Limits of space telescope? links to the video 4 Future Space Telescopes NASA wants to build and that page links to The New Great Observatories. These cover the four space-based instruments proposed by study groups for the 2020 Decadal Survey on Astronomy and Astrophysics.
The first one mentioned is Habitable Exoplanet Observatory or HabEx which will be two spacecraft in a halo orbit around Sun-Earth L2 separated by perhaps 60,000 kilometers. One is a telescope equipped with an internal coronagraph and active wavefront modulation, the other is a passive starshade which is an occulting disk with diffraction-reducing apodization (petals).
I can't understand how these two mechanisms for reducing/removing light from a star from the final image so that exoplanets around that start can be imaged.
Question: How do HabEx's internal coronagraph and external starshade work together and complement each other? What is it that each can do that the other can't?
