>>96148656
The Excellion was a hell of a ship, bit it was just a warship. The Eltreum was the literally indestructible one, built during one of the generations-long offscreen relativistic timeskips. By some science we don't understand, the ship's hull is all one single molecule. It cannot be broken down into anything smaller than it already is. The science notes say that this artificial molecule materials, also named Eltreum, can theoretically be destroyed but only by contact with its antimatter equivalent (anti-Eltreum) which would naturally annihilate both in a conversion to pure energy. But since neither material is naturally occurring, anti-Eltreum doesn't exist unless someone goes out of their way to try and make some of it.