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   Computes the sun sensor data for a spinning spacecraft. This computes
   the angle between the sun and the spin-axis. 
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   Form:
   sa = SunData( usun, uspin, quant, qtype, onesigma, bias )
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   Inputs
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   usun         (3,n)     Unit sun vector
   uspin        (3,1)     Unit spin axis vector
   quant                  Quantization
   qtype                  Type of quantization-either 'round' or 'truncate'
   onesigma               One sigma noise
   bias                   Sensor bias

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   Outputs
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   sa                     The angle between the sun line and the spin axis

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