This question is specifically about the Soviet engine RD-107, (although it can be generalized) a version of which was clustered in Soviet rocket 8K71 which launched their "Sputnik".

Each engine uses four fixed main combustion chambers. The RD-107 had additional two Vernier combustion chambers that could provide thrust in a single plane (the plane joining their center lines) to supply attitude control. The photo of the engine shows these Vernier engines completely off-set to one side.

The question is: Is it not essential to provide at least FOUR of such Vernier engines (similar to RCSs used on LEMs and perhaps Space shuttle nose also) on four, diametrically opposite points, which are equally spaced angularly, so as to control the attitude using their combination? Perhaps three might also be sufficient, but only two, that also completely off set on side? How did they control attitude effectively?

  • $\begingroup$ Further, Semyorka, the rocket that launched Sputnik, had four RD 107s engines mounted on four corners, with their vernier engines facing outwards, so as to provide arrangement as expected by me in the above question. The central engine did not have any vernier engines. Was this the way they controlled its attitude effectively? Further, Can we say that the clustering concept used on Saturn I, was inspired (if not copied) from this Russian rocket? (or vice -versa) Incidentally the clustering of F1 engines on Saturn V, was also in a "quincunx" fashion as in Semyorka.. $\endgroup$
    – Niranjan
    Jun 9, 2021 at 4:53

1 Answer 1


RD-107 seems to have been used in the R7 missile. It says in the article for the missile that

1st stage: 4x jettisonable four-chamber RD-107 booster engines each with 2x vernier rocket engines plus 1x four-chamber RD-108 core engine with 4x vernier rocket engines.

So the RD 107 stage was used in quadruplets. So vernier engines existed on diametrically opposite sides and that too in all four quadrants. So you do end up with full vector control.

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    $\begingroup$ Central engine as per the article does have 4 vernier engines. Picture indicates that there is one in each quadrant. $\endgroup$
    – AJN
    Jun 9, 2021 at 13:07
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    $\begingroup$ There are lots of great photos showing the 4 verniers on the core and the 2 verniers on each strapon, at least for the current Soyuz. Here's one nasa.gov/sites/default/files/thumbnails/image/… $\endgroup$ Jun 9, 2021 at 17:16
  • $\begingroup$ @AJN. The picture I saw did not have any vernier engine for the central engine which I had already mentioned in my (PS) comment on my question.. (unless the verniers were there but I could not spot them). Anyway, Overall, four quadrants together did provide full vector control. What happens if any rocket used only one of the RD 107 engine? How is the vector control in all directions achieved? $\endgroup$
    – Niranjan
    Jun 9, 2021 at 18:07
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    $\begingroup$ This picture shows the R-7 with four verniers on the core, just like the Soyuz. astronautix.com/graphics/r/r7back.jpg $\endgroup$ Jun 10, 2021 at 1:30
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    $\begingroup$ @Niranjan The RD-107 is only used on the boosters of the Soyuz/Sputnik/R-7 family of launchers. These boosters are always used in a group of four. The RD-108 could be used alone, since it has four verniers, but I don’t believe it’s used by anything but that launcher family. Apart from the arrangement of vernier rockets, the RD-107 and RD-108 are identical. $\endgroup$ Jun 10, 2021 at 4:18

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