 position of the target body relative to the
      observer. The one-way light time, lt, is given by

                | T(et) - O(et) |
         lt = -------------------
                        c

      The geometric relationship between the observer, target, and
      solar system barycenter is as shown:


         SSB ---&gt; O(et)
          |      /
          |     /
          |    /
          |   /  T(et) - O(et)
          V  V
         T(et)


      The returned state consists of the position vector

 