If the ISS had to be abandoned due to an imminent threat, how long before it becomes uninhabitable?

[Agent86]

If there were an impending threat to the ISS, and the station needed to be abandoned, but was not physically damaged in any way, how long could it be maintained in a livable condition for using teleoperation from the ground? Can its orbit be adjusted remotely to prevent orbital decay and eventual reentry? If this was indefinite, how long could it run with zero crew providing maintenance and repairs? Could it reach a state at which some combination of factors left it in orbit, but ultimately unlivable due to conditions onboard, such as a wholly failed life support system or toxic/corrosive interior atmosphere?

[Nibb31]

The ISS is controlled from the ground, so it can fly unmanned until something breaks down and needs repairing, or if it runs out of consumables. Ultimately, it would depend on why the ISS was evacuated in the first place.

Edited January 27, 2016 by Nibb31

[mikegarrison]

5 minutes ago, Nibb31 said:

The ISS is controlled from the ground, so it can fly unmanned until something breaks down and needs repairing, or if it runs out of consumables. Ultimately, it would depend on why the ISS was evacuated in the first place.

But it has a limited amount of propulsion. It relies on the visiting spaceships for countering atmospheric drag. It would definitely fall out of the sky without that. The question would be how long that would take.

Edited January 27, 2016 by mikegarrison

[Glaran K'erman]

Simple answer, long enough to send up another crew. Long answer involves taking into account all on orbit spares and the state of the station when it was left. In terms of ISS reboosts this chart shows the average height of the ISS over a year, you can see where the station is reboosted clearly by the periodic sharp increases. The importance of this chart though is that it shows a period where no significant reboots occurred giving a great chance to see the rate of descent for the station.

 

Edited January 27, 2016 by Glaran K'erman

[Nibb31]

Yes, that's why I said until it runs out of consumables. The time it takes to come down depends on the altitude, but also on solar activity.

https://qph.is.quoracdn.net/main-qimg-f40ac09e0a4e9ee309c651b5f9b0b6e1

Based on this chart, it looks like it loses 2 to 4 km every month without a reboost when it's around 400km. But of course, the lower it gets, the more it drops. However, it could probably stay up there several years. Skylab took 5 years to decay from a similar 400 km, but then again, it had less drag than the ISS.

However, the ISS typically uses Progress for reboosts, which is unmanned. Unless there is some manual reconfiguration necessary, you could rotate cargo vehicles while the ISS is unmanned, so as long as those systems work, there shouldn't be a problem.

Edited January 27, 2016 by Nibb31

[Glaran K'erman]

@Nibb31 I don't think the rate of decay is quite that high but it definitely fluctuates for sure. Good point bringing up how solar activity affects atmospheric density, especially when talking about the ISS which is being about as aerodynamically efficient as a stretched plastic bag. 

Edited January 27, 2016 by Glaran K'erman

[mikegarrison]

1 hour ago, Glaran K'erman said:

@Nibb31 I don't think the rate of decay is quite that high but it definitely fluctuates for sure. Good point bringing up how solar activity affects atmospheric density, especially when talking about the ISS which is being about as aerodynamically efficient as a stretched plastic bag. 

Much, much less so than that.

[fredinno]

4 hours ago, Nibb31 said:

Yes, that's why I said until it runs out of consumables. The time it takes to come down depends on the altitude, but also on solar activity.

https://qph.is.quoracdn.net/main-qimg-f40ac09e0a4e9ee309c651b5f9b0b6e1

Based on this chart, it looks like it loses 2 to 4 km every month without a reboost when it's around 400km. But of course, the lower it gets, the more it drops. However, it could probably stay up there several years. Skylab took 5 years to decay from a similar 400 km, but then again, it had less drag than the ISS.

However, the ISS typically uses Progress for reboosts, which is unmanned. Unless there is some manual reconfiguration necessary, you could rotate cargo vehicles while the ISS is unmanned, so as long as those systems work, there shouldn't be a problem.

The ISS also has its own propulsion, and things like Cygnus would also be able to reboost (though it's not usually done).

 

So, it should stay up for at least a few years. Definitely long enough to fix whatever problem going on and re-man the station.

[WestAir]

Well, the chart suggests it loses 4km / month. That's a little less than 50km / year. Assuming the lowest altitude it can complete 1 orbit without re-entry is 150km, and assuming it started at 400km, it should remain up there for ~5 years.

EDIT: Extremely rough math, though.

Edited January 27, 2016 by WestAir

[razark]

Of course, if the ISS were to be evacuated for an unknown length of time, one of the first steps would probably be to boost it's altitude, anyway.

NASA doesn't want another littering ticket from Australia.

