The launch of the Hipparcos spacecraft marked the beginning of space astrometry. Hopefully, this will be followed in the near future by the launch of the Hubble Space Telescope, which is not primarily an astrometric instrument, but has astrometric capabilities which will be described in this paper. In addition, there are plans and proposals for future astrometric spacecraft. These include the launch of a radio antenna, which combined with Earth-based antennae would provide a very, very long base line interferometer (Levy, 1986, 1988). There are proposals for launching optical interferometers, such as POINTS (Reasenberg et al 1988). There are also proposals by York and Gatewood (Gatewood et al., 1986; Gatewood 1987, 1989) for launching astrometric instruments using gratings and detectors. Thus, the future holds the prospects for a whole new capability in the field of astrometry.

The lomonosov project is aimed at developing a high-accuracy coordinate system of the entire sky to be used for sufficiently long period of time (30 to 50 years) in order to ensure the solution of a variety of applied and basic scientific tasks. This goal can be feasible as a result of comprehensive work, the basis of which is the space experiment, i.e., observations of stars with a telescope on board the Earth satellite. This method can be instrumental in overcoming the distortions characteristic of terrestrial astrometric observations performed through the atmosphere, and to achieve a high degree of efficiency. The other part of the lomonosov project involves international backing of the space experiment through preparation of the input catalogue for 400 000 stars, and organization of high-precision ground observations of stars and other celestial objects in accordance with special programs.

The REGATTA-ASTRO project provides a great set of astrometric and photometric measurements from Small Space Laboratory (SSL). SSL is a special spacecraft being designed at the Space Research Institute, USSR Academy of Sciences. The main feature of this spacecraft is the attitude control by solar light pressure. The main objective of the project is to compile precise global catalogues of star positions, parallaxes and proper motion containing stars with magnitude up to 8-9 and a position accuracy of 0.″01. The astrometric concept of the project is based on a highly deterministic spacecraft angular motion and numerous observations of each star using wide-angle TV cameras with CCD detectors. The SSL computer provides measurement data pre-processing, photometric referencing and data compression. Ground-based computers process the data statistically. The estimated vector includes star coordinates, SSL angular motion parameters and generalized distortion of the instruments used.

The questions connected with constructing modern systems of autonomous navigation for spacecraft are considered. Increasing importance of these systems is shown, which is due to: a sharp increase in a number of spacecraft launches and congestion of on-ground control centers; and a necessity to provide more accurate and timely determination of motion parameters and motion control of spacecraft during their flights to the Solar System's celestial bodies. Importance of the star sighting and angular measurements connected with stars for adequate solution of space navigation problems is shown. Thus the star catalogues play a significant role for constructing navigational algorithms.

The USNO (Flagstaff Station) is in the process of modernizing its 8-inch transit telescope. The upgraded instrument will use a CCD detector to measure the positions of both bright and faint stars directly with respect to extragalactic sources. Moreover, it will be able to observe large numbers of stars very rapidly, and improvements in accuracy are expected with further upgrades (e.g. CCD circle scanners, an interferometric telescope monitoring system, networks of environmental sensors). Many research opportunities related to coordinate systems exist for this telescope.

Work on all parts of the FK5 is near to completion. The Basic FK5 has been published in the course of 1989 so that this catalogue is now officially released; the data have been made available to the various data centres. Work on the bright part of the FK5 Extension is finished since the end of 1988 and a tape version was sent to various institutions on request. Work on the Faint Extension is also nearly finished and the complete FK5 Extension will presumably be available on magnetic tape in a few months.

Some results obtained from new observations of FK5 stars are presented. Comparisons of the FK5 with FC, NFK, FK3, FK4, GC, N30 were performed and are discussed with respect to systematic and individual accuracy. The parameters of galactic rotation and precession, and the distance to the Hyades cluster have been derived using proper motions which were obtained within the work on the FK5.

To study the motion of the celestial objects in a reference frame one should Know the evolution of the frame itself, In our case it the motion of the origin of coordinates and the proper motions of the objects, the system is based upon.

Observations of Fundamental Faint Star Catalogue (FKSZ) stars, made with the Repsold Meridian Circle at Cerro Calán National Astronomical Observatory, began in 1979 and finished in 1988. Today International Reference Star (IRS) observations are in progress. These observations correspond to the second epoch of the Santiago 67 Catalogue (Carrasco and Loyola 1981) and they are going to be used for determining the proper motions of these stars.

On the basis of the observational materials of the photoelectric astrolabe from 1976 to 1977 at Shanghai Observatory, the possible increase improvement in observational precision after adopting the FK5 catalogue is estimated. The calculation proves that the improvements are about 6 per cent and 9 per cent in the right ascension and declination respectively.

Astronomical observations of time and of geographical latitude carried out by means of Danjon's astrolabe OPL No. 31 in the years 1982-1988 have been reduced to the system FK4. After the introduction of the FK5 catalogue in 1989, the earlier observations were re-reduced. The geographical latitude results, before and after introducing the FK5 catalogue, are given.

