How long before launch are the fuel and oxidizer loaded into a Falcon 9 rocket?

And how much time does it take to load it?


1 Answer 1


Most of this is from memory, watching live streams. Also, some sources contradict each other, so this is my best guess.

  • T-0:35:00: RP-1 fuel loading begins on both stages.
  • T-0:35:00: Liquid oxygen (LOX) oxidizer loading begins on stage 1.
  • T-0:31:00: Liquid oxygen (LOX) oxidizer loading finished on stage 1.
  • T-0:16:00: Liquid oxygen (LOX) oxidizer loading begins on stage 2.
  • T-0:15:00: Liquid oxygen (LOX) oxidizer top-off begins on stage 1.
  • T-0:05:20: RP-1 fuel loading finished on stage 1.
  • T-0:02:40: Liquid oxygen (LOX) oxidizer at flight levels on stage 1.
  • T-0:02:05: Liquid oxygen (LOX) oxidizer at flight levels on stage 2.
  • T-0:01:00: Liquid oxygen (LOX) top-off finishes.
  • T-0:00:40: Pressurising tanks for flight.
  • T-0:00:20: Tanks at flight pressure.

At some point in between, there is also the point where they stop bubbling cryogenic Helium through the tanks to super chill the propellant.

  • $\begingroup$ What is the reason for not loading the RP-1 one day before? Or some hours before? $\endgroup$
    – Joe Jobs
    Sep 19, 2020 at 14:14
  • 2
    $\begingroup$ Because an empty rocket is just a metal cylinder, a fueled rocket is a bomb. Also, keeping the RP-1 at its temperature of -7°C is expensive. And detanking in case of a scrub or delay takes a lot of time. Also, SpaceX want to achieve rapid turnaround. $\endgroup$ Sep 19, 2020 at 15:24
  • $\begingroup$ What does top-off mean and what is pressurization? $\endgroup$
    – Joe Jobs
    Oct 31, 2020 at 19:49
  • 1
    $\begingroup$ @JoeJobs: "to top sth. off" means "to fill completely to the rim": dictionary.cambridge.org/us/dictionary/english/… That's exactly what it means here as well: replace the boiled off LOX (well, technically the OX is no longer L when it boils off :-D ) to keep the tanks filled to maximum capacity. Pressurization refers to pumping extra gas into the top of the tanks to increase the pressure to "push" more propellant out into the pumps. F9 uses helium tanks (COPVs) inside the propellant tanks for pressurization. It was one of those that blew up the AMOS-6 mission. $\endgroup$ Nov 1, 2020 at 2:17

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