ＩＳＳで培われる「無重力の科学」

【パリＡＦＰ＝時事】地球の軌道を周回して２０年──国際宇宙ステーション（ＩＳＳ）は最先端の宇宙実験施設となった。滞在する宇宙飛行士らは、ブラックホールから病気やガーデニングに至るまでのさまざまな研究を微小重力環境で行っている。（写真は資料写真）
　地球の上空約４００キロを周回するＩＳＳはサッカー場ほどの大きさで、ハチの巣のように区画が分割されている。各区画では、乗組員が地上の研究者らからの指導に基づき実験を行うことができる。
　ＩＳＳでは、有人ミッションが開始された２０００年以降で、３０００件以上の科学実験が実施されている。

■「ミニ脳」
　米国のシェーン・キンブロー、メーガン・マッカーサー両飛行士、日本の星出彰彦飛行士、欧州宇宙機関（ＥＳＡ）のトマ・ペスケ飛行士の４人が搭乗した米宇宙開発企業スペースＸの宇宙船「クルードラゴン」運用２号機は２３日、ＩＳＳに向けて打ち上げられた。
　４人は６か月間にわたるミッションで、ＩＳＳの維持管理作業と並行して、約１００件の実験を行う予定になっている。
　実験の中には、超音波を用いて物体や液体を触ることなく移動したり操作したりする音響技術などが含まれている。
　計画されている研究の中で、フランスのペスケ飛行士が最も楽しみにしているのは、無重力が脳のオルガノイドに及ぼす影響の調査だという。脳オルガノイドは、幹細胞技術を使って作製される「ミニ脳」だ。
　科学者らは、ゆくゆくはこの研究が脳疾患治療に役立ち、また遠距離探査ミッションを視野に入れる宇宙機関を助けることにもなると期待を寄せる。遠距離ミッションでは、乗組員が過酷な宇宙環境に長期間さらされる。
　ＩＳＳではまた、「生体組織チップ」として知られる小型の人体臓器モデルの研究が進められている。組織チップはさまざまな種類の細胞で構成され、免疫系の老化、腎臓機能、筋肉減少などの研究に利用される。
　ＩＳＳ米国立研究所のシニア・プログラム・ディレクターを務めるリズ・ウォーレン氏は「理由が完全に解明されているわけではないが、細胞間コミュニケーションは、微小重力下と地球上の細胞培養瓶の中とでは機能の仕方が異なる」と指摘。細胞の集まり方も異なるという。
　「こういった特徴によって細胞は、人体内にあるときにより近い挙動を示すことができる。従って、微小重力は組織工学にとって、またとない機会を提供すると考えられる」と、ウォーレン氏は話した。

■研究を進めるための唯一無二の施設
　運用費用について懸念する声が一部から上がる中、米航空宇宙局（ＮＡＳＡ）自体は、より遠方の宇宙へと関心が移るのに伴いＩＳＳからの撤退を模索している。
　だが、宇宙空間での微小重力科学実験を計画するフランスの研究施設Ｃａｄｍｏｓのセバスティアン・バルデ氏によれば、２０２８年に運用を終了する予定のＩＳＳは、一部の科学者にとっては研究を進めるための唯一無二の施設となっているという。これらの研究には、医薬であれ材料科学であれ、重力のない環境が不可欠だ。
　バルデ氏は、知る必要があることはすべて学んだという考えを一蹴し、「それはまるで、『十分な数の』星を見たという理由で、望遠鏡を大きくする必要が本当にあるのか疑問に思うようなものだ」と語った。【翻訳編集ＡＦＰＢＢＮｅｗｓ】

