FixedPitchControl:
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Correct sail pitch using elevation, dElevation = -dPitch.
Since version 7.
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Form:
dGamma = FixedPitchControl( z, rho, nu, eta )
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Inputs
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rho (1,1) Target radius
z (1,1) Target out of plane displacement
nu (1,1) Displacement in rho direction
eta (1,1) Displacement in z direction
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Outputs
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Reference: Colin R. McInnes, "Solar Sailing: Technology, Dynamics and Mission
Applications", Springer Praxis, London, 1999, p. 193
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