From FreeSpace Wiki
ship-invulnerable Causes the ships listed in this sexpression to be invulnerable to weapons. Use with caution!!!! Takes 1 or more arguments... 1+: Name of ships to make invulnerable to weapons.
- Used to make the given ship invulnerable. This can be quite noticeable, especially if the player or a capital ship attacks and no damage can be dealt. Many feel that ship-guardian is better for this purpose, as it will allow ships to take damage without being destroyed.
- The biggest problem with using ship-guardian insread of ship-invulnerable is that ships that are only guardianed can be disabled. If that ship was meant to escape, it will break the mission. This can be easily resolved by using ship-guardian-subsystem.
- The effects of this can be removed by using Cheats. Likewise, certain cheats can have an identical effect.
- This is what Volition used to shield the Lucifer.