Recent picture on DA got me thinking: Self Propelled Autonomous Rail Gun
http://www.deviantart.com/art/Enforcer-378801855
as a setting objective/nemesis
Potential PC interactions:
1. as light infantry taking out the "war elephant" essentially a throw back to the Punic Wars where war elephants were the tanks of the battlefield but when flanked by light infantry they were easily neutralized. PCs must neutralize the SPARG so that other ships may enter orbit. the counter for light infantry taking out a war elephant was assigning light infantry to escort the war elephant thus the PCs will encounter other opposition scaled to their size- robotic escorts or living escorts.
2. using SPARG to defend a planet almost a space invaders themed encounter.
3. espionage- steal the plans etc
4. "Scotty I need that SPARG now or we're all dead!" rail guns experience deteriation of their rail system if not fired in vacuum thus when used for planetary defense they need plenty of TLC- PCs need to repair the SPARG before the alien swarm arrives or everyone dies.
5. Ghost in the Machine- rogue SPARG pushes its own agenda.
6. "One flew over the clockworks nest" PC mission lobotomize the SPARG and take over manual control of the weapon system for mission X
SPARG are designed to be anti siege weapons- mobile making them tough to localize for orbital bombardment. they are designed to level cities and shoot stuff in orbit.