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While docking with the ISS, the live stream showed this diagram with a green line starting at the capsule and looping around the area of the ISS. It would sporadically change and loop around the screen.

Some sort of relative motion indication, perhaps not relevant after docked and just showing accelerometer noise?

SpaceX Dragon Capsule Docking

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    $\begingroup$ It does look like an extrapolated difference in orbits over the next several Earth orbits, ignoring the mechanical connection. And not just noise: the station has active attitude control thrusters and control moment gyroscopes that were making adjustments during this process (they called out switching from thrusters to CMGs to reduce jostling while doing the hard dock). $\endgroup$
    – Christopher James Huff
    Commented May 31, 2020 at 16:20
  • $\begingroup$ @ChristopherJamesHuff They didn't go to free drift for docking? Interesting. I guess they had to for shuttle because it was so much more massive. $\endgroup$
    – Organic Marble
    Commented May 31, 2020 at 17:03
  • $\begingroup$ @OrganicMarble IIRC, the Shuttle took over attitude control duties while it was docked, and you wouldn't want the systems fighting each other. The Dragon probably inhibited its attitude control system before it made physical contact. $\endgroup$
    – Christopher James Huff
    Commented May 31, 2020 at 17:18
  • $\begingroup$ @ChristopherJamesHuff The ISS had to be in free drift for docking, after that "it depends" on which took over control. But only one at a time. $\endgroup$
    – Organic Marble
    Commented May 31, 2020 at 17:30
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    $\begingroup$ For reference, youtu.be/AIyonw6LEOs?t=23925 is one of the SpaceX stream timestamps showing this display after soft-capture. $\endgroup$
    – Erin Anne
    Commented Jun 4, 2020 at 15:56

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As mentioned on the livestream, the green line is the projected future trajectory of the Dragon spacecraft relative to the ISS, assuming no outside forces (eg. thruster firings). Once Dragon is docked to the ISS, it's meaningless, as there's a rather large outside force in the form of the docking latches.

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    $\begingroup$ Do you have a reference for this? Otherwise, it's Some Guy on the Internet Saying Something. $\endgroup$
    – Organic Marble
    Commented May 31, 2020 at 22:09
  • $\begingroup$ It was mentioned on the livestream. $\endgroup$
    – Mark
    Commented May 31, 2020 at 22:12
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    $\begingroup$ Editing that fact into your answer would be somewhat of an improvement. $\endgroup$
    – Organic Marble
    Commented May 31, 2020 at 22:14
  • $\begingroup$ Some guy on the ISS? Cool. :) $\endgroup$
    – CGCampbell
    Commented Jun 1, 2020 at 22:34
  • $\begingroup$ NASA's relative motion display on the ISS, RPOP, also showed this kind of relative trajectory after docking too. We just didn't bother propagating it more than about 10 minutes out. During sims on the ground it was even worse, because sims would cut data at soft-dock and RPOP would extrapolate the drift right through the ISS (no contact model in RPOP). $\endgroup$
    – Erin Anne
    Commented Jun 4, 2020 at 15:43

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