Splashdown could lead to splashback as four astronauts will be forced to wear mess-friendly 'undergarments' on their return journey from the International Space Station, NASA has revealed.

An ongoing problem with the toilet onboard SpaceX's Crew Dragon capsules means that astronauts returning to Earth this month won't be able to use the bathroom until they land.

As a result, they'll be forced to wear something resembling nappies, according to NASA's Commercial Crew Program manager, Steve Stich.

During its last outing, in which four civilians spent three days in orbit, a SpaceX Crew Dragon reportedly sprang a major leak in zero-gravity.

The returning astronauts will have to wear special 'undergarments' - or just hold it
The returning astronauts will have to wear special 'undergarments' - or just hold it

An alarm went off when urine apparently got sucked into a fan system and sprayed out of the toilet in all directions.

Luckily, the leak was contained to a storage area under the floor, which meant the crew were able to avoid getting drenched.

Scientists at NASA and Elon Musk's SpaceX investigated other Crew Dragon shuttles and found out they had the same problem—as did the four intrepid nappy-wearing astronauts aboard the ISS.

SIPA USA via PA Images May 15, 2021; Kennedy Space Center, FL, USA; A SpaceX Falcon 9 rocket lifts off from Kennedy Space Center on Saturday, May 15, 2021. The rocket is carrying a batch of Starlink communications satellites. Mandatory Credit: Craig Bailey/FLORIDA TODAY via USA TODAY NETWORK/Sipa USA
SpaceX's Crew Dragon capsules have a major plumbing problem that can't be fixed in time for the ISS astronauts to return home

SpaceX has been working to fix the problem on future flights, but for the astronauts who have been aboard the Space Station since April, there's no time to call out a plumber as their Crew Dragon capsule is still up there with them.

The crew should be fine for now as the space station has its own toilets, but once they start their journey home, they'll have to resort to the 'undergarments'.

Astronaut in the outer space over the planet Earth. Elements of this image furnished by NASA (url: https://www.nasa.gov/sites/default/files/thumbnails/image/iss060e007297.jpg https://images-assets.nasa.gov/image/sts069-714-046/sts069-714-046~medium.jpg)
All that tech and they can't fix the toilet

NASA have not said how long the journey home will take from the ISS, but it could be anywhere between six and nineteen hours judging from previous trips. The astronauts will just have to go before they leave.