We established a Free Drift (FD) method to remotely measure the force generated on an isolated object simulated using an Electrostatic Levitation Furnace (ELF). The FD method can be applied in high power laser ablation experiments, where the electric charge of the sample changes drastically during the irradiation. The analyses to deduce the thrust are described in detail. Using this method in the ELF on the International Space Station (ISS), we successfully measured the thrust generated by laser beam irradiation to an Al droplet for the first time. The momentum coupling coefficient (Cm ) when irradiated by a laser beam with a laser power density of 103 -104 W/cm2 was around 10-9 N/W.

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Space agriculture has attracted attention as a solution to the logistical and psychological challenges of long-term missions, such as those planned under the Artemis program. We investigated the effect of soil pressure on the early stage enlargement of sweet potato root tubers, a promising crop for space agriculture. Growth experiments were conducted under three soil pressure treatments—low, high, and control—in planters filled with different media. Sweet potatoes were grown in a controlled environment, and growth parameters, including the fresh weights of shoots, roots, and root tubers, were measured 40 days after transplanting. Root lengths were analyzed using WinRHIZO software. The results showed a negative correlation between soil pressure and the fresh weight of shoots and roots, whereas root tubers indicated a positive correlation. Total root lengths decreased under the high pressure, while the mass of fine-diameter roots remained relatively unchanged. These findings suggest that moderate soil pressure may be beneficial for storage root development, although it may suppress the growth of other organs. Our study highlights the importance of maintaining appropriate soil pressure in microgravity environments to promote successful sweet potato growth.

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This study experimentally evaluated the effect of internal bubbles (void fraction) on the combustion behavior of polypropylene (PP) spheres under microgravity. In previous research, it has been demonstrated that bubble generation during the burning of polymethyl methacrylate (PMMA) spheres clearly affected the burning rate constant. However, because PMMA exhibits unique pyrolysis characteristics —being composed predominantly of monomers— the observed void effect may not necessarily apply to other polymers. In this study, PP spheres with various initial internal void fractions were used as test specimens and burned under microgravity conditions generated using a drop tower test facility. A total of thirteen productive runs were successfully conducted, showing that the burning rate constant of PP spheres exhibited a positive correlation with the initial void fraction in the range of 0–40%, while remaining nearly constant above 40%. This trend indicates that the material-dependent physical properties play a dominant role in the process from bubble growth to bursting. Extrapolation to zero initial void fraction yielded an ideal (with the least initial void effect) burning rate constant of 0.60–0.72 mm²/s (indicating the potential uncertainty range), with the corresponding B-number ranging from 0.42–0.53. These findings suggest that bubble dynamics still significantly influence the burning behavior of PP and confirm the validity of void-fraction-based evaluation methods for identifying the intrinsic burning properties of polymers.

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