The positions of about 306,000 common stars of the recently published catalogs ACRS and PPM are compared. The positions agree very well (rms < 0″.1) at the epoch of 1950, but the differences become larger as the epoch becomes farther from 1950 due to the deficiency in the accuracy of proper motions. The rms at the epoch of 2000 is about 0″.36. The agreement is better for the stars in the southern hemisphere, as is shown in the figures below, although the southern part of PPM (1991 April version) is still preliminary.

At the 20th General Assembly of the IUGG in Vienna, Austria, in August, 1991, Resolution No. 5 recommended that the concept of an International GPS Service for Geodynamics (IGS) be explored over the next several years and that campaigns be conducted to test the practicality of the concept.

The International Earth Rotation Service (IERS) maintains a celestial reference frame and a terrestrial reference frame based on observations in Very Long Baseline radio Interferometry, Lunar and Satellite Laser Ranging, and Global Positioning System, as well as a time series of the Earth Orientation Parameters in a system that is consistent at the level of 0.001″.

Some basic conceptions of relativistic reference systems are given. The conventional solar-system barycentric reference system (B-system) and the conventional geocentric reference system (G-system) are discussed. It is suggested that the harmonic conditions be used in the definition of the B-system and the G-system be defined by the B-system and the coordinate transformation given by eqs (3–2), (3–3) and (3–4).

The results of an initial technical design of the AIST spacecraft and payload are presented. The spacecraft design is subjected to the main requirement: to supply the smooth rotation. Two telescopes are symmetrically placed around central beam combiner unit. The fine adjustment of the light pressure centre position by means of special-purpose sails is proposed. Scientific objectives of the project are the implementation of astrometric survey of the sky and obtaining a series of star position catalogues with milliarcsecond accuracy, including a second epoch of Hipparcos/Tycho catalogues. The survey list will consist of nearly 10–15 million stars brighter than 15th magnitude.

Based on the present status and projects of Chinese VLBI and SLR fixed stations, the applications of a mobile VLBI system are investigated in establishing a Chinese high accuracy geodetic VLBI network and terrestrial reference frame.

The paper deals with the relative coordinate-and-time determination in a ground based reference frame by using the NAVSTAR/GLONASS radio interferometry and duplex clock comparison techniques.

A terrestrial reference frame can be defined by the coordinates of a set of stations on the surface of the earth. It is possible to realize a reference frame through the GPS positioning. In this sense two basic approaches are available to realizing a terrestrial reference frame using GPS: absolute and relative. By the absolute approach we mean the point positioning, whereas by the relative approach is meant the relative positioning. At the present day the absolute approach should realize a reference frame at a meter or submeter level precision. By contrast, the relative approach could realize a reference frame with a centimeter or even better precision.

After the closing of Bureau International de L'Heure (BIH) and the establishment of International Earth Rotation Service (IERS) at the end of 1987. Shanghai Observatory has been the institute where the astrometric latitude and time observational data are collected and treated. During the past four years, about 75,293 measurements in latitude or time determination have been obtained by the 64 optical astrometric instruments over the world from which the five-day Earth Rotation Parameters of the 1988–1990 period have still been reduced. Twelve Quarterly Report on the optical ERP have been distributed. Since the beginning of 1991 the regular reduction of the ERP has been stopped but the collecting of the observational data is still going on in Shanghai Observatory in order to meet the requirements of the scientists who are still interested on the studies concerned with these observations. There are still 42 optical astrometric instruments taking part into the regular observations at the moment.

The World Space Congress comprised of the 43rd Congress of the International Astronautical Federation (IAF) and the 29th Plenary Meeting of the Committee of Space Research (COSPAR) was held in Washington, DC from 27 August to 4 September, 1992. Over 3000 people participated in the meetings where scientific papers were presented on such diverse topics as space travel, biological aspects of space travel, relativity, planetary atmospheres, space debris, space law, global change, launch vehicles, space station, space communication, navigation, Earth rotation, astrometry, satellite geodesy, use of lunar observations, and new observational techniques. Presentations dealing with the topics of this symposium are discussed, but complete reports will be forthcoming in the proceedings of the Congress.