Another Crew Dragon capsule that docked to the space station in April with four astronauts aboard has the same plumbing system as the Inspiration4 capsule. SpaceX engineers feared the same “contamination” might have occurred on that spacecraft.The engineers’ suspicions were correct.NASA astronauts living on the station snaked a borescope device — a cable with a tiny camera at the end — underneath the capsule’s floor and discovered traces of urine in places it shouldn’t be, Mr. Gerstenmaier said. “Yes, there was some indication of some contamination under the floor,” he said.That raised new concerns. In space, urine is mixed with a potentially corrosive compound, oxone, to eliminate ammonia. Could the oxone-laced urine, sitting in the capsule for months, have corroded any crucial hardware?To answer this question, Mr. Gersteinmaier said, SpaceX engineers on Earth gathered aluminum parts similar to those on the spacecraft and created a sampling of urine mixed with oxone. They soaked the parts and placed them inside a chamber that mimicked the humidity conditions aboard the space station for “an extended period of time,” Mr. Gerstenmaier said.The wayward waste inside the Inspiration4 capsule was more voluminous than the contamination found on the capsule attached to the space station, he said, because the passengers used the capsule for three days while astronauts launching to the space station are typically in orbit for about 24 hours. The results of the ground tests appear positive so far, he said: “Luckily, or, on purpose, we chose an aluminum alloy that is very insensitive to corrosion.”That capsule is scheduled to undock from the station in November and return home with the four astronauts it delivered in April. The ground tests with the oxone and urine are continuing.“We got a couple more samples we’ll pull out of the chamber,” Mr. Gerstenmaier said. He did not say who provided the samples.
Pretty confident urine and oxone won't react much at all (especially enough to corrode aluminum), but it seems reasonable to run some direct studies...
Is there a drug or drug metabolite excreted in urine that could react with Oxone and afford something corrosive to aluminum? While astronauts are generally healthier than most, they're old enough to present a chronic illness that can be treated with medication and not impact their flight status.
ReplyDeleteNot an expert on aluminum corrosion, but I think under most conditions outside of low and high pH extremes, where the natural oxide layer dissolves, Al is most susceptible to pitting attack. Halide ions, like Cl-, are the most notorious for causing pitting.
ReplyDeleteWithout thinking more about it, having a strong oxidizer and chloride both seem like a bad combination(assuming there might be Cl- in urine). But I'm thinking different alloys probably have differing pitting susceptibilties. Also, not sure if they are evaluating pitting attack specifically, or just general corrosion.
My usual source for human clinical chemistry (Wallach's Interpretation of Diagnostic Tests) gives a normal range of 110-250 mEq/L for chloride in urine.
Deleteproblem is that oxone contains 1:2 KHSO4 + KHSO5 mixture so it behaves as a strong acid and strong oxidizer.
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