A Discussion on the Maintenance of the Orientation of Radio Celestial Reference Frames

According to the present status and the ultimate aim of the establishment of the Celestial Reference Frames based on the extragalactic objects, the orientation maintenance method based on common primary sources is recommended. Calculations show that this maintenance model is more desirable than the IERS one, which was on the hase of all primary sources of a version of the frame, in the consideration of orientation stability for a long time span. The relationship between the selection standards of primary sources and the orientation maintenance process is also discussed. It is shown that the ratio of the substituted objects to the whole must not be too high in order to keep the orientation continuity. On the one hand, the selection standards must be perfect. On the other hand, when ever changes occurred in the standards, the selected objects based on old standards must be tested by the new one, and the orientation must be adjusted correspondingly. Otherwise, orientation gapes may be resulted in.