The tactical nuclear Mace Missile is one of the new Vision Engine additions for Standoff Episode 2. In every game it responds slightly differently, so the Standoff team has provided a few hints for maximizing its output. The Morningstar makes its appearance in the mission simulator.
Shooting down the missile is not a good idea. Secret Ops doesn't allow us to do a proper Mace Missile, so the way it works is a bit of a trick... which basically means that if you shoot it down or it hits something directly, there won't be a big explosion. In the case of small capships that consist of two components and no hull mesh, a shot in the right place might destroy the ship in one shot. If you attack from the flank, a Mace will kill a Ralatha in one shot if it explodes amidship, where the engine and bridge components meet.