Comments below this answer tell us that the International Space Station always remained in Earth's atmosphere. It orbits in the thermosphere and simultaneously the ionosphere.

This answer to How do spacecraft measure their own charge? explains in detail how the ISS measures it's "floating potential" and uses a charging model to understand how charged it is.

The ISS measures its charge using the Floating Potential Measurement Unit. This device works as follows (from Data Analysis of the Floating Potential Measurement Unit aboard the International Space Station):

The Floating Potential Measurement Unit (FPMU) was developed by Utah State University’s Space Dynamics Laboratory (USU-SDL) to study surface charging of the International Space Station (ISS). The surface charging of the ISS is a complex problem owing to its large size, its variety of conductive/dielectric areas, and the exposed solar cell edges on its high voltage solar arrays. Not only is severe charging of the ISS a hazard for astronauts on Extra Vehicular Activity, but any resultant surface arcing can lead to functional anomalies and surface degradation on the ISS. Thus, the FPMU was developed under intense oversite and reporting requirements as it was deemed critical for ISS safety operations.


  1. Do ISS crews have to worry about the ionosphere? Have hazards to EVAs or surface arcing/functional anomalies happened due to ionospheric charing? 2 .Have any immediate hazards to astronauts on EVAs or surface arcing leading to functional anomalies every happened on the ISS due to ionospheric charing?
  • $\begingroup$ Saint Elmo's fire on the ISS? What are these green glowing balls of plasma on a solar panel? Dangerous? seems to have been a false alarm $\endgroup$
    – uhoh
    Commented Feb 5, 2021 at 5:26
  • 2
    $\begingroup$ I don't have enough for an answer, but I do have three parts: first -- ISS has the Plasma Contactor Unit (PCU), which kicks out a stream of ionized xenon gas (IIRC) to help ground ISS relative to surrounding plasma. This is primarily used during EVA. Second -- there are no-touch regions of ISS specifically because of the charging aspect. Solar arrays in particular can reach several hundreds of volts from the plasma ground. Third -- while I'm not sure about ionospheric charging, I seem to recall either an SSU or BCDU failure (can't remember) that was due to internal corona discharge. $\endgroup$
    – Tristan
    Commented Feb 5, 2021 at 15:52
  • $\begingroup$ @Tristan that gets pretty darn close to an answer, please consider posting it as a partial answer. Also see How did three 1.2 meter spheres and a Xe+ plasma contactor keep the Shuttle “grounded”? What did they look like? $\endgroup$
    – uhoh
    Commented Feb 6, 2021 at 1:57
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    $\begingroup$ Reluctant to turn it into an answer only because I have no idea how any of that stuff actually works. All my knowledge on this is adjacent but not related to my work $\endgroup$
    – Tristan
    Commented Feb 6, 2021 at 4:38
  • $\begingroup$ Look up space flights where a tether was employed. These can build up kV of potential, which is enough to arc and ablate material (or people). It's not the ionosphere that causes it though, but the motion through an effectively stationary magnetic field. $\endgroup$ Commented Feb 24, 2021 at 15:38


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