Today Rocket Lab launched the Electron from Launch Complex 1 Pad A in New Zealand, and there was something about

...the first time a helicopter will be stationed in the recovery zone offshore to track and observe the descending stage. Today is about testing comms and tracking to refine operations for future Electron aerial captures.

From the countdown in the Rocket Lab video Rocket Lab 'Love At First Insight' Launch:

T-00:01:29 LOX load is complete, system is in recirculation

T-00:01:08 Anti-geysering is disabled.

Question: What is "anti-geysering" and why would you turn it off 70 seconds before launch?

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    $\begingroup$ Explained here but not a duplicate space.stackexchange.com/a/21349/6944 for the anti-geysering part read my comment on this answer. There are other posts about geysering on the site. $\endgroup$ Nov 18, 2021 at 5:21
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    $\begingroup$ @OrganicMarble hmm... so sometimes the injecting helium bubbles provide a space for oxygen to boil into to cool itself, and sometimes they provide a mixing function to prevent localized heating of the LOX from producing some kind of liquid-in-liquid geyser? $\endgroup$
    – uhoh
    Nov 18, 2021 at 5:32

1 Answer 1


Partial answer to

What is "anti-geysering"...

tl;dr Anti-geysering systems are intended to stop geysering, which is a phenomenon that can occur in long vertical pipes of cryogenic fluid that results in fluid erupting out of the pipe into the tank ullage with potentially bad results on the vehicle.

  • What is geysering in the first place?

The geyser phenomenon is the rapid expulsion of a boiling liquid and it’s vapor from a vertical tube. For example, in the case of a long vertical column of fluid connected to a reservoir, such as the LO2 downcomer to the LO2 tank of the Space Shuttle, the line is subject to ambient heating from top to bottom. As this heating begins, the fluid adjacent to the wall is warmed and becomes less dense than the fluid in the center of the line. Because of this density difference, a convection pattern is established, and warm fluid rises along the tube wall while cooler fluid from the reservoir descends down the center of the line, keeping the system in equilibrium.

As heating continues, a boundary layer is established along the wall and grows in thickness with time. This layer also grows in thickness from the bottom of the tube toward the top of the tube. If the heating rate is sufficient to cause the boundary layer to grow and fill the tube, the cool fluid flow from the reservoir is stopped, thereby halting the convection pattern. With the cessation of convection, additional heating causes the temperature to rise in the fluid. Eventually, a portion of the fluid becomes saturated and boiling begins. Bubbles form on the wall of the feedline and then detach and start to rise in the liquid. As they rise, they coalesce and form a large "Taylor" bubble. The formation of the large bubble results in reduced pressure below it, and consequently, more bubbles are formed in the saturated liquid. This self-sustaining reaction occurs rapidly and forms vapors faster than they can escape the feedline. As a result, the vapor is rapidly and violently expelled from the feedline as a geyser. The geyser and subsequent water hammer effect, caused by rapid tube refill from the reservoir, can cause severe damage to the system.

The expulsion of cryogenic liquid from the feedline into the vehicle tank by the rapidly rising bubble, generally does not result in damage to the tank or feedline. However, if this expulsion occurs when the tank contains a large warm ullage volume, implosion of the propellant tank can occur. Large quantities of cold liquid droplets are expelled into the ullage volume. The expelled droplets cause rapid cooling and contraction of the warm ullage gas. As a result, the tank pressure may fall below atmospheric pressure as shown in Figure 6.4-I. If the tank pressure falls significantly, tank implosion is possible.

graph showing ullage pressure during time for a geyser

This condition is prevented by the installation of a simple deflector over the tank outlet. The deflector will disperse the expelled liquid and prevent rapid ullage gas cooling. Once the tank is filled with liquid, and the ullage is small and cold, this geyser effect presents no problem.

The main geysering effect that can cause vehicle damage does not occur during the geyser but during feedline refill immediately following the geyser. When the geyser occurs, the feedline is emptied of essentially everything except cold propellant vapors. As the line refills with cold liquid, the vapors condense at the interface of the liquid. As the vapors condense, they provide no cushioning for the falling liquid.

The impact pressure at the bottom of the line, resulting from the uncushioned refill can be extremely high and is unpredictable. This water hammer effect is shown in Figure 6.4-II. High pressures resulting from the refill can result in catastrophic failure of low pressure, lightweight, feedlines.

graph showing water hammer for a geyser

  • "anti-geysering" is the provision of systems in the launch vehicle to prevent geysering.

To prevent geysering, the liquid in the feedline must be maintained in a subcooled condition.

  • examples of anti-geysering systems
  1. systems that circulate cool fluid through the feedline
  2. cooling by helium injection which

...consists instead of the injection of helium directly into the aft portion of the main feedline. Local saturation is prevented by the evaporation of LO2 into the rising helium bubbles. When the bubbles of helium rise, their volume is increased as the local pressure in the line is decreased. Evaporation of LO2 into the bubble continues, keeping the bubble saturated with LO2 vapor.

Source: Space Shuttle Booster Systems Briefs section 6.4

How this cooling by helium injection works physically is well explained in the answer here Why would sub-cooled LOX tanks need to "topped-off" until the last minute or so?

  • without any knowledge of specifics on the Electron, I cannot comment on what system they use, or why they disable it at a particular point in the countdown. Shuttle turned off its anti-geyser system about 250 seconds before launch but for reasons that may or may not apply to Electron. This good answer Role of ground-supplied helium in S-1C stage explains that Saturn V turned off their anti-geyser system prior to ignition in order to provide bubble-free fluid to the engines.
  • $\begingroup$ Very educational!! This would only occur with cryogenic systems that are at/near their boiling point, I wonder if a possible side-effect of using subcooled propellants such as the Falcon9 does, also serves to completely remove this as a possible failure mode? $\endgroup$ Nov 18, 2021 at 16:13
  • $\begingroup$ @CuteKItty_pleaseStopBArking possibly, I know nothing about Falcon $\endgroup$ Nov 18, 2021 at 16:28
  • $\begingroup$ It seems to be the case—but if so would be worth calling explicitly in the answer—that the formation of the conditions that cause a geyser takes some time, so at a certain point prior to launch, it is safe to remove anti-geysering as there will not be enough time for those conditions to form before launch. This isn’t necessarily a reason to remove anti-geysering, but still goes a long way towards explaining why they can remove anti-geysering, despite having needed it earlier. $\endgroup$
    – KRyan
    Nov 18, 2021 at 23:19
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    $\begingroup$ @KRyan I explicitly state that "...I cannot comment on...why they disable it at a particular point in the countdown." If you know the answer to that. please post it as an answer. Not having enough time for geysering to develop is not why Shuttle turned theirs off when they did, so I don't feel comfortable generalizing. $\endgroup$ Nov 18, 2021 at 23:29
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    $\begingroup$ Your text mentions "However, if this expulsion occurs when the tank contains a large warm ullage volume, implosion of the propellant tank can occur." which could explain why they can turn it off, as the tank is full at that point of the count. Further, avoiding the warming of the liquid probably involves continuous flow in the pipes, which could conflict with the venting and QD (Disconnect) of the ground equipment $\endgroup$
    – Brianorca
    Aug 23 at 23:53

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