Found at the end of a long mission chain.

Limit: 1 (1 completion)

Planetary Effect: When placed on a planet, the first successful invasion of that planet instead gives the owner a decoy, which instead is a blockade type NPC which drops a module of some sort. Previous owner of planet keeps the planet, attempted invader receives module from NPC. Limit of 3 of these modules installable on your ship.

Note: If player has been a member of your legion at any time in the last 3 months, NPC drops nothing. If the planet has more than 3 ships scanned, NPC drops nothing. Not addable to contested planets.

im confused as to how a SHIP mod affects a PLANET of unknown stats.... do you assign a planet when you install the mods?
i see this as an easy cop out on your very nice planets...
id have one on my top 3 mega colossals, and i would immediately be fluxing them and tripling defences if i happened to miss being online when they were attacked...

as I understand it, what Rarek is proposing a trap that can be placed on a planet.
When successfully invaded, the owner keeps the planet and as opposed to getting the conquered planet the attacker gets an NPC. The NPC drops a ship module artifact.

would people still have to pay the invasion costs?

You would not pay the invasion costs, nor do you get a badge. You would simply gain an NPC.