The astronauts who will depart the International Space Station on Sunday will be stuck using diapers on the way home because of their capsule's broken toilet.

Nasa astronaut Megan McArthur described the situation on Friday as "suboptimal but manageable". She and her three crewmates will spend 20 hours in their SpaceX capsule, from the time the hatches are closed until Monday morning's planned splashdown.

"Spaceflight is full of lots of little challenges," she said during a news conference from orbit. "This is just one more that we'll encounter and take care of in our mission. So we're not too worried about it.”

After a series of meetings on Friday, mission managers decided to bring McArthur and the rest of her crew home before launching their replacements.

That SpaceX launch already had been delayed more than a week by bad weather and an undisclosed medical issue involving one of the crew. SpaceX is now targeting liftoff for Wednesday night at the earliest.

French astronaut Thomas Pesquet, who will return with McArthur, told reporters that the past six months have been intense up there.

The astronauts conducted a series of spacewalks to upgrade the station's power grid, endured inadvertent thruster firings by docked Russian vehicles that sent the station into brief spins, and hosted a private Russian film crew — a space station first.

Toilet trouble

They also had to deal with the toilet leak, pulling up panels in their SpaceX capsule and discovering pools of urine.

The problem was first noted during SpaceX's private flight in September, when a tube came unglued and spilled urine beneath the floorboards. SpaceX fixed the toilet on the capsule awaiting liftoff, but deemed the one in orbit unusable.

Engineers determined that the capsule had not been structurally compromised by the urine and was safe for the ride back. The astronauts will have to rely on what Nasa describes as absorbent undergarments.

On the culinary side, the astronauts grew the first chili peppers in space — a nice moral boost, according to McArthur. They got to sample their harvest in the past week, adding pieces of the green and red peppers to tacos.

"They have a nice spiciness to them, a little bit of a lingering burn,” she said. “Some found that more troublesome than others."

Also returning with McArthur and Pesquet: Nasa astronaut Shane Kimbrough and Japanese astronaut Akihiko Hoshide.

SpaceX launched them to the space station on April 23. Their capsule is certified for a maximum 210 days in space, and with Friday marking their 196th day aloft, Nasa is eager to get them back as soon as possible.

One American and two Russians will remain on the space station following their departure.

While it would be better if their replacements arrived first in order to share tips on living in space, Kimbrough said the remaining Nasa astronaut will fill in the newcomers.