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There still seems to be uncertainty about how long the ISS will remain flying, mainly due to political wrangling and budgetary concerns. Even the longest plans state that operations are not expected to last beyond 2024.

However, leaving aside political and budgetary considerations, how long could the ISS, as it currently exists, remain operational and safe enough for habitation and use by crew?

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    $\begingroup$ Until the first malfunction renders it uninhabitable / useless? I.e. you can't really leave aside political and budgetary considerations, they go hand in hand with its maintenance and with it its operability. I'm not sure there's an answer to be had for how you framed the question. If, say, its ECLSS (Environmental Control and Life Support System) is left unattended and failed equipment unreplaced, it's anyone's guess when it'll fail to the point it's useless, dangerous even. There were quite a few maintenance & repair EVA's in its recent past, some more urgent than others. $\endgroup$ – TildalWave Nov 11 '14 at 12:26
  • $\begingroup$ @TildalWave I was thinking more of the expected lifetime of the main structure, pressure hull, ECLSS or other systems that are vital to operations. $\endgroup$ – ForgeMonkey Nov 11 '14 at 12:31
  • $\begingroup$ ECLSS is vital to operations as long as it's supposed to be habitable. It's one of the most complex, frequently repaired and vital parts of the US segment. If that goes, you've lost its atmospheric control (composition, temperature, humidity,...), you're using up potable water supply dangerously fast since it's not recycled, its cooling would be greatly affected, carbon dioxide, ammonia would build-up,... you name it. Its structural integrity is then barely an issue if you'll want to evacuate long before that, the station's orbit isn't regularly reboosted and it simply decays and deorbits. $\endgroup$ – TildalWave Nov 11 '14 at 12:39
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    $\begingroup$ Similar question: space.stackexchange.com/questions/237/why-decommission-the-iss $\endgroup$ – Jerard Puckett Nov 11 '14 at 13:42
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There's a lot of uncertainty at all levels, mainly because we've never had a manned structure in space for this long. Mir set the previous record at 15 years. The ISS reached that milestone in 2013. We've already found that the station lasts longer than its initial design life (PDF, page 3):

In November 2013, the International Space Station (ISS or Station) completed 15 years of continuous operation in low Earth orbit, marking a significant achievement in the history of human spaceflight. Two months later, the Administration announced its intent to extend Station operations until 2024. Originally designed and tested for a 15-year life span, the ISS may now operate for 26 years.

At one point, NASA was working on certifying the station for use until 2028:

Hardware Assessment and Certification. NASA and its international partners designed and tested the ISS for a 15-year life span – a benchmark the oldest segments of the Station surpassed in November 2013. The NASA Authorization Act of 2010 extended the life of the Station until 2020, and NASA and its Canadian, Japanese, and European partners have certified that the ISS structure and hardware are sufficient to continue operations until that date.16 In January 2014, the President announced his support for extending Station operations until at least 2024.17 Prior to this announcement, NASA had initiated a feasibility assessment for continuing operations until 2028. (NASA defines an assessment as the method for performing verification or certification. For ISS certification, the focus is primarily on analytical assessments using the performance data from the 15 years of ISS operation. NASA expects to complete its 2028 assessment in 2018.)

Investigations into extending ISS lifespan to 2028 started in 2010.

There are several components that are seen as 'most likely to cause trouble':

  • the hardware that attaches the truss to the pressurized modules.
  • high-pressure oxygen lines
  • solar panels (power levels are dropping faster than expected)
  • EPROMs that lose their stored data

Then there are things like the seals between modules that would be difficult to replace if they failed.

So at some point, there are components you need to replace (in some cases, in a very expensive operation) before they fail. Then prolonging the life of the station becomes a political and budgetary issue: you're weighing risks to the crew against the cost of refurbishment.

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  • $\begingroup$ A question arises! Could newer modules be reassembled to a new station, while dumping modules which have reached their end-of-life. In this way with a continuous replenishment and restructuring (by adding new modules) the station could be kept up there indefinitely, just that no module would be older than say 20 years. Old modules could also be downgraded to serve as storage or as reserve-excess systems, but I guess that that probably isn't worth it. $\endgroup$ – WalyKu May 27 '17 at 14:49
  • $\begingroup$ Theoretically yes, but the oldest modules are in the middle, so you have to disassemble half the station to get to them. That's at least a risky and expensive operation that leaves part or all of the station inoperable if there's a problem. $\endgroup$ – Hobbes May 27 '17 at 16:10

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