On something like a gravity-bound automobile, fuel is measured with a float that moves a variable resistor but I would think this would not be possible on a rocket, one because of extreme G-forces upon launch/acceleration via rocket propulsion and two a second stage (or even a Falcon9 first stage) that might have to coast for any length of time in space will have it's propellant "float" right? (this is why you have to have ullage motors on some stages) Ultimate question: So what systems do modern rockets use to measure the quantity of propellant in their tanks?

  • $\begingroup$ Yes, thank you! $\endgroup$
    – YuccaWorks
    May 9, 2020 at 22:24
  • $\begingroup$ See also answers to How do they know how much liquid propellant is in a rocket just before launch? $\endgroup$
    – uhoh
    May 10, 2020 at 5:46
  • 1
    $\begingroup$ Just to be clear, your question asks about both rockets and spacecraft and, in the present time, there is a demarcation between them. The link to "This question already has answers here" only has the shuttle as a tangible answer which actually uses quite an unusual system as both rockets and spacecraft go. $\endgroup$
    – Puffin
    May 10, 2020 at 10:57
  • 1
    $\begingroup$ Just added an answer there to indicate the range of solutions used. $\endgroup$
    – Puffin
    May 10, 2020 at 11:31


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