A battleship, with space for small fighters to be attached, it is going to carry food for colonies far away. It can move very fast, but not for long because it have not much energy repositories. It is going to carry shuttles aswell, for transporting passengers. It`s main purpose is to bring resources [food, ammunition] to distant colonies, but within the galaxy as the specie has not yet managed to travel outside the galaxy, they have only managed to colonize five planets. The spaceship is powered by a yellow power source, which is outdated for the technology that the specie posses. It is going to look old and have bad energy, but it should also be a sovreign fighter when it engages in combat.
When i said realistic i meant for the eye, not for our current technology, as it is not going to be a cartoon.
