Student Interview | Yuta Sunaga

――Thank you very much for your time. First of all, please tell us why you chose to study at the Department of Aerospace Engineering.

I have had an interest in space development since I was a child. When I was in elementary school, my father showed me the launch of the space shuttle on his computer, and that’s how I became interested in rockets flying into space. Furthermore, I wanted to learn about satellites and probes that rockets deliver to space, and space engineering, which is the logic behind the operation of these spacecraft.

――I see, that's interesting. What was the deciding factor in joining your current laboratory?

My interest was triggered by the Space Shuttle, and I gained a specific interest in manned space activities within space development. Although space technology for small unmanned vehicles such as nano-satellites has been actively studied in the world recently, I predict that the time will come when people will actually be active in space, and I believe it is necessary to promote research on structures for human activity in space. Therefore, I wanted to join Prof. Yokozeki's laboratory, where I can conduct research on the structure and materials of space structures.

――That's wonderful. Could you tell us about your research?

My research is on CFRP (carbon fiber reinforced plastic) space-deployable structures.

(Figure 1) Space-deployable structure

――What is CFRP?

CFRP is a material composed of carbon fiber and resin (plastic). Carbon fiber is a very thin fiber with few crystalline defects and is strong in the longitudinal direction. When carbon fiber is inserted into the plastic that we use in our daily lives, a material that is strong in the direction of the fiber is produced. Such light and strong materials are especially important in the aerospace field. Lightness is important because aircraft fly in the sky and space vehicles are launched by rockets.
Unlike ordinary metals, CFRP has a property called anisotropy, which means that its hardness and strength vary depending on the direction. By devising the way carbon fibers are aligned and stacked, the stiffness and strength of a structure can be designed to take advantage of its anisotropy, and structures that are stable in two different shapes can be realized. For example, this structure (Figure 1) is stable in both unrolled (Figure 2) and rolled-up (Figure 3) states.

(Figure 2) Structure in unrolled state

(Figure 3) Structure in rolled-up state

――What are the applications?

Japan is currently developing a lunar rover (a vehicle for exploring the moon) that can carry a person. The rover is designed to operate in the polar regions of the Moon. In the polar regions of the Moon, sunlight  shines down sideways, so it is necessary to raise and spread solar cells vertically to receive light from the side to provide power (Figure 4). On the other hand, when the rover is in motion, the solar panels need to be closed, so the solar panels must be opened and retracted many times. If they are left open, the solar cells may lose power generation efficiency due to the accumulation of regolith, which is lunar soil. Therefore, this structure is being considered for application as a support component for solar cells.

(Figure 4) Image of a solar cell panel in the polar region

――I now have a good understanding of the background of the project. Could you tell us again about the topic of your graduation research?

Since space is a very harsh temperature environment and the stiffness and strength of materials change with temperature, I was measuring, analyzing, and simulating the stiffness and strength of structures at room temperature, 100°C, and -150°C.

――I see. How did your classroom lectures at the university come in handy in your research?

I think that my daily classroom lectures are the base of my research. My stance on learning is to build up from the basics to my current research steadily, without taking leaps and bounds, so my daily classroom lectures are useful. Even though research requires specialization, the general knowledge I learned as an undergraduate is still helpful.

――Are there any classes in the Department of Aerospace Engineering that you found interesting?

In Professor Yokozeki's Elastic Mechanics laboratory class, I realized how deep and fascinating the field of materials and structures is. If I read technical books on science and engineering on my own, I end up learning in a shallow manner as if I were chasing mathematical formulas, but when I attend lectures by professors, I can hear concepts from technical fields explained in a way that’s closer to spoken language, which helps to deepen my understanding.

(Figure 5)Sunaga conducting a tensile test of a structural specimen. Before operating actual structures in the high and low temperature environments expected in space, material properties are obtained and used for numerical simulations.

――Is there any secret to your studies at the university?

The biggest difference compared to how we study up through high school is that it is important to reach a mental state where you can remember things immediately, even if you forget them. My academic advisor told me that it is important to make a table of contents in your mind. I also tried to take notes of what I learned in lectures as much as possible while it was fresh in my mind.

(Figure 6) Sunaga's class summary notebook

――Aside from studying, was there anything else you did while you were in high school?

When I was in the second year of junior high school, I started a club about space development, and at first, our club activities were building models of satellites and probes. In high school, when I was accumulating knowledge of mathematics and physics, I took data and made calculations to see what kind of motion a plastic bottle rocket would have.

――Your passion for space is remarkable! Finally, do you have a message for high school students?

My research, for example, is related to and based on the high school subjects of physics, mathematics, and information science. The more you understand at a deep level in high school, the more easily you will learn in university, and I believe that having a base of knowledge will expand the world you can understand. I know that to start with, studying for entrance examinations is important, but I hope that students will continue to enjoy their studying with the motivation that it will not be wasted after they enter university.

――Thank you so much.

*This interview was organised and edited by members of the Scool of Engineering Public Relations Office TA Ttime!

Interviewing, writing, video shooting/editing:
Shiho Sugiyama, Kango Minakata, Hiroki Takita