You simply go to battle manager and drag them from the bar at bottom to the circles on the system map similar to how you place space stations except they can be placed anywhere in system you control. However, at the moment, the Drone sats are broken and dont launch any drones.
Doesn't work for me:
when you open up the battle manager and drag the DS over to one of the defence platform slots in the system it doesn't recognise it as a valid placement even though the platform slot will glow as compatible.
Guess I must have a bug. Tried it in 3 different systems now and each time when I drag it over the platform slot the cursor shows a 'x' next to the pointer to indicate the location is invalid, trying to place it does nothing.
Did also notice that in the design screen DS have module slots. And whilst it looks like nothing is being displayed as an option there are actually invisible options to add things like sensors, docks, warehouses and such.
Edit: As for them being broken and not launching drones, I gave it a shot in the weapons test and after clicking on the drone option to launch them I did notice a swarm of tiny blips leaving the platform.... however the platform is so large it actually goes beyond the perimeter of target pads and clips through them, making it very hard to notice the drones leaving.