Long-duration stays on ISS mark a quarter century: Former Commander Onishi Says "Japan's presence has grown"

Long-duration stays by astronauts on the International Space Station (ISS) reached a quarter-century milestone earlier this month. During this period, Japan has accumulated technology and expertise through the operation of the Japanese Experiment Module "Kibo," the cargo transporters "Kounotori" (HTV) and HTV-X, and 14 long-duration missions. At the end of October, Kimiya Yui (55), currently aboard the station, captured the HTV-X1 vehicle with the robotic arm and successfully brought it to the ISS. Takuya Onishi (49), who returned to Earth after handing over to Yui, reflected on his mission as the third Japanese person to serve as ISS Commander at a press conference, saying, "It became an extremely valuable asset, and Japan's presence has grown."

"Even though it looks different..."

A total of 15 countries, including the United States, Russia, Japan, Europe, and Canada, participate in the ISS program. Construction began in 1998 in orbit at an altitude of 400 kilometers, and on November 2, 2000, three American and Russian astronauts began the first long-duration stay. Since then, astronauts from participating countries have been stationed on board, rotating approximately every six months, and have continued conducting experiments utilizing microgravity.

Japan has experienced long-duration stays almost every year since Koichi Wakata (62) in 2009. "Kibo" was completed in that same year. By 2020, Japan had successfully operated nine "Kounotori" vehicles and passed the role onto HTV-X. Japan has also enhanced its expertise in ground control, astronaut training, and support. Meanwhile, in recent years, air leaks have continued in parts of the Russian segment of the ISS, which the American National Aeronautics and Space Administration (NASA) has identified as "the highest safety risk." The ISS will end operations in 2030, but participating countries will apply the knowledge they have gained to international lunar exploration and commercial space stations.

Yui, who captured the HTV-X on the 30th of October, posted on X (formerly Twitter) the following day (the 31st) that work had begun to unload the cargo. He wrote, "Once you get inside, you realize that even though it looks different on the outside, it's still a sibling of 'Kounotori.' I felt very nostalgic remembering what happened 10 years ago (when he captured Kounotori 5)."

In addition to conducting experiments and other tasks, Yui has focused on photography. He has been actively posting his "works" - photographs and videos featuring Earth and the stars - on X attracting online attention. He has also captured images of the HTV-X while it is berthed at the ISS, appearing fulfilled as he wrote, "Thanks to the HTV-X, I can now take beautiful photos even when shooting casually before bed."

ISS "has entered a fairly mature stage"

Meanwhile, Onishi, who spent 146 days in space starting in March and returned to Earth in August, held a press conference in Tokyo on the 3rd of November after undergoing rehabilitation to re-adapt to Earth's gravity.

Summarizing his second stay, Onishi stated the following: (1) Although the flight of the American cargo spacecraft "Cygnus" was canceled due to a ground accident and some equipment failed to arrive, he was able to maximize the use of "Kibo" within those constraints; (2) He drew on his experience as a "Flight Director" for Kibo's operations control on the ground to lead the astronauts aboard as Commander; and (3) Together with Yui, who is currently aboard following Onishi's stay, the Japanese astronauts will have maintained a continuous presence on the ISS for nearly a year. He expressed his satisfaction, saying, "I believe I was able to contribute to enhancing Japan's presence."

It was his first flight in nine years, and he said the changes to the ISS were impressive. "During my previous visit in 2016, it had only been a few years since the ISS was completed. This time, I felt it had entered a fairly mature stage. Tasks that astronauts used to do by hand have become more remote-controlled and automated. Experimental equipment has also become more labor-saving and efficient." NASA states the ISS was completed in 2011. He offered his perspective on future human space development: "It is important to pass on the knowledge we have accumulated through the ISS to commercial space stations."

