Satoshi Furukawa. (Kyodo)

Japan's space agency said Friday that a research team headed by astronaut Satoshi Furukawa tampered with data from an experiment simulating life on the International Space Station, indicating that it would subject him to disciplinary action.

Although there are no changes to Furukawa's scheduled voyage to the ISS around next year, the 58-year-old astronaut will be "appropriately" punished as he bore partial responsibility due to his supervisory role in the experiment, the Japan Aerospace Exploration Agency said at a press conference.

JAXA said the team "fabricated" and "altered large amounts of data" concerning the psychological well-being of participants in the experiment.

The experiment involved 40 people confined to a closed environment for about two weeks at a facility in Tsukuba, Ibaraki Prefecture, northeast of Tokyo, between 2016 and 2017 to assess their stress levels and mental well-being.

Two researchers who conducted interviews to ascertain the mental state of the participants fabricated data including making it seem as if other researchers had also participated.

The pair claimed they had done so as they had been too busy to devote themselves to the research, according to JAXA Vice President Hiroshi Sasaki.

Apologizing for the incident, Sasaki said, "sloppy management of the experiment has damaged the credibility of (our) research data and the scientific value of research as a whole."

In November 2017, JAXA began investigating the project after noticing something amiss about the analysis of experimental data, subsequently suspending it in November 2019.

JAXA said it will take appropriate action regarding the return of the approximately 96 million yen ($692,000) grant the project had received from the Ministry of Education, Culture, Sports, Science and Technology.

Furukawa became the third Japanese to have completed a long-term mission in space, after Koichi Wakata and Soichi Noguchi, when he traveled aboard the Russian spacecraft Soyuz and stayed at the ISS for 165 days.

He was officially certified as an astronaut in 2001 after working as a gastrointestinal surgeon.

Japan Aerospace Exploration Agency Vice President Hiroshi Sasaki (L) bows in apology during a press conference in Tokyo on Nov. 25, 2022. (Kyodo)