Four astronauts were preparing to leave the International Space Station and head back to Earth on Monday after spending six busy months aboard the orbital outpost.

The Crew-2 mission, which includes two Americans, a Frenchman and one Japanese astronaut, have been living and working on the space lab since April 24, carrying out hundreds of experiments and upgrading the station's solar panels.

They are now set to board their SpaceX Dragon capsule named "Endeavour" and undock from the ISS at 2:05 pm US Eastern Time (1905 GMT) before splashing down off the coast of Florida at 10:33 pm (0333 GMT Tuesday). NASA will provide a livestream.

"Last minute packing, getting ready to depart ISS," tweeted Japan's Akihiko Hoshide.

"It has been a fun 6+ months - pleasure and honor working with ALL the incredible people from around the world, both on & off the planet."

Their activities have included documenting the planet's surface to record human-caused changes and natural events, growing chile peppers and studying worms to better understand human health changes in space.

Crew-2's departure was delayed a day by high winds. 

Bad weather and what NASA called a "minor medical issue" have also pushed back the launch of the next set of astronauts, on the Crew-3 mission, that is now set to launch Wednesday.

SpaceX has provided astronauts a taxi service to the ISS since 2020.

"As we were preparing to leave it's kind of a bittersweet feeling, we might never come back to see the ISS," said Thomas Pesquet of France, in a weekend press conference.

"It's really a magical place that flies in the sky -- it's almost impossible to get to, and gives you superpowers of floating and seeing the Earth and doing good things for the people on Earth. To me, that's what dreams are made of."  

The crew will face a final challenge on their journey home: They will have to wear diapers after a problem was detected with the capsule's waste management system, forcing it to remain offline.

They will have no access to a toilet from the time the hatch closes at 12:40 pm (1740 GMT) until after splashdown -- around 10 hours.

"Of course that's sub-optimal, but we're prepared to manage," NASA astronaut Megan McArthur said at the press conference.

"Space flight is full of lots of little challenges, this is just one more that we'll encounter and take care of in our mission."

SpaceX's all-tourist crew encountered a similar waste-related problem during its September flight, which triggered an alarm system. NASA later said a tube had come unglued, sending urine to the capsule's fan system instead of a storage tank.