[cantab]

If it was to be vacated for a while, I suspect NASA and Roscosmos would put the solars edge-on all the time to minimise orbital decay, since it's likely less power would be needed.

[Agent86]

12 hours ago, Nibb31 said:

Yes, that's why I said until it runs out of consumables. The time it takes to come down depends on the altitude, but also on solar activity.

https://qph.is.quoracdn.net/main-qimg-f40ac09e0a4e9ee309c651b5f9b0b6e1

Based on this chart, it looks like it loses 2 to 4 km every month without a reboost when it's around 400km. But of course, the lower it gets, the more it drops. However, it could probably stay up there several years. Skylab took 5 years to decay from a similar 400 km, but then again, it had less drag than the ISS.

However, the ISS typically uses Progress for reboosts, which is unmanned. Unless there is some manual reconfiguration necessary, you could rotate cargo vehicles while the ISS is unmanned, so as long as those systems work, there shouldn't be a problem.

Can the unmanned progress modules be fully docked remotely, without any assistance from crew on station?

[Glaran K'erman]

11 minutes ago, Agent86 said:

Can the unmanned progress modules be fully docked remotely, without any assistance from crew on station?

Yes they could

[Umlüx]

this brings me to another question.

lets say the ISS is obsolete, how would they dispose of it?

it surely is too big and massive to burn up? just let it reentry and crash? disassemble the modules first?

[shynung]

Just let it fall into the ocean. Any large pieces that doesn't burn up on the way down will fall onto a vast expanse of water.

[Nibb31]

3 hours ago, Umlüx said:

this brings me to another question.

lets say the ISS is obsolete, how would they dispose of it?

it surely is too big and massive to burn up? just let it reentry and crash? disassemble the modules first?

There is a plan. The plan is to launch a Progress and perform a controlled deorbit burn to splash it into the Pacific.

http://forum.kerbalspaceprogram.com/index.php?/topic/130021-letting-the-iss-burn-upwhy/#comment-2364491

Edited January 28, 2016 by Nibb31

[RizzoTheRat]

21 hours ago, Nibb31 said:

Skylab took 5 years to decay from a similar 400 km, but then again, it had less drag than the ISS.

There were even plans to reuse Skylab if the shuttle had been ready in '79 as planned, but I guess it would have been a close run thing as to whether they got to it in time.

Some pretty big chunks of skylab reached the ground too so I guess there'd be some sizeable chunks of the ISS surviving when it eventually de-orbits

 

[Nibb31]

1 hour ago, RizzoTheRat said:

There were even plans to reuse Skylab if the shuttle had been ready in '79 as planned, but I guess it would have been a close run thing as to whether they got to it in time.

Yes, Skylab actually decayed faster than planned. Very little was known at the time about the effects of solar activity in the upper atmosphere. There was also a planned reboost mission using an unmanned vehicle, but that was abandoned too, as the US had no use for developing unmanned docking in their plans at the time.

Shuttle visiting Skylab would have needed a bit of creative engineering too. Although there were intentions, there was no docking module planned for Shuttle, so it would have needed an Apollo docking module with an airlock because the atmospheres of Apollo and Shuttle were different (Skylab was at 5 psi (0.3 bar), whereas Shuttle ground air pressure). There was also the question of whether Skylab would have been suitable for breathing. It was expected that as everything was powered down, fugus and bacteria would covered everything, making the atmosphere toxic and most of the equipment unusable.

In the end, the decay of Skylab was a bit of a relief for NASA, as it helped to justify building Space Station Freedom (even though we all know that it took over a decade to turn into the ISS) instead of being forced to keep on running Apollo-era legacy hardware.

Edited January 28, 2016 by Nibb31

[fredinno]

18 hours ago, Nibb31 said:

Yes, Skylab actually decayed faster than planned. Very little was known at the time about the effects of solar activity in the upper atmosphere. There was also a planned reboost mission using an unmanned vehicle, but that was abandoned too, as the US had no use for developing unmanned docking in their plans at the time.

Shuttle visiting Skylab would have needed a bit of creative engineering too. Although there were intentions, there was no docking module planned for Shuttle, so it would have needed an Apollo docking module with an airlock because the atmospheres of Apollo and Shuttle were different (Skylab was at 5 psi (0.3 bar), whereas Shuttle ground air pressure). There was also the question of whether Skylab would have been suitable for breathing. It was expected that as everything was powered down, fugus and bacteria would covered everything, making the atmosphere toxic and most of the equipment unusable.

In the end, the decay of Skylab was a bit of a relief for NASA, as it helped to justify building Space Station Freedom (even though we all know that it took over a decade to turn into the ISS) instead of being forced to keep on running Apollo-era legacy hardware.

In hindsight, they probably should have scrounged up the little money needed to launch the Apollo Rescue Mission as Skylab V.