@John Smith 23 April 12:48
Sorry for being off line have been tied up in teaching!
Yes within in individual system, the planets ought to be reasonable
coplanar, if they've formed out of an accretion disc as we expect (and
conservation of momentum is a strong prior!). But that only means
within a few degrees, once they've had a bit of post-formation
battering - I think back-of-an-envelope for example, if Kepler found
Earth, it would have a about a 50/50 chance of getting one transit of
Mars; Mercury and Venus would be out through inclination, Jupiter and
further would be out through mission length.
But between stars - the ecliptics will be pretty much at random. So
Kepler would still need 200 solar systems to detect one Earth.
I hadn't head about the Daedalus revisit - will keep my eyes open for
that, it's still the horse I'd put my money on. Starwisp though -
unsteerable mirror that has to be also a Fresnel lens from Earth?
Free-flying optical arrays in ~AU orbit would have much greater senstivity
& mapping power - local angular resolution at a wavelength where the
targets are dim and with an unsteerable antenna isn't FTW! Seriously - blackbody in the Rayleigh-Jeans regime goes as nu^2. Push me offline and I'll calculate precisely how close you'd need to be to Earth with an off-axis 30-m cm-wave antenna to detect it. There's several orders of magnitude on the back of my bus ticket in favor of going for a local optical/IR search!