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Answers to Rockets with n-engines, for n = 1, 2, 3… cover all single digit nontrivial† values except for seven, so...

Question: Have there been any rockets that run seven engines at the same time?

Thrusters on spacecraft already in space don't count. This should probably be a launch vehicle of some kind.

†zero would be the trivial single digit non-negative valule

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    $\begingroup$ Technically, SpaceX Falcon 9 is built with 9 engines, but on the first trip to ISS, two of them failed. Because of that, for some part of the propulsed flight, it was running seven engines at the same time, it was designed to work under this circumstance despite not being the nominal case or intention. $\endgroup$
    – Mefitico
    Mar 2 '20 at 18:20
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    $\begingroup$ The Falcon 9 can tolerate two engine failures, but only one engine failed on CRS-1. $\endgroup$
    – Christopher James Huff
    Mar 2 '20 at 22:05
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    $\begingroup$ @ChristopherJamesHuff thanks for that. I want to say "too bad a second engine didn't fail" but I won't. Oh, wait...oops $\endgroup$
    – uhoh
    Mar 2 '20 at 22:12
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    $\begingroup$ This is genuinely surprising to me considering how nicely seven engines close-pack on the bottom of a cylindrical launcher. $\endgroup$
    – ikrase
    Mar 5 '20 at 7:32
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    $\begingroup$ Not gonna lie, I suspected that on the basis of Kerbal Space Program experience. $\endgroup$
    – ikrase
    Mar 5 '20 at 8:44
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Yes.

enter image description here

(Image source)

Some configurations of the Delta II used nine solid boosters.

In launches from both the ER and WR, the first-stage RS-27A main engine and six of the nine strap-on solid-rocket motors are ignited on the ground at liftoff. Following burnout of these six SRMs, the remaining three are ignited.

Delta II Payload Planners Guide (emphasis mine)

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    $\begingroup$ Well since we are counting solids PSLV-XL and retd. PSLV-G would meet the criteria as well. $\endgroup$
    – Ohsin
    Mar 2 '20 at 12:39
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    $\begingroup$ @Ohsin sounds like an answer! $\endgroup$
    – Organic Marble
    Mar 2 '20 at 13:21
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    $\begingroup$ That design reminds me a bit of Kerbal Space Program... $\endgroup$
    – nick012000
    Mar 3 '20 at 4:44
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Besides the Delta II and PSLV-G/PSLV-XL, there are a few proposed/in-development stages that would fire 7 engines at once.

Blue Origin’s New Glenn booster is designed with 7 BE-4 engines powering its first stage.

ULA has put forth a paper design for a “Delta Super Heavy”, 6 boosters surrounding the central first stage core of the Delta IV. I don’t know if the idea was for it to be flown with all 7 engines firing together, or if it ever got beyond a vague concept stage. I note that the Delta IV is currently a horizontally integrated launcher, and that going to 4 or 6 boosters would raise difficulties with that strategy.

The Angara family has a proposed A7 configuration with 6 boosters around one core stage; this is likewise unlikely to ever be built.

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  • $\begingroup$ Thanks! I'd thought that I'd seen six boosters on some core on some launchpad somewhere, sometime, but maybe it was a drawing. $\endgroup$
    – uhoh
    Mar 2 '20 at 3:26
  • $\begingroup$ Maybe Conestoga 1620, but that fired the 6 boosters without the center core at liftoff. en.wikipedia.org/wiki/Conestoga_(rocket). I assume you aren't counting something like a Proton rocket hot-staging the second stage while the 6 engines of the first stage are still firing... $\endgroup$
    – Russell Borogove
    Mar 2 '20 at 3:36
  • $\begingroup$ Double check the careful wording of the question ;-) I think one or possibly both might "fly". $\endgroup$
    – uhoh
    Mar 2 '20 at 3:43
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    $\begingroup$ Proton doesn't count even if it hot-stages. Second stage is 4-engine ;) $\endgroup$
    – Russell Borogove
    Mar 2 '20 at 3:51
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    $\begingroup$ @TemporalWolf In the Smarter Every Day tour of ULA, Tony Bruno mentions that Vulcan will be able to take up to 6 boosters $\endgroup$
    – Tim
    Mar 3 '20 at 18:37
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The USSR's failed Moon rocket, the N1, had 30 engines on the first stage. This is significantly more than the limit of 7 you mentioned.

Picture of the Soviet N1

Source: Aerospaceweb

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    $\begingroup$ The question is asking about exactly 7 rockets, not at least 7 rockets. The question is rather confusingly worded, in my opinion. $\endgroup$
    – isaacg
    Mar 3 '20 at 19:28
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    $\begingroup$ @isaacg Would "Have there been any rockets that run exactly seven engines at the same time at some point during ascent by design?" work better? I wouldn't change the title but where I restate the question in the body of the text I can clarify. I'd thought the reverence to the previous N = 1, 2, 3... question made it clear that seven meant seven because if N = 1 meant "one or more" then every rocket with engines would have answered that question and there'd be no 2nd question in the first place. $\endgroup$
    – uhoh
    Mar 3 '20 at 23:17
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    $\begingroup$ +1 because maybe the question was unclear, and it's a cool photo ;-) $\endgroup$
    – uhoh
    Mar 3 '20 at 23:18
  • $\begingroup$ Ah! Oops, I completely misunderstood the original question. I can remove my answer if you like. $\endgroup$
    – Burgi
    Mar 4 '20 at 9:11

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