The Satellite Drones are used when Tau advance into space and set up out posts.
Do to the fact that these outposts have limited support the Tau Earth Cast came up with Satellite Gun Drones to be placed in orbit around an outpost to catch ships by surprise when they drop out of the warp.
The Satellite Gun Drones detect approaching ships and open fire on them ripping them to shreds before they even know what hit them.
This is a major support and step up in securing the many Tau Outposts.
Some of the tau are using them on the ground to help support the outpost directly with Ion Cannons etc. instead of just Rail Guns.
Rules? up to you? Fluff up to you. Model.. here is one version I made.
and with a simple snap of a magnet the Ion cannon and Rail gun can be switched out for whichever you prefer.
Thanks for looking.