Institute of Applied Astronomy of Russian Academy of Sciences, 8 Zhdanov st., St. Petersburg, 197042 Russia
Observations of satellites of outer planets made on a stellar background are considered now as a one of the most promising techniques to improve positions of outer planets (due to starlike images of the satellites). In the work by D.B. Taylor et all ( Astron. Astrophys. 249, 1991) such an approach was successfully applied to meridian observations of Titan and Iapetus. Unfortunately it appears that corrections to the longitudes of the pericenters and to the eccentricities of the satellites strongly correlate with corrections to positions of Saturn and all these parameters cannot be evaluated simultaneously with a good accuracy. This difficulties may be overcome if observations of several satellites are treated simultaneously. We have discussed photographic observations of the eight satellites of Saturn made at Pulkovo in 1974-1982 by two instruments (normal astrograph and 26' refractor) to improve elements of the satellites and derive normal points for positions of Saturn at 8 oppositions. Results for each instrument are in a good accordance and significant correlations between corrections to elements of satellites with corrections to the position of Saturn were not noticed. So the formal accuracy of the normal points is rather high but a serious problem arises to separate systematic errors of the reference photographic catalogue with corrections to positions of Saturn.