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Falcon 9 can complete its mission with the loss of any one engine. The Space Shuttle could reach orbit with one engine out starting a few minutes into flight. Most other rockets don't have any engine-out capabilities at all.

NASA is currently planning to launch Artemis 1 despite a temperature sensor on engine #3 giving an out-of-spec reading on the assumption that the sensor is faulty. If the sensor isn't faulty, what would happen if the engine starts but fails to keep running?

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  • $\begingroup$ When the CZ-5 Y2 failed due to a one-engine-out failure (of two center stage engines) at T+346s (center stage separation is at T+500s), it it said that, had the engine held for another 50s, the spacecraft could still have made it to the orbit. CZ-5 and SLS are very similar that they are both 1.5-stage and both use LH2/LO2 center stage and center stage both burns for ~500 seconds. Considering SLS has 4 engines, I have reasons to believe a one-out-of-four failure after T+400 will not directly lead to mission failure. $\endgroup$ Sep 1, 2022 at 11:47
  • $\begingroup$ @user3528438: CZ-5 and SLS are 2-stage, even if you consider only the core and the SRBs. 1.5-stage means you drop engines or empty fuel tanks but not both. Sustainer engines with side boosters are still considered 2-stage rockets. $\endgroup$ Sep 2, 2022 at 20:39
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    $\begingroup$ @OrganicMarble No need to delete your answer, it perfectly answers what the OP was looking for. As an addendum, NASA probably scrubbed the launch because they want to make sure E2058 was working properly so they won't encounter a failure mode which they already know. If they went ahead and launched anyways with E2058 running, it may pose a hazard to the other three functioning engines as RUD and associated debris may impact the engine block / SRBs (potential Challenger-like failure mode) $\endgroup$
    – WarpPrime
    Sep 4, 2022 at 21:28
  • $\begingroup$ @fasterthanlight Thanks, after reviewing the question I became convinced it was specific to this next planned mission, which my answer was not. Feel free to use the source I found and write an answer if you think it fits. $\endgroup$ Sep 5, 2022 at 3:00
  • $\begingroup$ Are you just interested about any orbit, or are you specifically interested about an orbit which allows the mission to proceed? The two are very different - the Shuttle had at least one abort to orbit occurrence, but the one I have in mind was minimally affected because the mission was entirely self contained, it just needed an orbit. But an abort to orbit occurrence where the mission is, for example, docking with the ISS or Hubble would have meant those missions would probably not have gone ahead so the outcome is just saving the orbiter for a return to earth, which is pointless for the SLS $\endgroup$
    – Moo
    Sep 6, 2022 at 0:18

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NASA is currently planning to launch Artemis 1 despite a temperature sensor on engine #3 giving an out-of-spec reading on the assumption that the sensor is faulty. If the sensor isn't faulty, what would happen if the engine starts but fails to keep running?

The mission wouldn't exactly fail, provided that the engine doesn't shutdown in the first few seconds of flight, but contingencies would have to be made.

This NASA report regarding Exploration Flight Test 1, which initially was planned to launch on SLS, states that

The SLS Launch vehicle has four RS-25’s on the Core and analysis has shown that the Block 1 configuration can recover from an unplanned engine shutdown in almost all phases of flight. Late in flight, SLS would press to Main Engine CutOff (MECO) and continue on its nominal mission profile. Two other targets, an Alternate MECO Target (AMT) High for engine failures in the middle portion of flight, and an AMT Low target for failures very early in flight rounds out the engine out capability of SLS. For Artemis I, the AMT High target was derived to ensure Orion could meet its high-speed reentry test objective for its heat shield by inserting the Interim Cryogenic Propulsion Stage (ICPS) and Orion stack into an orbit where the ICPS could insert Orion into a highly elliptical Earth orbit. The Artemis I AMT Low target was derived to help Orion achieve all its other flight test objectives in Low Earth Orbit. The switching between targets is handled either through flight software or by Mission Control. Both the vehicle and Mission Control will monitor SLS’s velocity on ascent to make the determination as to which AMT the vehicle is capable of achieving. The AMT’s are also derived so that the Core reentry, even in the event of an engine failure, has a high probability of impacting water instead of land.

This implies that for a 3600 km apogee, SLS would be capable of pushing to the target orbit even with an engine failure after 198 seconds. However, for the current Artemis 1 mission, I would estimate that a press to MECO would only be possible after at least 230 seconds of nominal flight due to the higher-energy injection.

As the graph shows, an near-immediate engine failure would cause the mission to reach only LEO, but as this was for EFT-1, the current Artemis 1 cannot afford to lose an engine almost immediately after launch as that would cause imminent mission failure.

enter image description here

This might be a little incomplete/inconclusive, so please feel free to edit to add extra details that I may have missed.

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  • $\begingroup$ Where did you get the 230 second figure for this next planned mission from? $\endgroup$ Sep 6, 2022 at 23:56
  • $\begingroup$ @OrganicMarble To be honest, a complete guess, but it seems like a reasonable estimate. I probably should just remove it $\endgroup$
    – WarpPrime
    Sep 7, 2022 at 0:20
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    $\begingroup$ At least be upfront about it. That sort of thing - implying that the number came from a source you quoted when in fact you made it up - is terrible for your credibility. $\endgroup$ Sep 7, 2022 at 0:23
  • $\begingroup$ @OrganicMarble Done. $\endgroup$
    – WarpPrime
    Sep 7, 2022 at 0:32
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SLS is capable of reaching orbit with one engine out. It's immense power in the lower stage allows it to do so with the help of both Solid Rocket Motors (SRMs) mounted on either side of the big orange 1st stage. kinda like the space shuttle tank

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    $\begingroup$ Do you have a reference to back up your assertions? $\endgroup$ Sep 4, 2022 at 17:47
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    $\begingroup$ I read it on NASA.gov (I think, maybe it was somewhere else) but anyway, while we're on the subject of a big orange 1st stage, why does the space shuttle tank look like a big orange banana. (hm, maybe that deserves it's own question!) $\endgroup$ Sep 4, 2022 at 17:53
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    $\begingroup$ ntrs.nasa.gov/api/citations/20205004525/downloads/… $\endgroup$ Sep 4, 2022 at 22:01
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    $\begingroup$ I'm a fan of proper spelling and grammar. $\endgroup$ Sep 4, 2022 at 22:52
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    $\begingroup$ Immense power is not enough to give engine out capability - effective use of that power will mean you loaded more payload onto it. It also requires more complex control logic and more capable engine gimbals that may not exist. It can probably be argued that Artemis 1 will have spare power but a good answer would at least compare the mass of this mission vs SLS max payload and confirm 3 engine thrust still more than vehicle mass. $\endgroup$ Sep 5, 2022 at 8:34

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