Official rule text
87.4 A unit can use its “Sustain Damage” ability any time a hit is 89.2 STEP 2—MOVEMENT: The active player may move any produced against it. This includes hits produced during combat number of ships that have a sufficient move value from any and from unit abilities such as the “Space Cannon” ability. number of systems that do not contain one of their command tokens into the active system, following the rules for a A unit can only use the “Sustain Damage” ability if it movement. is eligible to be hit. For example, a player cannot use a dreadnought’s “Sustain Damage” ability to cancel a hit from a Ships that have capacity values can transport ground forces “Anti-Fighter Barrage.” and fighters when moving.