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I have been analyzing frames from the video of IFT-6 (to extract the juicy data, though it might require more processing power than my PC can handle) and noticed something I do not understand. Note the levels of oxygen and methane:

enter image description here

In more detail:

enter image description here enter image description here

The LOX levels in both ship and booster are lower than the CH4 levels!

For a fevered moment, I thought it might be related to active cooling:

When going to ~1750 Kelvin, specific heat is more important than latent heat of vaporization, which is why cryogenic fuel is a slightly better choice than water
Elon Musk on X

That 'victory' at figuring it out was brief, and shattered when I realised that even if this was some form of testing for future implementation of active cooling, there would be no need of it for the booster!

So, any ideas on why the Starship seems to be emptying the tanks of LOX faster than CH4?

Oh, and yes, the LOX tanks are larger, but the fuel gauges have been standardised to the same length, implying they are not depicting the remaining mass but simply a percentage of the full tanks.

Update: Snapshots of the Gauges

Snapshots of the Gauges at 7 Times During IFT-6

Seven snapshots of the gauges during the 6th IFT of Starship, from T+00:00:00 through T+00:07:50.

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    $\begingroup$ I wonder if it is related to boiloff and venting in the moments before launch. I suspect LOX escapes the vehicle more readily than CH4. $\endgroup$
    – A McKelvy
    Commented Dec 3 at 15:08
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    $\begingroup$ I know during engine shutdown they keep flowing CH4 after shutting off the O2 flow to burn off anything that could cause oxidation or make a bang on reignition... Maybe they're keeping a little extra aboard for that purpose? $\endgroup$
    – Darth Pseudonym
    Commented Dec 3 at 16:52
  • $\begingroup$ Is the percentage difference consistent from near the start of the first stage run to near the end? i.e. is it actually using LOX at a greater relative rate, or is it starting with a relative underload of LOX? $\endgroup$
    – Russell Borogove
    Commented Dec 3 at 18:07
  • $\begingroup$ @RussellBorogove Have to admit, I'm not sure. Today I'll prioritize parsing the information from those gauge displays and perhaps be able to give you a better answer, but until then the best I can do is to note that I've looked at frames from various parts of the video and it does seem consistently lower. $\endgroup$
    – Andrew Thompson
    Commented Dec 3 at 18:34
  • $\begingroup$ @DarthPseudonym Interesting thought! Yeah, I guess having excess oxygen around could cause some problems. Damn. You. OXYGEN! P.S. I'd vaguely wondered why liquid methane released on re-entry into an atmosphere containing oxygen would not immediately burst into flames. But I guess the rocket engineers have considered that! $\endgroup$
    – Andrew Thompson
    Commented Dec 3 at 18:40

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