〔ＡＦＰ＝時事〕（2021/04/28-13:29）

In two decades orbiting the Earth the International Space Station has become a cutting-edge cosmic laboratory, with astronauts researching everything from black holes to disease and even gardening in microgravity.
The ISS, which orbits about 250 miles above Earth, is as large as a football field inside and divided up like a beehive into spaces where the crew can carry out experiments with guidance from researchers on the ground.
Often, the astronauts are also the guinea pigs.
More than 3,000 scientific tests have been carried out at the ISS since its manned missions began in 2000.
From a science perspective, there have been some major discoveries, said Robert Pearlman, space historian and co-author of Space Stations: The Art, Science, and Reality of Working in Space.
The latest mission -- named Alpha after Alpha Centauri, the closest star system to our own -- will be no exception.
- 'Mini-brains' -
On Thursday, US astronauts Shane Kimbrough and Megan McArthur, the Japan Aerospace Exploration Agency's Akihiko Hoshide and the European Space Agency's Thomas Pesquet will blast off for the ISS aboard the SpaceX mission Crew-2.
They are likely to be busy.
Alongside work to maintain the space station itself, around a hundred experiments are in the diary for their six-month mission.
These include an acoustic technique using ultrasonic waves to move and manipulate objects or liquids without touching them.
France's Pesquet has said his favourite planned research is a study examining the effects of weightlessness on brain organoids -- mini brains created using stem cell technology.
Scientists hope this research can eventually help space agencies prepare for distant space missions which will expose crews to the rigours of space for long periods of time, and even help fight brain disease on Earth.
It really sounds like science fiction to me, joked Pesquet, an aerospace engineer.
There is ongoing research into what are known as tissue chips -- small models of human organs that are made up of different types of cells and used to study things like ageing in the immune system, kidney function and muscle loss.
We don't fully understand why, but in microgravity, cell-to-cell communication works differently than it does in a cell culture flask on Earth, said Liz Warren, senior program director at the ISS US National Laboratory, adding cells also gather together differently.
These features allow cells to behave more like they do when inside the body. Thus, microgravity appears to provide a unique opportunity for tissue engineering.
Another important element of the mission is upgrading the station's solar power system by installing new compact panels that roll open like a huge yoga mat.
Crew-2's launch day coincides with Earth Day, and by the time the crew returns they will have also contributed to environmental research by taking 1.5 million images of phenomena like artificial lighting at night, algal blooms, and the breakup of Antarctic ice shelves.
- Experimental evolution -
The experiments are designed for the long term, beyond individual missions, said Sebastien Barde of France's Cadmos, which organises microgravity science experiments in space.
The study of weightlessness -- or microgravity -- has gone from pioneering to something standardised, with increasingly precise methods of measurement, Barde said.
Twenty years ago, there was no ultrasound machine on board, he added.
Claudie Haignere, the first French woman to fly in space, visited the ISS in 2001 and remembers it as rather poorly equipped.
Now she says she it boasts exceptional laboratories.
The astronauts also stay longer -- six months, versus a fortnight for the first manned flights -- giving researchers more time to measure the effects of microgravity on them.
- 'Enough stars' -
Spaceflight changes the human body.
It weakens muscle and bone and affects the heart and blood vessels. Some of the effects resemble a speeded-up progression of ageing and diseases on Earth.
Whilst being guinea pigs for this research, the ISS crew has also collected data on black holes, pulsars and cosmic particles to help expand our understanding of the Universe.
With the ability to grow supplemental food seen as an important step to helping humans venture deeper into Space, they have even done some experimental gardening.
In 2015, astronauts sampled their first space-grown salad and they have since tried growing radishes.
Pearlman said the discoveries range from those related to human health -- like a treatment for salmonella -- to experimental engineering.
One very promising technology right now that's just on the cusp of happening is 3D printing body parts, he said.
Some have raised concerns about the cost of the ISS, while NASA itself is seeking to disengage as its attention shifts to deeper space.
But Barde said the space station, scheduled to retire in 2028, is the only platform for some scientists to pursue their research, whether that is in medicine or material sciences that need an environment without gravity.
He dismissed the idea that we have learned everything we need to know: It's like wondering if you really need to enlarge a telescope, because you have seen 'enough' stars!