Ars Technica's SpaceX loses up to 40 satellites to geomagnetic storm after Starlink launch explains that a geomagnetic storm heated Earth's upper atmosphere (circa 200 km) so much that the aerodynamic drag due to the higher density was too much for its ion propulsion to overcome.

There are now several Sun observing spacecraft and spacecraft that observe the magnetic fields and solar wind between the Sun and Earth. But it seems there was no warning before launch that this would happen?

Question: Why didn't SpaceX see that geomagnetic storm coming? Was this a fluke or could this happen more frequently in the future?

We're currently between solar maxima, so I wonder if the current scheme only works circa solar minima when the chances of this happening are low?

note: This particular question is primarily about and not aerodynamics nor Starlink but there are certainly separate questions possible from those points of view as well.

Ars Technica quotes a SpaceX statement:

Unfortunately, the satellites deployed on Thursday were significantly impacted by a geomagnetic storm on Friday. These storms cause the atmosphere to warm and atmospheric density at our low deployment altitudes to increase. In fact, onboard GPS suggests the escalation speed and severity of the storm caused atmospheric drag to increase up to 50 percent higher than during previous launches. The Starlink team commanded the satellites into a safe-mode where they would fly edge-on (like a sheet of paper) to minimize drag—to effectively "take cover from the storm"—and continued to work closely with the Space Force's 18th Space Control Squadron and LeoLabs to provide updates on the satellites based on ground radars.

Preliminary analysis shows the increased drag at the low altitudes prevented the satellites from leaving safe-mode to begin orbit-raising maneuvers, and up to 40 of the satellites will re-enter or already have re-entered the Earth's atmosphere. The deorbiting satellites pose zero collision risk with other satellites and by design demise upon atmospheric re-entry—meaning no orbital debris is created and no satellite parts hit the ground.

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    $\begingroup$ @BradV reading the linked article it seems more like not enough thrust combined with an unexpected headwind rather than something to do with the avionics (other than a safety protocol in software that couldn’t be overridden perhaps) $\endgroup$
    – uhoh
    Feb 10 at 3:09
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    $\begingroup$ @BradV Scott Manley just posted SpaceX Loses 40 Satellites To Solar Storm The first five minutes nicely covers it. $\endgroup$
    – uhoh
    Feb 10 at 4:21
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    $\begingroup$ Scott Manley says equipment was put to sleep and then couldn't be brought back to function. Does not sound like drag from increased environment density caused problem. Why couldn't wake up? $\endgroup$
    – BradV
    Feb 10 at 14:51
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    $\begingroup$ @BradV we know what we know, and we know there's over a thousand Starlinks that didn't have problems, and that increased atmospheric drag is being given as the reason these were lost. There's no reason to think it was a problem with design robustness. Possibly they just need to rethink the logic that controls entering and leaving safe mode. $\endgroup$ Feb 11 at 2:18
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    $\begingroup$ You might think an operator could override safe mode, perhaps not though $\endgroup$ Feb 11 at 3:15

1 Answer 1


I think one possible reason that they didn’t see it coming was that the it was extreme ultraviolet photons that only took roughly 8 minutes to travel from the sun and to start heating the thermosphere. Then the heating and expansion of the atmosphere would take a few hours to change its density.

In terms of warning with solar observation satellites, the charged particles and other mass that gets ejected take a much longer time to arrive with that time depending on the violence of the event but probably at least 14 hrs and probably longer. The charge particles are probably not as important for the LEO satellites since there is protection from the earths magnetic field.

So perhaps it is a matter of timing of when they realized that the drag was increasing or had increased. Then after that it appears there were a series of decisions as to what the best course of action was. Either by design or by command the satellites were put into a safe mode. From the video mentioned in the comments above, it might be that with increased drag that satellites couldn’t reposition with reaction wheels or magnetic torquers to get out of safe mode to be able to thrust to higher orbit.

Edited to include this from a Time magazine story I just found. Apparently they did have some warning and decided to launch even though the storm has been detected a couple of days earlier.

But that plan assumes that the sun behaves, and on Jan. 29 it didn’t, releasing a storm of charged particles toward Earth known as a coronal mass ejection. Such solar storms usually present little danger to Earth, and the Space Weather Prediction Center, a division of the National Oceanic and Atmospheric Administration, rated the storm as a 2 on a 1 to 5 scale, a severity it calls “moderate.” The catch: the tidal wave of charged particles was expected to reach Earth on Feb. 2 or 3—or just as SpaceX was planning its Starlink launch.

  • $\begingroup$ So actually there was information about solar activity ahead of the launch, and the answer to "Why didn't SpaceX see that geomagnetic storm coming?" is something along the lines of "They did actually; it was a '2 on a 1 to 5 scale, a severity it calls moderate'. But it seems they likely made a judgement call." $\endgroup$
    – uhoh
    Feb 15 at 23:20
  • $\begingroup$ It was initially rated G2, decreasing to G1 on the day of the launch (swpc.noaa.gov/news/…). But the storm itself isn't really what did the satellites in, the ensuing effect on Earth's atmosphere is. There's very limited monitoring of that part of the atmosphere. $\endgroup$ Feb 16 at 1:27

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