There are comets in space, so there is water and water can be made into propellant. Ceres also seems to have a lot of water: https://astronomy.com/news/2020/08

There are comets in space, so there is water and water can be made into propellant. Ceres also seems to have a lot of water: https://astronomy.com/news/2020/08/ceres-an-ocean-world-in-the-asteroid-belt https://astronomy.com/news/2020/08/ceres-an-ocean-world-in-t...