Format for Mariner 9 Ranging Observations

columns  1-20  Ephemeris Time of Observation

        21-36  Geometric, Round-Trip Light-Time [microseconds],
                 Earth Center of Mass - Mars Center of Mass

        37-44  A priori uncertainty

        45-52  Residual with respect to DE405

The "Observation" is simply twice the Euclidean Earth-Mars distance,
computed at the given Ephemeris Time.