What is the Circut Condition for the Presence of a Space Platform?

[plumbthumbs]

Let's say you want an inserter to activate somewhere deep in your factory when a Space Platform arrives at a planet.

What is the icon / condition that I use in the 'Enable/disable' gui and how is that signal transmitted? Do I connect the inserter
to a rocket silo, a radar dish, or a cargo landing pad?

Thanks!

[h.q.droid]

You can get it:

- From the rocket silo reading platform request, by requesting something improbable from each platform, like a rare jelly or an epic barrel of light oil.
- In 2.1 by checking planet arrival (planet signal == 3 when reading both source and destination) from the platform and broadcasting to the universe and receiving it. Both from radars.