SpaceX’s Bill Gerst says Crew Dragon’s toilet mechanics were redesigned after the toilet issues on the Inspiration4 mission. A tube that sends urine into a container broke off during the mission and leaked into a fan which sprayed the urine in an area beneath the capsule floor.
Gerst says the crew didn’t notice anything during flight; it only affected the internal section under the floor. Redesign involves a fully welded system with no joints that could come “unglued” like the faulty Inspiration4 system did.
SpaceX, concerned that the same toilet issues are plaguing its other vehicles, had astronauts use a borescope to investigate the Crew Dragon currently docked to the ISS. They confirmed SpaceX’s suspicions and indeed found similar contamination under the floor, Gerst said
Astronaut pee is mixed with a compound called Oxon, and SpaceX worried that might corrode hardware on Crew Dragon if pools around the system unchecked for months. So SpaceX did "extensive tests" on the ground that involved soaking aluminum parts in an Oxon-pee mixture
For "an extended period of time," the Oxon-pee-soaked aluminum parts were placed in a chamber that mimicked the humidity conditions on the ISS. SpaceX found "that corrosion growth" caused by Oxon pee "limits itself in the low-humidity environment onboard station."
typo correction - I’ve been told that the correct spelling of the ammonia-removing compound in the astronaut pee is oxone, not “oxon”
So anyway, Crew Dragon appears to be resilient to piss. Gerst: "Luckily, or, on purpose, we chose an aluminum alloy that is very insensitive to corrosion." The study is ongoing — "We got a couple more samples we'll pull out of the chamber"
This was a really good example of how a engineering problem was detected, studied and fixed. Gotta commend Gerst’s transparency here.
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