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This question originates from the video "The Vanishing of Flight 370", by Lemmino.

At 6:00 he says

While these transmissions did not contain any information about the flight's position, investigators were able to measure the distance between the satellite and the aircraft at the time of each transmission, based on how long it took those transmissions to be sent and received. This generated seven rings of possible locations, from which seven of these transmissions are thought to have originated.

And this diagram is displayed:

enter image description here

But something about the visual strikes me as odd: don't satellites move? I thought they had to keep orbiting or they would crash. So why do these rings of transmission locations, taken over a roughly six-hour period, all show the satellite above the exact same place? Clearly something about my reasoning must be wrong if the investigators never considered it.

(I'll understand if this belongs more on Space Exploration stack exchange.)

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    $\begingroup$ That looks more like a visual aid than something that's supposed to be looked at critically. But many satellites are kept in geosynchronous orbit so they can stay roughly over the same spot by orbiting at the same speed of the Earth's rotation. $\endgroup$
    – Pheric
    Aug 6, 2020 at 2:03
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    $\begingroup$ Maybe geosynchronous, maybe geostationary. Either way, I'd agree that the for-TV graphic may well contain over-simplifications. The guys went pondered on this for weeks & weeks undoubtedly considered the satellite's position & movement relative to the earth, even if the video's graphics didn't. $\endgroup$
    – Ralph J ♦
    Aug 6, 2020 at 3:44
  • $\begingroup$ There were two incoming SAT phone calls at 18:39 UTC and another much later in the flight at 23.13 UTC. All incoming calls were initially acknowledged and then abandoned by the SDU for voltage irregularity, or signal stability issues. its also evident that whilst we know power returned to MH370’s SATCOM system at 18:25 UTC, the ACARS system itself never resumed operation. What we’re left with is pings sent to the aircraft asking if it’s still online and ready to receive $\endgroup$
    – George Clooney In a Mooney
    Aug 6, 2020 at 9:42

1 Answer 1

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Because the Inmarsat 3 series satellites that were used to transfer the ACARS system data are geostationary. They orbit at a speed and altitude that causes them to stay in the same location with reference to the earth. The signals were received specifically by the Inmarsat 3 F1 satellite which was, at the time, geostationary over the Indian Ocean.

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