Do they use a tungsten wires or something else?

  • Hi! Can you add a bit more definition to your question? Do you want to know what specific mechanism is used? – Rickest Rick Feb 8 '16 at 15:28

Falcon 9 uses TEA-TEB to ignite its engines both on launch and during all the landing burns. The mixture is pyrophoric - it ignites spontaneously when it comes to contact with oxygen (both in air or the liquid supercooled).

The rocket carries limited amount of the stuff so the number of possible re-ignitions is limited too.

Currently it needs to re-ignite 3 engines for the boostback burn (when doing RTLS or limited downrange landing - usually for LEO missions, GTO ones do not execute this burn), 3 again for the re-entry burn and 1 or 3 for the landing. That means it should have enough for 7-9 uses.

The second stage may need to reignite its engines too, depending on the mission so it needs to carry some amount of the igniter fluids too.

On the first launch of Falcon Heavy there was some problem on the center core which caused the outer two engines to run out of igniter fluid and not start for the landing burn, meaning the core was not able to slow down enough and hit the water at about 500 km/h (~300 mph). The cause is currently unknown or at least unpublished - possibilities including bad valve, human error or some FH specifics.

From what I gathered reading various comments about that incident, it seems that there is no specific "dosage" of the TEA-TEB mixture per engine startup, instead the mixture is allowed to flow to the engine until proper startup is detected. But I do not know about any official source for this and it may be just wrong understanding on my side.

Another speculation on my part: because SpaceX uses 1-3 or 1-3-1 scheme for multi-engine landing burns and according to currently public information both outer engines failed to ignite, it seems reasonable that there is just one common reservoir of the TEA-TEB mixture per stage, supplying all 3 restartable engines, instead of a reservoir per engine. That way the center engine would start fine because it was first to get started during the burn, but some problem (possibly greater airflow because of heavier and thus faster center core?) made it use more fluids for the last ignition, leaving just scraps for the outer engines.

  • 7 + 9 for launch. – Nick T Feb 7 '16 at 18:17
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    The amount for launch ignition is supplied from some launchpad-based facility - To save weight on the first stage apparently they are flowing the TEA-TEB from a tank on the ground. (an older article about an aborted launch because of problems with ignition) – jkavalik Feb 7 '16 at 18:22
  • Falcon 9 doesn't have ullage rocket motors to make the fuel fall down an acceleration pull during reignition of the big liquid engine. So how does it make sure that the fuels in half empty weightless tanks get into the engine at the right mixture? – LocalFluff Mar 18 '17 at 22:57
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    @LocalFluff - cold nitrogen thrusters provide enough push for ullage, per EchoLogic's answer space.stackexchange.com/a/7766/14637 – Tom Goodfellow Mar 19 '17 at 1:40
  • This question and answer is suddenly pertinent due to the Falcon Heavy's core booster failing to reignite as it tried to land. – Daniel Griscom Feb 12 at 23:21

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