The issues with SpaceX's Dragon capsule toilets are going to leave four astronauts with a tough trip home from the International Space Station (ISS) this month.
The problem, identified onboard the Elon Musk-owned company's Inspiration4 flight that sent the first all-civilian crew into orbit, caused urine leaks in the capsule.
Unfortunately a fix, which is being trialled on the Dragon Endurance capsule that took new astronauts to the ISS at the weekend, has come too late for those already there.
NASA's Shane Kimbrough and Megan McArthur, Japan's Akihiko Hoshide and French astronaut Thomas Pesquet of the European Space Agency will be returning to earth on the Dragon Endeavour capsule later this month, which docked with the ISS in April.
The fix, which involves making an all-welded structure with no joints that can come unglued and disconnected, can't be applied until Endeavour returns to terra firma.
That leaves all four having to rely on their "undergarments" during the flight home which has taken between six and 18 hours in the past depending on conditions.
"Our intent is to not use the system at all for the return leg home because of what we've seen with the fluids we are talking about," NASA's commercial crew program manager, Steve Stich told reporters.
Any kind of liquid getting into systems onboard a spacecraft could cause major issues, including corrosion damage that could make returning to Earth complicated.
It was what caused an alarm to sound on the Inspiration4 systems, indicating there was a "significant" issue.
After working with ground control the crew were able to identify a problem with the "waste management system", with fans designed to pull waste away from astronauts failing to fire.
Further investigation revealed a tube hooked up to a toilet storage tank had come loose during the flight.
This "allowed urine to not go into the storage tank but, essentially, to go into the fan system", William Gerstenmaier, vice president of mission assurance at SpaceX, said.
The astronauts having to rely on their underwear will face a similar experience to those aboard the Apollo mission flights, who didn't get toilets but had plastic bags taped to their buttocks.
On Apollo 10 the plastic bags had significant issues, causing solid waste to end up floating around the cabin.