OS3-7
浮遊金属液滴への低出力 CW レーザーアブレーション推力の測定
Measurement of low-power CW laser ablation thrust on
levitated metallic droplets.
皆川尚樹 1, 森浩一 1, 石川毅彦 2, 小山千尋 2, 織田裕久 2, 渡邉勇基 3
Naoki MINAGAWA1, Koichi MORI1, Takehiko ISHIKAWA2, Chihiro KOYAMA2, Hirohisa ODA2, andYuki WATANABE3
大阪公立大学大学院 工学研究科 航空宇宙海洋系専攻，Osaka Metropolitan University Aerospace Engineering,JAXA，Japan Aerospace Exploration Agency.
3 株式会社エイ・イー・エス，Advanced Engineering Services Co., Ltd. (AES)12

1. Introduction
In recent years, the increase in space debris has become a major problem. Space debris orbiting the earthcomes in all sizes. In this study, we consider the removal of debris smaller than 10 cm, 1) which is difficult toobserve and impossible to avoid debris collision by orbit control. In a research case study by Ebisuzaki et al.2) ,using an ultra-wide angle telescope, a search laser , debris of about 1-10 cm in size is deactivated by repeatedirradiation of nanosecond pulsed lasers with a time-averaged power of 500 kW. When such high-power laser
beam is irradiated to such a small space debris as described above, most of the debris melts and turns into amolten droplet. Moreover, experiments in which a pulsed laser is irradiated on a droplet have been extensively
studied in the field of fluid dynamics in recent years. By analogy with the results, if pulsed laser beam isapplied to a droplet and a large thrust is applied, the droplet can be deformed greatly and cracked, leading tofragmentation and increase of space debris.3-4) Therefore, a method to avoid debris by using a low-power
density laser to generate thrust is favorable. And, previous laser ablation thrust experiments aboutmeasurement of laser ablation thrust have used target materials that are sufficiently large for the thermal input
and do not simulate thermomechanical isolation and high power density(108[W/cm2]~ 1012[W/cm2]).5)

But

space debris in real space is thermo-mechanically isolated, and when CW lasers are irradiated for a long time,
space debris smaller than 10 cm would dissolves and becomes droplets. So, in our laboratory, we used anelectrostatic levitation furnace (ELF), which can simulate a thermomechanical isolated space debris in spaceby levitating a sample using electrostatic force. This device can be used to measure the laser ablation thrust byirradiating CW laser beam to a molten metal. Previous studies have measured laser ablation thrust using aground-based ELF. However, there is an problems with levitation of aluminum and convection currents in themetallic droplets, which reduce the heat transfer characteristics. Therefore, in this study, we measured thelaser ablation thrust generated in aluminum, the main material of debris, by using ELF installed in the ISS,and eliminate the above effects.
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2.

Experimental Methods

2.1. Experimental equipment
In this study, experiments were conducted using an ELF installed in the ISS. A schematic diagram of the ISSELF is shown in Figure 1. electrodes are installed in each of the three axial directions, and the voltage applied
between the electrodes is controlled by PD control based on data from the position sensor called IVS to enablestable levitation. In addition, four semiconductor lasers are installed, each of which can independently
determine its output. This experiment was performed under Ar , 2 atm atmosphere.
2.2. Experimental proceduresFirst, the sample was allowed to float stably in the chamber. After that, the voltage applied to the sample
was OFF and the sample was allowed to free drift until it moved 2[mm] from the initial position. After the2[mm] sample move, the application of voltage was restarted, and the sample was returned to the initial
position again by PD control. This operation will be referred to as FD in the following text. Next, the output
power of the four lasers was increased simultaneously to melt the sample. Once it was confirmed that thesample could be melted and was stably levitated, the output power of laser 4 was increased while the output
power of lasers 1, 2, and 3 was decreased while maintaining the melted state. When the output of lasers 1, 2,and 3 reached 0 and only laser 4 was being irradiated, FD was performed. After that the output of all lasers
was reduced to 0, and after cooling, FD was performed again, and the sample was collected.

Figure 1. A schematic diagram of ISS-ELF

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3.

Result and Future vision

Figures 2. show the positions of the samples detected by the IVS and the results of fitting with a quadratic
function when FD was performed under the experimental conditions shown in Table 1. The IVS data arerounded up to the first decimal place.6)
From these results, it was found that the motion of the sample during FD could be captured and fitted,
making it possible to measure the force generated on the sample during laser irradiation. Each of the fitting
results is 𝑦 = (0.0 ± 0.0)𝑥 2 + 0, 𝑦 = (0.55 ± 0.02)𝑥 2 + 0.05, 𝑦 = (0.57 ± 0.05)𝑥 2 + 0.09, for x, y and z direction.
The measured forces are shown in Table 2. However, the ISS is in orbit at an altitude of about 400[km] andis slightly affected by the Earth's gravity. Furthermore, it is possible that offset voltage is applied when thecontrol voltage is applied, so that even when the control voltage is turned off, the voltage is not completelyzero. Therefore, we are planning to study an analysis method to remove these effects and to discuss the data
after the analysis.
Acknowledgement
I would like to thank the researchers at JAXA's Ishikawa Laboratory for allowing us to use their electrostatic
levitation furnace as an experimental device, for their advice and cooperation on experimental methods, andfor giving us the opportunity to conduct on-orbit experiments on the ISS.

I would like to take thisopportunity to express our deepest gratitude.

(a) x-direction(b) y-direction(c) z-direction

Figure 2. Change in sample position during laser irradiation FD

Table 1. Experimental conditions

Material

Mass[mg]

Radius[mm]Laser Power[W]

Zirconium

23.0700.945

30Powerdensity[106W/cm2]
2.5

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Table 2. Measured thrust

x-direction[nN]y-direction[nN]z-direction[nN]

0.0±0.0-25.4±0.8-26.4±0.5

References
1)
2)
3)
4)
5)
6)

Kawamoto, Satomi et al. Overview of Space Debris Removal. Proceedings of the 56th Space Science and Technology
Conference, 2012
Ebisuzaki, S., T. Wada, A. Sasou, et al. Space Debris Deorbit by Laser. JAXA Special Publication: 7th Space Debris
Workshop Proceedings, 2017.
https://www.youtube.com/watch?v=Oog-DZ_Kti4Aaa
Gelderblom, H., Lhuissier, H., Klein, A., Bouwhuis, W., Lohse, D., Villermaux, E., & Snoeijer, J. (2016). Dropdeformation by laser-pulse impact. Journal of Fluid Mechanics, 794, pp. 676-699.
Phipps, C., Birkan, M., Bohn, W., Eckel, H., Horisawa, H., Lippert, T., Michaelis, M., Rezunkov, Y., Sasoh, A., Schall,W., Scharring, S. and Sinko, J.: Laser ablation Propulsion, J. Propul. Power, 26, 4 (2010), pp. 609–637.
Takehiko ISHIKAWA , Chihiro KOYAMA, Haruka TAMARU, Hideki SARUWATARI, Masato OHSHIO andYasuhiro NAKAMURA, Status of the Electrostatic Levitation Furnace in the ISS– Evaluation of Sample PositionControl–, International Journal of Microgravity Science and Application, 2018, Volume 35 , 2 , p. 350205© 2023 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

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