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I saw a satellite launch recently (launch link) which used the Soyuz 2.1a rocket. Shortly after the launch I observed 4 symmetrical thrusters at an angle to the main thrust line.

Is this for stabilization /attitude control? And is this present in other rockets too but is inconspicuous?

enter image description here

enter image description here

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They are the verniers, gimbaled on one axis (tangentially), used to control pitch, yaw and roll. (the main engine nozzles are not gimbaled).

Soyuz launcher engines

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  • $\begingroup$ All the Soyuz series (and their predecessors back to Sputnik and the R-7 ICBM have used these vernier thrusters for attitude control. Early US rockets like Atlas also had verniers, but modern practice is to gimbal the main engines for attitude control instead. $\endgroup$ – Russell Borogove Mar 31 '18 at 11:43
  • $\begingroup$ "...gimbaled on one axis..." Is it radially, or tangentially, or pitch/yaw? $\endgroup$ – uhoh Apr 1 '18 at 2:00
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    $\begingroup$ Not 100% sure, but I believe it's tangential -- the bulges inboard and outboard of the nozzle contain the hinges. Better view here: spaceflightinsider.com/wp-content/uploads/2016/04/… $\endgroup$ – Russell Borogove Apr 1 '18 at 2:05
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    $\begingroup$ And another (observe callout #20): airandspace.si.edu/exhibitions/space-race/online/sec500img/… $\endgroup$ – Russell Borogove Apr 1 '18 at 2:13
  • $\begingroup$ @RussellBorogove interestingly, when there is fourfold symmetry, both "tangentially" and "pitch/yaw" could be true at the same time. Thanks, those images are really helpful! $\endgroup$ – uhoh Apr 1 '18 at 9:32

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