 Both Aerojet and Rocketdyne carried out engine design studies for the project, but Ares was ultimately cancelled in favour of solid-fuel ICBMs, which were safer to store and could be launched with much less notice.The Ares missile series was canceled due to the inconvenience of using liquid fuel.Some reasons included extensive protection from corrosion within the silos, as well as the liquid fuel propellant, ideally used in the proposed Ares missiles, being more expensive to maintain.