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Have there ever been significant changes in the altitude of the ISS?

By significant, I mean changes greater than about 40 km, thus by far exceeding the periodic reboosts.

If there haven't been, then why not?

Would the ISS technically be able to change its altitude and be able to surive at other altitudes?

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  • $\begingroup$ Except for the initial launches and assembly, you mean? $\endgroup$
    – John Dvorak
    Commented Aug 15, 2016 at 22:21
  • $\begingroup$ @JanDvorak: Yeah, I made a comment stating I'm interested in cases purposed for science or simply beeing required for stability or that alike. but that comment got lost. So yeah except those. $\endgroup$
    – Zaibis
    Commented Aug 15, 2016 at 22:25

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Yes, there have been changes of > 40 km, as shown in this graph. The X axis scale is not showing, but it is from Nov 1998 to July 2008.

enter image description here

Reference

Edit: I checked to make sure the graph is not just a theoretical math problem. It's not, the same graph appears here.

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    $\begingroup$ Fair enough, that would probably make a good follow up question. $\endgroup$
    – called2voyage ♦
    Commented Aug 15, 2016 at 18:48
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    $\begingroup$ The period covered by the graph doesn't show the largest change, when the orbit was raised from ~ 350 km to ~ 420 km after the retirement of the space shuttle. $\endgroup$
    – pericynthion
    Commented Aug 15, 2016 at 20:11
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    $\begingroup$ My guess is that it's the altitude the station was supposed to stay above, to be safe in case no visiting vehicles could come and reboost for 90 days. But that doesn't explain why it fell below that... $\endgroup$
    – Organic Marble
    Commented Aug 15, 2016 at 20:39
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    $\begingroup$ @OrganicMarble: Those are the exact same 2 questions I made up my self when seeing it. Would this be a reasonable followup question? $\endgroup$
    – Zaibis
    Commented Aug 15, 2016 at 22:27
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    $\begingroup$ The 90 day minimum is based on high solar activity. Solar activity peaked in 2001, but the very long and very deep solar min from mid 2007 to early 2010 meant that that 90 day margin no longer applied during that period. The reason solar activity is important is that high solar activity makes the upper atmosphere swell, which in turn increases drag on the ISS. The atmosphere contracts with low solar activity, decreasing drag on the ISS. $\endgroup$
    – David Hammen
    Commented Aug 15, 2016 at 23:03

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