ARGUMENT 1

UPLINK GAIN HAS TO BE LIMITED AT OPTICAL WAVELENGTHS

While it is accepted that one of the most important advantages of optical transmitter uplinks is that they can have much higher gain than their microwave counterparts, for relatively small apertures, such gains cannot be realized in practice. The ETI civilization would need to have precise knowledge of the peculiar and proper motion of the targeted star with respect to their star system in order to accomplish the very high accuracy point-ahead targeting required.

Counter Argument

It is a classic mistake to ascribe to ETIs, who will be very advanced technical civilizations, the technical limitations of 20th Century mankind. While we cannot presently achieve this sophisticated targeting capability, this should be trivial for ETIs. They will have space-based optical telescope arrays that will allow the imaging of earth-size planets around stars in their neighborhood. This is something we shall probably be able to do within 50 years. It will be easy for them to target beams into nearby star systems that are comparable or even smaller in diameter that the zones of life around such systems. They will also know what extrasolar planets have life, and even technologically-based civilizations, by observing composition of planetary atmospheres and perhaps even detecting radio-frequency leakage. The ETIs will only target their beams to those stars and planets which support intelligent life.