You may be looking for:
Sentinel watchtowers were four Umojan Protectorate defensive space platforms designed to defend the Keep. They were heavily armed, and designed to attack anything larger than a pebble that came in range. They also served as evacuation points for the Keep's staff should it have come under attack.
Agent Nova Terra bypassed the watchtowers by using a captured freighter Charon, faking it being disabled and using a toxin to fake her death. The Keep's security personnel brought Nova and the Charon inside the platform. Later, Nova planted bombs in the Keep, forcing the staff to evacuate to the watchtowers. Unbeknownst to them, the bomb was fake, and the actual bombs were on the evacuation transports. The bombs detonated, destroying all four sentinel watchtowers.