Clarifying roles during the "gray period"

He served as Commander for three and a half months, from April 19 to August 5. He fulfilled the weighty responsibility of supervising astronauts and monitoring conditions aboard the station as the on-site leader. Among Japanese astronauts, he followed Wakata in 2014 and Akihiko Hoshide (56) in 2021 in assuming this role. "It was a very responsible and important role, but I was blessed with good colleagues and was able to perform my duties without major problems. It became an extremely valuable asset for me personally. I believe I was able to contribute somewhat to enhancing Japan's presence by becoming Commander alongside the two major powers of the United States and Russia."

As Commander, he also paid attention to the astronauts' mental well-being. "The U.S. side (non-Russian) and the Russian side perform daily tasks mostly separately, and living quarters are also divided, so there is little communication. So, we made sure to have dinner together at least once a week. We all celebrated occasions like astronauts' birthdays or milestones such as how many days we had been in space."

Before returning to Earth, Onishi posted on X that clarifying roles during the "gray period" between handing over command and actually departing the ISS was important. When asked about his intent, he explained: "From the moment of the command handover, the overall coordination role for the entire ISS transferred to Russia's Sergey (Ryzhikov), but if coordination of U.S.-side astronauts had also transferred, everyone would have had to completely change the roles they had been fulfilling for just about five days (until Onishi and others departed the ISS). That's one approach, but I thought it would cause confusion. So, even though the Commander position had transferred, I declared that I would remain responsible for coordinating the U.S. side until the moment our spacecraft departed, and everyone reached a consensus on this. Making clear who has command authority in which situations is extremely important in gray situations."

Mars flight brings "high hurdle in terms of astronaut mental health"

As a major program following the ISS, the "Artemis program" to build a station above the Moon and conduct crewed lunar surface exploration is underway through international cooperation. Japan and the United States have already agreed that Japanese astronauts will land on the Moon. When asked if he himself aims for the Moon, Onishi immediately replied, "Yes, of course." He spoke with conviction: "Only a handful of humans have ever stood on the Moon, but I believe I am at least qualified to take on that challenge, so I am grateful for that and want to participate in the Artemis program by bringing all my experience to bear."

The United States and other countries aim to develop technology around the Moon through the Artemis program and work toward crewed Mars flights. However, Onishi cautiously pointed out it is "a high-hurdle challenge." "On the ISS, Earth spreads out outside the window, and if important equipment breaks, replacements can be quickly launched from Earth, or if supplies don't arrive once, they can be redistributed to other resupply flights. But going to Mars, the vast distance becomes an enormous obstacle. Opportunities and capability for resupply are limited, which directly translates to difficulty. The impact on astronauts' mental health is also hard to imagine. The psychological burden is orders of magnitude different between living with the reassurance of being able to return to Earth at any time versus traveling eight months one-way to Mars under the tension that if something happens, you might not survive. Mental care for astronauts is a challenge."

At the press conference, Onishi also spoke of his dream of a "Japanese crewed spacecraft." "Watching SpaceX in the United States, I strongly feel that by launching both the (uncrewed cargo spacecraft) Dragon and the crewed spacecraft Crew Dragon in increasing numbers, they are generating positive effects for both. Watching them, I hope Japan will also accumulate knowledge through HTV-X following Kounotori, and my personal hope is that this will lead to the development of our own crewed spacecraft. Countries that possess core technologies gain significantly greater voice and presence in international cooperation."

Regarding the HTV-X, Norishige Kanai (48), a colleague of Yui and Onishi, also shared an idea at the Ministry of Education, Culture, Sports, Science and Technology's Working Group on Space Development and Utilization in September: "Couldn't something like the HTV-X be flown for a year or a year and a half and used to advance private-sector research and development, functioning like Japan's own mini-station?" On the topic of a Japanese crewed spacecraft, Kanai also proposed at the meeting: "Owning and operating one is important. Even if we cannot leap directly to that point, initially operating by purchasing crewed spacecraft from other countries and accumulating technology and expertise would be important for maintaining our country's strengths and advantages."