Discussion below What is the maximum thrust of the Starlink satellites? raise the question of the Starlink communications satellites' power budget and use of their ion thruster in daylight when the panels are illuminated and delivering power, and "at night" during each eclipse phase when they must run only on batteries.

For the initial orbit raising phase when they are not generating continuous broadcast, the thrusters could potentially run continuously depending on the details of the power budget.

But once they are operational, it's possible that the batteries can not provide enough energy to broadcast to Earth and run the ion thruster at full power for the full duration of the eclipse, or even if they could, if the discharge would be so deep that it shortens the battery's life time, or if that matters since SpaceX plans to use them in pseudo-disposable mode.

I also don't know if the thrusters are just binary "on/full power" and "off", or if they can be run at lower power for station-keeping/altitude maintenance.

So to start to address these issues I'd like to ask:

Question: Do operational Starlink satellites run their ion engines at night on batteries? And if so, do they have hi/low settings?

  • $\begingroup$ Is night about 92 minutes long (ISS?) or much shorter due to lower orbit or longer due to higher orbit? $\endgroup$
    – fred_dot_u
    Commented Nov 28, 2021 at 1:41
  • 1
    $\begingroup$ @fred_dot_u orbits in the 300 to 600 km range all have about 90 minute periods. The fraction of that period that's in night time is at most roughly half (45 minutes) but for higher inclination orbits like those for the ISS or current Starlinks (e.g. circa 50°) as they precess around the Earth they sometimes have much shorter eclipses or even no eclipse (continuous sunlight) for periods of time. How often does the ISS orbit align with the day/night terminator? and... $\endgroup$
    – uhoh
    Commented Nov 28, 2021 at 1:46
  • $\begingroup$ @fred_dot_u Would a lower LEO ISS orbit really have a shorter eclipse duration than a higher one? and especially ISS nodal precession $\endgroup$
    – uhoh
    Commented Nov 28, 2021 at 1:47
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    $\begingroup$ thanks for the links! $\endgroup$
    – fred_dot_u
    Commented Nov 28, 2021 at 10:15


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