Project Cyclops, A Design... - Department of Earth and Planetary ...

13. SEARCH STRATEGY
The high directivities that inevitably accompany
coherent collecting areas many hundreds of wavelengths
in diameter, together with the cost of replicating the
necessary data processing equipment, force us into a
serial search mode, in which we examine one star at a
time. The fundamental objective of the search strategy is
to organize the serial search process in such a way as
to achieve contact in the least time. More precisely, we
wish to maximize the probability of having made
contact after any given length of search time.
If the Cyclops system were to materialize overnight in
its full size, if we had a complete catalog of all stars by
spectral type within 1000 light-years of the sun, if we
knew the relative probabilities of the occurrence of
advanced life on planets belonging to stars of different
spectral types, and, finally, if we knew how the
probability of detecting a signal decreased with increasing
range, the search strategy would be quite straightforward.
We could then compute an a priori probability
p for the existence of a detectable stgnal from any given
star. This probability would be the product of a function
f of the spectral class S and a function g of the range R.
That is, we would have
equation
(1) will be
p = kf(S)g(R,t) (2)
This merely means revising our tables ofp as we go along
and working always with the most probable stars on the
most up-to-date list.
At present we do not know the exact forms of the
functions f and g. Throughout this study we have
assumed, on the basis of available knowledge, that f is a
unimodal distribution centered on main sequence stars
of spectral class G. This may be an anthropocentric view,
but for the reasons given in Chapter 2 we fend the
assumption quite a logical one. For equally compelling
reasons, the function g may be taken to decrease
monotonically with range. Thus, the model that guides
our thinking may be represented schematically as shown
in Figure 13-1, where we have plotted p vertically as a
..4
p = kf(S)f(R) (1)
/f_ 17
where k is a constant that absorbs such factors as the
longevity of the communicative phase. The optimum
search strategy would then be to list all stars in order of
decreasing p, begin at the top of the list, and work our
way down.
Because the Cyclops system will grow in size with
time, this simple procedure is complicated by the fact
that g will be a function of both R and t; that is,
Figure 13-1. Contours of equiprobable detectability.
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