You may be interested in thishttp://en.wikipedia.org/wiki/New_Worlds_Mission

Thanks a lot, that's exactly what I was asking about. From this
article, still a lot of things remain unclear:

1. James Webb Telescope is to be placed 1.5 mln km from Earth, on 1
year orbit (I think it is called Lagrange point). The article says
that the Starshade will be placed 238,600 miles (400,000km) from
Earth. How come it then will be 80,000 km from the telescope ?

2. Why does the article says that ~10 parsec is the limit ? By moving
the Starshade further from the telescope, they should be able to cover
more distant planet systems.

3. I am curious about the math - how this flower shape reduces
diffraction ? I thought one cannot reduce the diffraction much better
than w / D, where w is the wavelength, and D is the diameter of the
screen. If screen is ~10m (as the article says), it will be about the
order of 10 million, not 10 billion.