In article ,
dave schneider wrote:
At what point would it be worth it to add a long leg to the net of
earth-based dishes by placing a dish at, say, a [Lagrange] point?
I don't think this would pay much in terms of making the effective
antenna any larger than building another eb dish...

Not at all, for spacecraft communications. For that sort of work, you
need a big dish not for angular resolution, but for collecting area.
Using multiple antennas far apart improves angular resolution, but does
nothing much for collecting area.
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