Author Topic: What is the limiting factor in ISS life expectancy?  (Read 3805 times)

Offline Nascent Ascent

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I keep reading that the ISS might be nearing the end of its life in 5-10 years.  Other than the shifting tides of political support, what is the technical limiting factor that would limit the life of the ISS?
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Online Jorge

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Re: What is the limiting factor in ISS life expectancy?
« Reply #1 on: 02/05/2009 04:05 AM »
I keep reading that the ISS might be nearing the end of its life in 5-10 years.  Other than the shifting tides of political support, what is the technical limiting factor that would limit the life of the ISS?

Potentially many, and not easily identified.

The original requirement for Space Station Freedom was a design lifetime of 30 years. That was reduced to 15 years for ISS, to reduce development costs. And all that really means is that all the individual components of ISS need to be able to last at least 15 years in the orbital environment, and that the system (as a combination of individual components) also needs to last 15 years.

Complicating factors include:

1) ISS has not been assembled all at once, so for some components the "clock" started earlier than for others.

2) Ground storage has some effect on component lifetime, but the effects will differ component-to-component.

3) Russian standards for design lifetime may differ from those used by the US segment. Many components of the Russian segment are reportedly unmodified from those used on Mir, which had a design lifetime of five years (but wound up lasting fifteen).

Bottom line is that 2013 marks the 15th anniversary of ISS first element launch and beyond that point components will begin to exceed their design lifetimes. That does not mean those components will immediately fail, because there is always a factor of safety designed in. However, it does mean that the component failure rate will gradually start growing after that point and the station will become progressively more expensive to maintain.
JRF

Offline gomorrha

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Re: What is the limiting factor in ISS life expectancy?
« Reply #2 on: 02/05/2009 07:27 AM »
That´s the point. Just take a look at your flat or your house.

After a couple of years the washer or the freezer quits, then the cooker. The water tap starts leaking a.s.o.
A tile on the roof becomes loose and maybe the windows don´t close properly anymore.

In space you can repair the interior altough it´s quite expensive.
But if some of the exterior components brake or the life support systems fail it´s getting hazardous.

I think that´s the point Jorge meant.

Offline Norm Hartnett

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Offline catfry

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Re: What is the limiting factor in ISS life expectancy?
« Reply #4 on: 02/06/2009 07:50 AM »
Is there anything OTHER than the pressurized structure itself that cannot be replaced on orbit? I mean the first time I heard about problems with the truss structure race rings I thought for sure that these would HAVE to be fixed on orbit and there would be no way to fly a replacement, due to size, lack of spares, and lack of Shuttle flights it could go on, and yet we have heard about a plan to actually fly another if the current plan to grease it up wasn't enough.

So I'm just trying to come up with another single component that should be more difficult than a race ring.
Only structural things are more difficult is all I can think of.

Offline wjbarnett

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Re: What is the limiting factor in ISS life expectancy?
« Reply #5 on: 02/06/2009 01:04 PM »
The trust structure is not "pressurized" and I'm having really difficulty imagining how one of those elements (e.g. S0, or even S/P5) might be replaced (perhaps re-enforced would work). The Lab to S0 connections was one of the stress points identified by the analysis.
Jack
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Offline catfry

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Re: What is the limiting factor in ISS life expectancy?
« Reply #6 on: 02/06/2009 02:27 PM »
Yes, sorry I was confusing. Basically what I meant, pressurized space can be compromised in unsalvageable ways, and structural components are ALSO critical and really difficult to replace.
Two separate kinds of components of the ISS that are irreplaceable and are thus critical for determining the lifetime. (Although habitable modules are also structural and thus has to be considered in two ways; has it lost livability or has it lost structural strength. Probably both happen at the same time)
My question is, since the race ring for the SARJ is apparently a replaceable component, what structural components are not?
The race ring sits in between other components that would have to be seperated and apparently serious planners have thought they could acomplish a replacement. Obviously at some point replacement becomes inpractical. Is the SARJ at the limit of this practicality?
« Last Edit: 02/06/2009 02:31 PM by catfry »

Offline Analyst

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Re: What is the limiting factor in ISS life expectancy?
« Reply #7 on: 02/06/2009 02:40 PM »
With enough effort you can replace virtually every component. Sure, replacing Destiny or S0 is way complex - and would probably end in not replacing but supplementing these components - but not impossible. Even this this may be more cost effective than building ISS2.

Analyst

Offline catfry

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Re: What is the limiting factor in ISS life expectancy?
« Reply #8 on: 02/06/2009 03:30 PM »
To my mind replacement of those large structures like a truss segment or a module is not economically or politically possible with the best of will.
So their lifespan will largely determine ISS lifespan.

In some instances though the program could continue with a loss of one of those big things. Lose any component of the port truss and you still have the starboard truss. The ISS continues to live at half power.
Lose any 'end' module and you seal it off and the rest of the ISS continues.
So only some large structures are critical to the lifetime, like Unity.

Freak events can of course occur, like mmod impacts or unchecked hazardous fungal growth(!) or similar. These are risks that could cut the lifetime short at any time.

Lastly there is the question of fatique resistance. As far as I know the 15 year lifetime comes from the engineering spec that required an ability to withstand this number of years on orbit without failure. What is the likelihood this can be reached or exceeded?
This is a key question.
MIR was built for 5 years or something and lasted 15.
No guarantee that the ISS can overperform similarly.
« Last Edit: 02/06/2009 03:30 PM by catfry »

Offline Jim

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Re: What is the limiting factor in ISS life expectancy?
« Reply #9 on: 02/06/2009 03:39 PM »

Lose any 'end' module and you seal it off and the rest of the ISS continues.
So only some large structures are critical to the lifetime, like Unity.

Even more with Destiny, it central to control of the USOS

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