PS38
⾼校内における微⼩重⼒実験装置の開発と実験
Development of dropping experimental apparatus andmicrogravity experiments in high school
惠下樹 1, 荒井千代⼦ 1, 安⻄伽織 1, 江連奏汰 1, 實升理沙⼦ 1, 信太結⽉ 1, 中原颯太 1
Itsuki ESHITA1, Chiyoko ARAI1, Kaoru ANZAI1, Sota EZURE1, Risako SANEMASU1, Yuzuki SHIDA1
Sota NAKAHARA1
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東京学芸⼤学附属⾼等学校，Tokyo Gakugei University Senior High SchoolIntroduction

1.1. Background
The Zero-Gravity Experiment Team at Tokyo Gakugei University Senior High School has been continuously
conducting microgravity experiments through drop experiments within school and has presented its results.
Last year, the team participated in JAXA's "Asian Try Zero G 2023," where experiments on capillary action
were conducted on the ISS, among other activities related to microgravity (see 5. Appendix for details).
However, the traditional method of conducting experiments by dropping a cardboard box containing theexperimental apparatus within a classroom does not allow precise microgravity experiments. Therefore, toconduct high-precision microgravity experiments within school, we have developed a drag shield-type dropexperiment device (hereinafter referred to as TGµ-DS1).

Figure1 .

TGµ-DS1

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1.2. Objective
We have been conducting experiments to observe the behavior of gas and liquid in a horizontal acrylic
tube under microgravity conditions. These experiments were conducted using the drop tower at the FacultyIndustrial Technology, Nihon University. This drop tower can maintain a g-quality of 10-3G for 1.2 seconds1).
Under these conditions, we were able to observe changes in the behavior of gas and liquid within thehorizontal tube, as shown in figure 2,3."
Next, we attempted a simple experiment at our high school by placing the experimental apparatus insidea single-layer cardboard box. However, in this setup, we were unable to observe any changes in the behaviorof the gas and liquid within the horizontal tube.
From this, we concluded that the reason for the lack of observable behavior was due to the insufficient gquality of the cardboard box experiment compared to the drop tower at Nihon University. Therefore, our goal
is to replicate the g-quality obtained with the Nihon University drop tower within our high school setting.

Figure 2 . Behavior of Gas and Liquid in a Horizontal Tube Observed in the Drop Tower at Nihon
University2) and in the Cardboard Box

2. Experimental Method
2.1. Experiment System
Our experimental setup can be primarily divided into two parts: the drop capsule TGµ-DS1 and theholding device TGµ-DD1. The setup allows for a drop distance of 10 meters from the third floor of the schoolbuilding to the ground, creating a fall time of approximately 1 second. To ensure the procedures during theexperiment are conducted accurately and safely, we have implemented various measures, including aprocedure checklist and forbidden access to the drop area.
In pursuit of replicating the g-quality obtained at the Nihon University drop tower within our high school,
we quantitatively measure the gravity levels using a Vernier wireless accelerometer (GDX-ACC E31-8200-08).
This accelerometer can measure within a range of ±156.80 m/s² with an accuracy of ±0.01 m/s². Additionally,
the experiment is recorded using the slow-motion function of an iPhone at 240 fps.

2 of 10Figure 3. Side-view of the drop experiment using TGµ-DS1 and TGµ-DD1.

2.2. Drop Capsule
The TGµ-DS1 is a drop capsule that adopts a double-structure design. The outer capsule drag shield hasa diameter of 380 mm, a total height of 800 mm, and weighs approximately 7 kg. The experimental spacewithin the inner capsule measures 250 mm × 250 mm × 250 mm, and the inner capsule has a vertical movement
range of 130 mm within the drag shield. The TGµ-DS1 is primarily constructed using an aluminum frame andwood, with some parts made with a 3D printer.
As shown in the figure, the TGµ-DS1 is hung using a hanging wire, and the drag shield and inner capsule
are released at the same time for an independent free fall and independent free fall by cutting this wire. Scissors
are generally used for cutting. Additionally, guide wires are passed through wire guides attached to the sidesof the TGµ-DS1, preventing rotational motion during the fall and ensuring that the capsule does not fly off
after the fall. The lower part of the TGµ-DS1 is equipped with a shock absorbing material and nose cone,“haack-kun” (figure 2).

3 of 10Figure 4. Structure of TGµ-DS1.

Figure 5. The nose cone named “haack-kun”.

2.3.

