This picture from Elon shows us the methane header tank positioned inside the main tank. I understand that one of the reasons for header tanks is to keep them pressurized when the main tanks do not need to be and have them ready for engine restarts in 0 G or for landing.

But here the header tank appears to be some sort of flow-through structure that would be impossible to pressurize on its own. Is it because it's maybe not finished or am I missing something?

enter image description here

Link: https://twitter.com/elonmusk/status/1247056590340947969?lang=en

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    $\begingroup$ Can you edit your question, include the image, and annotate it to show the "many holes" you are asking about? $\endgroup$ May 8, 2020 at 13:40
  • $\begingroup$ Nice, thanks very much. +1 $\endgroup$ May 8, 2020 at 13:49
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    $\begingroup$ After seeing what you mean by "many holes", I'm 100% sure its just not finished yet. Something's going to be connected to those holes. The big hole is where the plumbing towards the turbopump goes. The small ones might be there for pressurization while in use (autogeneous, using heated methane), but not sure about that so this is not an answer. Also unsure about the seemingly irregular distribution of those little holes. $\endgroup$ May 8, 2020 at 13:57
  • $\begingroup$ Personally, I believe this is not the actual pressurized outlet, just some sort of shield, possibly anti-sloshing or anti-vortex, protecting the actual outlet and only meant to deflect/break the flow, not prevent it $\endgroup$
    – SF.
    May 8, 2020 at 14:14
  • $\begingroup$ @SF. Are you thinking about some sort of double-walled tank? We definitely see the structure that's going to take the pressure loads (in contrast to something that would just guide/break the flow). Else it wouldn't be made of steel. $\endgroup$ May 8, 2020 at 14:35

1 Answer 1


The reason for the multiple inlets is to ensure that the header tank can be filled from the main tank when the tank level is low and the rocket is leaning to one side, whichever side that might be.

  • $\begingroup$ It seem obvious now, but the methane header tank, unlike oxygen header tank is kind of flow-through, until 0 G, before which it closes off, right? $\endgroup$ Feb 17, 2021 at 12:52
  • $\begingroup$ I suspect that it will be kept full during assent by flow through. The main tank will then be isolated from it at the point the engines cut out. Only the header tank will be used for the reentry and landing burns. $\endgroup$
    – Slarty
    Feb 17, 2021 at 18:29
  • $\begingroup$ Do you have any insight into the largest hole at the top? Maybe some assembly-phase opening only, to be closed off permanently later on? $\endgroup$ Feb 17, 2021 at 19:33
  • $\begingroup$ Yes I think that is correct $\endgroup$
    – Slarty
    Feb 17, 2021 at 21:23

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