Darkspace is the name for the spaces between planets, moons, and stars. Air, not a vacuum, fills darkspace. The further one gets from celestial bodies with atmospheres, the thinner the air gets. Some of these celestial bodies are aflame, usually because of a connection to the plane of fire. These suns provide almost all the heat in a given celestial system.
Darkspace vessels must be sealed to safely traverse between celestial systems because of the lack of heat and breathable air. However, within a system, it’s typically safe to walk about on their decks.
A gravity generator operates in the center of each darkspace vessel to keep the crew from floating out into space. These magical devices create a gravity plane that provides an up and down. This plane also has a flipside: the underside of this plane has an opposing up and down perspective. Thus, it’s possible to construct a ship with decks on the top and bottom, with a space in the middle where the gravity flips.
The larger ships navigate the gravity fields using the mind of a magically created suspended in fluid. The mind performs all the required calculations required for darkspace navigation.