VLBI observations at 2.3 GHz were conducted using an antenna of the Tracking and Data Relay Satellite System (TDRSS), in geosynchronous orbit, and two ground stations. Twenty-three of 24 sources were detected, on baselines as long as 2.15 Earth diameters. These baseline lengths gave the interferometer much better sensitivity to high brightness temperatures than any Earth-based observations. Brightness temperatures of 1-4 times the 10^12^ K inverse Compton limit were measured for 10 sources, suggesting bulk relativistic motion in these sources. Coherence values of approximately 85% for integration times of 360 s were obtained.
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Linfield et al. (1989) studied this question.