SpaceX's Falcon 9 uses TEA-TEB as a ignitor for its Merlin engines. My question is if the rocket has more TEA-TEB, can the engine be shut down and restarted more than 4 times?
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$\begingroup$ You get 4 as 1=launch, 2=boostback, 3=reentry, 4=landing? $\endgroup$– geoffcCommented Mar 2, 2021 at 21:41
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$\begingroup$ @geoffc Yes, was just wondering if engines could be reignited more times or there are other technical aspects. $\endgroup$– AshvinCommented Mar 2, 2021 at 23:54
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1 Answer
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The engines can most definitely be ignited more than 4 times.
Every engine is separately test-fired at McGregor after it is built. The entire booster is then again test-fired at McGregor before being delivered.
In general, there will be a static fire of the fully integrated vehicle 1–2 days before launch.
So, even for a drone ship landing which has no boost back burn, the outer engines will have been ignited four times, the middle engines five times and the center engine six times.
And that is assuming the booster crashes on the first landing.
If the booster survives the first landing, the engines will be fired many more times; at least once for each launch.
Recently, SpaceX has launched Falcon9s without a static fire, so that reduces the number of ignitions somewhat. However, they always do a static fire on new boosters, and typically also on life leaders (i.e. on ones that are either not yet flight-proven or that are pushing the limits of reuse).
They might be swapping out engines when they see some anomalous readings, but we don't really know that. Unlike for Starships, this doesn't happen in plain view on the side of a public road, it happens inside the hangar.
However, even assuming that they have swapped some engines, it is likely that at least one of the engines on B1051 was ignited more than ten times.
answered Mar 3, 2021 at 6:36
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$\begingroup$ Which suggests the FEMA (failure analysis) work done during design was aimed at a mean lifetime of more than 100 ignition cycles to meet reliability requirements. $\endgroup$ Commented Mar 3, 2021 at 15:10
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$\begingroup$ The design target for F9 was 10 flights with minimal refurbishment. That implies at a minimum 30 firings for the center engine, assuming absolutely no test firings and only RTLS landings. As most landings are drone ship landings, and there are a couple of test firings as well, it's more like 40+. We have one booster that as flown 8 times, so it looks like they at least hit their target, maybe they even found during the last checkouts that they can go higher. Soot buildup / coking is going to be one of the major problems where they will at some point have to strip and clean the engines.# $\endgroup$ Commented Mar 3, 2021 at 18:21