Gravity Well
A gravity well module—which includes gravity generators, gravity well generators, and interdiction arrays—manipulates gravitational forces around the targeted starship, slowing the starship considerably. Until the end of the next piloting phase, the target’s speed is halved, and its maneuverability becomes one step worse (to at worst clumsy maneuverability). A gravity well module requires tremendous energy to operate; it cannot be activated unless an engineer succeeds at a divert crew action to divert power to the weapons that round.
Source
Starship Operations Manual pg. 14