RADIO TELESCOPE IN SPACE!

In February 1997 Japan's Institute of Space and Astronautical Science launched their Highly Advanced Laboratory for Communications and Astronomy (HALCA) - which is in ordinary terms, the first radio telescope in space (that is, leaving the 'communications' bit aside...).

Radio telescopes have always been at a disadvantage when compared with optical telescopes.  Radio waves are so much longer than light waves that radio telescopes have to be many times larger than their optical equivalents in order to be able to resolve a given object.  The technique of Very Long Baseline Interferometry (VLBI) greatly reduced the disparity between the resolution obtainable using radio and optical telescopes, in fact it put radio telescopes ahead of optical telesopes.  The technique involves using telescopes on different continents to observe the same source at the same time and then combining the observations subsequently so that one has in effect synthesized a radio telescope the size of the distance between the continents.

The resloving power of radio telescopes using this technique has just been increased by the launch of HALCA - now a radio telescope bigger than the size of the earth can be synthesized by bringing HALCA into the network of radio telescopes used for VLBI experiments.  HALCA's orbit reaches up to 21 000 km from Earth, tripling the resolution obtainable using ground-based VLBI.

HALCA will be used to observe the structure of the radio lobes and of the jets emanating from distant quasars in unprescedented detail.

Marion West