Bracewell (1960) asks the following question: How will civilizations of equal or greater intelligence try to initiate communication with nearby, unknown civilizations. He mostly elaborates on this by following semi-informal chains of thought. He argues that it is unlikely that they are running megawatt level transmitters pointed towards every nearby star that could possibly be hosting (or nurturing future) intelligent life. He instead argues that it is more feasible to search for life by sending out a swarm of armored, radio-transmitting probes to rapidly explore the nearby stellar neighborhood and a selection of further, promising target stars.
I think some of his reasoning is flawed here as one of his arguments against the interstellar transmitters is that they have a “dependence on our ingenuity in selecting the right star and the right wavelength”. It seems like he is suggesting that his probe swarm is a better idea than using a single transmitter. I would agree, but I think the swarm would be more comparable to using a network of many transmitters. Maybe the cost of building and maintaining thousands of transmitters continuously pointed at all of the targets is significant, but I would imagine the cost of launching thousands of autonomous probes would be pretty high as well.
He postulates that if there are already several advanced civilizations that know about each other, they will be connected and communicating, so we would only find evidence of the nearest community that is looking for us.
It is noted that by looking for probes within our own solar system we are in a way looking for signs that there are any advanced civilizations capable of reaching us. A cool idea. The probe within our solar system might only be a listener that reports back to home base via a star to star relay system.
This paper seems to have significance due to its documentation of several novel communication ideas and its introduction of extraterrestrial civilization network ideas.