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The VSOP mission is a Japanese-led project to image radio sources with sub-milliarcsec resolution by correlating the signal from the orbiting 8-m telescope, HALCA, with a global array of telescopes. Twenty-five percent of the scientific time of this mission is devoted to a survey of 402 bright, small-diameter extra-galactic radio sources at 5 GHz. The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure; to provide a source list for use with future space VLBI missions; and to compare radio properties with other data throughout the EM spectrum. This paper describes: the compilation of a complete list of radio sources associated with active galactic nuclei (AGN); the selection of the subsample of sources to be observed with VSOP; the extensive ground resources used for the Survey; the status of the observations as of 2000 July; the data-analysis methods; and several examples of results from the VSOP Survey. More detailed results from the full sample will be given in future papers.

Aims. We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). Methods. We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5 h 230 GHz VLBI track with baseline lengths of 2800 Mλ to 7200 Mλ and a finest fringe spacing of 28.6 µas. Results. Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ∼0.3 Jy beam −1 , out of a total flux density of 19.8 Jy. Visibility data suggest an emission region 38 µas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 10 10 K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ∼ 38 µas. Conclusions. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 µas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40 µas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.

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