I'm a researcher in the humanities so I'm not familiar at all with physics, but if you give an object in space a push, will it never stop moving? Because there's no air resistance in a vacuum.

Yes, it won't stop. Strictly speaking, there's actually a slight amount of gas and dust floating around in space so it isn't a perfect vacuum, but we can basically say that there is "no" air, and objects will keep moving forward without stopping. On the ground, it's easy to stop and make a sudden right or left turn, for example, but in space, it becomes more difficult. While it's not impossible to force a left or right turn, the efficiency is extremely poor.

Conversely, what kind of trajectory would be more efficient?

A trajectory that embraces dynamics and goes with the flow. There's no air in space, but there is gravity. The use of celestial bodies' gravity is a very important part of the dynamics when designing a spacecraft trajectory.

A swing-by, right? I love HIGASHINO Keigo's Detective Galileo series of mystery novels and I've watched the dramatizations as well, so I learned about this through a scene portraying an experiment in which the main character, the genius physicist Dr. Yukawa, corrects the trajectory of a satellite using the gravity of a celestial body.

That's exactly right. When a satellite or spacecraft passes near a celestial body, the effect of universal gravitation becomes stronger, and it's pulled by the tremendous gravity of the celestial body. By utilizing this force and the orbital speed of the celestial body, we can increase the degree of freedom we have in trajectory control, such as accelerating or decelerating and correcting the flight direction. This is called swing-by. For an intuitive understanding of the concept, you can imagine "Earth" running on a tennis court that represents the "solar system" and hitting a ball called a "probe" with a tennis racket. In reality, the Earth doesn't physically hit the probe, but rather bends its trajectory through gravity.

I see. That's an interesting analogy.

A spacecraft must be loaded with a lot of fuel to reach a distant celestial body but, if it performs a swing-by, it can change its trajectory with less fuel. So we designers have to ask ourselves, how can we design a more efficient trajectory while performing a swing-by? We design the optimal trajectory to solve this problem by calculating the equations and simulating the trajectory on a computer.

You're showing us the results of such a simulation in a two-dimensional diagram (see image ➊ below) but, in reality, celestial bodies and spacecraft are in constant motion, so it seems a difficult task beyond my imagination.

There are so many possible trajectories that there's no end to the pursuit, and they can't be calculated in a realistic amount of time. Therefore, we try to narrow down the trajectories and then optimize them, but what is needed at that point is intuition and sense cultivated through experience. This is where the individuality of the designer comes into play.

Actually, I think trajectory design and figure skaters' thinking have very similar patterns.

I was sure there would be similarities.

Figure skating got its name from the fact that skaters draw figures as they skate on the ice, and this eventually evolved into a competition over the precision of the figures. Nowadays, it's not only technique but also choreography and skill in expressing the choreography that are scored, so skaters compose the space by considering how they can use the 30m wide x 60m long skating rink to appeal to the largest number of people. Figure skating is a world dominated by air resistance and frictional resistance from the ice, the exact opposite of outer space where there is no air resistance in a vacuum. If you push off the ice, your body will eventually come to a stop, so you need to keep pushing to keep moving. And what if you wanted to do a triple axel, for example? You'd first need the proper speed to jump. In other words, what would be the best steps to take to follow a trajectory from point A to point B? Can you get up the speed to jump efficiently? It's also important to create a line with your body that appears the most beautiful to many people.

It would seem even more complicated if we consider the external factor of music.

Machida: That's right. I think about how to take steps backward so I can land on the ice at the moment a particular sound is made. Even though there are tens of thousands of expressions in choreography, it's important to find the best way to adapt to those external factors and constraints. This is where a skater's sense shines the brightest. This process is exactly the same as your trajectory design, isn't it?That's right. I think about how to take steps backward so I can land on the ice at the moment a particular sound is made. Even though there are tens of thousands of expressions in choreography, it's important to find the best way to adapt to those external factors and constraints. This is where a skater's sense shines the brightest. This process is exactly the same as your trajectory design, isn't it?

Under the laws of physics that govern the universe, things that have been pushed to their utmost limits of functionality are imbued with beauty. For example, humans naturally tend to find beauty in the Fibonacci sequence (in which every number is the sum of the previous two numbers) and fractal structures (in which each part has a similar shape to the whole), and I think this trajectory design is just an extension of that. In fact, the lines and shapes of the trajectory are beautiful, and it would be interesting if we could connect them to the creation of art.

