VLBI IN THE 1990S

Radio telescopes in more than 20 different countries on five continents are being used for VLBI observations of galactic and extragalactic radio sources, as well for applications to geodesy and geophysics. New radio telescopes and networks of radio telescopes dedicated to VLBI which are being built in the United States, the U.S.S.R., Italy, China, Poland, the U.K. as well as in Australia will greatly improve the sensitivity, resolution, image quality, and frequency coverage of the existing networks. The Mk II VLBI recording system, which is based on consumer type Video Tape Recorders, is widely used but the sensitivity is limited. Broad band recording systems are expensive, but are becoming more popular due to their much greater sensitivity. They are expected to dominate VLBI systems in the 1990s. The first tests of an earth-to-space VLBI system took place in 1986, and by the mid 1990s dedicated VLBI antennas will be launched into earth orbit by the U.S.S.R. and by Japan in collaboration with Australia and other countries throughout the world. Space VLBI missions will give an order of magnitude improvement in resolution over the ground based VLBI networks operating at the same wavelengths.