Abstract for the 2nd International Workshop "The Art and Science of Interstellar Message Composition", Paris, France, March 23-24, 2003

Limitations on Volume of Interstellar Radio Messages


Alexander L. Zaitsev, IRE RAS


There are three possible sources of transmission of the interstellar radio messages (IRMs) now: Arecibo Radar Telescope (ART, 305-m dish, 1000-kW transmitter at 12.6 cm wavelength), Goldstone Solar System Radar (GSSR, 70 m, 480 kW, 3.5 cm), and Evpatoria Planetary Radar (EPR, 70 m, 150 kW, 6.0 cm). The ART is the most powerful instrument, so it can provide the most fast transmission, but unlike the GSSR and EPR, which can track given celestial target during ~ 10 hours per day, the ART has fixed dish and therefore the 2.5 hour tracking duration, only.


If we assume that They are situated in the neighbourhood at a distance of 70 light years from us and have the same, or even a little more sensitive, SETI receivers, like to our future ATA (Allen Telescope Array) or SKA (Square Kilometer Array), then daily volumes of IRMs, which we can transmit from ART, GSSR, and EPR toward given celestial target are equal 75, 200, and 20 kilobits for ATA-like receiver, or 7.5, 20, and 2 megabits for SKA-like receiver, respectively. And this volume is in inverse proportional dependence from squared distance. Consequently, we should aspire to be laconic now in our IRM compositions.


Otherwise, if we assume an infinite potentiality of Their ancient and advanced civilizations, we should neither design nor transmit any IRMs, because in such case They are everywhere already and studying us long ago.