Drop Device

The TGµ-DD1 is a device used to hold the TGµ-DS1, which is a drop capsule, in place during its drop.
This device is normally fixed to a wall using panel clamps. The device has a structure as shown in the figure,with a total length of 2000 mm, a total width of 500 mm, a height of 2000 mm, and a mass of approximately 75kg. The TGµ-DD1 is primarily constructed from carbon steel using single-tube pipes.

4 of 10Figure 6. Structure of TGµ-DD1.

2.4. Conducted Experiments
2.4.1.

Horizontal Tube Experiment (Experiment Ⅰ)

Experiment I was conducted to the g-quality of experiments using TGµ-DS1. The objective was todetermine whether the same phenomena observed in the experiments conducted at the drop tower at Nihon
University, as introduced in section 1.2, could be replicated using TGµ-DS1. At the time of this experiment,
the TGµ-DD1 was still under development, and a simplified drop apparatus was used for the drop tests.
2.4.2.

Experiments aimed at quantitative evaluation of g-quality (ExperimentⅡ)

Experiment II was conducted to quantitatively evaluate the g-quality of experiments using TGµ-DS1. The
TGµ-DD1 was used for this experiment. Five tests were conducted under the same condition. From theapproximately 1.4 seconds of fall, a 1.0-second interval with the smallest standard deviation in the gravity
level was extracted. The average and standard deviation of the gravity level in this interval were calculated.
Data points with the maximum average gravity level and the initial data were removed as outliers.
Additionally, graphs of the gravity levels for these data are also presented.

3. Results
3.1 Experiment Ⅰ

5 of 10Figure 7. Horizontal tube experiment with TGµ-DS1.

In Experiment I, changes in the behavior of gas and liquid in a horizontal tube were observed.
3.2 Experiment Ⅱ
In Experiment II, five experiments were conducted. The following are the results of the analysis
performed using the method shown in 2.4.2.

6 of 10Figure 8.

Typical graphs in Experiment II

Table 1.

The result of Experiment IIExperiment code

Average Gravity Level [G]Start Time [s]Standard Deviation [G]240720a240720b

0.011
0.040

0.064
0.031

240720c240720d240720e

0.040
0.040
0.019

0.210
0.072
0.015

0.018
0.085
0.045
0.052
0.039

4. Discussion & Conclusions
4.1.1 Experiment 1 Discussion
The state of gas and liquid within the horizontal tube observed in Experiment I was more similar to theobservations made during the experiments at the Nihon University drop tower than to those from the previous
free-fall experiments conducted using the cardboard box. This suggests that the g-quality of experiments using
TGµ-DS1 is closer to that of the Nihon University drop tower compared to the g-quality achieved with thecardboard box experiments.

7 of 10Figure 9. Comparison of three types of free fall experiments.

4.1.2 Experiment Ⅱ Discussion
In Experiment II, the average gravity level during the 1.0-second interval of the approximately 1.4-second
fall was 0.033G, with a standard deviation of 0.045G. Given that the gravity level in the cardboard box
experiment was approximately 0.1G, it can be concluded that the g-quality of the experiments using TGµ-DS1
has improved compared to the cardboard box experiments. However, the graph from Experiment II showsthat the gravity level fluctuates significantly during the fall. These fluctuations are believed to result fromimpacts when the inner capsule disrupted its orientation and collided with the drag shield, as observed in thevideo recordings of the inner capsule.
4.1.3 Discussion
Based on these findings, it can be qualitatively and quantitatively concluded that the g-quality ofexperiments using TGµ-DS1 is higher than that of the experiments using the cardboard box. However, theappearance of the horizontal tube in Experiment I differed from that observed in the experiments at the Nihon
University drop tower, and the gravity levels achieved in Experiment II did not reach the target of 10-3G as
obtained at the Nihon University drop tower. Therefore, it can be said that the quality of microgravity
experiments conducted within the high school could not be made equivalent to the quality of microgravity
experiments conducted at the Nihon University drop tower.
4.2. Conclusion
Since changes in the behavior of the horizontal tube were observed with TGµ-DS1, it can be said that theg-quality of the experiments was improved using TGµ-DS1. This improvement has been confirmed
quantitatively. However, the initial target of 10-3G was not achieved, and significant vibrations during the fall
were also observed. In the future, we aim to further enhance the g-quality by improving methods such as theseparation of the inner capsule.

