A hyperdrive is used to move a ship into an alternate dimension, where the laws of physics are different. Maybe in this alternate dimension, points in space that are congruent to points in normal space are closer together. Maybe there are odd shortcuts between places. Maybe the alternate dimension is so thoroughly non-Euclidean that one can move in directions that simply don't exist in real space. Or maybe in hyperspace, the speed of light is higher, or just isn't a thing.

Hyperdrives need to hold the ship in hyperspace, or provide some degree of movement within hyper. Because of this, hyperdrives require an initial activation cost, and a constant cost. This cost might be in raw power, or in an exotic “hyper fuel”.

A hyperdrive can transit one tonne of ship for every 5kg of hyperdrive—so your hyperdrive will occupy 5% of the ship's total mass. It occupies one cubic meter per every 750 tonnes it can transit, but this space requirement is halved if the hyperdrive is located entirely externally. Mind you, external hyperdrives like this cannot be worked on from inside the ship. You have to land the ship, or go EVA, in order to fix it, and you certainly cannot work on it while it is in operation.

Hyperdrives are rather expensive, at ₠400 per tonne of ship to which they are fitted.