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Today, the realization of the International Terrestrial Reference System (ITRS) and the International Celestial Reference System (ICRS) is performed separately. Consequently, the two realizations are not fully consistent and show differences in the network geometry and the realized scale of the terrestrial reference frame (TRF) and in the simultaneously estimated Earth Orientation Parameter (EOP) series. The paper deals with the common adjustment of the Terrestrial Reference Frame (TRF), the Celestial Reference Frame (CRF) and the linking EOP. It presents a computation strategy, which is based on the combination of normal equations. The main focus of the paper is on the impact of a combination of different space geodetic techniques on the CRF, which was not in detail studied so far. The influence of the local tie handling as well as the impact of the EOP combination are studied. The results show, that the combination leads only to small but partly systematic changes of the CRF. The maximum systematic effect is about 0.5 mas for source positions derived in regional networks only.

Consistent and homogeneous long-time series of the space geodetic techniquesGlobal Positioning System (GPS), Satellite Laser Ranging (SLR), andVery Long Baseline Interferometry (VLBI) provide the basis for thecombination efforts of GGOS-D. For a consistent combination, thedefinition of common standards for parameterization and modeling isessential. These standards and the technique-specific processingoptions of all individual GPS, SLR, and VLBI solutions as well asthe combined SLR and VLBI solutions are discussed.

The generation of the GGOS-D global terrestrial reference frame is based on VLBI, SLR, and GPS observations. The respective observation blocks, analysed as individual units, depend on the technique and cover either full weeks, full days (GPS and SLR) or observing sessions of 24 h duration (VLBI). From these observation units, time series of parameters have been inferred and studies of the quality of the results have been carried out for the identification of deficits in the analyses. In this paper, we describe examples of time series of site coordinates, Earth orientation, and atmosphere parameters as well as peculiarities in the behaviour of these parameters.