The contribution of the Carlsberg Meridian Catalogue La Palma Number 4 to the determination of the optical reference frame is discussed. This catalogue of almost 51000 stars provides one of the most accurate optical reference frames at the present epoch, having a density of 1 star per square degree, and an average accuracy of 0.″12 in position and 0.″003 per year in proper motion for stars with V<9. The catalogue also contains positions of reference stars with V>11 in the fields of benchmark extragalactic radio sources which can be used in linking the optical reference frame defined by the FK5 to the extragalactic frame.

A new micrometer has been in operation on the Carlsberg Automatic Meridian Circle since May 1988. The zenith mean error for one observation has improved from O.″19 to 0.″14 and the limiting magnitude from 13m.2 to 14m.8. The first meridian observations of Pluto and observations of nine extragalactic objects are briefly discussed.

High precision work in photographic astrometry requires accurate monitoring of the telescope+filter+emulsion system being used.

The Lick proper motion program, one of several using galaxies as a reference frame, is summarized with a statement of work accomplished for the non-Milky Way sky. The problem of identifying relatively transparent regions at low galactic latitudes is discussed, with tabular results presented for 41 windows from the literature having observable galaxies. These fields may be helpful for attaching stellar proper motions directly to the extragalactic frame.

The Southern Proper Motion Program (SPM) is described and progress in the execution of the second-epoch is outlined, as are the reduction methods. Recent changes in the instrumentation, including the addition of a computer control room to the astrograph building and the construction and operation of a new survey machine are discussed.

The IAS-Galaxy model (Ratnatunga, Bahcall and Casertano 1989) is a software interface between theoretical models of the Galaxy and observed kinematic distributions. It has been developed for analysis of many kinematic catalogs to study global galactic structure. In addition, the IASG model can be used to estimate corrections needed to derive absolute parallax and absolute proper motion by evaluating, on a star-by-star basis, the expected mean motion of the reference stars.

A theoretical Galaxy model is defined on an inertial coordinate frame. Proper motions are measured in a reference frame defined by a fundamental catalog. The observed distribution of proper motions in star catalogs can be directly compared with the expected distributions evaluated using IASG to check the accuracy of the adopted reference frame in realizing the inertial coordinate frame in the sky.

The precise positions and proper motions (J2000.0) of 1535 Basic FK5 stars in the FK5 system have been used in the reduction of the local vertical monitoring and the catalog observations at Beijing Astronomical Observatory. In addition, similar data for 1987 FK4 Sup stars, in which 980 stars indicated by “F” will be included in the FK5, were made available recently by Heidelberg via Prof. Tong Fu, director of Purple Mountain Observatory. The positions and proper motions of the other 1007 FK4 Sup stars in the FK5 system are provided by the Astronomisches Rechen-Institut with relatively low accuracies. However, the physical data, such as the visual magnitudes and the spectral types of these rs with rather large uncertainties have their origin in the Henry Draper Catalogue since the compilation of the FK4 and the FK4 Sup. More accurate visual magnitudes available in the well-defined photoelectric system and the spectrum types in the MK-system may be found, for example in the Bright Star Catalogue and its supplement.

For the convenience of users of astrometric observations and for geodetic purposes, visual magnitudes (V), color indices (V-B), spectral types (Sp), tritonometric parallaxes (p in mas), and radial velocities (RV in km/sec) for the 1535 FK4 stars and 1987 FK4 Sup stars are available.

These data are available from the authors in machine-readable form which includes the mean positions and proper motions of J2000.0 in the FK5 system and the cross-references to the GC of FK4 stars and FK4 Sup stars. Printed or magnetic versions of the data may be requested from the authors.

There are two kinds of geocentric frames: local inertial and non-inertial geocentric frames. Ashby et al successfully constructed a local inertial geocentric frame in the neighborhood of the gravitating Earth. In the frame with origin at the Earth's center, the gravitational effects of the sun and of planets other than the Earth are basically reduced to their tidal forces, with very small relativistic corrections.

However, the spatial base vectors of the local inertial frame essentially experience the geodesic (or deSitter) precession with respect to the solar system barycentric frame. Hence the realization of the local inertial frame requires that the general precession should exclude the geodesic precession. This requirement is inconsistent with the convention that the amount of geodesic precession is included in that of the general precession given by Lieske et al.

Within the limits of the programme of studying of the Main Meridional Section of the Galaxy the General Catalogue of astrometric data of 26500 stars has been compiled. Corrections to the precession constants and stellar secular parallaxes have been determined.

Three major reference star projects have been completed recently at the USNO: the Southern International Reference Stars (SIRS − 19, 827 stars) the southern part of the Faint Fundamentals (1,169 stars) and the Astrographic Catalog Reference Stars (ACRS - 325,416 stars). The compilation of the mean positions and proper motions of each is discussed. Reports on the progress of the USNO's Pole-to-Pole Fundamental Program and the Working Group on Star Lists are also presented.