5. Appendix
We have been conducting several experiments using the apparatus we created.
5.1. Capillary action
The first experiment focuses on the capillary rise in a microgravity environment.
In March 2023, we conducted an experiment on capillary action under microgravity using the drop tower at
Nihon University. The results showed that the rise speed of the liquid gradually decreased.
In August 2023, we needed to verify the capillary action using materials other than glass in preparation forexperiments on the ISS. We tested various combinations of materials (acrylic, polycarbonate, ABS, fluororesin)and coatings (abrasives of 7 µm, 1 µm, 0.2 µm, and glass coating) using the drop tower at Nihon University.
Among the tested conditions, acrylic with a 1 µm abrasive coating showed the best results.
8 of 10In September 2023, an experiment was conducted using our school's drop tower to observe the capillary action
under microgravity. The rise speed of the liquid resembled the Bosanquet equation (√t-(1-e-t), approximately
a linear function). Additionally, a narrower tube radius resulted in a greater rise per unit time.
In December 2023, we again conducted an experiment using our school's drop tower. The rise speed initiallyfollowed the Bosanquet equation (approximately a linear function) for the first 0.2 seconds, then it resembled
the Lucas-Washburn equation (√t).
In March 2024, a further experiment was conducted, and the rise speed followed the Quéré equation (t/√2) for
about 0.05 seconds, then the Bosanquet equation (approximately a linear function) until 0.5 seconds, after
which it resembled the Lucas-Washburn equation (√t).
In summary, different trends were observed in each experiment, and we have not yet established a
reproducible theoretical model.

5.2. Horizontal Tube
The second topic concerns the pitch (periodicity) of liquid plug formation in a horizontal tube undermicrogravity conditions.
Previous experiments have shown that when an acrylic tube containing air and tap water is subjected tomicrogravity, a liquid plug forms, and the gas-liquid interface becomes convex towards the liquid phase. It
has also been determined that an inner diameter of approximately 12 mm is suitable for a simple free-fallexperiment, with an appropriate gas volume fraction of about 0.5 to 0.4. Moreover, a previous study(Takamatsu et al., 1998) indicated that "the pitch of the liquid plug formation closely matches the mostdangerous wavelength derived from the linear stability theory of the annular liquid film within the tube."
However, the equation for the pitch of liquid plug formation in glass tubes, as given by Takamatsu et al.
(1998)3)(1)

Χ = 𝜆! ≈ 4.45 × ϕ

where x is the pitch, ϕ is the inner diameter of the tube, and λ is the most dangerous wavelength, does
not hold for acrylic tubes.
dThe ultimate goal of this experiment is to derive an accurate equation to determine the pitch in acrylic
tubes and to identify the factors that determine the length of the liquid plug. Currently, we are investigating
the ease of plug formation and the pitch length in a tube with a 12 mm inner diameter, which is the mostconducive to observing liquid plug formation, by varying the gas volume fraction.

5.3 Shock absorbing material
The third experiment focuses on the shock absorbing material used inside the nose cone part (haack-kun).
The goal of this study is to develop shock absorbing material that can protect the TGµ-DS1 and its internal
experimental apparatus from the impact of landing and reduce the bounce back after landing.
We primarily use cushioning materials such as bubble wrap and air pillow bag, polyethylene foam, andpolyurethane foam as shock absorbing material.
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In previous drop experiments, TGµ-DS1 and the internal experimental apparatus were basicallyundamaged, regardless of the material used, as long as the shock absorbing material had enough thickness. In
particular, by using only air cushioning material, the height of the bounce could be reduced to about 0.2 m,
one-fourth of the total length of TGµ-DS1.
Future research will focus on the difference in bounce height depending on the size and number of air
cushioning material and the use of low rebound polyurethane foam as a shock absorbing material.
Currently, the challenge is that there is no method to evaluate the degree of shock absorption at landing
other than analysis of the bounce height. We are also considering the use of honeycomb structures as a typeof shock absorbing material.

References
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2)
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4)

H. Nomura, T. Tuji, Y. Ujiie, T. Hiaki : “小型落下塔を利用した超臨界雰囲気中の燃料液滴蒸発に関する研究”, 日本
大学生産工学部研究報告 A, 39, (2006), pp9-18.
A. Okazaki : The 67th Japan Student Science Award, Tokyo, (2023), 20page.
H. Takamatsu, M. Fuji, H. Honda and H. Uchiyama : “微小重力下における環状液膜の安定性”, 日本機械学会論文集(B 編), 64, (1998) pp. 256-261
A. Osawa : The 67th Japan Student Science Award, Tokyo, (2023), 14page.

© 2024 by the authors. Submitted for possible open access publication under
the terms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

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