While observations of the mutual phenomena of the planetary satellites can deliver high precision astrometry, about +/-0.02 arcsec (Arlot et al. 1989) and detailed surface photometry (Descamps et al. 1992), mutual phenomena cannot be observed for most of the satellites, and are quite rare for the remainder. On the other hand, astrometric observations in the tangent plane can provide precise positions for all planetary satellites, and if the observations are made with a CCD, differential photometry can supply colors, albedos and rotations (Pascu et al. 1992a, Pascu et al. 1993, Pascu and Rohde 1993, Pascu et al. 1994a). The precision of such observations is generally limited by instrumental parameters (scale, orientation) and atmospheric seeing to +/-0.1 arcsec (Pascu 1977). However, when two satellites are separated by less that 50 arcsec, their measured coordinates in the tangent plane are independent of these limitations, as are phenomena observations, and have an external error of +/-0.03 arcsec (Pascu et al. 1991, Pascu 1994).