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I just saw some footage of the ISS in which a dish antenna could be seen, constantly rotating.

The dish looked more-or-less parabolic, meaning that it is presumably sending/receiving along a fairly confined path. The central axis of the parabola (and what appeared to be a bit of terminal equipment at its focus) was inclined something like 45 degrees to its axis of rotation, and was rotating at something like 30RPM.

It would seem to suggest that the antenna was essentially sweeping a hollow cone. If used for ranging or detection, it seemed as though it would not be covering a large volume inside the swept cone.

Is that what was actually happening? For what purpose?

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  • $\begingroup$ I wanted to point out that the antenna referred to in this question (and in the answer) was decommissioned in August 2016 (according to Wikipedia) "On 13 January 2018, the trunk section and ISS-RapidScat re-entered Earth's atmosphere and were destroyed as planned" -- Now there is one usually prominently visible in NASA's live stream from the ISS which appears to be similar, but I have no idea what it does. $\endgroup$ – Daniel F Aug 24 '18 at 22:57
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You probably mean RapidScat. It is a microwave scatterometer that measures near-surface wind speed and direction.

rotating beam

Here's RapidScat in action, installed on Columbus module's External Payloads Facility (CEPF), as seen from one of ISS external cams:

                                     enter image description here

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  • $\begingroup$ Wikipedia claims that "NASA formally terminated operations on 28 November 2016". But it's still spinning. Is that because there's no off switch? $\endgroup$ – djsadinoff Nov 13 '17 at 10:22
  • $\begingroup$ Why do you think it's still spinning? $\endgroup$ – Mark Adler Nov 13 '17 at 18:47
  • $\begingroup$ because the NASA Live feed is showing it. ( or something that looks very similar) youtube.com/watch?v=RtU_mdL2vBM&feature=youtu.be $\endgroup$ – djsadinoff Nov 13 '17 at 23:42
  • $\begingroup$ ...and I have apparently been suckered into thinking that it was still spinning by the "live" tag on that video. It's a tape after all, so that's tape from 2016 showing RapidScat still alive. Never mind. $\endgroup$ – djsadinoff Nov 14 '17 at 19:55
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The constantly rotating antenna is a good sign that the AE-35 unit is working correctly, and that the ISS astronauts should therefore avoid any unnecessary EVAs regardless of the advice of their onboard computer.

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    $\begingroup$ Somebody upvoted this, and this is not April 1st. O tempora, oh mores. $\endgroup$ – Deer Hunter Apr 14 '15 at 21:21
  • $\begingroup$ In fact it looks like I got two upvotes and five downvotes so far. I bet the people on the ISS think this is funny. I bet they're laughing right now if they have internet up there in low orbit. ;) $\endgroup$ – dodgethesteamroller Apr 15 '15 at 0:12
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    $\begingroup$ Thanks for not deleting the best joke I've ever made on this site, everyone. Despite the party-pooping downvoters. $\endgroup$ – dodgethesteamroller May 29 '15 at 20:29
  • $\begingroup$ news.avclub.com/… $\endgroup$ – uhoh Apr 4 '18 at 7:12
  • $\begingroup$ I'm imagining a super-advanced 2130 society that has a rotating antenna on all modules still, simply because "dodgethesteamroller" stated it was the perfect debugging module. Hundreds die, because they hired a man who relied on an ancient stackexchange DB dump to decide design requirements. $\endgroup$ – Magic Octopus Urn Jun 27 '18 at 20:41

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