The Maintenance of the Orientation of IERS Celestial Reference Frames from 1988 to 1995

The maintenance of orientation of the international Earth Rotation Service(IERS)celestial reference frames from 1992 to 1995 are analyzed in this paper. In combination with the maintenance for years from 1988 to 1992, it is concluded that there are detectable variations in the orientation of IERS celestial reference frames from 1988 to 1995. The biggest shifts of the origin of right ascension and of the celestial pole are about 0.4mas. Till 1995, the deviations of the origin of right ascension and the celestial pole from their originally expected positions are no less than 0.4mas. The orientation of the 1993's IERS frame was maintained by the 1994 and 1995 IERS frames at a precision of 0.05mas rather than 0.005mas. The precision of 0.005mas is a result of mathematical mean. The coordinate differences of a considerable number of primary (or defining)sources in successive IERS frames are bigger than 0.5mas, which demonstrates that the orientation of the celestial reference frames can be maintained in a relatively high precision if a suitable method for identifying or removing the local relative deformations between individual frames was adopted.