docs: def _compute_mjd(self, kw, val):
          """
          Sometimes that MJD-OBS-CENTER keyword maps to a three component string, instead of a single value.
          @param kw: a list of keywords
          @param val: a list of matching values
          @return: the MJD-OBS-CENTER as a julian date.
          """
          try:
              idx = kw.index('MJD-OBS-CENTER')
          except ValueError:
              return
          if len(val) == len(kw):
              return
          if len(val) - 2 != len(kw):
              raise ValueError("convert: keyword/value lengths don't match: {}/{}".format(kw, val))
          val.insert(idx, Time("{} {} {}".format(val.pop(idx), val.pop(idx), val.pop(idx)),
                               format='mpc',
                               scale='utc').mjd)
          logging.debug("Computed MJD: {}".format(val[idx]))