I'm trying to do some research on this but very much struggling to work it all out. I'm looking for a cutaway diagram of said rocket engine (ideally one used on a first-stage), but I can't for the life of me work out what rocket uses what engine. Can anyone help?

In terms of "widely used", I'm looking for either (or perhaps both) the engine used on the most number of launches per year, or the engine used on the most varied number of rockets (e.g. is there an engine used on many different rockets?).

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    $\begingroup$ This website contains many diagrams of various rocket engines. It might be a good place to start. $\endgroup$
    – Stu
    Commented Jan 21, 2014 at 15:18

4 Answers 4


The most numerous launcher is the Soyuz-U, with more than 700 launched. Its 4 boosters use the RD-107 engine (manufactured by Energomash), so you'd have ca. 2800 engines of a single type.
PDF with some drawings of RD-107

The RD-107 is maybe not the best engine to find details on, being a soviet-era design. Other rocket engines may have been built in smaller quantities, but more information is available on them. A Google Image search for 'rocket engine cutaway' gave me a pile of results, the first two being nice diagrams of the F-1 engine used in the Saturn V.

  • $\begingroup$ Thanks Hobbes, guess that would be the RD-107A then. My only issue is I can't find a cutaway of that anywhere... Any tips? $\endgroup$
    – Jonny
    Commented Jan 21, 2014 at 16:05
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    $\begingroup$ And confusingly, the RD-107 has one turbopump, but four chambers, right? So it looks like each side booster has four bells, but really only counts as one engine. $\endgroup$
    – geoffc
    Commented Jan 21, 2014 at 22:48
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    $\begingroup$ If you consider the RD-107 and RD-108 to be the same engine (the only major difference is the number of vernier thrusters), the total number built is around 9800 for rockets, and an unknown number for missiles. $\endgroup$
    – Mark
    Commented Mar 1 at 22:43
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    $\begingroup$ Yeah, I noticed the same thing. Back then I just found the launcher with the largest number of launches, without considering that the same engine might be used in other launchers as well $\endgroup$
    – Hobbes
    Commented Mar 2 at 14:56

The NK-33 has been used successfully on two different rockets' first stages (Antares and Soyuz-1), and was planned to be used on several more, including the Soviet N-1F, and I think for Rocketplane Kistler as well.

The RD-170 family of engines have been used on a number of different launch vehicles as a first stage. It was used for the boosters of the Energiya rocket, it's used as the first stage of the Zenit rocket (which is very similar to an Energiya booster).

A half size version called the RD-180 is used on the American Atlas V and is being considered for use on Antares. A much smaller version called RD-150 was used on South Korea's Korea Space Launch Vehicle, and a quater sized version called the RD-190 is being developed for use on Russia's Angara series of rockets.

All those engines - RD-150/170/180/190 are of the same basic design, but will have different flowrates and a different number of nozzles. Everything was essentially scaled down from RD-170 to some degree.


If you have some patience, I will bet on Merlin engines, flown on SpaceX Falcon 9 and Falcon Heavy launchers. They use 10 per launch. 9 on the first stage, one on the upper stage.

In only the first 8 launches (as I write this in early 2014) that is 80 engines. With 50 flights on their manifest to clear, they will hit several hundred engines flown in the next year or two.

Updating this at the end of 2019, there were 76 Falcon 9 flights (760 engine flights), and 3 Falcon Heavy with 28 per flight (84), ignoring the Falcon 1's 5 engines, that is 844 with 20+ flights planned for 2002. That exceeds the SSME and SRB combined numbers already.

Burn time would be fun to compare:

  • SSME burn time, 480 s (405 burns)
  • SRB burn time, 124 s (270 burns)

Total: 227,880s, 63 hours, 18 min

  • First stage Merlin burn time, 158 s (765 burns)
  • Second stage Merlin burn time, 397 s (79 burns)

Total: 152,233s, 42 hours, 17 min.

But with 75,000 seconds difference, and about 1819s per mission, Merlin only needs 41 more flights to catch up.

Of course first and second stage burn times vary somewhat based on mission flight profile, this is meant only as an approximation. However, as of the current time, the Soyuz booster with the RD-107 is the clear winner with 700+ launches.

SSME with 135 launches X 3 engines per launch is 405 full duration firings (Maybe -3 for Challengers last flight). Then of course the SRB's with 270 full duration firings on those same launches. Now, are the SSME's still in use? Well not on the Space Shuttle, but in theory on the SLS now known as RS-25D or RS-25E engines.

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    $\begingroup$ SSME was my first thought as well, but they were reused, so only a couple dozen of them were built. $\endgroup$
    – Hobbes
    Commented Jan 22, 2014 at 8:09
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    $\begingroup$ Ten per Falcon 9 launch. Falcon Heavy launches use 28 Merlins per launch. $\endgroup$
    – Vikki
    Commented Jun 4, 2020 at 20:39
  • $\begingroup$ Re-use means the number of Merlin engines isn't going up very fast. The Merlin probably surpassed the no-longer-used LR-89 from the Atlas family late last year, putting it into sixth place. At the current pace, it's about six years away from beating the RD-0110 (an upper-stage engine) for fifth place. $\endgroup$
    – Mark
    Commented Mar 1 at 22:49

Per Wikipedia as noted 3/1/2024, Falcon-9 has launched 312 times over 14 years. Each launch requires 9 merlin sea-level engines and one merlin vacuum engine, ten total. Even though these have been re-used and swapped between rocket fuselages at an unknown frequency, this means 3120 engine flights have occurred.

The claim of 2800 engine-flights for the Russian RD-107 is now LESS THAN the 3120 Merlin engine flights. Merlin is the clear leader now. And, with over 100 lauches in 2023 and possibly 130+ launches in 2025, the SpaceX Merlin engine's dominance will continue to increase. Almost all flights of both engines were successful so no adjustment is needed.

However: The SpaceX Raptor engine mounted on Starship and SuperHeavy Booster have already flown will fly 3 times this year (anticipated). Each flight will launch with 42 engines (33 on the booster and either 6 or 9 on the upper Starship stage). As both are fully re-usable, and production rates of this engine projected at one every 3 days, it's likely the highest engine-launches by an engine will be dominantly RAPTOR in by 2028 or sooner, depending heavily on both launch cadence and Boca Chica rocket factory output.

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    $\begingroup$ The 2800 is an under-estimate. The RD-107 isn't just used on the Soyuz-U, but also the Voskhod (300 launches), the Molniya-M (297 launches), and another 20 rockets with fewer than a hundred launches each. Total number just for the RD-107 (not the very-closely-related RD-108) is around 7800 engine-flights. $\endgroup$
    – Mark
    Commented Mar 1 at 22:54
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    $\begingroup$ As of today en.wikipedia.org/wiki/R-7_(rocket_family) shows just shy of 2000 launches of all variants (not counting the completely different 2.1v) thus 8000 RD107 and 10,000 (RD107 +RD108) $\endgroup$
    – Puffin
    Commented Mar 2 at 21:49

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