The SpaceX Super Heavy booster, carrying the Starship vehicle, is powered by 33 Raptor engines. On the April 20 test flight, 5 of them shut down before the vehicle exploded.
On the next test flight of the fully integrated vehicle, how many engines will operate as intended for the full intended duration of first-stage flight?
Planned engine shutdowns count as nominal operation; this question is about unplanned shutdowns, like the ones seen in the first test flight.
"First stage flight" ends at stage separation or vehicle explosion. If the launch feed includes an engine health display like the last one, we'll use that. Otherwise, we'll defer to reporting from credible sources. If there's no credible reporting within a day, I'll determine based on the best available video evidence at the last time we could see the engines on video.
Final state of the previous vehicle, for reference:
https://youtu.be/-1wcilQ58hI?t=2944
If the launch is significantly delayed I'll extend the close date. If the Starship program is cancelled or replaced with a vehicle that does not have 33 Raptor engines installed I'll resolve N/A.
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@Eliza I'm a little unsure about how the streaming on X will work. On the prior test, with good streaming replay ability, the answer was knowable as soon as the vehicle exploded. It could in principle have been resolved very shortly after that.
I'm expecting (but not promising) to be awake and watching the test and paying attention to Manifold. I doubt I'll pause to review the replay and resolve this in the middle of the flight, but if someone posts a screencap and timestamp then I would resolve based on those very shortly after stage separation, aka during stage 2 flight.
If we don't have clear indication from something like an on-screen engine indicator (like we had for the last launch), then expect resolution to be delayed until at least shortly after the flight for credible reporting and/or my analysis.
@Eliza According to spacex's launch page, stage separation is at 2m 41s if everything is nominal. We might want to re-watch some footage and see other angles if things are unclear at that point, but hopefully the automated display will be clear.
@chrisjbillington I guess I was wondering, specifically about the clauses that say an engine shutting down intentionally before others could be still nominal performance. If one or more engines shuts down "early", how will we know if it was intentional or not? Or do we just have a general assumption that all engines should run for the same amount of time?
@chrisjbillington If the engine health indicator isn't present / doesn't make the answer clear (aka any scenario where I need extra angles), I'm going to defer to credible reporting. I think I'm fully competent to assess engine health from videos, but as I'm participating in the market I'd like that to be a last resort. Support on the video analysis would be welcome, of course.
@EvanDaniel I just don't want to be the idiot live betting my entire life savings on 33 No when I see one light blink off and then find out an hour later that "we programmed that one to turn off after 90 seconds"
@Eliza Gotcha. The timeline:
https://www.spacex.com/launches/mission/?missionId=starship-flight-2
AIUI, they're planning to shut down most of the engines at 2:39, leaving a few (the center 3, I think? Might be more?) running during the hot staging. (Some thrust helps control, stability, propellant settling, etc.) I think they'll stay running for the whole of the hot staging event until after the second stage has cleared the first. (I think those will stay running for the reorient and boostback, but that no longer matters to this market.)
I'm a little unclear whether to expect the 30 (?) engines to shut down all at exactly the same time, or in groups over the course of a second or two.
I believe any engine shutdowns before the 2:39 mark are unplanned shutdowns. Unless I see good evidence otherwise (like an announcement on stream before the shutdown that it's planned), that will be what I'm judging on. Shutdowns between 2:39 and successful stage sep might be tricky to judge and might cause a judging delay, but if they look orderly and symmetric I'll default to assuming they're planned.
AIUI, one random engine turning off at 90 seconds is clearly off nominal.
I've made a few tweaks to wording to improve consistency and clarity, especially surrounding what happens at shutdown around stage separation. My current understanding is that some of the first stage engines will shut down shortly before stage separation.
If this change has caused any new wording problems, or significantly changes how someone is predicting, please let me know sooner rather than later.
@Mqrius Good point. This is trying to ask about "the last time the engines were supposed to be running". If the first stage shuts down nominally, we'll count the engines that were running immediately prior to commanded shutdown.
If an engine comes back online and is operating at stage shutdown, it gets counted as operational. (I don't see any particular reason to go one way or the other on this piece of the question, and it seems especially hard to forecast well. I'm just picking an answer there so we have something clear to bet on.)
@EvanDaniel Yeah, just having it clear before it's relevant is what I was going for :)
@Mqrius Ok you have set an impossible question… with Super Heavy Booster B9 :- The first SHB with hot staging ring retro fitted, will rely on the centre 3 engines Of STARSHIP IGNITING TO CLEAR SHB. if any of the outer ring of raptors go out (off line) They cannot be restarted (common to all prototypes of shb) … And Nominal should not be used in a test flight… due to the indicative nature of the word “Nominal”… :- ie you cannot have a normal test, as expected if the experiment has no hypothesis and as such cannot be proven “Nominal”—
So with that in mind I think it will get to stage seperation call out… and fail to seperate . And terminate together as a whole with the activation of Fts
@DeeMan I don't know if it's still true that Booster Raptors can't be ignited. It used to be true, but they changed the ignition method of raptors to something secret (probably spontaneous combustion due to heat and pressure), so they might reignite. Or maybe they can catch a bit of flame from the raptor next to it? Probably not.
@Mqrius More to the point… if any raptors go out the whole thing will go BOOM at seperation….with the hot staging the raptors on SHB get trimmed back to the inner ring at 50% … STARSHIP FIRES ITS RAPTORS TO DISENGAGE FROM SHB… SHB then attempts flip and boost back! Starship heads to the stars baby!!!
@EvanDaniel Changing this to improve consistency:
If an engine comes back online and is operating at stage shutdown, it gets counted as operational. (I don't see any particular reason to go one way or the other on this piece of the question, and it seems especially hard to forecast well. I'm just picking an answer there so we have something clear to bet on.)
Uncommanded shutdowns are failures. This seems like the cleanest way to keep the spirit of the question ("are there engine failures like on flight 1, and if so how many") and not have weird definitional issues around shutdowns related to staging.