Most spacecraft in the continuum are engineered similarly and rely on three types of engines; The primary engines, usually at the rear of the spacecraft, rapidly propell the craft through space to travel the distances between planets. This engine is mostly a Nuclear Pulse Engine. This lets out a powerful explosion which is created by releasing hot plasma which is then ignited. The explosion propels the spacecraft forward at rapid speeds relying on inertia to move. This engine only needs to be fire once, if the route is changed, then the engine must be fired again to regain inertia. In some spacecraft, only a Nuclear Pulse Engine is present, these are ships that only operate in space.