Actually, the idea of a 'planetary' defense weapon is very old. The first one, as far as I know, was "Planetary Defenses", by Howard Lopez. It can be downloaded from ev.com
As far as I can see, it shouldn't be graphicless. If it was, it would be impossible to hit, and therefore impossible to destroy. That'd make planets impossible to dominate, and we wouldn't like that, now would we? Also, I think that EV would probably screw something up if a ship doesn't have a graphic. I guess an 8*8 pict would be your best shot.
Also, these things can't be used in system defense dudes. That causes them to float around mindlessly without being able to do anything, which, quite frequently, is pretty silly. I know, I've tried.
However, they should work as planetary defences - they stay put and shoot when people are around. If it has a long-range beam weapon, it would become fairly impossible to dodge though, which (yet again) is pretty unfair and unbalanced.
I suggest you download the 'Planetary Defenses' from EV Webpage and experiment with it.
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"I don't say yes or no, more like the other way around"
Ankh Starrunner, The Diamond Blaster
(This message has been edited by Ankh Starrunner (edited 02-06-2000).)