when a missile is locked on a target send its target a signal every 3 seconds.

basically, the missile will try to call a "missile lock" method of its target every 3 seconds (with a timer)

for the player it will be a ping noise notice, for a fighter it will mean lunch a flare (once), for a big ship it will tell one of its turrets to shot the missile (a point defense capable hardpoint) or lunch flares.

for a big ship maybe also tell nearby fighters/interceptors to defend it.