of nucleation processes. Of particular note is the size distribution of the produced particle, which was monotonical in microgravity experiments against a double peak for particles produced in the laboratory. Under a microgravity environment, nucleation tends to suppress because of smaller density fluctuation due to convection free and less turbulence due to smaller Reynolds number which gives atoms/molecules (particles) smaller chance to collide with each other for nucleation (coagulation).

View full abstract