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The body flaps on Starship have the responsibilty of controlling attitude during atmospheric flight. They are also needed to deal with the large moments created by carrying payloads in the nose.

Movable control surfaces are useless for Starship when it is outside an atmosphere, whereas RCS can be used anywhere. So, what if Starship omitted the flap movement in favor of RCS for attitude control and adjusted fin geometry to keep the center of pressure within a range of acceptable limits for various CGs? Would the existing RCS thrusters be able to cope? Would thruster reliability be a deal breaker?

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    $\begingroup$ The grid fins are not fixed - they still steer, and are essential for returning to Earth with the fuel profile they use. If you read the article you linked to you will see they are "fixed in a deployed position" $\endgroup$
    – Rory Alsop
    Aug 12 at 16:26
  • $\begingroup$ @RoryAlsop I am removing the reference to them. $\endgroup$
    – Abdullah
    Aug 12 at 16:28
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    $\begingroup$ Aerodynamic braking means less fuel used, meaning less weight, meaning less fuel etc etc etc $\endgroup$
    – Rory Alsop
    Aug 12 at 16:29
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    $\begingroup$ "Would the existing RCS thrusters be able to cope". No.. by 2 magnitudes.Thruster reliability is not the problem, thruster Power is. The proposed hot gas methalox thrusters might be sufficient, but would consume a great deal of fuel. $\endgroup$ Aug 12 at 16:36
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    $\begingroup$ @PcMan: Also, Elon Musk has talked about potentially getting rid of dedicated RCS thrusters entirely, instead using intelligent venting of the ullage gas (which they have to vent anyway). $\endgroup$ Aug 12 at 19:47

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