As you say, trajectory design becomes beautiful by eliminating any waste and using the flow of dynamics as much as possible. At the same time, I think that "beauty" is subjective. Having seen many trajectories myself, I feel that an optimized trajectory is beautiful but this beauty includes not only the resultant trajectory but also the story behind it, such as the designer's hard work. A trajectory finally emerging after about a year of grueling mathematical equation-solving looks especially beautiful.

The sensitivity to see something and find it beautiful doesn't happen overnight. Even if they see the same thing, person A may be moved by it but person B may not think anything of it. That's why it's important to navigate so that not only the creators but also the general public find something beautiful. No matter how many elite artists you bring together to perform, people who have never been exposed to figure skating or theater will not know how to appreciate it or what the beautiful points are. When trying to develop the arts, it's also very important to educate the audience and cultivate their sensitivity. This holds true not only in the world of art but also in the world of science.

With my days as a competing athlete behind me, I'm now a researcher specializing in sports science and engaged in research and educational activities, but I concurrently work as a figure skating choreographer and commentator. Take the "Études Project" that I started in July of this year, for example. This project offers not choreographic works for athletes but universal design works that allow anyone to freely experience the true joy of skating, and they're available on a dedicated YouTube channel.

If that were to happen, is there any fear that your expertise and craftsmanship would be lost, that AI would take over your role?

There's a position in the world of performing arts called a dramaturg, and you're like a dramaturg for space exploration.

Dramaturg ... I've never heard that term before.

They're involved in all the intellectual work that takes place in the creative arena, so they're always keeping eyes on the whole creative process to determine what we should be creating in the current era and in what form it should be presented to the public. Dramaturgs oversee everything, planning things from scratch, giving them shape and presenting them to the world.

May I call myself a dramaturg from now on? (Laughs)

By all means (laughs).

But I really am a dramaturg. As an trajectory design specialist, I believe we are at a time when it's no longer enough to think just about trajectories and missions. Instead, what's important is properly grasping current trends and proposing missions based on what the world expects of us today and what we should do within that context.

As a researcher, I'm exactly the same way. I believe it's important to think about how my research can benefit society and then put this into practice. Writing papers, publishing them in academic journals, and properly producing research results in the world of academia are the primary responsibilities of any researcher, but I'd like to focus on generating new knowledge and giving back to society by actively collaborating with outside parties rather than confining myself to my own laboratory. This is because I believe that the nucleus of innovation arises more from combining existing things in different ways rather than creating them from scratch. In that sense, today's dialogue is one such example.

For me, too, today's dialogue has been a good inspiration that could well lead to innovation.

Machida: That's why my research is interdisciplinary. Sometimes I take a sociological approach, sometimes an artistic approach, and sometimes I incorporate law and economics. I explore each discipline horizontally instead of vertically, connecting each theory and creating new analytical tools to deepen my research. That's my own research style. Adopting this style lets me not only capture trends but also create them.

It really does.

In terms of creation, there's a space exploration project that we're currently considering. The idea is to send multiple probes to explore many asteroids at a frequency of about one per month.

In terms of creation, there's a space exploration project that we're currently considering. The idea is to send multiple probes to explore many asteroids at a frequency of about one per month.

Why target so many asteroids?

There's a scientific explanation that water was first brought to the Earth by countless asteroids and comets: asteroids with rock-bound water and comets containing chunks of ice flew into the Earth, and their moisture may have been the source of water on the Earth. Asteroids are good research matter from the perspective of understanding the Earth's water.

It's exciting for us as ordinary citizens to see that the mission will create new scientific value while also exploring the origins of the Earth's water.

I really hope we can make it happen. What kind of path do you want to take in the future?

Well, I'm a researcher and an artist, so I'd like to create new value through this dual identity as I press forward on these two wheels. Given the interplay between these two personae, I feel the more research results I actually produce, the richer my artistic creativity becomes. When I want to create valuable choreographic works that I've never produced before as an artist, for instance, how I stand on the shoulders of giants is important. In other words, I can ultimately find my sweet spot as an artist by refining my scholarship as a researcher.

I think I understand. I myself am exploring cutting-edge science and technology while conducting advanced research within the cross-fertilization between academia and engineering. It's true that the possibilities expand only when both wheels are involved.

I'd like to create new value by switching back and forth between the two faces.