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I noticed that the Ariane 5 does not have wings. It also does not have RCS thrusters except for sometimes with its payload, but that is not being used during liftoff. I tried to find some methods it could use to turn and this is what I came up with:

  • Reaction wheels
  • Gimbal engines
  • Magnetic torquers
  • Control moment gyros
  • Something else

I was wondering which of these things it uses to turn?

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2 Answers 2

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Like most large modern launchers, Ariane uses gimbaled engines for attitude control during ascent.

Both the Vulcain liquid-hydrogen engine and the nozzles of the solid rocket boosters on the Ariane are gimbaled.

Unlike movable fins, gimbaled engines don’t incur much drag; they are much more fuel-efficient than perpendicular RCS thrusters for a given torque requirement.

Reaction wheels, CMGs, and the like are very low-powered in real life, unlike Kerbal Space Program; they aren’t practical for rapid attitude control in dynamic environments.

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    $\begingroup$ Should you desire a reference: esa.int/Enabling_Support/Space_Transportation/Launch_vehicles/… $\endgroup$ Commented Jul 31, 2022 at 18:33
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    $\begingroup$ Thanks, linked that and a few others. $\endgroup$ Commented Jul 31, 2022 at 20:40
  • $\begingroup$ If you want to be technical, that’s “gimbaled engine”. The Vulcain gimbals in that the entire engine pivots on its mount. The boosters are thrust vectored , in that a frustrum turns against a smaller frustrum. The motor doesn’t pivot. Yeah, semantic debate, I know. $\endgroup$ Commented Aug 4, 2022 at 15:46
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The first stage of Ariane V has in fact RCS thrusters, but only for roll control. While the solid boosters are burning, roll control of the whole stack is exercised by differential gimbaling of the EAP solid rocket boosters. After burn out and separation of the solid busters, there`s a problem: The EPC main stage with its Vulcain engine is a single engine stage. Gimbaling of the Vulcain takes care of yaw and pitch, but not roll. This is dealt with a cluster of GH2 thruster. Unfortunately, I lack detailed specification on them, but there description as GH2 points to a rather low thrust / performance regime. As the relevant flight regime is already in the thinner parts of the atmosphere (EAP separation occurs at ~75km altitude) and Ariane 5 a very axisymmetric shape at this point only small roll forces need to be compensated

Ariane 5 user`s manual (page 203): https://www.arianespace.com/wp-content/uploads/2016/10/Ariane5-users-manual-Jun2020.pdf

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    $\begingroup$ Only small roll forces now . L502 led to a Vulcain fix, where marginal forces hadn’t shown up in ground tests. $\endgroup$ Commented Aug 4, 2022 at 15:53

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