However, it is also possible to fit extra fuel tanks in a ship's hold. Collapsible 'fuel bladders' and more permanent conversions are both commercially available. Using this system, the ship jumps as far as possible and emerges in deep space. Fuel is then pumped from the extra tanks to the main ones, ready for a second or third jump. This can take time and is not 100% safe, but it does make long voyages possible with a jump-1 ship.