The International Space Station (ISS) returned to full strength with Saturday’s arrival of four new astronauts to replace colleagues who bailed early because of health concerns.

SpaceX delivered the US, French and Russian astronauts a day after launching them from Cape Canaveral.

Last month’s medical evacuation was Nasa’s first in 65 years of human spaceflight. One of four astronauts launched by SpaceX last summer suffered what officials described as a serious health issue, prompting their hasty return. That left only three crew members to keep the place running – one American and two Russians – prompting Nasa to pause spacewalks and trim research.

Moving in for eight to nine months are Nasa’s Jessica Meir and Jack Hathaway, France’s Sophie Adenot, and Russia’s Andrei Fedyaev. Meir, a marine biologist, and Fedyaev, a former military pilot, have visited the ISS before. During her first space station visit in 2019, Meir took part in the first all-female spacewalk.

Adenot, a military helicopter pilot, is only the second French woman to visit space. Hathaway is a captain in the US navy.

Nasa has refused to divulge the identity of the astronaut who fell ill in orbit on 7 January or explain what happened, citing medical privacy. The ailing astronaut and three others returned to Earth more than a month sooner than planned. They spent their first night back on Earth at a hospital before returning to Houston.

The space agency said it did not alter its preflight medical checks for their replacements.