Space missions for SETI

Radio Telescopes for SETI searches are less demanding than general purpose astronomical radio telescopes. This provides an opportunity to exploit econ omical approaches in designing SETT systems. Radio Telescopes in low Earth orbit offer no discernible advantages to SETI; indeed, they probably would perform more poorly than a telescope in any other location. Telescopes in g eosynchronous orbits would be sufficiently far from Earth to mitigate great ly the deleterious effect of human radio transmissions. Telescopes on the f ar side of the moon would be superb both from a radio interference standpoi nt, and from a civil engineering standpoint. Single-reflector telescopes as large as 50 kilometers in diameter could be constructed with conventional materials. However, their costs appear prohibitive. The asteroid belt and t he outer solar system are unpromising places to place a large radio telesco pe. Perhaps the ultimate radio telescope would utilise the sun as a gravita tional lens, focusing radiation on free-flying 10-meter class or possibly l arger radio telescopes located at distances of the order of 1000 A.U. from the sun. Such a combination has an energy collecting area at 10 centimeters wavelength equivalent to that of a radio telescope about 11 kilometers in diameter, or of the order of 3000 Arecibo radio telescopes. Such a system c ould detect transmitters with EIRP of the order of a gigawatt at a distance of the order of the distance to the galactic center. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.