OrbNEq

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   Computes the orbit normal from equinoctial elements.
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   Form:
   n = OrbNEq( eq )
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   Inputs
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   eq                    Elements vector [a,P1,P2,Q1,Q2,l]

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   Outputs
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   n               (3,1) Orbit Normal

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 References: Battin, R.H., An Introduction to the Methods and Mathematics
             of Astrodynamics, AIAA, New York, 1987, p. 494.
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