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On February 28 2016, Falcon 9 attempted a second launch for its 22nd flight. However, it was put on hold for about 20 minutes at T-01:33 and had its countdown reset to T-11:44, giving a total of about 30 minutes between fueling and ignition. The liquid oxygen is cooled to -207 °C before being transferred to the rocket where, I'm guessing, it starts to warm up.

How long does it take for LOX to get to a temperature where launch becomes unfeasible?

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Normal vehicles that use LOX, use it at the normal temp (-183C) and what they do is let the LOX boil off, and refill it right up to the latest possible moment their hardware allows.

The Falcon 9 1.1 Full Thrust (or whatever it is finally called) uses the LOX supercooled to -207C which is a different problem. The answer is unclear and is obviously something SpaceX is working on figuring out since it seems based on an Elon Musk tweet that the ignition issue was due to rising LOX temperatures.

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  • $\begingroup$ Interesting. How long would LOX at -183 last, then? What's the range of temperatures where LOX is usable? Does it warm up fast? $\endgroup$ – isanae Feb 29 '16 at 7:42
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    $\begingroup$ The answer to these extra questions is going to depend, to an extent, on the tank design and airspeed but also on the thickness of any layer of frosting on the tank exterior (i.e. frozen from atmospheric water vapour) and its insulative properties. I did see someone have a go at some hand calcs a few days ago on, ahem, forum.nasaspaceflight.com, though I can't find it now. Really though, if this is new territory for launch services in general then its just going to be guesswork. $\endgroup$ – Puffin Feb 29 '16 at 12:09
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    $\begingroup$ @isanae On the pad, you see the LOX venting as a white cloud, from the moment they start filling the vehicle till it starts moving. The entire time, they keep topping up the LOX, so that as it warms up and boils, that is released (taking the heat with it, keeping the rest cool). But for sub-cooled LOX, you cannot quite do it that way. $\endgroup$ – geoffc Feb 29 '16 at 16:18
  • $\begingroup$ Why not? What's so different between these two temperatures? $\endgroup$ – isanae Feb 29 '16 at 16:42
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    $\begingroup$ @isanae Boiling points are magic! :) The heat, which is causing the change, is converted to energy to change from liquid to gas, without really affecting the temperature. So AT the boiling point, the fluid stays basically at the same temperature, with the evaportating gas taking the excess heat away. At the sub-cooled, it heats up and up, until it hits the boiling point. So very different, $\endgroup$ – geoffc Feb 29 '16 at 17:06
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They're subcooling the LOX in order to get more oxygen in the tank. The lower temperature translates to something like 3% more oxygen (by weight) in the same volume. When the LOX warms up, it expands so tank pressure will rise rapidly unless you vent the oxygen. So if you use subcooled oxygen, a launch delay will leave you with less oxygen than you need.

As Geoff said, once the LOX reaches its boiling point, temperature stabilizes until all the oxygen has boiled off, and you can keep it at that temperature by replenishing.

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