月面探査とその意義
Hello everyone, SCIENSPOT is a podcast that shines a spotlight on the latest scientific technology from Japan.
Your host is REN from SCIEN-TALK. So today I'm going to talk about the lunar aquaponics.
Have you ever seen themes of lunar bases in sci-fi movies or anime? The international lunar
exploration project, the Artemis program, is aiming to make the dream a reality.
It plans to send humans back to the moon for the first time in about half a century since
the Apollo program, with the long-term goal of enabling extended stays on the lunar surface.
Two Japanese astronauts are now planned to explore the moon, making an important step
toward building a lunar base and eventually human exploration of Mars. However, there's a huge
challenge for long-term activities on the moon, food supply. Currently, the International Space
Station relies on the space food transported from Earth, but shipping supplies into space
comes with enormous costs. Imagine this, transport just one liter of water all the way to the moon,
which is 38,000 kilometers away, is estimated to cost a staggering 100 million Japanese yen,
about 1 million U.S. dollars. It's an incredible expense. To solve this economic challenge and
enable autonomous activities without relying on Earth's resupply, it's crucial to develop
in-situ resource utilization technology. This means extracting, processing, and utilizing
resources available directly on the moon, such as water and lunar soil or some food supply.
But it's not just about the cutting costs. Maintaining the physical and especially the
mental health of astronauts is extremely important. Eating the same monotonous space food
アクアポニックスの仕組み
for long periods can lead to the menu fatigue and reduce the appetite.
In contrast, eating fresh vegetables and fish not only provides essential nutrients,
but also offers psychological comfort and stress relief through the act of cultivation itself,
which is expected to improve astronauts' QOL. So how can we produce fresh food on the moon?
The answer lies in a system called aquaponics. Aquaponics combine aquaculture and hydroponics
to create a circulating production system. In short, it mimics a small Earth ecosystem.
Here's how it works. Fish excrete ammonia, which bacteria in the water tank break down into
nitrates, a fertilizer for plants. This nitrate-rich water is then supplied to the plants,
which absorb the nitrates and purify the water. The purified water then returns to the fish tank,
creating a continuous loop of water and nutrients. It's like the fish tank and the garden
holding hands and helping each other. Aquaponics is known on Earth for its low environmental impact
and high water-saving efficiency. For example, it can save over 80% more water compared to
traditional hydroponics. This is because it doesn't require frequent water changes. You
just replace the water that evaporates. It also eliminates the need for pesticides or chemical
fertilizer, so there's no concern about soil pollution. While there might be challenges on
Earth, like lower demand for freshwater fish compared to saltwater fish on the moon,
animal protein is extremely valuable. Thus, the value of freshwater fish becomes very high.
It's a clever reversal. What's the challenge on the Earth becomes an advantage in space.
月面水産養殖のリーダー
So towards realizing lunar aquaponics, Japanese research institutions and experts are leading
the world. One of the key figures is distinguished professor Yoshiaki Kitaya from
Osaka Metropolitan University. He's a leading expert in plant factory research and has
long worked on sustainable, closed-space food production systems that minimize environmental
impact. This system, by minimizing energy input and circulating resources within the system,
in his current aquaponics research, he combines freshwater fish like tilapia,
rainbow trout, and loach with leafy ground and wasabi. He builds loaches which have soft bones and
can be eaten whole and are particularly suitable for space. Another important person is associate
professor Masato Endo from Tokyo University of Marine Science and Technology. He has been
researching fish farming in space for nearly 30 years. Since his student days, he plays a central
role in aquaculture research within the lunar food system working group organized by JAXA.
Researcher considers the most suitable for lunar aquaculture is tilapia. Tilapia is a freshwater
fish native to Africa, known for being resilient to water production, fast-growing, and having a
mild white flesh. In Japan, it's sold as Izumidai, white tilapia. He has conducted several microgravity
experiments simulating one-sixth of Earth's gravity, similar to the moon, and has confirmed
that tilapia can swim and feed normally in the environment. Unlike land animals, which might
thrash around in low gravity, fish can be safely contained in water, offering a significant
advantage for aquaculture production. Furthermore, associate professor Endo's research isn't just
月面での養殖の挑戦
about growing fish. He has also developed the concept of material circulating aquaculture,
where tilapia waste is used as a fertilizer to cultivate chlorella, which in turn refills
diphenia, and finally diphenia used as a feed for tilapia fly. This suggests that in the extremely
lunar environment, to achieve the ultimate system where almost all substances circulate
without waste, tilapia serves as an ideal hub for circulation,
where even its waste can be utilized as a crucial resource within the system.
And of course, realizing aquaponics on the moon requires overcoming the extremely harsh
environment factors unique to the moon, in addition to Earth-based challenges. The lunar
surface experiences extreme temperatures from 120°C during the day to freezing minus 170°C at
night, and is constantly bombarded by space radiation. Lunar dust, or regolith, is also very
sharp and electrostatic, which can cause equipment malfunctions and health issues for astronauts.
To address these, building facilities underground is being considered to avoid
the effect of radiation and temperature fluctuations. The surface temperature is
stable at around minus 20°C. Additionally, water extracted on the moon could not only
support life but also serve as a radiation shield. Lunar regolith is not just an obstacle,
research is also underway to use it as an artificial soil for plant cultivation
by combining it with organic fertilizers. There are clever ways to maximize the use of
the moon's own resources, a testament to the wisdom of living off the land without
bringing anything from Earth. Lunar aquaponics is not just about satisfying astronauts' appetites,
月面での水産養殖の重要性
it is strategically positioned as essential rather than just nice to have. This is due to
several factors. It cuts cost down or exorbitant transportation costs,
maintaining the physical and mental health of astronauts, and enables astronauts' space
activities without relying on supplies from Earth. Moreover, the innovative technologies
developed in this extreme lunar environment, such as closed-loop systems, ultra-water-saving,
high-efficiency, and zero-waste solutions have the potential to become the ultimate solutions for
pressing global challenges like water, scarcity, food security, and climate change.
That's all for today's SciencePod. This podcast is broadcast daily on weekday morning
in Japanese and English. I'd love for you to listen to the podcast and post your notes
with the hashtag SciencePod. Thank you for listening. See you next time.
