The space-geodetic technique, Very Long Baseline Interferometry (VLBI), is based on the simultaneous observation of faint signals emitted by extragalactic radio sources using globally distributed radio telescopes. The observational principle of VLBI enables the establishment of the celestial reference frame and the determination of the Earth’s orientation in space. Moreover, VLBI contributes significantly to the realization of the terrestrial reference system, the terrestrial reference frame (TRF), playing a particularly crucial role in defining its scale. A variety of research institutions and dedicated software systems are involved in the determination of TRFs. These efforts include inter-technique combinations, leveraging the strengths of various space-geodetic techniques and Analysis Centers (ACs), intra-technique combinations, forming single-technique solutions, and single-technique, single-AC solutions, serving as an essential tool for scientific investigations.

This thesis contributes to this field by developing and applying a newly implemented global solution software, VieCompy, which currently supports combining VLBI data from a single-AC based on the stacking of normal equation systems. VieCompy is a flexible platform, providing a foundation for future extensions toward inter- and intra-technique combinations and orbit-related parameter estimation. In this work, the capabilities of VieCompy are demonstrated through dedicated studies addressing key research questions related to the sensitivity of the TRF to different computational strategies, parameterization setups, and observation errors. 

The first study investigates the impact of various terrestrial datum realization methods on the TRF and the corresponding formal errors. The results emphasize the importance of transparency within the VLBI community regarding the choice of datum realization method and applied constraint strength, as these factors can significantly influence the comparability of different TRF solutions.

The second study explores the debated origin of a scale drift observed after epoch 2013.75 in the most recent official realization of the International Terrestrial Reference System, the ITRF2020. A significant reduction of the trend by 50-60\% is achieved by introducing modified station motion models for the station NYALES20 (Norway) in the determination of TRFs. These results underline the need for continuous VLBI data monitoring and accurate station behavior modeling.

The final study examines the potential of VLBI observations to the European Space Agency's Genesis satellite, which integrates the main space-geodetic techniques on a platform in space. A preliminary study demonstrates that precise phase center calibration of the VLBI transmitter at the mm-level and accurate group delay measurements are essential for deriving high-accuracy VLBI station coordinates solely derived from satellite observations. 

In summary, these studies highlight the importance of a robust and adaptable combination software. With VieCompy, this thesis presents a functional tool for current VLBI global solutions and a foundation for future advancements in geodetic software, including orbit-related parameter estimation.