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The angular resolution of an
array of radio telescopes becomes finer as the distance between the
telescopes increases. There is therefore a natural limit to
Very Long Baseline Interferometry (VLBI) imposed
by the diameter of the Earth! However, this constraint can be
overcome by placing a radio telescope in orbit about the Earth -- Space VLBI.
After some technical demonstrations of the technique were made with a
TDRSS satellite in the 1980s, two dedicated Space VLBI missions were
developed: the VLBI Space Observatory Programme (VSOP), led by Japan,
and RadioAstron, led by Russia. The VSOP satellite, HALCA, was launched
from Japan on 12 February 1997, and the mission conducted over 600
observations at 1.6 and 4.8 GHz with arrays of ground radio telescopes
over its lifetime. The ATCA, Mopra, Hobart and Ceduna radio telescopes
all contributed to the VSOP Survey Program of Active Galactic Nuclei
and to Guest Observing Time.
Fittingly, today is the first day of the
"VLBI in the SKA Era" conference, which will review the past,
consider the present, and contemplate the future of VLBI.
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