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I have viewed ISS images for about 18 months and only twice seen partial glimpses of FSAL. Other areas of the world between 51 N&S latitudes routinely appear, although the camera is off sometimes.

The camera deactivates as ISS approaches FSAL and subsequently reactivates after passing. But for the two partial glimpses, the camera remains active only when cloud cover obscures views.

Other world areas at similar latitude routinely appear, including the Aleutian Islands, Falkland Islands, New Zealand and Northern Asia & Europe. That images of FSAL have appeared at all indicates that out-of-range communication is not a factor.

Designated NASA folks responsible for the HDEV camera either ignore my queries or give evasive answers. WHY? If there’s nothing to “see” there, then let’s see FSAL routinely!

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    $\begingroup$ Please quote some of the "evasive answers". Perhaps you just didn't understand them. $\endgroup$ Jun 26, 2022 at 0:52
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    $\begingroup$ What makes you think that "the ISS camera (nearly) always off", and not that due to the static nature of ground stations and geostationary communications satellite links it's just a bad spot for live video linking? $\endgroup$
    – uhoh
    Jun 26, 2022 at 1:55
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    $\begingroup$ if you want images from space of FSAL, why do you want them from the ISS HDEV cameras? why not any of the other publicly-available satellite imaging that's made for the purpose of looking at particular places? $\endgroup$
    – Erin Anne
    Jun 26, 2022 at 3:05
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    $\begingroup$ I don't understand the logic behind your argument "If there’s nothing to “see” there, then let’s see FSAL routinely" Can you explain that to me? Surely, it is logical that if there is nothing to see there, it does not make sense to see it? Why would you want to waste extremely expensive and limited TDRS bandwidth to see a place where you already know there is nothing to see there? $\endgroup$ Jun 26, 2022 at 9:15
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    $\begingroup$ I would like to give you some constructive advice on posting here. I have no problem with your question, it may have an interesting answer, however speaking for myself I wouldn't upvote or answer this because of the tone. You allude to some sort of conspiracy, which usually means you will vigorously argue every answer that doesn't fit the narrative you are trying to get. That could be why nobody has answered this. If you are looking at this site as a way to forward conspiracy theories then you're in the wrong place, if not leave that aspect out and you may get answers. $\endgroup$
    – GdD
    Jun 27, 2022 at 16:00

1 Answer 1

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Short answer

The reason is because of where they are located. FSAL resides in/near the TDRSS Zone of Exclusion, illustrated by the notation ZOE in the map below, bordered by the yellow line on the left and the green line on the right.

ISS Mission Control map display   "Main Screen in the ISS Mission Control Center", by AGeekMom, CC BY 2.0

More detail

The ISS uses Ku-band communications to relay video to the ground stations via NASA's Tracking and Data Relay Satellite System. ISS uses satellites positioned in three different slots around the world to relay telemetry, voice, video, and commanding. These are located at longitudes of 46 degrees (TDRS E), 171 degrees (TDRS W), and 275 degrees (TDRS Z).

In the map above, you can see yellow, green, and blue lines outlining regions in orbit where those satellites are shadowed by the earth. The region marked ZOE happens to correspond to where TDRS Z is the only satellite in range. Why is this important? NASA often will not use TDRS Z during quiescent operations, for several reasons: 1) ISS is not the only customer of the TDRSS system (and it's not even the #1 priority customer), and 2) data relay through TDRS Z is not as good as data relay through TDRS E and W (both of which are within range of the primary TDRSS ground station at White Sands, New Mexico).

In general, TDRS Z is only activated for ISS when station is undergoing what they call "TDRSS Critical" ops. These would be things like visiting vehicle ops, EVAs, and the like. Otherwise, the roughly 5-10 minute loss of signal is acceptable and even provides flight controllers an opportunity to take a quick break while their console displays go blank.

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    $\begingroup$ Great info! I immediately thought of the ZOE when I read the question since that was definitely a thing in the shuttle days, but I thought it had been closed. That was certainly when everyone broke for the bathroom/coffee machine back then. $\endgroup$ Jun 30, 2022 at 19:51
  • $\begingroup$ ESAs Colka antenna should be fully operational soon which uses the EDRS constellation. Maybe this will finally close this loss of signal window at all times. $\endgroup$ Jul 1, 2022 at 8:35
  • $\begingroup$ TY for the answer, it does make sense. Still, I don’t understand why the camera frequently is ON when passing over/near FSAL … for views obscured by clouds. Makes no sense to me that the camera is OFF when clear views present. ColKa was installed in Jan 2021. Any idea when to be fully operational? So far, I’ve seen no change in views over southern Indian Ocean. $\endgroup$
    – CA Joe W
    Jul 1, 2022 at 20:33
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    $\begingroup$ @CAJoeW the ZOE shifts north and south over time, as the TDRS satellites are not perfectly geostationary, but rather make small figure 8 patterns as they drift north and south in their orbits. No conspiracy here, just geography and coincidence. $\endgroup$
    – Tristan
    Jul 2, 2022 at 21:19

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