Possible modification of the Shkadov thruster and its prospects to solve SETI problems.
So far, the search for signs of extraterrestrial intelligence activities (EI) within framework of SETI programs, and primarily radio transmission, did not give encouraging results. One possible explanation for this may be that the distance between both existing technically advanced civilizations is large (approximately hundreds of light-years or more), that defeats the purpose of an interactive signal exchange. A possible way out in this case could be astroengineering efforts to reduce distance between the stars, which are located near the EI.
The simplest device for this purpose, known as the Shkadov thruster  is a grand solar sail with dimensions comparable to the size of star. Such astroengineering construction was firstly proposed by USSR team of the Moscow Palace of Pioneers  and further explicitly developed by Leonid Shkadov at the end of 1980s . Known methods can theoretically detect similar objects in transit across stellar disk by a characteristic change of its emission .
The author has previously proposed schematic of an unmanned space probe with electric solar sail (ESS), which in the simplest case is positively electrically charged retro-reflector panel made of thin film . Such construction, which is a combination of classical solar sail and electrical sail (E-sail) by P. Janhunen , allows to use for the creation of thrust photon and ion solar radiation.
This makes possible to create in the future a new type of astroengineering construction which is modified, or electric Shkadov thrust (EST), which is a set of unmanned spacecrafts with ESS (possibly reproducing the principle of von Neumann cellular automaton of substance asteroids), arranged in the shape of reflector of one pole star, and also to solve a number of problems associated with the controllability and resource structure.
A characteristic feature of such thrust operation, along with a relatively high linear speed of the accelerated star can be specific jet of relatively slow ions. It should be noted that objects with similar characteristics can be detected by modern technical means. So, in 2007 within the framework of orbital telescope GALEX in ultraviolet part of the spectrum has been fixed gas tail of star Mira (Omicron Ceti) extending in several light years. 
Using engines such as EST, highly-developed EI could combine their star systems in stable artificial star clusters made of the millions of stars in which the terms of radio signals exchange between them would constitute from hours to months, and spacecrafts – from months to years, – which would correspond to the level of supercivilization between II and III types of Kardashev scale. However, their radio contact with the “outside world” would be extremely limited due to the low efficiency and informativeness.
In the future, these EI within astroengineering activity using EST could implement even more large-scale projects, including controlled collapse of the star clusters to form objects like supermassive black holes. Due to the known effects such as relativistic time dilation, this would enable them to get maximum information about the surrounding universe for the shortest period.
As part of the latest initiative by Yuri Milner (Breakthrough Initiatives) under the supervision of Stephen Hawking on the SETI , it would be appropriate to include in the list of possible searched objects rapid stars with signs of EST job in the form of expressing ion jets, as well as allegedly artificial star clusters.
Within the framework of own activities of the modern human space colonization in this field there is short-term perspective for the project on creation and testing of unmanned spacecraft with ESS with longevity, including clustering, as well as self-reproduction of automatic devices and development of technologies of asteroid substance usage as raw materials.
Fig. 1. The modern concept of Shkadov thrust (NASA)
Fig. 3. Picture of World Stars gas tails in the UV range (GALEX, 2007). This is how possibly looks operating EST for outside viewer
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- URL: http://www.electric-sailing.com/publications.html.
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