Interdiction torpedoes are a feature added on August 18, 2014. They were designed to make space combat more common. Their function is to disable fleeing ships to make it remotely possible to catch a moving ship.
These fire an EMP generator that shorts out electrical systems. When one of these projectiles hits a ship, the ship will stop and its control signs will pop off.
Interdiction torpedoes work exactly the same way as normal torpedoes, except that the ammunition is copper dust (redstone) rather than firework rockets. The projectile also flies the same way as a normal torpedo, except that the pulse generator is housed inside a cobweb rather than TNT. They can also be fired on planets.