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In 2015, technicians entered the retired Space Shuttle Endeavour to remove the water tanks, with the goal of reusing these tanks on ISS.

The space shuttle Endeavour is retired and on display at the California Science Center, but it's still contributing to the space program.

NASA engineers are working this week to remove four tanks from the shuttle for use as potable water storage on the International Space Station.

Looks like a strange idea to reuse worn equipment as trivial as a water tank that is exhibited in a museum, when whole rockets are built brand new for a typical flight.

Are these tanks somehow special and unusually expensive to make to justify such an idea? If they are just metal cans as I envision, the only reason I could imagine would be a "symbolic meaning".

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    $\begingroup$ What an intriguing question! I'm sometimes really surprised by what is going on in the aerospace sector. This is such a nice bit of information. I hope you'll get a satisfactory answer. $\endgroup$ – Polygnome May 28 at 17:37
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    $\begingroup$ designing a water tank for use in free-fall and vacuum is non-trivial $\endgroup$ – JCRM May 29 at 8:00
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They're already made, have plenty of usable life left, were stored in a way that facilitates reuse, and apparently cost less than building and certifying brand new ones.

https://www.nasa.gov/feature/proposed-station-water-system-looks-to-retired-shuttles

In order to reduce the cost and complexity of the proposed system, NASA engineers looked at reusing the water tanks from shuttles Atlantis and Endeavour. The tanks meet the station’s stringent requirements for potable water quality, while preventing the accumulation of free gas. The shuttle water tanks were designed to support 100 missions each. Approximately 70 percent of design life remains in the Atlantis tanks based on 33 total missions flown, while Endeavour’s tanks were used on 25 missions, leaving an estimated 75 percent of design life.

Personnel at NASA’s Kennedy Space Center in Florida carefully preserved the water tanks from the retired shuttles with pressurized dry nitrogen to maintain cleanliness and minimize unintentional fatigue of moving parts. As a result, minimal preparation and processing activities would be required to ready the tanks for integration into the proposed storage system.

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    $\begingroup$ Never underestimate the cost of certification, especially for NASA program. $\endgroup$ – RocketDocRyan May 29 at 5:28
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    $\begingroup$ The key word here is indeed certification. This is more than just a rubber-stamp. It is a verified, audited history of the component that details the numerous quality assurance and reliability tests it has undergone. Specifically to do with reliability, this would include long-duration burn-in tests that are very expensive and time-consuming to repeat. I wouldn't be surprised if the cost profile of a NASA component is 1 part manufacture, 9 parts quality assurance. $\endgroup$ – Oscar Bravo May 29 at 7:43
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    $\begingroup$ If you include engineering in that 9 parts, you're not far off. NASA stuff is also more often than not a one off item, which is expensive. Especially since NASA is what we call a hands-on customer. They like to inspect and critique not just their subcontractor's facilities and procedures, but all of the sub's suppliers as well. It's understandable, given how expensive failure is for them. Congress is less than understanding of failure, but tolerant of budget overruns. $\endgroup$ – RocketDocRyan May 29 at 13:27
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    $\begingroup$ One would also have to assume, at first blush, that said tanks would last longer on the ISS than they would have lasted in the Shuttle, if said Shuttle was still flying. The fact that said tanks were designed to survive dozens of ascent/entry load cycles probably makes them a bit "over-designed" for ISS use...not necessarily a bad thing. $\endgroup$ – Digger May 29 at 16:03
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    $\begingroup$ Not sure if this bolsters the argument about certification or weakens it but this seems relevant "19-year fraud scheme that included falsifying thousands of certifications" $\endgroup$ – JimmyJames May 29 at 17:23

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