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On Earth, we have a good reason to deploy electric devices with an "Earthing system": this helps to avoid dangerous leak currents on surfaces.

Now how is this solved on a spacecraft?

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    $\begingroup$ Not all devices on Earth are grounded, see chapter Ungrounded systems in Wikipedia about ground. Automobiles, air crafts, ships and also space crafts don't use an electrode buried into the ground. The frames may be used as a common ground, but this is not the only solution. $\endgroup$
    – Uwe
    Mar 14, 2018 at 15:34
  • $\begingroup$ The answers at space.stackexchange.com/questions/5062/… may be helpful $\endgroup$
    – Erin Anne
    Mar 14, 2018 at 19:29
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    $\begingroup$ Am I the only one who keeps seeing Earthling System by mistake? $\endgroup$
    – uhoh
    Mar 15, 2018 at 13:48
  • $\begingroup$ No. No, you are not. $\endgroup$ Mar 17, 2018 at 0:12

2 Answers 2

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The frame of the spacecraft is used as a common ground. See this diagram from this handbook.

enter image description here

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    $\begingroup$ They usually have quite a bit of capacity. It isn't that dissimilar from Cars and Airplanes, and those don't really have major grounding concerns either. $\endgroup$
    – PearsonArtPhoto
    Mar 14, 2018 at 15:27
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    $\begingroup$ Using the frame of the spacecraft as a common ground is not the only solution used, see capter 4.3 of the handbook. Table V mentiones Viking and Seasat as isolated from structure. $\endgroup$
    – Uwe
    Mar 14, 2018 at 15:33
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    $\begingroup$ @J.Doe The ISS does NOT use the frame as a power return path. It is ground, yes, but all electric loads have a power supply and a power return wire correctly sized to handle the load supplied. But let's say that it used the frame as power return: The ISS has a maximum bus voltage of 160V, and a regulated bus of 124V. The solar panels can produce a maximum of 120kW, and the batteries 158kW. At 124V that's just north of 1,250A. Aluminum can carry 700A per square inch of cross section. At 14 feet diameter, 2 square inches of aluminum cross section would only require 0.000316" thick aluminum. $\endgroup$
    – Adam Davis
    Mar 14, 2018 at 16:26
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    $\begingroup$ And that's considering just the one outermost shell, and that's less than half the thickness of even thin aluminum foils (range between 0.0008" and 0.001"), which is far less than what the shell of the space station is made of. There's a lot more aluminum in a lot more layers and framework, and aluminum is a good conductor. They don't use it for power return, but if they did, and even if they put the full capacity of the batteries across the entire length of the structure, any gradient would be very, very small. $\endgroup$
    – Adam Davis
    Mar 14, 2018 at 16:31
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    $\begingroup$ @WillCrawford No, the batteries are charged and discharged with each pass when the orbit leaves the station with no solar power. I used worst case calculations, but neither the solar panels nor the batteries will ever see 1,200A in normal usage. $\endgroup$
    – Adam Davis
    Mar 14, 2018 at 16:50
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What PearsonArtPhoto said in the answer above, but also, if there is a need to ensure the vehicle is "grounded" relative to the plasma environment it's in (i.e., to prevent arcing or corona discharge), a plasma contactor is used.

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