Nasa is making plans to de-orbit the ISS safely over the pacific ocean, this eventually leads to the question of whether or not an ISS module can survive reentry (survive meaning it is recognizable upon being retreived)
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6$\begingroup$ Do you mean reentry or reentry and then high-speed contact with the ocean? $\endgroup$– GdDCommented Nov 8, 2021 at 19:48
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$\begingroup$ @GdD, Hopefully both, but just reentry is fine. $\endgroup$– Guest2204Commented Nov 8, 2021 at 19:54
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$\begingroup$ @GdD Hydrobraking? $\endgroup$– chrylis -cautiouslyoptimistic-Commented Nov 10, 2021 at 1:34
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4$\begingroup$ More like Hydrobreaking @chrylis-cautiouslyoptimistic- $\endgroup$– GdDCommented Nov 10, 2021 at 8:49
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2 Answers
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“Aluminum, rather than steel, comprises most of the outer shell of the modules” https://science.nasa.gov/science-news/science-at-nasa/2001/ast14mar_1 . Aluminum has low melting point and softens significantly before it melts. Aluminum and Titanium are major components of the modules. Both are combustible. Titanium will burn in nitrogen, in the absence of oxygen. https://umdearborn.edu/offices/environmental-health-and-safety/lab-safety/chemical-safety/combustible-metals , https://umdearborn.edu/offices/environmental-health-and-safety/lab-safety/chemical-safety/combustible-metals Kevlar melts at an even lower temperature (500*C). A module is unlikely to survive re-entry intact. Try burning a beer can with a propane soldering torch for a good visual. The steel components of the module have a much better chance of landing as debris.
A component that is much more likely to survive than modules are the four NORS oxygen and nitrogen cylinders. They are 1m long and weigh about 100kg. https://www.nasa.gov/content/air-supply-high-pressure-tanks-ready-for-space-station . Their operational pressure is 6000 psi, about twice that of SCUBA or welding tanks. They are seriously beefy components. I couldn’t source their construction, but they are likely Type IV Composite Overwrapped Pressure Vessels
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$\begingroup$ +1 aluminum readily reacts with oxygen to form a protective aluminum oxide barrier so I don't think "oxidized readily" has much significance. $\endgroup$– uhohCommented Nov 9, 2021 at 7:15
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11$\begingroup$ @uhoh But that only works below the melting point of the metal. There's no stable oxide layer on hot aluminium droplets. $\endgroup$– TooTeaCommented Nov 9, 2021 at 8:50
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1$\begingroup$ @TooTea at which point the oxide continues to be irrelevant. I'm saying that "I don't think 'oxidizes readily' has much significance." Do you disagree? Do you think oxidation has some relevance here? $\endgroup$– uhohCommented Nov 9, 2021 at 9:31
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4$\begingroup$ @uhoh: Well, yes. Once it has turned into aluminum oxide dust floating in the upper atmosphere, it's no longer "recognizable upon being retrieved" as specified by the OP. I suspect you may have understood the phrase "oxidizes readily" somewhat differently than the rest of us. Maybe phrasing it in simpler words, such as "burns easily in air", would make the answer more understandable? $\endgroup$ Commented Nov 9, 2021 at 12:25
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1$\begingroup$ @IlmariKaronen that's IF rather than "once". I'd predict a mix of big and small chunks and a spray of droplets rather than dust, but a good authoritative source would be better than speculation. Related: How many kilograms of nickel particles will be dispersed in Earth's atmosphere by dumping old ISS batteries overboard? remains unanswered. $\endgroup$– uhohCommented Nov 9, 2021 at 13:05
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This (not so new) article says it can:
"NASA estimates that 16 percent of the ISS would likely survive the burn and stresses of reentry, between 53,500 and 173,250 pounds falling to earth. "
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8$\begingroup$ The parts will not be recognizable. 16% of the mass might make it in solid form to splash-down, but approximately 0% of it will be functional parts in the milisecond before metal meets wave. $\endgroup$ Commented Nov 9, 2021 at 7:47