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   Compute possible right ascensions and declinations given
   a sun angle as a function of the angular distance from the 
   nominal orientation. 
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   Form:
   [rA, dec, phi] = DSunCone( uSun, rAI, decI, beta )
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   Inputs
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   uSun         (3,1)     Sun Vector
   rAI                    Nominal right ascension (rad)
   decI                   Nominal declination (rad)
   beta                   Sun angle (rad)

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   Outputs
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   rA            (:)     Right Ascension (rad) 
   dec           (:)     Declination  (rad) 
   phi                   Dot product of nominal vector sun cone         

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