A SpaceX Crew Dragon capsule is slated to take a group of professional astronauts to space this weekend. But first, NASA must look over and approve some changes SpaceX made to address some issues with a key component — the toilet. A problem with the Crew Dragon toilet was first identified during SpaceX’s Inspiration4 mission in September, which carried four people on the first all-tourism mission to orbit, where they spent three days. Jared Isaacman, the commander and financier of the “Inspiration4” mission, as it was called, told CNN Business last month that an alarm went off during the mission, alerting the crew to an unforeseen problem with the toilet’s fan. He said he and his fellow passengers had to work with SpaceX controllers on the ground to troubleshoot. The issue did not cause any serious problems for the Inspiration4 crew, nor were there any instances of bodily fluids getting loose inside the capsule. “I want to be 100% clear: There were no issues in the cabin at all as it relates to that,” Isaacman said. But after the Inspiration4 crew’s return to Earth, SpaceX disassembled their spacecraft to further inspect what might have gone wrong. “There’s a storage tank where the the urine goes to be stored [and] there’s a tube that came disconnected or came unglued,” said William Gerstenmaier, a former associate administrator at NASA who now works as SpaceX’s head of mission assurance. “That allowed urine essentially to not go into the storage tank, but essentially go into the fan system.” The situation highlights how spacecraft that have conducted all the necessary test flights, been vetted and approved, and even completed full missions can still prove to have unforeseen design risks. Fans are used on spacecraft toilets to create suction and control the flow of urine because, in the microgravity environment of space, waste can — and does — go in every possible direction. In this particular case, the Inspiration4 crew, however, did not notice any excreta floating around the cabin because the leakage was still relegated to contained areas underneath the floor, Gerstenmaier said. But when a SpaceX team pried up the floor, they confirmed there was “contamination,” he added. As it turns out, another Crew Dragon capsule that was launched earlier but is still in space is also dealing with a similar leak. The capsule that had been used to take professional astronauts to the International Space Station in April, on a mission dubbed Crew-2, experienced similar problems. But because those astronauts only had to rely on Crew Dragon’s on-board toilet while in transit to the ISS — rather than the full three days the Inspiration4 crew spent aboard their capsule — the mess wasn’t as bad. That Crew Dragon capsule, however, is still attached to the ISS and will have to be used to return that crew of astronauts to Earth next month. So, SpaceX ran a series of ground tests to make sure the Crew Dragon’s aluminum structure could hold up to the leaked urine and that the substance hadn’t become dangerously corrosive. Basically, SpaceX researchers coated some pieces of metal in urine mixed with Oxone — the same substance used to remove ammonia from urine on board Crew Dragon — to see how it would react with the aluminum. They put it inside a chamber to mimic the vacuum of space, and they found limited corrosion, Gerstenmaier said. “We’ll double check things, we’ll triple checks things, and we got a couple more samples we’ll pull out of the chambers and inspect,” he said. “But we’ll be ready to go and make sure the crew is safe to return.” And to make sure that such a situation never crops up again, SpaceX designed a fix for its upcoming mission, opting to weld the wayward tube in place to eliminate the risk of it coming unglued. NASA still has to give a final OK for that fix, but, all things considered, NASA and SpaceX officials are confident these issues will be put to rest, and this weekend’s mission will move forward. In this case, “that Inspiration4 flight was really a gift for us,” said Steve Stich, NASA’s Commercial Crew Program manager. This weekend’s flight will mark the fourth SpaceX Crew Dragon mission to carry professional astronauts to the space station as part of a deal SpaceX inked with NASA. On board will be NASA astronauts Raja Chari, Tom Marshburn, Kayla Barron, as well as ESA (European Space Agency) astronaut Matthias Maurer. They’ll spend six months aboard the ISS, continuing the space station’s 20-year history of hosting astronauts from all over the world to conduct scientific research.