parent direction of a target for a remote-sensing
         observation.

            Use 'LT+S' or 'CN+S: apply both light time and stellar
            aberration corrections.

         Note that using light time corrections alone ('LT' or 'CN')
         is generally not a good way to obtain an approximation to
         an apparent target vector: since light time and stellar
         aberration corrections often partially cancel each other,
         it may be more accurate to use no correction at all than t