[headwayoldest]

I realize their orbit is relatively clear of debris and micro meteors, but is this materials decomposing or degrading and not random damage and happenstance?

The ISS has no doubt been important and I remember how excited I was when it was being assembled. Is it really so historically significant it's worth the amount of effort you're describing?

[lmilcin]

Hull is definitely not decomposing or degrading. If left in peace at sufficiently high altitude it would look the same in a million years.

My bet is the issue is most likely stresses due to vibrations under pressure and pressure changes. It is complex but also well known problem. As the astro/kosmonauts move about the station, resupply dock, pressure changes, etc. some parts are being subject to constantly changing stresses while already being stressed due to pressure.

It might also be possible that there are some additional thermal stresses but I think it is less likely these are source of the problem.

[sailingparrot]

> My bet is the issue is most likely stresses due to vibrations under pressure and pressure changes.

So you are saying it's degrading?

[maxerickson]

These discussions about materials are often difficult, because there are meaningfully different processes that are lumped together in everyday language.

Mechanical stresses leading to failure at a particular point are certainly a form of degradation, but I believe they mean degradation in the sense where the entire body of the material is undergoing some change (like a plastic bottle fogging or such).

I think seeking clear descriptions is fine, treating it as a "gotcha" game is tedious and unnecessary.

[lmilcin]

I took liberty to look through the literature and it seems change of physical and chemical properties of material due to all types conditions (including physical stresses) is covered by the term.

I am not into mechanical science that much, I have always treated degradation as a kind of surface or volume phenomena where the material looses its properties due to temperature, radiation, age, chemical reaction, etc. For mechanical effects there are already very good terms like metal fatigue and stress induced cracking.

[waheoo]

> "gotcha" game is tedious

I agree but you can say the same thing in reverse. This is a public forums, you don't need to claim something isn't right because it doesn't fit the technical description.

[lmilcin]

Just stop this already.

The post said "is this materials decomposing or degrading".

While I may have not been precise about "degrading" part, we can assume the metal is definitely not "decomposing".

[waheoo]

Ah I think my reply went to the wrong person. Edit: Nope just under your comment is all.

My remark is at the person claiming tit for tat about the tat instead of the tit.

[HPsquared]

Degradation of the structural integrity, I'd say.

[thescriptkiddie]

Cracks are a common sign of metal fatigue, which can be caused by repeated stress cycles. Imagine bending a piece of plastic back and forth until it snaps.

[pengaru]

Especially for "cold butter" metals like aluminum and copper.

[ben_w]

I’ve never heard that phrase used in this content before. How does “cold butter” apply to these metals?

[pengaru]

I don't recall which of the many print books I read in my gearhead/TIG-welding days had used the term, but the lack of a distinct fatigue/endurance limit [0] for these metals was put into practical terms with something along the lines of "like slightly bending a cold stick of butter".

It's why aluminum airplanes are supposed to get inspected for cracks regularly, and why aluminum bicycle frames must be so uncomfortably rigid. If there's cyclic stress occurring, it's a question of when, not if they will crack.

If I had to guess it's from Carroll Smith's 80s-era Engineer to Win, it sounds like something he'd write.

[0] https://en.wikipedia.org/wiki/File:S-N_curves.PNG

[fao_]

I think it refers to the type of break the joint makes?

However, while searching I found this search excerpt:

    Which metals diffuse into other metals and how? | Naked ...
    www.thenakedscientists.com › forum
        Sodium and potassium metal (both *soft solids, like cold butter*) react

So perhaps it is used to designate 'soft solids' versus 'hard solids'

[elihu]

> Is it really so historically significant it's worth the amount of effort you're describing?

Space launches are getting a lot cheaper, so moving the ISS to another orbit might not be such a big deal as it used to be. We don't really need to keep the ISS around forever, but on the other hand, losing it would in some ways be similar to the burning of Notre Dame in 2019 (I can't believe that was less than two years ago). It's mankind's first permanent foothold in space. In that sense, it's irreplaceable.

Let's say moving the ISS at the end of its usable lifespan costs a half billion dollars. That's like asking every U.S. taxpayer to pay about two dollars. Is it worth it? To me I think it's worth a lot more than two dollars, even if it unlikely that i'll ever actually be able to visit the ISS in my lifetime.

[jarofgreen]

> It's mankind's first permanent foothold in space.

Mir?

[elihu]

Good point, I forgot about Mir. According to wikipedia it lasted from 1986 to 2001.

I had briefly considered Skylab, but figured it didn't really count as "permanent". Wikipedia says it was up for 24 weeks.