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I understand that the ISS is somewhat capable of unmanned control unless a catastrophic error occurs with core instruments, however when the crew is onboard, there is usually a crew of around 6 at any given time.

My question is, to be able to safely control and maintain the station including spacewalks and interior functionality, how many people are required? Can it be run with a minimum of 2 people? One to do spacewalks and the other suits them up, etc?

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    $\begingroup$ Solo spacewalks are not done. $\endgroup$ – Organic Marble Feb 5 '17 at 2:31
  • $\begingroup$ Depends on what date you decide as the beginning on ISS, the first modules arrived unmanned. $\endgroup$ – SF. Feb 5 '17 at 2:51
  • $\begingroup$ @SF. As of now. Even though it can be unmanned, for correct operations, whats the minimum amount of people required? $\endgroup$ – finnrayment Feb 5 '17 at 7:39
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    $\begingroup$ After the Columbia tragedy, the ISS was manned with crews of two until the Shuttle started flying again. $\endgroup$ – Digger Feb 6 '17 at 17:49
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    $\begingroup$ @frayment They both went outside. There have been a few times (I posted in another answer on this site) in which the ISS was empty for a few hours or less. Most of them were from moving a Soyuz from one docking port to another, but there were, by my count, 9 EVAs during the two-crew time period that left ISS empty inside. $\endgroup$ – Tristan Feb 9 '17 at 15:35
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ISS crew regularly drops to 3 these days. But in the early days, expeditions 7-12 had 2 crew members. Without the Shuttle and before COTS, ATV and HTV, it wasn't practicable to keep a crew of 3 supplied with Progress alone. (thanks @Pericynthion for the addition)

These days, the ISS needs about 5 people to keep up with its maintenance requirements. With less than 5 aboard, you'll get behind on scheduled maintenance, so I suspect a crew of 3 is not a situation the planners will want to allow for long periods.

So there won't be a hard limit. You could leave the station empty for a couple of hours or days, but maintenance starts to pile up soon.

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While the already accepted answer is great, I just want to add that I made a plot about a year ago where you can see exactly how many people were in space for every day since Gagarin.

Here's the picture, it's about 20k pixels wide (sorry for russian labels): http://tossha.com/space/plot_1961_01_01_2016_04_30.png

And here's my post about the project with some historic highlights (entierly russian as well): https://geektimes.ru/post/274988/

So as you can see the last time there were two people on the ISS was in the end of 2009. And before that there was such period from May 2003 to July 2006.

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